WO2022126300A1 - 一种光伏***及环流抑制方法 - Google Patents

一种光伏***及环流抑制方法 Download PDF

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Publication number
WO2022126300A1
WO2022126300A1 PCT/CN2020/136008 CN2020136008W WO2022126300A1 WO 2022126300 A1 WO2022126300 A1 WO 2022126300A1 CN 2020136008 W CN2020136008 W CN 2020136008W WO 2022126300 A1 WO2022126300 A1 WO 2022126300A1
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Prior art keywords
inverter
component
inverters
output current
common
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PCT/CN2020/136008
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English (en)
French (fr)
Inventor
于心宇
辛凯
张彦忠
高拥兵
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华为数字能源技术有限公司
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Priority to PCT/CN2020/136008 priority Critical patent/WO2022126300A1/zh
Priority to AU2020481237A priority patent/AU2020481237A1/en
Priority to CN202080031664.8A priority patent/CN115176412A/zh
Priority to EP20965321.1A priority patent/EP4246802A4/en
Publication of WO2022126300A1 publication Critical patent/WO2022126300A1/zh
Priority to US18/328,140 priority patent/US20230308009A1/en

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/123—Suppression of common mode voltage or current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/493—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode the static converters being arranged for operation in parallel
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/0074—Plural converter units whose inputs are connected in series
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
    • H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
    • H02M5/10—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using transformers
    • H02M5/14—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using transformers for conversion between circuits of different phase number
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Definitions

  • the present application relates to the technical field of photovoltaic power generation, and in particular, to a photovoltaic system and a circulating current suppression method.
  • photovoltaic power generation is getting more and more attention, and the voltage level is getting higher and higher.
  • the traditional photovoltaic power generation is that the photovoltaic array outputs direct current, which is converted into alternating current by the inverter and then connected to the grid, or provided to the load.
  • a common implementation method is to connect multiple inverters in series and parallel to transmit more power.
  • a circulating current is often formed between the inverters. Circulating current will cause the following negative effects. On the one hand, it will increase power consumption, reduce efficiency, and affect the life and reliability of power devices; on the other hand, large circulating current spikes may cause the inverter to trigger overcurrent protection and shut down; It may cause the leakage current detected by the inverter to be too large, which may cause the leakage current protection to operate incorrectly.
  • the present application provides a photovoltaic system and a circulating current suppression method, which can suppress the circulating current between parallel inverters, thereby reducing loss, improving efficiency, and avoiding overcurrent protection and leakage current protection caused by circulating current.
  • the embodiments of the present application provide a photovoltaic system, which may be a unipolar photovoltaic system or a bipolar photovoltaic system, as long as the photovoltaic system includes at least two inverters whose output terminals are connected in parallel with the AC side.
  • the photovoltaic system includes: a controller and at least two inverters; the controller is only a general term, and the specific control can include multiple controllers, that is, the controller and the inverter correspond one-to-one, and the controller can Integrated with the inverter, i.e. the controller is located in the cabinet of the inverter. Multiple inverters can also share one controller, and the controller can communicate with multiple inverters.
  • each inverter is connected to the corresponding photovoltaic array. It is not limited here whether the input end of the inverter is directly connected to the photovoltaic array or indirectly connected to the photovoltaic array through a DC/DC converter; the AC output of at least two inverters The terminals are connected in parallel; the controller obtains the DC component of the common-mode output current of at least one of the at least two inverters, that is, the DC component of the common-mode output current of each inverter, or the DC component of the common-mode output current of each inverter.
  • the DC component of the common mode output current of a part of the inverters to suppress the circulating current between at least two inverters.
  • the DC bus voltage of the corresponding inverter is adjusted according to the size of the DC component of the common mode output current.
  • the DC bus voltage of the inverter is the same, there will be no circulating current between the inverters whose output terminals are connected in parallel.
  • the reason for the circulating current is that the DC bus voltage of each inverter is different.
  • the DC component is used to adjust the DC bus voltage of the inverter, thereby suppressing the circulating current between the inverters whose output terminals are connected in parallel.
  • the DC bus voltages of the multiple inverters connected in parallel are made equal as much as possible, thereby suppressing the circulating current between the multiple inverters connected in parallel.
  • the technical solutions provided by the embodiments of the present application can suppress the circulating current between multiple inverters connected in parallel, thereby reducing the loss caused by the circulating current and improving the power supply efficiency.
  • leakage current misprotection and overcurrent protection caused by circulating current can also be avoided, and excessive circulating current may also cause damage to power devices inside the inverter. Therefore, the embodiment of the present application can protect the power devices from circulating current. influences.
  • a possible implementation method is that the photovoltaic system is a bipolar photovoltaic system, and the bipolar photovoltaic system includes an even number of inverters, in two groups, each group includes two inverters, one positive inverter, One negative inverter forms a bipolar inverter, for example, M groups of bipolar inverters are connected in parallel, and M is an integer greater than or equal to 2.
  • the embodiments of the present application do not limit the specific number of groups. The following introduces the situation that the inverters in the bipolar photovoltaic system do not distinguish between the master and the slave, and all inverters have the same position for circulating current suppression.
  • At least two inverters include: a positive inverter group and a negative inverter group , the positive inverter group includes at least a first inverter and a third inverter, and the negative inverter group includes at least a second inverter and a fourth inverter; the DC negative input end of the first inverter is connected to The DC positive input terminal of the second inverter; the DC negative input terminal of the third inverter is connected to the DC positive input terminal of the fourth inverter; the AC output terminals of the first inverter and the third inverter are connected in parallel together, the AC output terminals of the second inverter and the fourth inverter are connected in parallel; the controller is specifically configured to obtain the DC component of the common-mode output current of each of the at least two inverters, the positive pole When the DC component of the common mode output current of the inverters in the inverter group is greater than the preset threshold, the DC bus voltage of the corresponding inverter is reduced; the DC component of the common mode output current of the
  • the component is less than the preset threshold, increase the DC bus voltage of the corresponding inverter; if the DC component of the common mode output current of the inverters in the negative inverter group is greater than the preset threshold, increase the DC bus voltage of the corresponding inverter; When the DC component of the common-mode output current of the inverters in the inverter group is smaller than the preset threshold, the DC bus voltage of the corresponding inverter is reduced.
  • a possible implementation is to continue to introduce the bipolar photovoltaic system, in which the inverter distinguishes the master and the slave, and the master and the slave adopt different circulating current suppression methods.
  • the DC bus voltage of the master does not have to follow the DC component of the common mode output current, that is, it is controlled to a fixed value, while the DC bus voltage of the slave varies with the common mode output current, thereby inhibiting each unit.
  • Circulating current between inverters that is, at least two inverters include: a positive inverter group and a negative inverter group, the positive inverter group includes at least a first inverter and a third inverter, and the negative inverter group includes at least a second inverter.
  • the DC negative input terminal of the first inverter is connected to the DC positive input terminal of the second inverter; the DC negative input terminal of the third inverter is connected to the DC positive input terminal of the fourth inverter input terminal; the AC output terminals of the first inverter and the third inverter are connected in parallel, and the AC output terminals of the second inverter and the fourth inverter are connected in parallel; the first inverter and the third inverter are connected in parallel
  • One of the inverters is the master, the other is the slave, one of the second inverter and the fourth inverter is the master, and the other is the slave; the controller is specifically used to control all masters
  • the DC bus voltage is the preset voltage, and the DC component of the common-mode output current of the slave is obtained.
  • the DC component of the common-mode output current of the slaves in the positive inverter group is greater than the preset threshold, reduce the corresponding slave.
  • a possible implementation method is, in a bipolar photovoltaic system, in order to control the DC bus voltage of the inverter as little as possible, that is, to set as many hosts as possible and as few slaves as possible, so that the DC bus voltage of the host is not fixed. Change, only adjust the DC bus voltage of the slave to suppress the circulating current between the parallel inverters. That is, at least two inverters include: a positive inverter group and a negative inverter group, the positive inverter group includes at least a first inverter and a third inverter, and the negative inverter group includes at least a second inverter.
  • the DC negative input terminal of the first inverter is connected to the DC positive input terminal of the second inverter; the DC negative input terminal of the third inverter is connected to the DC positive input terminal of the fourth inverter input terminal; the AC output terminals of the first inverter and the third inverter are connected in parallel, and the AC output terminals of the second inverter and the fourth inverter are connected in parallel; the first inverter and the third inverter are connected in parallel Both inverters are the master, one of the second inverter and the fourth inverter is the master, and the other is the slave; or, both the second inverter and the fourth inverter are masters, the first inverter One of the inverter and the third inverter is the master, and the other is the slave; the controller is specifically used to control the DC bus voltage of all masters to be the preset voltage; the common mode output current of the slaves is obtained.
  • the slave is located in the positive inverter group, the DC component of the common mode output current is greater than the preset threshold, reduce the DC bus voltage of the slave, and the DC component of the common mode output current is less than the preset threshold, increase the slave DC bus voltage; the slave is located in the negative inverter group, the DC component of the common mode output current is greater than the preset threshold, increase the DC bus voltage of the slave, and the DC component of the common mode output current is less than the preset threshold, reduce the corresponding slave DC bus voltage of the machine.
  • a possible implementation method is that the photovoltaic system described above is a bipolar photovoltaic system.
  • the following describes the situation of a unipolar photovoltaic system, and does not distinguish between the master and the slave. All parallel inverters have the same status, and at least The DC negative input terminals of the two inverters are connected together; that is, multiple inverters have a common input negative terminal, and the controller obtains the DC component of the common mode output current of each inverter in at least two inverters.
  • the DC component of the output current is greater than the preset threshold, the DC bus voltage corresponding to the inverter is reduced; the DC component of the common mode output current is less than the preset threshold, and the DC bus voltage corresponding to the inverter is increased.
  • a possible implementation method is to continue to introduce the unipolar photovoltaic system, and the DC negative input terminals of at least two inverters are connected together, that is, the negative input terminals are shared and the negative electrodes are shared.
  • the inverters connected in parallel distinguish the master and the slave.
  • the DC bus voltage of the master is fixed, and only the DC bus voltage of the slave is adjusted to suppress the circulating current between the parallel inverters. That is, one inverter of at least two inverters is the master, and the other inverters are slaves; the controller is specifically used to obtain the DC component of the common-mode output current and the DC component of the common-mode output current of each slave.
  • a possible implementation method is to continue to introduce the unipolar photovoltaic system.
  • the DC positive input terminals of at least two inverters are connected together, that is, the positive input terminals and the positive terminals are shared; machine, the same status.
  • the controller obtains the DC component of the common-mode output current of each inverter, the DC component of the common-mode output current is greater than the preset threshold, and increases the DC bus voltage of the corresponding inverter; the DC component of the common-mode output current is less than the preset threshold. , reduce the DC bus voltage of the corresponding inverter.
  • a possible implementation method is to continue to introduce the unipolar photovoltaic system, in which the DC positive input terminals of at least two inverters are connected together, that is, the positive input terminals and the positive terminals are shared.
  • Each inverter connected in parallel distinguishes the master and the slave.
  • the DC bus voltage of the master is fixed, and the DC bus voltage of the slave is only adjusted according to the DC component of the common mode output current to suppress the circulating current. That is, one inverter of at least two inverters is the master, and the other inverters are slaves; the controller is specifically used to obtain the DC component of the common-mode output current of the slaves, and the DC component of the common-mode output current is greater than the preset value.
  • Set the threshold to increase the DC bus voltage of the slave; if the DC component of the common mode output current is less than the preset threshold, reduce the DC bus voltage of the slave; control the DC bus voltage of the host to the preset voltage.
  • a possible implementation is that the controller obtains the average value of the three-phase output currents of at least one inverter as the common-mode output current, and extracts the DC component of the common-mode output current from the common-mode output current.
  • controller obtains the respective DC components of the three-phase output currents of at least one inverter, and obtains the average value of the DC components of the three-phase output currents according to the respective DC components of the three-phase output currents as the common mode The DC component of the output current.
  • a possible implementation manner is that the controller, specifically for an inverter with constant input power, reduces the output power to increase the DC bus voltage, and increases the output power to decrease the DC bus voltage.
  • controller specifically for an inverter with constant output power, increases the input power to increase the DC bus voltage, and reduces the input power to decrease the DC bus voltage.
  • a possible implementation manner is that there are multiple controllers, and the inverters and the controllers are in one-to-one correspondence.
  • the controller can be integrated in the cabinet of the inverter, and each controller can communicate with each other.
  • the photovoltaic system includes at least two inverters; the DC input terminals of the inverters are connected to the corresponding photovoltaic arrays; the AC output terminals of the at least two inverters are connected in parallel; and at least one inverter of the at least two inverters is obtained.
  • the DC component of the common mode output current of the inverter is adjusted; the DC bus voltage of the corresponding inverter is adjusted according to the magnitude of the DC component of the common mode output current, so as to suppress the circulating current between at least two inverters.
  • the at least two inverters include: a positive inverter group and a negative inverter group, the positive inverter group at least includes a first inverter and a third inverter, and the negative inverter group
  • the inverter group includes at least a second inverter and a fourth inverter; the DC negative input terminal of the first inverter is connected to the DC positive input terminal of the second inverter; the DC negative input terminal of the third inverter is connected to the first inverter.
  • the at least two inverters include: a positive inverter group and a negative inverter group, the positive inverter group at least includes a first inverter and a third inverter, and the negative inverter group
  • the inverter group includes at least a second inverter and a fourth inverter; the DC negative input terminal of the first inverter is connected to the DC positive input terminal of the second inverter; the DC negative input terminal of the third inverter is connected to the first inverter.
  • One of the inverter and the second inverter is the master, the other is the slave, and one of the third and fourth inverters is the master, and the other is the slave; obtain at least DC component of the common-mode output current of at least one of the two inverters; adjusting the DC bus voltage of the corresponding inverter according to the size of the DC component, specifically including: controlling the DC bus voltage of all hosts to be preset voltage; obtain the DC component of the common mode output current of the slaves; if the DC component of the common mode output current of the slaves in the positive inverter group is greater than the preset threshold, reduce the DC bus voltage of the corresponding slaves; the positive inverter If the DC component of the
  • a possible implementation is as follows: connect the DC negative input terminals of at least two inverters together; obtain the DC component of the common-mode output current of at least one of the at least two inverters; The magnitude of the DC component of the current is used to adjust the DC bus voltage of the corresponding inverter, which specifically includes: obtaining the DC component of the common-mode output current of each of the at least two inverters; the DC component of the common-mode output current is greater than The preset threshold value reduces the DC bus voltage of the corresponding inverter; the DC component of the common mode output current is less than the preset threshold value, and the DC bus voltage corresponding to the inverter is increased.
  • a possible implementation is that the DC negative input terminals of at least two inverters are connected together, and one inverter of the at least two inverters is the master, and the other inverters are slaves; at least two inverters are obtained.
  • the DC component of the common mode output current of at least one inverter in the inverter; according to the magnitude of the DC component of the common mode output current, the DC bus voltage of the corresponding inverter is adjusted, which specifically includes: obtaining the common mode of each slave.
  • the DC component of the output current, the DC component of the common mode output current is greater than the preset threshold, reducing the DC bus voltage of the corresponding slave; the DC component of the common mode output current is less than the preset threshold, increasing the DC bus voltage corresponding to the slave; control
  • the DC bus voltage of the host is the preset voltage.
  • a possible implementation is as follows: connect the DC positive input terminals of at least two inverters together; obtain the DC component of the common-mode output current of at least one of the at least two inverters; The magnitude of the DC component of the current is used to adjust the DC bus voltage of the corresponding inverter, which specifically includes: obtaining the DC component of the common-mode output current of each inverter, and the DC component of the common-mode output current is greater than the preset threshold. The DC bus voltage of the inverter; the DC component of the common mode output current is less than the preset threshold, reducing the DC bus voltage of the corresponding inverter.
  • a possible implementation is that the DC positive input terminals of at least two inverters are connected together, one inverter of at least two inverters is the master, and the other inverters are slaves; at least two inverters are obtained.
  • the DC component of the common mode output current of at least one inverter in the inverter; according to the magnitude of the DC component of the common mode output current, the DC bus voltage of the corresponding inverter is adjusted, which specifically includes: obtaining the common mode of each slave.
  • the DC bus voltage of the host is the preset voltage.
  • a possible implementation is to obtain the DC component of the common mode output current of at least one inverter in the at least two inverters; obtain the average value of the three-phase output current of the at least one inverter as the common mode output current, extract the DC component of the common-mode output current from the common-mode output current; or, obtain the respective DC components of the three-phase output currents of at least one inverter, and obtain the three-phase output current according to the respective DC components of the three-phase output currents The average value of the DC component is taken as the DC component of the common-mode output current.
  • a possible implementation is to adjust the DC bus voltage of the inverter, which specifically includes: for an inverter with constant input power, reducing the output power to increase the DC bus voltage, and increasing the output power to reduce the DC bus voltage; For inverters with constant output power, increase the input power to increase the DC bus voltage, and decrease the input power to decrease the DC bus voltage.
  • the embodiments of the present application have the following advantages:
  • the photovoltaic system includes at least two inverters whose AC output terminals are connected in parallel. Since the AC output terminals are connected in parallel, when there is a voltage difference between the inverters, the AC output terminals of each inverter may be connected in parallel. There is circulation.
  • the technical solution provided by this embodiment is to obtain the common mode output current of at least one inverter, and then extract the DC component from the common mode output current. When the corresponding three-phase inverter is used, the three-phase output current of the inverter is independently detected to obtain the common-mode output current, and the DC component of the common-mode output current is extracted.
  • the DC bus voltage of the corresponding inverter is adjusted according to the magnitude of the DC component of the common-mode output current, thereby suppressing the circulating current between the inverters. Since there may be high-frequency components in the common-mode output current of the inverter, and the magnitude, positive and negative of the high-frequency components have no fixed relationship with the DC bus voltage, while the DC component in the common-mode output current has a fixed relationship with the DC bus voltage, Therefore, in the embodiment of the present application, the DC component of the common-mode output current is extracted, and the DC bus voltage is adjusted according to the relationship between the DC component and the DC bus voltage, so as to make the DC bus voltages of multiple parallel inverters equal as much as possible , thereby suppressing the circulating current between multiple inverters connected in parallel.
  • the technical solutions provided by the embodiments of the present application can suppress the circulating current between multiple inverters connected in parallel, thereby reducing the loss caused by the circulating current and improving the power supply efficiency.
  • leakage current misprotection and overcurrent protection caused by circulating current can also be avoided, and excessive circulating current may also cause damage to power devices inside the inverter. Therefore, the embodiment of the present application can protect the power devices from circulating current. influences.
  • FIG. 1 is a schematic diagram of a bipolar photovoltaic system provided by an embodiment of the present application
  • FIG. 2 is a schematic diagram of a unipolar photovoltaic system provided by an embodiment of the present application.
  • FIG. 3 is a schematic diagram of a photovoltaic system provided by an embodiment of the present application.
  • FIG. 4 is a schematic diagram of another photovoltaic system provided by an embodiment of the present application.
  • FIG. 5 is a schematic diagram of a bipolar photovoltaic system provided by an embodiment of the present application.
  • FIG. 6A is a schematic diagram of still another bipolar photovoltaic system provided by an embodiment of the present application.
  • 6B is a schematic diagram of another bipolar photovoltaic system provided by an embodiment of the present application.
  • 6C is a schematic diagram of yet another bipolar photovoltaic system provided by an embodiment of the present application.
  • 6D is a schematic diagram of still another bipolar photovoltaic system provided by an embodiment of the present application.
  • 6E is a schematic diagram of another bipolar photovoltaic system provided by an embodiment of the present application.
  • 6F is a schematic diagram of yet another bipolar photovoltaic system provided by an embodiment of the present application.
  • 6G is a schematic diagram of still another bipolar photovoltaic system provided by an embodiment of the present application.
  • FIG. 7 is a schematic diagram of a unipolar photovoltaic system with a common negative electrode provided by an embodiment of the present application.
  • FIG. 8 is a schematic diagram of a photovoltaic system corresponding to FIG. 7 for distinguishing a master and a slave;
  • FIG. 9 is a schematic diagram of a unipolar photovoltaic system with a common anode provided by an embodiment of the present application.
  • FIG. 10 is a schematic diagram of the photovoltaic system corresponding to FIG. 9 for distinguishing the master and the slave;
  • FIG. 11 is a flowchart of a method for suppressing circulation of a photovoltaic system according to an embodiment of the application.
  • FIG. 12 is a flowchart of another method for suppressing circulation of a photovoltaic system according to an embodiment of the present application.
  • FIG. 13 is a flowchart of still another method for suppressing circulation of a photovoltaic system provided by an embodiment of the present application.
  • FIG. 14 is a flowchart of a method for suppressing circulating current of a unipolar photovoltaic system according to an embodiment of the present application
  • FIG. 15 is a flowchart of another method for suppressing circulating current of a unipolar photovoltaic system according to an embodiment of the present application.
  • FIG. 16 is a flowchart of still another method for suppressing circulating current of a unipolar photovoltaic system provided by an embodiment of the present application.
  • FIG. 17 is a flow chart of still another method for suppressing circulating current of a unipolar photovoltaic system according to an embodiment of the present application.
  • directional terms such as “upper” and “lower” may include, but are not limited to, definitions relative to the schematic placement of components in the drawings. It should be understood that these directional terms may be relative concepts, They are used for relative description and clarification, which may vary accordingly depending on the orientation in which the components are placed in the drawings.
  • connection should be understood in a broad sense.
  • connection may be a fixed connection, a detachable connection, or an integrated body; it may be directly connected, or Can be indirectly connected through an intermediary.
  • coupled may be a manner of electrical connection that enables signal transmission.
  • Coupling can be a direct electrical connection or an indirect electrical connection through an intermediate medium.
  • FIG. 1 this figure is a schematic diagram of a bipolar photovoltaic system provided by an embodiment of the present application.
  • bipolar photovoltaic system includes three bus bars, namely: DC positive bus BUS+, neutral bus M and DC negative bus BUS -.
  • the bipolar photovoltaic system provided in the embodiment of the present application can be applicable to the safety regulation of 1500V, thereby reducing the withstand voltage requirements for the power converter and the power tube in the inverter.
  • the input end of the power converter 200 is used to connect to the photovoltaic array 100 , the first output end of the power converter 200 is connected to the first end of the DC positive bus BUS+, and the second output end of the power converter 200 is connected to the first end of the neutral bus M. terminal, the third output terminal of the power converter 200 is connected to the first terminal of the DC negative bus BUS-.
  • the bipolar photovoltaic system includes at least two inverters: a first inverter 300 and a second inverter 400 .
  • the first input end of the first inverter 300 is connected to the second end of the DC positive busbar BUS+, and the second input end of the first inverter 300 is connected to the second end of the neutral busbar M;
  • the first input end of the second inverter 400 is connected to the second end of the neutral bus M, and the second input end of the second inverter 400 is connected to the second end of the DC negative bus BUS-.
  • FIG. 2 is a schematic diagram of a conventional monopolar photovoltaic system.
  • the power converter 200 includes two output ends. The first output end of the power converter 200 is connected to the DC positive bus BUS+, and the second output end of the power converter 200 is connected to the DC negative bus BUS-.
  • the inverter 1000 includes two There are two input terminals, wherein the first input terminal of the inverter 1000 is connected to BUS+, and the second input terminal of the inverter 1000 is connected to BUS-. The input end of the power converter 200 is connected to the photovoltaic array 100 .
  • the monopolar photovoltaic system shown in Fig. 2 includes two DC bus bars, namely BUS+ and BUS-. If the total DC bus voltage continues to be 3000V, and the voltage level connected to the input terminal of the inverter 1000 is 3000V, the withstand voltage of the power tube inside the inverter 1000 is higher than that of the single inverter shown in FIG. 1 . The pressure resistance of the tube is twice as high. Therefore, the bipolar photovoltaic system shown in FIG. 1 can reduce the voltage drop borne by the power devices, which is beneficial for device selection.
  • the total voltage of the DC bus corresponding to Figure 1 is 3000V. The higher the voltage, the smaller the corresponding current, which can reduce the loss on the DC bus.
  • M groups of bipolar inverters may be connected in parallel, for example, M groups of bipolar inverters are connected in parallel, M is an integer greater than or equal to 2, and each group includes 2 inverters.
  • Inverter, one positive inverter, one negative inverter, M groups of parallel bipolar inverters include M*2 inverters, such as 4, 6, 8, etc.
  • M is 2, that is, two groups of bipolar inverters are connected in parallel as an example to introduce, that is, corresponding to four inverters, including two positive inverters and two negative inverters.
  • the following describes the circulating current suppression methods provided by the embodiments of the present application, which mainly include the following two methods.
  • One is to divide multiple parallel inverters into a master and a slave, that is, one inverter is the master, and the other inverters are the master.
  • the inverters are all slaves.
  • the positive inverter group includes 3 inverters
  • the negative inverter group includes 3 inverters.
  • the three parallel positive inverters one is the master and the other two are slaves.
  • the 3 negative inverters connected in parallel 1 is the master and the other 2 are slaves.
  • the controller When the controller suppresses the circulating current, it adopts the same control method for the master and the slave. At this time, the master and the slave can not be distinguished. The other is to adopt different control methods for the master and the slave.
  • the DC bus voltage of the fixed master remains unchanged.
  • the DC bus voltage of the master can be controlled to be the preset voltage, and the DC bus voltage of the slave can be adjusted to suppress the parallel connection. Circulating current between inverters.
  • this figure is a schematic diagram of a photovoltaic system provided by an embodiment of the present application.
  • the photovoltaic system provided by the embodiment of the present application includes: a controller and at least two inverters below; the DC input end of each inverter is connected to the corresponding photovoltaic array; the AC output ends of the at least two inverters are connected in parallel ;
  • a power converter may also be included between the corresponding photovoltaic arrays of the inverters, for example, the power converter may include a boost circuit, etc.
  • the embodiment of the present application does not specifically limit the implementation type of the power converter.
  • the controller is used to obtain the DC component of the common mode output current of each at least one inverter in the at least two inverters, and adjust the DC bus voltage of the corresponding inverter according to the magnitude of the DC component to suppress circulating current between the at least two inverters.
  • the controller here is a general term. In practical applications, one inverter may correspond to one controller, and the implementation form of the controller is not specifically limited in the embodiment of the present application. For example, it may be a single-chip microcomputer, a microprocessor, or a digital signal. processor etc. The specific position of the controller is not limited in the embodiments of the present application. For example, when each inverter corresponds to one controller, the controller may be integrated inside the inverter. When multiple inverters jointly correspond to one controller, the controller can be independently arranged outside each inverter, and the control can be completed as long as the controller and each inverter can communicate and interact.
  • the inverters connected in parallel in the embodiments of the present application may be inverters in a unipolar photovoltaic system or inverters in a bipolar photovoltaic system, and both can be implemented by using the technical solutions provided in the embodiments of the present application. Circulating current suppression between parallel inverters.
  • each inverter corresponds to a controller.
  • the first inverter INV1 corresponds to the first controller 500
  • the second inverter INV2 corresponds to the second controller 600
  • the input terminal of the first inverter INV1 is connected to the corresponding photovoltaic array 100a
  • the input terminal of the second inverter INV2 is connected to the corresponding photovoltaic array 100a.
  • the terminals are connected to the corresponding photovoltaic array 100b. That is, each controller independently controls the corresponding inverter.
  • the first controller 500 is configured to obtain the first DC component of the common mode output current of the first inverter INV1, and the first controller 500 controls the first inverter according to the first DC component of the common mode output current DC bus voltage of INV1.
  • the second controller 600 is configured to obtain the second DC component of the common mode output current of the second inverter INV2, and the second controller 600 controls the DC bus of the second inverter INV2 according to the second DC component of the common mode output current Voltage.
  • the DC bus voltage of the inverter refers to the voltage of the DC input terminal of the inverter. When the DC output terminal of the inverter is connected to the power converter, it can also be understood that the DC bus voltage is the output of the power converter. Voltage.
  • each controller independently completes the control of the inverter.
  • the common-mode output current is obtained according to the output current, and the DC component is extracted from the common-mode output current.
  • the three-phase output current of the inverter is independently detected to obtain the common-mode output current, and the DC component of the common-mode output current is extracted.
  • the DC component of the common-mode output current is extracted, and the DC bus voltage is adjusted according to the relationship between the DC component and the DC bus voltage, so as to make the DC bus voltages of multiple parallel inverters equal as much as possible , thereby suppressing the circulating current between multiple inverters connected in parallel.
  • the current detection circuit corresponding to each inverter detects its own three-phase output current i a , i b , i c in real time. It should be noted that the three-phase output current of the inverter can be obtained through the current detection circuit, such as current sensor. The current sensor obtains the three-phase output current and sends it to the controller corresponding to the inverter.
  • the controller calculates the common mode output current i cir according to the following equation.
  • the controller can extract the DC component from the common mode output current by any of the following methods: hardware filtering, software filtering, average value calculation, Fast Fourier Transform (FFT, Fast Fourier Transform) calculation, extracting the common mode output current. the direct current component.
  • FFT Fast Fourier Transform
  • the controller obtains the respective DC components of the three-phase output currents of the inverter, and obtains the average value of the DC components of the three-phase output currents according to the respective DC components of the three-phase output currents of the inverter as the DC component of the common-mode output current.
  • the controller extracts the DC components of the three-phase output currents i a , i b , and ic by means of hardware filtering, and denote them as i a_dc , i b_dc , and ic_dc respectively ; calculate the DC components of the common mode output current as follows i dc :
  • the first method to obtain the DC component of the common mode output current is to first obtain the average value of the three-phase output current, and then extract the DC component of the average value as the DC component of the common mode output current.
  • the second method of obtaining the DC component of the common mode output current is to first extract the DC component of the three-phase output current, and then obtain the average value of the corresponding DC components of the three phases as the DC component of the common mode output current.
  • the controller of each inverter controls the DC bus voltage according to the DC component of the common-mode output current.
  • the master may not control its DC voltage.
  • Bus voltage only the controller of the slave adjusts the DC bus voltage according to the DC component of the common mode output current to realize the circulating current suppression between the parallel inverters.
  • the DC component of the common mode output current is simply referred to as the DC component below.
  • FIG. 4 this figure is a schematic diagram of yet another photovoltaic system provided by an embodiment of the present application.
  • the first inverter is used as the master INV1
  • the second inverter is used as the slave INV2
  • the second controller 600 of the slave INV2 obtains the DC component of the common mode output current of the slave INV2
  • the DC bus voltage of the slave INV2 is controlled according to the magnitude of the DC component, thereby controlling the circulating current between the master INV1 and the slave INV2.
  • the size of the DC component determines the size of the adjusted DC bus voltage, and the two are positively correlated. For example, the larger the DC component, the greater the adjusted amount of the DC bus voltage.
  • the first does not distinguish between master and slave.
  • FIG. 5 is a schematic diagram of a bipolar photovoltaic system provided by an embodiment of the present application.
  • the first inverter 300 a and the second inverter 400 a in FIG. 5 are equivalent to the first inverter INV1 in FIG. 3
  • the third inverter 300 b and the fourth inverter 400 b in FIG. 5 It corresponds to the second inverter INV2 in FIG. 3 .
  • At least two inverters include: a positive inverter group and a negative inverter group. Since four inverters are used as an example in this embodiment, the positive inverter group includes two inverters, and the negative inverter group includes two inverters. As shown in FIG.
  • the positive inverter group includes at least a first inverter 300a and a third inverter 300b
  • the negative inverter group includes at least a second inverter 400a and a fourth inverter 400b; the first inverter 300a and the fourth inverter 400b;
  • the DC negative input terminal of the inverter 300a is connected to the DC positive input terminal of the second inverter 400a;
  • the DC negative input terminal of the third inverter 300b is connected to the DC positive input terminal of the fourth inverter 400b;
  • the AC output terminals of the inverter 300a and the third inverter 300b are connected in parallel, and the AC output terminals of the second inverter 400a and the fourth inverter 400b are connected in parallel.
  • the AC output terminals of the first inverter 300a and the third inverter 300b are connected in parallel, connecting the first primary winding of the transformer T1, and the AC outputs of the second inverter 400a and the fourth inverter 400b.
  • the terminals are connected in parallel to connect the second primary winding of the transformer T1. That is, all inverters share the same transformer, and the secondary winding of transformer T1 can be connected to the AC grid.
  • a circulating current may exist between the first inverter 300a and the third inverter 300b.
  • a possible circulating current method is that the output current of the first inverter 300a reaches the inductance at the output end of the third inverter 300b through the filter inductor L1, the grid-side inductor L2, and the common mode inductor Lcm at the output end of the first inverter 300a. , and then reach the input end of the third inverter 300b through the filter capacitor Cflt at the output end of the third inverter 300b.
  • L1 and L2 are both filter inductors
  • Lcm is an equivalent common-mode inductor. It should be understood that each figure in the embodiments of the present application only takes three inductors as an example for introduction, or there may be only one inductor in the system. For example there is only one filter inductor. On the one hand, the circulating current between the parallel inverters brings power consumption and reduces the efficiency; on the other hand, when the circulating current is large, it may trigger overcurrent false protection.
  • a controller (not shown in the figure), specifically configured to obtain the DC component of the common mode output current of each of the at least two inverters, the DC components of the inverters 300a and 300b in the positive inverter group
  • the component is greater than the preset threshold, the DC bus voltage of the corresponding inverter is reduced; the DC components of the inverters 300a and 300b in the positive inverter group are less than the preset threshold, and the DC bus voltage of the corresponding inverter is increased;
  • the DC components of the inverters 400a and 400b in the inverter group are greater than the preset threshold, the DC bus voltage of the corresponding inverters is increased; the DC components of the inverters 400a and 400b in the negative inverter group are less than the preset threshold, Decrease the DC bus voltage of the corresponding inverter.
  • the first inverter 300a and the third inverter 300b are both positive inverters, and when the DC component corresponding to the first inverter 300a is greater than a preset threshold, the DC bus voltage of the first inverter 300a is reduced . If the DC component corresponding to the third inverter 300b is smaller than the preset threshold, the DC bus voltage of the third inverter 300b is increased.
  • the second distinguishes between master and slave.
  • this figure is a schematic diagram of still another bipolar photovoltaic system provided by the embodiment of the present application.
  • At least two inverters include: a positive inverter group and a negative inverter group, the positive inverter group includes at least a first inverter and a third inverter, and the negative inverter group includes at least a second inverter inverter and the fourth inverter; the DC negative input terminal of the first inverter is connected to the DC positive input terminal of the second inverter; the DC negative input terminal of the third inverter is connected to the DC positive input terminal of the fourth inverter terminals; the AC output terminals of the first inverter and the third inverter are connected in parallel, and the AC output terminals of the second inverter and the fourth inverter are connected in parallel; the first inverter and the second inverter are connected in parallel
  • One of the inverters is the master and the other is the slave.
  • One of the third and fourth inverters is the master and the other is the slave.
  • the first inverter is the master 300a in the positive inverter group
  • the second inverter is the master 400a in the negative inverter group
  • the third inverter is the slave in the positive inverter group machine 300b
  • the fourth inverter is the slave machine 400b in the negative inverter group.
  • the controller is specifically used to control the DC bus voltage of all the masters (300a and 400a) to be a preset voltage, and obtain the DC component of the common mode output current of the slaves.
  • the DC bus voltage corresponding to the slave (400a) is reduced; the DC component of the slave (400a) in the positive inverter group is less than the preset threshold, and the DC bus voltage corresponding to the slave (400a) is increased ; for the DC component of the slave (400b) in the negative inverter group is greater than the preset threshold, increase the DC bus voltage of the corresponding slave (400b); the DC component of the slave (400b) in the negative inverter group is less than
  • the preset threshold value reduces the DC bus voltage corresponding to the slave (400b).
  • the embodiment of the present application does not specifically limit the specific value of the preset voltage, and the preset voltage must ensure that the DC bus voltage cannot be too high or too low.
  • the preset voltage may be a value equal to the effective value of the line voltage of the AC side power grid times.
  • 4 inverters can include 3 masters and 1 slave.
  • this figure is a schematic diagram of another bipolar photovoltaic system provided by the embodiment of the present application.
  • the master includes 300a, 400a, and 300b, and the slave is 400b as soon as possible.
  • the at least two inverters provided by the embodiments of the present application include: a positive inverter group (300a and 300b) and a negative inverter group (400a and 400b), and the positive inverter group includes at least the first inverter and The third inverter, the negative inverter group includes at least a second inverter and a fourth inverter; the DC negative input terminal of the first inverter is connected to the DC positive input terminal of the second inverter; The DC negative input terminal of the third inverter is connected to the DC positive input terminal of the fourth inverter; the AC output terminals of the first inverter and the third inverter are connected in parallel, and the second inverter The AC output ends of the inverter and the fourth inverter are connected in parallel; the first inverter and the third inverter are both hosts (300a and 300b); one of the second inverter and the fourth inverter is the master and the other is the slave. Or, both the second inverter and the fourth inverter are master
  • One of the slaves is to regulate its DC bus voltage.
  • the principle of adjusting the DC bus voltage is that the sum of the DC bus voltages of the master 300b and the slave 400b is adjusted to be equal to the sum of the DC bus voltages of the master 300a and the master 400a. Since the DC bus voltages of the master 300a and the master 400a are both set to the preset voltage unchanged, and the DC bus voltage of the master 300b is also set to remain unchanged at the preset voltage, only the bus voltage of the slave 400b can be adjusted to achieve two sets of The sum of the corresponding DC bus voltages of bipolar inverters is equal.
  • the controller is specifically used to control the DC bus voltage of all hosts to be the preset voltage; obtain the DC component of the common mode output current of the slaves, the slaves are located in the positive inverter group, and the DC component is greater than the preset threshold, reducing all the The DC bus voltage of the slave machine, the DC component is less than the preset threshold, and the DC bus voltage of the slave machine is increased; the slave machine is located in the negative inverter group, and the DC component is greater than the preset value. Threshold, increase the DC bus voltage of the slave, and decrease the DC bus voltage of the corresponding slave when the DC component is less than the preset threshold.
  • the fourth inverter is taken as the slave as an example, and the second inverter may also be the slave.
  • two positive inverters are used as the master, and one of the two negative inverters is used as a slave.
  • the two negative inverters may both be the master, and one of the two positive inverters may be the master and the other may be the slave.
  • the two positive inverters include a master 300a and a slave 300b, and the two negative inverters include a master 400a and a master 400b.
  • the bipolar photovoltaic system introduced above is introduced with 4 inverters as an example, and more inverters can be included.
  • the following describes the bipolar photovoltaic system corresponding to 6 inverters when M is 3.
  • FIG. 6D is a schematic diagram of another bipolar photovoltaic system provided by the embodiment of the present application.
  • 6D includes two masters, wherein the master 300a of the positive inverter group, the master 400a of the negative inverter group, and the slaves of the positive inverter group include two slaves 300b and 300c.
  • the slaves of the negative inverter group include two: slave 400b and slave 400c. That is, 6 inverters include 2 masters and 4 slaves.
  • the 6 inverters include 4 masters and 2 slaves.
  • the four masters are: a master 300a, a master 400a, a master 300b, and a master 300c, and the two slaves are a slave 400b and a slave 400c.
  • Fig. 6E is only a schematic diagram. All positive inverters are masters, and two of the negative inverter groups are slaves. In addition, all negative inverters may be masters. , 4 of the positive inverters are slaves.
  • One possible implementation method is for the inverter with constant input power, that is, the input power of the inverter remains unchanged, and the controller needs to increase the DC bus. It can be achieved by reducing the output power when the voltage is reduced. On the contrary, when the controller needs to reduce the DC bus voltage, it can be achieved by increasing the output power.
  • 5 , 6A and 6B above are the positive inverter group and the negative inverter group corresponding to one transformer T1, wherein the positive inverter group is connected to the first primary winding of the transformer T1, and the negative inverter group is connected to the first primary winding of the transformer T1.
  • the group is connected to the second primary winding of the transformer T1, and the first primary winding and the second primary winding share the secondary winding.
  • positive inverter group and the negative inverter group may respectively correspond to independent transformers.
  • FIG. 6F is a schematic diagram of yet another bipolar photovoltaic system provided by the embodiment of the present application.
  • the positive inverter group corresponds to the first transformer T1A
  • the negative inverter group corresponds to the second transformer T1B.
  • the number of transformers is not limited in the embodiments of the present application. One transformer may be used, or two independent transformers may be used.
  • each inverter in parallel corresponds to the DC power supply DC.
  • the DC power supply DC is used as the photovoltaic array for the introduction.
  • it can also be a fan or a storage battery. battery.
  • the embodiments of the present application do not specifically limit the specific form of the DC power supply connected to the input end of the inverter, and a possible specific implementation manner is described below by taking the application in the field of photovoltaic power generation as an example.
  • this figure is a schematic diagram of still another bipolar photovoltaic system provided by the embodiment of the present application.
  • the photovoltaic system corresponding to Figure 6G can be applied to a larger photovoltaic power station.
  • the power of the inverter can be relatively large.
  • the input end of each inverter can be connected to a corresponding combiner box.
  • the combiner box can include a power converter.
  • each combiner box may include multiple parallel power converters.
  • the input end of each power converter is connected to the corresponding photovoltaic array PV.
  • FIG. 6G is only a schematic diagram of the photovoltaic array PV.
  • the implementation form of the photovoltaic array is not specifically limited in each embodiment of the present application, for example, it may include multiple photovoltaic strings , each PV group is connected in series and parallel.
  • Each photovoltaic string may include photovoltaic panels connected in series or in parallel.
  • the first inverter 300a is connected as a positive inverter to the corresponding positive MPPT combiner box 200a.
  • the third inverter 300b as a positive inverter is connected to the corresponding positive maximum power point tracking (MPPT, Maximum Power Point Tracking). ) combiner box 200c.
  • MPPT Maximum Power Point Tracking
  • the second inverter 400a as a negative inverter is connected to the corresponding negative MPPT combiner box 200b, and similarly, the fourth inverter 400b as a negative inverter is connected to the corresponding negative MPPT combiner box 200d.
  • the combiner box may not be included, the input end of the inverter is directly connected to the power converter, and the input end of the power converter is connected to the corresponding photovoltaic array.
  • the technical solutions provided in the embodiments of the present application do not limit the power size and specific topology of the photovoltaic system. As long as there are parallel inverters, the circulating current suppression at the output ends of the parallel inverters can be achieved.
  • the above is the bipolar photovoltaic system.
  • the following describes the circulating current suppression method when multiple inverters are connected in parallel in the unipolar photovoltaic system.
  • the AC output terminals of multiple inverters can be connected in parallel.
  • the terminals share a positive electrode or a common negative electrode, which are described below with reference to the accompanying drawings.
  • this figure is a schematic diagram of a unipolar photovoltaic system with a common negative electrode provided by an embodiment of the present application.
  • FIG. 7 only takes two inverters in parallel as an example for introduction. It should be understood that more inverters with AC output terminals connected in parallel may also be included.
  • the AC output terminals of N inverters are connected in parallel, and N is an integer greater than or equal to 2, that is, the AC output terminals of the N inverters are connected in parallel to the primary windings of the same transformer T.
  • the AC output terminal of the first inverter 1000a and the AC output terminal of the second inverter 1000b are connected in parallel, and the DC negative input terminal of the first inverter 1000a and the DC input terminal of the second inverter 1000b are connected in parallel.
  • the negative input terminals are connected together, that is, the two inverters have a common DC negative pole, which is referred to as a common negative pole.
  • both inverters are negative inverters.
  • a circumstance where a circulating current exists is that the AC output terminals of the two inverters pass through the filter inductor L1, the grid-side inductor L2, the common mode inductor Lcm and the filter capacitor Cflt.
  • a circulating current loop will be formed, that is, from the AC output end of the first inverter 1000a to the AC output end of the second inverter 1000b, and then to the DC input end of the second inverter 1000b.
  • the DC negative input terminal and the DC negative input terminal of the second inverter 1000b are connected together, and thus flow back from the DC input terminal of the second inverter 1000b to the DC input terminal of the first inverter 1000a.
  • the above is only an example of a circulating current path. In addition, it may also flow from the AC output end of the second inverter 1000b to the AC output end of the first inverter 1000a, which is not specifically limited in the embodiment of the present application.
  • control methods There are two control methods. One is to divide multiple parallel inverters into a master and a slave, that is, one of the inverters is the master, and the other inverters are the master. for the slave. For example, when three inverters are connected in parallel, one inverter is the master and the other two inverters are slaves.
  • one method is to adopt the same control method for the master and the slave, and the other is to adopt different control methods for the master and the slave.
  • the DC bus voltage of the fixed master remains unchanged, that is, the master can be controlled.
  • the DC bus voltage of the slave is the preset voltage, and the DC bus voltage of the slave machine is adjusted to suppress the circulating current between the inverters.
  • the first method of suppressing the circulating current of the common anode is introduced below.
  • the controller (not shown in the figure) is specifically used to obtain the DC component of the common-mode output current of each inverter.
  • the DC component is greater than the preset threshold, the DC bus voltage of the corresponding inverter is reduced; the DC component is less than When the threshold is preset, increase the DC bus voltage of the corresponding inverter.
  • the preset threshold can be set according to specific circulating current suppression requirements. For example, the preset threshold can be set to 0, that is, when the DC component is greater than 0, the DC bus voltage is controlled to decrease, and when the DC component is less than 0, the DC bus is controlled. voltage increases. When the preset threshold is set to 0, the circulation can be better suppressed. For example, if the DC component of the first inverter 1000a is greater than 0, the DC bus voltage of the first inverter 1000a is decreased, and the DC component of the second inverter 1000b is less than 0, then the DC voltage of the second inverter 1000b is increased bus voltage.
  • the positive and negative of the DC component that is, the direction
  • the control of the DC bus voltage that is, to determine whether the DC component flows out of the inverter or flows into the inverter.
  • control methods in each embodiment of the present application are all directed to the control of a single inverter, that is, for the first method, the master and all slaves use the above control methods, and for each inverter, separate detection For its output current, the common-mode output current is obtained according to the output current, and then the DC component is extracted from the common-mode output current.
  • the three-phase output current of the inverter is independently detected to obtain the common-mode output current, and the DC component of the common-mode output current is extracted.
  • FIG. 8 this figure is a schematic diagram of the photovoltaic system corresponding to FIG. 7 for distinguishing the master and the slave.
  • the DC negative input terminals of at least two inverters are connected together, and one inverter of at least two inverters is the master, and the other inverters are slaves;
  • Figure 8 takes two inverters as an example to introduce , distinguish the master and the slave, in which the master 1000a and the slave 1000b only suppress the circulating current of the slave 1000b, and it is unnecessary to adjust the DC bus voltage of the master 1000a.
  • each inverter corresponds to one controller
  • only the controller corresponding to the slave 1000b can suppress the circulating current. That is, the controller obtains the DC component of the common mode output current of the slave 1000b.
  • the DC component is greater than the preset threshold
  • the DC bus voltage of the slave 1000b is reduced; when the DC component is less than the preset threshold, the DC bus voltage of the slave 1000b is increased.
  • the controller of the host can control the DC bus voltage of the host 1000a to be a preset voltage.
  • the following describes the circulating current suppression scheme of a photovoltaic system with multiple inverters with a common anode connected in parallel.
  • FIG. 9 is a schematic diagram of a unipolar photovoltaic system with a common anode provided by an embodiment of the present application.
  • N is an integer greater than or equal to 2, that is, the AC output terminals of the N inverters are connected in parallel to the primary windings of the same transformer T.
  • FIG. 9 only takes the parallel connection of two inverters as an example for description.
  • the AC output terminal of the first inverter 1000a and the AC output terminal of the second inverter 1000b are connected in parallel, and the DC positive input terminal of the first inverter 1000a and the DC input terminal of the second inverter 1000b are connected in parallel.
  • the positive input terminals are connected together, that is, the two inverters have a common DC positive pole, which is referred to as a common positive pole.
  • both inverters are positive inverters.
  • a circumstance where a circulating current exists is that the AC output terminals of the two inverters pass through the filter inductor L1, the grid-side inductor L2, the common mode inductor Lcm and the filter capacitor Cflt.
  • a circulating current loop will be formed, that is, from the AC output end of the first inverter 1000a to the AC output end of the second inverter 1000b, and then to the DC input end of the second inverter 1000b.
  • the DC positive input terminal and the DC positive input terminal of the second inverter 1000b are connected together, and thus flow back from the DC input terminal of the second inverter 1000b to the DC input terminal of the first inverter 1000a.
  • the above is only an example of a circulating current path. In addition, it may also flow from the AC output end of the second inverter 1000b to the AC output end of the first inverter 1000a, which is not specifically limited in the embodiment of the present application.
  • the first method does not distinguish between the master and the slave, that is, all paralleled inverters use the same circulating current suppression method.
  • the DC positive input terminals of at least two inverters are connected together; the controller obtains the DC component of the common-mode output current of the inverter, and the DC component is greater than the preset threshold, and the DC bus voltage of the inverter is increased; Set the threshold to reduce the DC bus voltage of the inverter. It can be seen that the circulating current suppression mode for inverters with common anodes is exactly opposite to that of inverters with common cathodes.
  • the preset threshold can be set according to specific circulating current suppression requirements. For example, the preset threshold can be set to 0, that is, when the DC component is greater than 0, the DC bus voltage is controlled to increase, and when the DC component is less than 0, the DC bus is controlled. voltage decreases.
  • the preset threshold is set to 0, the circulation can be better suppressed. For example, if the DC component of the first inverter 1000a is greater than 0, the DC bus voltage of the first inverter 1000a is decreased, and the DC component of the second inverter 1000b is less than 0, then the DC voltage of the second inverter 1000b is increased bus voltage.
  • the positive and negative of the DC component that is, the direction
  • the control of the DC bus voltage that is, to determine whether the DC component flows out of the inverter or flows into the inverter.
  • control methods in each embodiment of the present application are all directed to the control of a single inverter, that is, for the first method, the master and all slaves use the above control methods, and for each inverter, separate detection For its output current, the common-mode output current is obtained according to the output current, and then the DC component is extracted from the common-mode output current.
  • the three-phase output current of the inverter is independently detected to obtain the common-mode output current, and the DC component of the common-mode output current is extracted.
  • FIG. 10 the figure is a schematic diagram of the photovoltaic system corresponding to FIG. 9 for distinguishing the master and the slave.
  • the second circulating current suppression method distinguishes the master and the slave.
  • the DC bus voltage is not adjusted, but only the DC bus voltage of the slave is adjusted to suppress the circulating current between the master and the slave, as well as the circulating current between each slave.
  • the DC positive input terminals of at least two inverters are connected together, one inverter of at least two inverters is the master, and the other inverters are slaves; the controller is specifically used to obtain the common mode output of the slaves If the DC component of the current is greater than the preset threshold, the DC bus voltage of the slave is increased; if the DC component is less than the preset threshold, the DC bus voltage of the slave is reduced; the DC bus voltage of the control host is the preset voltage.
  • two inverters are used as an example to distinguish the master and the slave.
  • the master 1000a and the slave 1000b only perform circulating current suppression on the slave 1000b, so there is no need to adjust the DC bus voltage of the master 1000a.
  • the DC bus voltage of the control host remains unchanged at a preset voltage, which can be specifically implemented by the controller of the host.
  • each inverter corresponds to one controller
  • only the controller corresponding to the slave 1000b can suppress the circulating current. That is, the controller obtains the DC component of the common mode output current of the slave 1000b.
  • the DC component is greater than the preset threshold
  • the DC bus voltage of the slave 1000b is increased; when the DC component is less than the preset threshold, the DC bus voltage of the slave 1000b is decreased.
  • the controller of the host can control the DC bus voltage of the host 1000a to be a preset voltage.
  • the embodiments of the present application further provide a method for suppressing the circulation of a photovoltaic system, which will be described in detail below with reference to the accompanying drawings.
  • FIG. 11 is a flowchart of a method for suppressing circulation of a photovoltaic system provided by an embodiment of the present application.
  • the circulating current suppression method for a photovoltaic system is applied to a photovoltaic system that includes at least two inverters; the DC input end of each inverter is connected to a corresponding photovoltaic array; The AC output terminals are connected in parallel;
  • the DC component of the common-mode output current of all inverters can be obtained, or only a part of the DC components of the inverters can be obtained. For example, for an inverter that distinguishes between the master and the slave, only the common-mode output of the slave can be obtained. The DC component of the current.
  • S1102 Adjust the DC bus voltage of the corresponding inverter according to the magnitude of the DC component, so as to suppress the circulating current between at least two inverters.
  • the DC components of the respective common-mode output currents of the inverters are detected, and the DC busbars of the inverters are closed-loop adjusted according to the magnitude of the DC components. voltage, thereby avoiding the circulating current caused by the difference in the DC bus voltage of the parallel inverters.
  • the technical solution provided in this embodiment does not require additional new hardware devices to solve the technical problem of circulating current, and is convenient and simple to implement and low in cost.
  • the method for suppressing circulating current provided in the embodiments of the present application can be applied not only between inverters connected in parallel in a unipolar photovoltaic system, but also between inverters connected in parallel in a bipolar photovoltaic system.
  • the accompanying drawings introduce the circulating current suppression method between parallel inverters in a bipolar photovoltaic system.
  • FIG. 12 is a flowchart of another method for suppressing circulation of a photovoltaic system according to an embodiment of the present application.
  • the photovoltaic system includes at least four inverters as an example, that is, at least two inverters include: a positive inverter group and a negative inverter group, and the positive inverter group has at least two inverters. It includes a first inverter and a third inverter, and the negative inverter group includes at least a second inverter and a fourth inverter; the DC negative input end of the first inverter is connected to the DC of the second inverter.
  • the DC negative input terminal of the third inverter is connected to the DC positive input terminal of the fourth inverter; the AC output terminals of the first inverter and the third inverter are connected in parallel, and the second inverter connected in parallel with the AC output terminal of the fourth inverter;
  • the DC component of the inverters in the positive inverter group is greater than the preset threshold, and the DC bus voltage of the corresponding inverter is reduced; the DC component of the inverters in the positive inverter group is less than the preset threshold, and the increase Corresponding to the DC bus voltage of the inverter;
  • S1202 and S1203 do not have a sequential order. Since the connection mode of the DC side of the inverters in the positive inverter group is different from the connection mode of the inverters in the negative inverter group, the inverters in the negative inverter group are all negative inverters. The inverters in the positive inverter group are all positive inverters. It can be seen from S1202 and S1203 that the adjustment directions of the DC bus voltages for the positive and negative inverters are opposite.
  • Figure 12 corresponds to the case where the bipolar photovoltaic system does not distinguish the master and the slave.
  • the following describes the circulating current suppression method of the parallel inverter that distinguishes the master and the slave.
  • FIG. 13 is a flowchart of still another method for suppressing circulation of a photovoltaic system according to an embodiment of the present application.
  • the photovoltaic system includes at least four inverters as an example, that is, at least two inverters include: a positive inverter group and a negative inverter group, and the positive inverter group has at least two inverters. It includes a first inverter and a third inverter, and the negative inverter group includes at least a second inverter and a fourth inverter; the DC negative input end of the first inverter is connected to the DC of the second inverter.
  • the DC negative input terminal of the third inverter is connected to the DC positive input terminal of the fourth inverter; the AC output terminals of the first inverter and the third inverter are connected in parallel, and the second inverter connected in parallel with the AC output terminal of the fourth inverter; one of the first inverter and the second inverter is the master, the other is the slave, the third inverter and the fourth inverter One of them is the master and the other is the slave;
  • S1301 Control the DC bus voltage of all the masters to the preset voltage; that is, the DC bus voltage of the master can remain unchanged without adjustment, only the DC bus voltage of the slaves is adjusted to suppress the circulating current between multiple parallel inverters.
  • S1302 and S1303 do not have a sequential order. It can be seen from S1302 and S1303 that the DC bus voltages are adjusted in opposite directions for the positive and negative inverters.
  • the above describes the circulating current suppression method of bipolar photovoltaic system.
  • the circulating current suppression method of unipolar photovoltaic system is introduced below.
  • the circulating current suppression method of unipolar photovoltaic system includes two categories based on the connection relationship of inverters. The first type The second type is the circulating current suppression for the positive inverter, and the second type is the circulating current suppression for the negative inverter.
  • the following first introduces the circulating current suppression method when the positive inverters are connected in parallel.
  • FIG. 14 is a flowchart of a method for suppressing circulating current of a unipolar photovoltaic system according to an embodiment of the present application.
  • the circulating current suppression method provided by the embodiment of the present application is suitable for positive inverters, that is, the DC negative input terminals of at least two inverters are connected together; all inverters do not distinguish between master and slave, and adopt the same control mechanism.
  • each inverter detects its own three-phase output current, obtains the DC component of the common-mode output current according to the three-phase output current, and adjusts the DC bus voltage according to the DC component, thereby suppressing the circulating current.
  • FIG. 15 is a flowchart of another method for suppressing circulating current of a unipolar photovoltaic system provided by an embodiment of the present application.
  • At least two inverters are used as an example for description. That is, the DC negative input terminals of at least two inverters are connected together, and one inverter of at least two inverters is the master, and the other inverters are slaves;
  • the DC bus voltage of the control host is the preset voltage; the DC component of the common mode output current of each slave is obtained;
  • S1502 and S1503 have no sequence relationship.
  • the following describes the circulating current suppression method for parallel connection of negative inverters in a unipolar photovoltaic system.
  • FIG. 16 is a flowchart of another method for suppressing circulating current of a unipolar photovoltaic system according to an embodiment of the present application.
  • At least two inverters are used as examples for introduction, and the DC positive input terminals of at least two inverters are connected together;
  • the paralleled inverters adopt the same control strategy, and complete current detection and circulating current suppression independently.
  • the DC component is less than the preset threshold, and the DC bus voltage of the corresponding inverter is reduced.
  • FIG. 17 is a flowchart of still another method for suppressing circulating current of a unipolar photovoltaic system according to an embodiment of the present application.
  • This embodiment is directed to the circulating current suppression method in which the negative inverters are connected in parallel, and the parallel negative inverters distinguish the master and the slave.
  • the DC positive input ends of at least two inverters are connected together, one inverter of the at least two inverters is the master, and the other inverters are slaves;
  • the DC bus voltage of the control host is the preset voltage; the DC component of the common-mode output current of each slave is obtained; it should be understood that the DC bus voltage of the control host in S1701 and the DC component of the slave are not in sequence.
  • the order may also have a sequential order, which is not specifically limited in the embodiments of the present application.
  • S1702 and S1703 do not have a sequential order.
  • the respective DC components of the three-phase output currents of at least one inverter are obtained, and the average value of the DC components of the three-phase output currents is obtained according to the respective DC components of the three-phase output currents as the DC component of the common mode output current.
  • the control strategy adopted for the positive inverter is: when the DC component is greater than 0, that is, the direction is flowing out from the output end of the inverter, it means that the DC bus voltage of the inverter is If it is higher, the DC bus voltage of the inverter needs to be reduced.
  • the DC component is less than 0, that is, the direction is to flow into the inverter from the output end of the inverter, it means that the DC bus voltage of the inverter is low, and the DC bus voltage of the inverter needs to be increased.
  • the control strategy adopted for the negative inverter is: when the DC component is greater than 0, that is, the direction is flowing from the output end of the inverter, it means that the DC bus voltage of the inverter is low, and the inverter needs to be increased. DC bus voltage of the device. When the DC component is less than 0, that is, the direction is to flow into the inverter from the output end of the inverter, it means that the DC bus voltage of the inverter is high, and the DC bus voltage of the inverter needs to be reduced.
  • the technical solutions provided by the embodiments of the present application are not only applicable to the parallel connection of multiple inverters in a unipolar photovoltaic system, but also applicable to the parallel connection of multiple inverters in a bipolar photovoltaic system.
  • the circulating current can be suppressed, so as to protect the output side of the inverter. If there is no voltage difference between multiple parallel inverters, there will be no circulating current.
  • the embodiment of the present application reduces or eliminates the voltage difference between the parallel inverters by adjusting the DC bus voltage.
  • At least one (item) refers to one or more, and "a plurality” refers to two or more.
  • “And/or” is used to describe the relationship between related objects, indicating that there can be three kinds of relationships, for example, “A and/or B” can mean: only A, only B, and both A and B exist , where A and B can be singular or plural.
  • the character “/” generally indicates that the associated objects are an “or” relationship.
  • At least one item(s) below” or similar expressions thereof refer to any combination of these items, including any combination of single item(s) or plural items(s).
  • At least one (a) of a, b or c can mean: a, b, c, "a and b", “a and c", “b and c", or "a and b and c" ", where a, b, c can be single or multiple.

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Abstract

一种光伏***及环流抑制方法，***包括：控制器（500、600）和至少两台逆变器（300、400）；每台逆变器的直流输入端连接对应的光伏阵列（100）；至少两台逆变器（300、400）的交流输出端并联在一起；控制器（500、600），用于获得至少两台逆变器（300、400）中至少一台逆变器的共模输出电流的直流分量，根据共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，以抑制至少两台逆变器（300、400）之间的环流。该技术方案可以抑制并联的多台逆变器之间的环流，从而降低环流带来的损耗，提高供电效率。另外，也可以避免由于环流引起的漏电流误保护以及过流保护，而且过大的环流还可能对逆变器内部的功率器件造成损坏，因此，该技术方案可以保护功率器件免遭环流的影响。

Description

一种光伏***及环流抑制方法 技术领域
本申请涉及光伏发电技术领域，尤其涉及一种光伏***及环流抑制方法。
背景技术
目前，光伏发电越来越受重视，而且电压等级越来越高。传统的光伏发电是光伏阵列输出直流电，经过逆变器转换为交流电后进行并网，或者提供给负载。
为了提高逆变器的功率容量，常用的实现方式是将多个逆变器通过串并联的方式连接在一起，传输更大的功率。但是，在多个逆变器串并联后，往往会在逆变器之间形成环流。环流会造成以下的负面影响，一方面会增加功耗，降低效率，影响功率器件的寿命和可靠性；另一方面较大的环流尖峰可能造成逆变器触发过流保护而关机；另外，环流可能导致逆变器检测的漏电流偏大，而致使漏电流误保护动作。
发明内容
本申请提供了一种光伏***及环流抑制方法，能够抑制并联的逆变器之间的环流，从而降低损耗，提高效率，同时避免环流引起的过流保护及漏电流保护。
本申请实施例提供一种光伏***，该光伏***可以为单极性光伏***，也可以为双极性光伏***，只要光伏***中包括至少两台输出端即交流侧并联在一起的逆变器，即该光伏***包括：控制器和至少两台逆变器；在此控制器仅是一个统称，具体控制时可以包括多台控制器，即控制器与逆变器一一对应，控制器可以与逆变器集成在一起，即控制器位于逆变器的机柜中。也可以多台逆变器共用一个控制器，控制器可以与多台逆变器实现通信。每台逆变器的直流输入端连接对应的光伏阵列，在此不限定逆变器的输入端直接连接光伏阵列还是通过直流/直流变换器间接连接光伏阵列；至少两台逆变器的交流输出端并联在一起；控制器获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量，即可以获得每台逆变器的共模输出电流的直流分量，也可以获得其中一部分逆变器的共模输出电流的直流分量，以抑制至少两台逆变器之间的环流。
因为共模输出电流的直流分量可以表征逆变器之间环流的大小，因此，根据共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，理想情况下，当各台逆变器的直流母线电压相同时，输出端并联在一起的逆变器之间不会存在环流，环流的起因就是因为各台逆变器的直流母线电压不同，因此，可以根据共模输出电流的直流分量来调整逆变器的直流母线电压，从而抑制各台输出端并联在一起的逆变器之间的环流。从而尽量使并联的多台逆变器的直流母线电压相等，进而抑制并联的多台逆变器之间的环流。本申请实施例提供的技术方案可以抑制并联的多台逆变器之间的环流，从而降低环流带来的损耗，提高供电效率。另外，也可以避免由于环流引起的漏电流误保护以及过流保护，而且过大的环流还可能对逆变器内部的功率器件造成损坏，因此，本申请实施例可以保护功率器件免遭环流的影响。
一种可能的实现方式为，光伏***为双极性光伏***，双极性光伏***包括偶数台逆变器，两两一组，每组包括2台逆变器，一台正极逆变器，一台负极逆变器形成双极性逆变器，例如M组双极性逆变器并联，M为大于等于2的整数。本申请实施例不限定具体的 组数。下面介绍双极性光伏***中的逆变器不区分主机和从机，所有逆变器位置相同进行环流抑制的情况，至少两台逆变器包括：正极逆变器组和负极逆变器组，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接第二逆变器的直流正输入端；第三逆变器的直流负输入端连接第四逆变器的直流正输入端；第一逆变器和第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出端并联在一起；控制器，具体用于获得至少两台逆变器中每台逆变器的共模输出电流的直流分量，正极逆变器组中的逆变器的共模输出电流的直流分量大于预设阈值，减小对应逆变器的直流母线电压；正极逆变器组中的逆变器的共模输出电流的直流分量小于预设阈值，增加对应逆变器的直流母线电压；负极逆变器组中的逆变器的共模输出电流的直流分量大于预设阈值，增加对应逆变器的直流母线电压；负极逆变器组中的逆变器的共模输出电流的直流分量小于预设阈值，减小对应逆变器的直流母线电压。
一种可能的实现方式为，继续介绍双极性光伏***，其中逆变器区分主机和从机，主机和从机采取不同环流抑制方式的情况。对于主机的直流母线电压不必跟随共模输出电流的直流分量来变化，即控制为一个固定不变的值，而对于从机的直流母线电压跟随共模输出电流的大小来变化，从而抑制各台逆变器之间的环流。即至少两台逆变器包括：正极逆变器组和负极逆变器组，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接第二逆变器的直流正输入端；第三逆变器的直流负输入端连接第四逆变器的直流正输入端；第一逆变器和第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出端并联在一起；第一逆变器和第三逆变器中的一台为主机，另一台为从机，第二逆变器和第四逆变器中的一台为主机，另一台为从机；控制器，具体用于控制所有主机的直流母线电压为预设电压，获得从机的共模输出电流的直流分量，对于正极逆变器组中的从机的共模输出电流的直流分量大于预设阈值，减小对应从机的直流母线电压；正极逆变器组中的从机的共模输出电流的直流分量小于预设阈值，增加对应从机的直流母线电压；对于负极逆变器组中的从机的共模输出电流的直流分量大于预设阈值，增加对应从机的直流母线电压；负极逆变器组中的从机的共模输出电流的直流分量小于预设阈值，减小对应从机的直流母线电压。
一种可能的实现方式为，双极性光伏***中，为了尽量少控制逆变器的直流母线电压，即设置尽量多数量的主机，尽量数量少的从机，使主机的直流母线电压固定不变，仅调节从机的直流母线电压来抑制并联的各台逆变器之间的环流。即至少两台逆变器包括：正极逆变器组和负极逆变器组，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接第二逆变器的直流正输入端；第三逆变器的直流负输入端连接第四逆变器的直流正输入端；第一逆变器和第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出端并联在一起；第一逆变器和第三逆变器均为主机，第二逆变器和第四逆变器中的一台为主机，另一台为从机；或，第二逆变器和第四逆变器均为主机，第一逆变器和第三逆变器中的一台为主机，另一台为从机；控制器，具体用于控制所有主机的直流母线电压为预设电压；获得从机的 共模输出电流的直流分量，从机位于正极逆变器组中，共模输出电流的直流分量大于预设阈值，减小从机的直流母线电压，共模输出电流的直流分量小于预设阈值，增加从机的直流母线电压；从机位于负极逆变器组中，共模输出电流的直流分量大于预设阈值，增加从机的直流母线电压，共模输出电流的直流分量小于预设阈值，减小对应从机的直流母线电压。
一种可能的实现方式为，以上介绍的光伏***为双极性光伏***，下面介绍单极性光伏***的情况，并且不区分主机和从机，所有并联的逆变器的地位相同，其中至少两台逆变器的直流负输入端连接在一起；即多台逆变器共输入负极，控制器获得至少两台逆变器中每台逆变器的共模输出电流的直流分量，共模输出电流的直流分量大于预设阈值，减小对应逆变器的直流母线电压；共模输出电流的直流分量小于预设阈值，增加对应逆变器的直流母线电压。
一种可能的实现方式为，继续介绍单极性光伏***，至少两台逆变器的直流负输入端连接在一起，即共输入负极，共负极。并联在一起的逆变器区分主机和从机，主机的直流母线电压固定不变，仅调节从机的直流母线电压来抑制并联的各台逆变器之间的环流。即至少两台逆变器中一个逆变器为主机，其余逆变器为从机；控制器，具体用于获得每台从机的共模输出电流的直流分量，共模输出电流的直流分量大于预设阈值，减小对应从机的直流母线电压；共模输出电流的直流分量小于预设阈值，增加对应从机的直流母线电压；控制主机的直流母线电压为预设电压。
一种可能的实现方式为，继续介绍单极性光伏***，至少两台逆变器的直流正输入端连接在一起，即共输入正极，共正极；并且各台逆变器不区分主机和从机，地位相同。控制器获得每台逆变器的共模输出电流的直流分量，共模输出电流的直流分量大于预设阈值，增加对应逆变器的直流母线电压；共模输出电流的直流分量小于预设阈值，减小对应逆变器的直流母线电压。
一种可能的实现方式为，继续介绍单极性光伏***，至少两台逆变器的直流正输入端连接在一起，即共输入正极，共正极。并联在一起的各台逆变器区分主机和从机，主机的直流母线电压固定不变，仅根据共模输出电流的直流分量调节从机的直流母线电压来抑制环流。即至少两台逆变器中一个逆变器为主机，其余逆变器为从机；控制器，具体用于获得从机的共模输出电流的直流分量，共模输出电流的直流分量大于预设阈值，增加从机的直流母线电压；共模输出电流的直流分量小于预设阈值，减小从机的直流母线电压；控制主机的直流母线电压为预设电压。
下面介绍获得共模输出电流的直流分量的两种方式。
一种可能的实现方式为，控制器获得至少一台逆变器的三相输出电流的平均值作为共模输出电流，从共模输出电流中提取共模输出电流的直流分量。
另一种可能的实现方式为，控制器获得至少一台逆变器的三相输出电流各自的直流分量，根据三相输出电流各自的直流分量获得三相输出电流的直流分量平均值作为共模输出电流的直流分量。
下面介绍逆变器工作方式不同时，调节直流母线电压的具体实现方式。
一种可能的实现方式为，控制器，具体用于对于输入功率恒定的逆变器，减小输出功率来增加直流母线电压，增加输出功率来减小直流母线电压。
另一种可能的实现方式为，控制器，具体用于对于输出功率恒定的逆变器，增加输入功率来增加直流母线电压，减小输入功率来减小直流母线电压。
一种可能的实现方式为，控制器为多个，逆变器和控制器一一对应。此时，控制器可以集成在逆变器的机柜内，各个控制器之间可以互相通信。
基于以上实施例提供的光伏***，本申请实施例还提供一种光伏***的环流抑制方法，以上***的各个优点适用于以下的方法，在此不再赘述。光伏***包括至少两台逆变器；台逆变器的直流输入端连接对应的光伏阵列；至少两台逆变器的交流输出端并联在一起；获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，以抑制至少两台逆变器之间的环流。
一种可能的实现方式为，至少两台逆变器包括：正极逆变器组和负极逆变器组，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接第二逆变器的直流正输入端；第三逆变器的直流负输入端连接第四逆变器的直流正输入端；第一逆变器和第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出端并联在一起；获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据直流分量的大小来调节对应逆变器的直流母线电压，具体包括：获得至少两台逆变器中每台逆变器的共模输出电流的直流分量；正极逆变器组中的逆变器的共模输出电流的直流分量大于预设阈值，减小对应逆变器的直流母线电压；正极逆变器组中的逆变器的共模输出电流的直流分量小于预设阈值，增加对应逆变器的直流母线电压；负极逆变器组中的逆变器的共模输出电流的直流分量大于预设阈值，增加对应逆变器的直流母线电压；负极逆变器组中的逆变器的共模输出电流的直流分量小于预设阈值，减小对应逆变器的直流母线电压。
一种可能的实现方式为，至少两台逆变器包括：正极逆变器组和负极逆变器组，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接第二逆变器的直流正输入端；第三逆变器的直流负输入端连接第四逆变器的直流正输入端；第一逆变器和第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出端并联在一起；第一逆变器和第二逆变器中的一台为主机，另一台为从机，第三逆变器和第四逆变器中的一台为主机，另一台为从机；获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据直流分量的大小来调节对应逆变器的直流母线电压，具体包括：控制所有主机的直流母线电压为预设电压；获得从机的共模输出电流的直流分量；对于正极逆变器组中的从机的共模输出电流的直流分量大于预设阈值，减小对应从机的直流母线电压；正极逆变器组中的从机的共模输出电流的直流分量小于预设阈值，增加对应从机的直流母线电压；对于负极逆变器组中的从机的共模输出电流的直流分量大于预设阈值，增加对应从机的直流母线电压；负极逆变器组中的从机的共模输出电流的直流分量小于预设阈值，减小对应从机的直流母线电压。
一种可能的实现方式为，至少两台逆变器的直流负输入端连接在一起；获得至少两台 逆变器中至少一台逆变器的共模输出电流的直流分量；根据共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，具体包括：获得至少两台逆变器中每台逆变器的共模输出电流的直流分量；共模输出电流的直流分量大于预设阈值，减小对应逆变器的直流母线电压；共模输出电流的直流分量小于预设阈值，增加对应逆变器的直流母线电压。
一种可能的实现方式为，至少两台逆变器的直流负输入端连接在一起，至少两台逆变器中一个逆变器为主机，其余逆变器为从机；获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，具体包括：获得每台从机的共模输出电流的直流分量，共模输出电流的直流分量大于预设阈值，减小对应从机的直流母线电压；共模输出电流的直流分量小于预设阈值，增加对应从机的直流母线电压；控制主机的直流母线电压为预设电压。
一种可能的实现方式为，至少两台逆变器的直流正输入端连接在一起；获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，具体包括：获得每台逆变器的共模输出电流的直流分量，共模输出电流的直流分量大于预设阈值，增加对应逆变器的直流母线电压；共模输出电流的直流分量小于预设阈值，减小对应逆变器的直流母线电压。
一种可能的实现方式为，至少两台逆变器的直流正输入端连接在一起，至少两台逆变器中一个逆变器为主机，其余逆变器为从机；获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，具体包括：获得每台从机的共模输出电流的直流分量；共模输出电流的直流分量大于预设阈值，增加对应从机的直流母线电压；共模输出电流的直流分量小于预设阈值，减小对应从机的直流母线电压；控制主机的直流母线电压为预设电压。
一种可能的实现方式为，获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；获得至少一台逆变器的三相输出电流的平均值作为共模输出电流，从共模输出电流中提取共模输出电流的直流分量；或，获得至少一台逆变器的三相输出电流各自的直流分量，根据三相输出电流各自的直流分量获得三相输出电流的直流分量平均值作为共模输出电流的直流分量。
一种可能的实现方式为，调节逆变器的直流母线电压，具体包括：对于输入功率恒定的逆变器，减小输出功率来增加直流母线电压，增加输出功率来减小直流母线电压；对于输出功率恒定的逆变器，增加输入功率来增加直流母线电压，减小输入功率来减小直流母线电压。
从以上技术方案可以看出，本申请实施例具有以下优点：
该光伏***包括至少两台交流输出端并联在一起的逆变器，由于交流输出端并联在一起，因此，当逆变器之间存在电压差时，各个逆变器的交流输出端之间可能存在环流。本实施例提供的技术方案是获得至少一台逆变器的共模输出电流，再从共模输出电流中提取直流分量。当对应的是三相逆变器时，单独检测逆变器的三相输出电流获得共模输出电流，提取共模输出电流的直流分量。根据共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，进而抑制逆变器之间的环流。由于逆变器的共模输出电流中可能存在高频 分量，而高频分量的大小和正负与直流母线电压没有固定关系，而共模输出电流中的直流分量与直流母线电压存在固定关系，因此，本申请实施例中提取共模输出电流中的直流分量，根据直流分量与直流母线电压之间的关系，来调节直流母线电压，从而尽量使并联的多台逆变器的直流母线电压相等，进而抑制并联的多台逆变器之间的环流。
本申请实施例提供的技术方案可以抑制并联的多台逆变器之间的环流，从而降低环流带来的损耗，提高供电效率。另外，也可以避免由于环流引起的漏电流误保护以及过流保护，而且过大的环流还可能对逆变器内部的功率器件造成损坏，因此，本申请实施例可以保护功率器件免遭环流的影响。
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图1为本申请实施例提供的一种双极性光伏***的示意图；
图2为本申请实施例提供的单极性光伏***的示意图；
图3为本申请实施例提供的一种光伏***的示意图；
图4为本申请实施例提供的又一种光伏***的示意图；
图5为本申请实施例提供的一种双极性光伏***的示意图；
图6A为本申请实施例提供的再一种双极性光伏***的示意图；
图6B为本申请实施例提供的另一种双极性光伏***的示意图；
图6C为本申请实施例提供的又一种双极性光伏***的示意图；
图6D为本申请实施例提供的再一种双极性光伏***的示意图；
图6E为本申请实施例提供的另一种双极性光伏***的示意图；
图6F为本申请实施例提供的又一种双极性光伏***的示意图；
图6G为本申请实施例提供的再一种双极性光伏***的示意图；
图7为本申请实施例提供的一种共负极的单极性光伏***的示意图；
图8为图7对应的区分主机和从机的光伏***的示意图；
图9为本申请实施例提供的共正极的单极性光伏***的示意图；
图10为图9对应的区分主机和从机的光伏***的示意图；
图11为本申请实施例提供的一种光伏***的环流抑制方法的流程图；
图12为本申请实施例提供的另一种光伏***的环流抑制方法的流程图；
图13为本申请实施例提供的又一种光伏***的环流抑制方法的流程图；
图14为本申请实施例提供的一种单极性光伏***的环流抑制方法的流程图；
图15为本申请实施例提供的另一种单极性光伏***的环流抑制方法的流程图；
图16为本申请实施例提供的又一种单极性光伏***的环流抑制方法的流程图；
图17为本申请实施例提供的再一种单极性光伏***的环流抑制方法的流程图。
具体实施方式
以下说明中的“第一”、“第二”等用词仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”等的特征可以明示或者隐含地包括一个或者更多该特征。在本申请的描述中，除非另有说明，“多个”的含义是两个或两个以上。
此外，本申请中，“上”、“下”等方位术语可以包括但不限于相对附图中的部件示意置放的方位来定义的，应当理解到，这些方向性术语可以是相对的概念，它们用于相对于的描述和澄清，其可以根据附图中部件附图所放置的方位的变化而相应地发生变化。
在本申请中，除非另有明确的规定和限定，术语“连接”应做广义理解，例如，“连接”可以是固定连接，也可以是可拆卸连接，或成一体；可以是直接相连，也可以通过中间媒介间接相连。此外，术语“耦接”可以是实现信号传输的电性连接的方式。“耦接”可以是直接的电性连接，也可以通过中间媒介间接电性连接。
光伏***实施例
为了使本领域技术人员更好地理解本申请实施例提供的技术方案，下面介绍本申请实施例提供的双极性光伏***。
参见图1，该图为本申请实施例提供的一种双极性光伏***的示意图。
本申请实施例提供的双极性光伏***，与传统的单极性光伏***的区别是，双极性光伏***包括三条母线，分别为：直流正母线BUS+、中性母线M和直流负母线BUS-。
例如，BUS+的电压为+1500V，BUS-的电压为-1500V，则该双极性光伏***的电压等级为正负1500V。但是BUS+和BUS-串联后的电压为3000V。因此，本申请实施例提供的双极性光伏***可以适用1500V的安规即可，从而降低对于功率变换器以及逆变器中功率管的耐压要求。
功率变换器200的输入端用于连接光伏阵列100，功率变换器200的第一输出端连接直流正母线BUS+的第一端，功率变换器200的第二输出端连接中性母线M的第一端，功率变换器200的第三输出端连接直流负母线BUS-的第一端。
而且该双极性光伏***至少包括两个逆变器：第一逆变器300和第二逆变器400。
第一逆变器300的第一输入端连接直流正母线BUS+的第二端，第一逆变器300的第二输入端连接所述中性母线M的第二端；
第二逆变器400的第一输入端连接中性母线M的第二端，第二逆变器400的第二输入端连接直流负母线BUS-的第二端。
为了使本领域技术人员更好地理解本申请实施例提供的双极性光伏***的优点，参见图2，该图为传统的单极光伏***的示意图。
功率变换器200包括两个输出端，功率变换器200的第一输出端连接直流正母线BUS+，功率变换器200的第二输出端连接直流负母线BUS-，同理，逆变器1000包括两个输入端，其中逆变器1000的第一输入端连接BUS+，逆变器1000的第二输入端连接BUS-。功率变换器200的输入端连接光伏阵列100。
对比图1和图2可以发现，图2所示的单极光伏***中，包括两条直流母线，分别为BUS+和BUS-。如果直流母线总电压继续为3000V，则逆变器1000的输入端连接的电压等级为3000V，则逆变器1000内部的功率管的耐压要比图1所示的单个逆变器中的功率管的耐压要高一倍。因此，图1所示的双极性光伏***可以降低功率器件所承受的压降，利于器件选型。
因为实际工作时，功率变换器与后级逆变器的距离可能较远，因此，在直流母线对应 的电力线缆上的损耗比较大，因此，为了提高发电效率，需要尽量降低该损耗。图1对应的直流母线总电压为3000V，电压越高，则对应的电流越小，进而可以降低在直流母线上的损耗。
实际工作中，对于双极性光伏***，可能多组双极性逆变器并联在一起，例如M组双极性逆变器并联，M为大于等于2的整数，每组包括2台逆变器，一台正极逆变器，一台负极逆变器，M组并联的双极性逆变器包括M*2台逆变器，例如4台、6台、8台等。本申请实施例不具体限定M的具体取值，可以根据实际的功率需要，来设置M的数值。下面以M为2，即2组双极性逆变器并联为例进行介绍，即对应4台逆变器，包括2台正极逆变器，2台负极逆变器。
下面介绍本申请实施例提供的环流抑制的方式，主要可以包括以下两种，一种是将并联的多台逆变器分为主机和从机，即其中一台逆变器为主机，其余逆变器均为从机。例如双极性光伏***对应6台逆变器时，正极逆变器组包括3台逆变器，负极逆变器组包括3台逆变器。3台并联的正极逆变器中，1台为主机，其余2台为从机。3台并联的负极逆变器中，1台为主机，其余2台为从机。控制器抑制环流时对于主机和从机采取同样的控制方式，此时可以不区分主机和从机。另一种是对于主机和从机采取不同的控制方式，例如固定主机的直流母线电压保持不变，具体可以控制主机的直流母线电压为预设电压，调节从机的直流母线电压来抑制并联的逆变器之间的环流。
下面以两台并联的逆变器为例进行介绍。
参见图3，该图为本申请实施例提供的一种光伏***的示意图。
本申请实施例提供的光伏***，包括：控制器和以下至少两台逆变器；每台逆变器的直流输入端连接对应的光伏阵列；至少两台逆变器的交流输出端并联在一起；
需要说明的是，在逆变器的对应的光伏阵列之间还可以包括功率变换器，例如功率变换器可以包括升压电路等，本申请实施例对于功率变换器的实现类型不做具体限定。
控制器，用于获得至少两台逆变器中每台至少一台逆变器的共模输出电流的直流分量，根据所述直流分量的大小来调节对应逆变器的直流母线电压，以抑制所述至少两台逆变器之间的环流。此处的控制器为一个统称，实际应用中，可以一台逆变器对应一个控制器，控制器的实现形式本申请实施例也不做具体限定，例如可以为单片机、微处理器或数字信号处理器等。本申请实施例中不限定控制器的具***置，例如每台逆变器对应一个控制器时，控制器可以集成在逆变器的内部。当多台逆变器共同对应一个控制器时，控制器可以独立设置在各台逆变器的外部，只要控制器与各台逆变器可以通信交互即可完成控制。
本申请实施例中并联的逆变器可以为单极性光伏***中的逆变器，也可以为双极性光伏***中的逆变器，均可以利用本申请实施例提供的技术方案来进行并联逆变器之间的环流抑制。
下面以两台逆变器为例进行介绍，例如每台逆变器对应一个控制器。
第一逆变器INV1对应第一控制器500，第二逆变器INV2对应第二控制器600，第一逆变器INV1的输入端连接对应的光伏阵列100a，第二逆变器INV2的输入端连接对应的光伏阵列100b。即每个控制器独自控制对应的逆变器。
其中，第一控制器500用于获得第一逆变器INV1的共模输出电流的第一直流分量，第一控制器500根据共模输出电流的第一直流分量控制第一逆变器INV1的直流母线电压。第二控制器600用于获得第二逆变器INV2的共模输出电流的第二直流分量，第二控制器600根据共模输出电流的第二直流分量控制第二逆变器INV2的直流母线电压。需要说明的是，逆变器的直流母线电压是指逆变器的直流输入端的电压，当逆变器的直流输出端连接功率变换器时，也可以理解为直流母线电压为功率变换器的输出电压。
当一台逆变器对应一个控制器时，各个控制器独自完成对逆变器的控制。
对于每台逆变器，单独检测其输出电流，根据输出电流获得共模输出电流，再从共模输出电流中提取直流分量。当对应的是三相逆变器时，单独检测逆变器的三相输出电流获得共模输出电流，提取共模输出电流的直流分量。
由于逆变器的共模输出电流中可能存在高频分量，而高频分量的大小和正负与直流母线电压没有固定关系，而共模输出电流中的直流分量与直流母线电压存在固定关系，因此，本申请实施例中提取共模输出电流中的直流分量，根据直流分量与直流母线电压之间的关系，来调节直流母线电压，从而尽量使并联的多台逆变器的直流母线电压相等，进而抑制并联的多台逆变器之间的环流。
下面介绍一种利用三相输出电流获得共模输出电流的具体实现方式。
每台逆变器对应的电流检测电路实时检测自身的三相输出电流i a,i b,i c,需要说明的是，逆变器的三相输出电流可以通过电流检测电路来获得，例如电流传感器。电流传感器获得三相输出电流后发送给逆变器对应的控制器。
控制器按照下式计算共模输出电流i cir。
Figure PCTCN2020136008-appb-000001
控制器从共模输出电流中提取直流分量具体可以通过以下任意一种方式：硬件滤波、软件滤波、平均值计算、快速傅里叶变换(FFT，Fast Fourier Transform)计算，提取共模输出电流中的直流分量。
下面介绍另一种利用三相输出电流获得共模输出电流的具体实现方式。
控制器获得逆变器的三相输出电流各自的直流分量，根据逆变器的三相输出电流各自的直流分量获得三相输出电流的直流分量平均值作为共模输出电流的直流分量。
例如，控制器通过硬件滤波方式，提取三相输出电流i a,i b,i c中的直流分量，分别记为i a_dc,i b_dc,i c_dc；按下式计算共模输出电流的直流分量i dc：
Figure PCTCN2020136008-appb-000002
即以上第一种获得共模输出电流的直流分量是先获得三相输出电流的平均值，然后提取平均值的直流分量作为共模输出电流的直流分量。第二种获得共模输出电流的直流分量是先提取三相输出电流的直流分量，再获得三相对应的直流分量的平均值作为共模输出电流的直流分量。
以上介绍的是每台逆变器的控制器均根据共模输出电流的直流分量来控制直流母线电压，下面介绍当并联的多台逆变器分主机和从机时，主机可以不控制其直流母线电压，只 有从机的控制器根据共模输出电流的直流分量调节直流母线电压来实现各个并联逆变器之间的环流抑制。为了方便描述，以下将共模输出电流的直流分量简称为直流分量。
参见图4，该图为本申请实施例提供的又一种光伏***的示意图。
图4与图3相比较，第一逆变器作为主机INV1，第二逆变器作为从机INV2，其中从机INV2的第二控制器600获得从机INV2的共模输出电流的直流分量，根据直流分量的大小控制从机INV2的直流母线电压，从而控制主机INV1和从机INV2之间的环流。
一般情况下，直流分量的大小决定了调节的直流母线电压的大小，两者成正相关的关系，例如直流分量越大，则直流母线电压的被调节量越大。
具体地，直流母线电压的调节是被增加还是减小，决定于直流分量的正负也决定于逆变器的类型，即为正极逆变器和负极逆变器，以下实施例中将着重介绍。
下面首先介绍双极性光伏***环流抑制的两种控制方式。
第一种不区分主机和从机。
参见图5，该图为本申请实施例提供的一种双极性光伏***的示意图。
对应图3中，图5的第一逆变器300a和第二逆变器400a相当于图3中的第一逆变器INV1，图5的第三逆变器300b和第四逆变器400b相当于图3中的第二逆变器INV2。
至少两台逆变器包括：正极逆变器组和负极逆变器组。由于本实施例中以4台逆变器为例，其中正极逆变器组包括2台逆变器，负极逆变器组包括2台逆变器。如图5所示，正极逆变器组至少包括第一逆变器300a和第三逆变器300b，负极逆变器组至少包括第二逆变器400a和第四逆变器400b；第一逆变器300a的直流负输入端连接第二逆变器400a的直流正输入端；第三逆变器300b的直流负输入端连接第四逆变器400b的直流正输入端；第一逆变器300a和第三逆变器300b的交流输出端并联在一起，第二逆变器400a和第四逆变器400b的交流输出端并联在一起。
图5中第一逆变器300a和第三逆变器300b的交流输出端并联在一起，连接变压器T1的第一原边绕组，第二逆变器400a和第四逆变器400b的交流输出端并联在一起，连接变压器T1的第二原边绕组。即所有逆变器共用同一个变压器，变压器T1的副边绕组可以连接交流电网。
由于第一逆变器300a和第三逆变器300b的交流输出端并联，因此，在第一逆变器300a和第三逆变器300b之间可能存在环流。例如一种可能的环流方式为，第一逆变器300a的输出电流通过第一逆变器300a输出端的滤波电感L1、网侧电感L2、共模电感Lcm到达第三逆变器300b输出端的电感，进而经过第三逆变器300b输出端的滤波电容Cflt到达第三逆变器300b的输入端。其中，L1和L2均为滤波电感，Lcm为等效的共模电感，应该理解，本申请实施例的各个图中仅是以三个电感为例进行介绍，也可以***中仅存在一个电感，例如仅存在一个滤波电感。并联的逆变器之间存在的环流一方面带来功耗，降低效率；另一方面环流较大时有可能触发过流误保护。
同理，由于第二逆变器400a和第四逆变器400b的交流输出端并联，因此，在第二逆变器400a和第四逆变器400b之间存在环流。
控制器(图中未示出)，具体用于获得至少两台逆变器中每台逆变器的共模输出电流的 直流分量，正极逆变器组中的逆变器300a和300b的直流分量大于预设阈值，减小对应逆变器的直流母线电压；正极逆变器组中的逆变器300a和300b的直流分量小于预设阈值，增加对应逆变器的直流母线电压；负极逆变器组中的逆变器400a和400b的直流分量大于预设阈值，增加对应逆变器的直流母线电压；负极逆变器组中的逆变器400a和400b的直流分量小于预设阈值，减小对应逆变器的直流母线电压。
例如，第一逆变器300a和第三逆变器300b均为正极逆变器，当第一逆变器300a对应的直流分量大于预设阈值，则减少第一逆变器300a的直流母线电压。第三逆变器300b对应的直流分量小于预设阈值，则增加第三逆变器300b的直流母线电压。
第二种区分主机和从机。
参见图6A，该图为本申请实施例提供的再一种双极性光伏***的示意图。
至少两台逆变器包括：正极逆变器组和负极逆变器组，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接第二逆变器的直流正输入端；第三逆变器的直流负输入端连接第四逆变器的直流正输入端；第一逆变器和第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出端并联在一起；第一逆变器和第二逆变器中的一台为主机，另一台为从机，第三逆变器和第四逆变器中的一台为主机，另一台为从机。
图6A中以第一逆变器为正极逆变器组中的主机300a，第二逆变器为负极逆变器组中的主机400a，第三逆变器为正极逆变器组中的从机300b，第四逆变器为负极逆变器组中的从机400b。
控制器，具体用于控制所有主机(300a和400a)的直流母线电压为预设电压，获得从机的共模输出电流的直流分量，对于正极逆变器组中的从机(400a)的直流分量大于预设阈值，减小对应从机(400a)的直流母线电压；正极逆变器组中的从机(400a)的直流分量小于预设阈值，增加对应从机(400a)的直流母线电压；对于负极逆变器组中的从机(400b)的直流分量大于预设阈值，增加对应从机(400b)的直流母线电压；负极逆变器组中的从机(400b)的直流分量小于预设阈值，减小对应从机(400b)的直流母线电压。
本申请实施例不具体限定预设电压的具体取值，该预设电压要保证直流母线电压不能太高，也不能太低。在一种可能的实现方式中，预设电压可以取值为交流侧电网的线电压的有效值的
Figure PCTCN2020136008-appb-000003
倍。
继续以4台逆变器为例进行介绍，为了减少从机的数量，4台逆变器中可以包括3台主机和1台从机。下面结合附图进行介绍。
参见图6B，该图为本申请实施例提供的另一种双极性光伏***的示意图。
从图6B中可以看出，主机包括300a、400a、300b，从机尽快400b。
即本申请实施例提供的至少两台逆变器包括：正极逆变器组(300a和300b)和负极逆变器组(400a和400b)，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接所述第二逆变器的直流正输入端；所述第三逆变器的直流负输入端连接所述第四逆变器的直流正输入端；第一逆变器和所述第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出 端并联在一起；第一逆变器和第三逆变器均为主机(300a和300b)；第二逆变器和第四逆变器中的一台为主机，另一台为从机。或，所述第二逆变器和所述第四逆变器均为主机，所述第一逆变器和所述第三逆变器中的一台为主机，另一台为从机。
其中有一个从机是为了调节其直流母线电压。直流母线电压的调节原则是，将主机300b和从机400b的直流母线电压之和，调节的与主机300a和主机400a的直流母线电压之和相等。由于主机300a和主机400a的直流母线电压均设为预设电压不变，而主机300b的直流母线电压也设为预设电压不变，因此，只能调节从机400b的母线电压，实现两组双极性逆变器对应的直流母线电压之和相等。
控制器，具体用于控制所有主机的直流母线电压为预设电压；获得从机的共模输出电流的直流分量，从机位于正极逆变器组中，直流分量大于预设阈值，减小所述从机的直流母线电压，所述直流分量小于所述预设阈值，增加所述从机的直流母线电压；所述从机位于所述负极逆变器组中，所述直流分量大于预设阈值，增加所述从机的直流母线电压，所述直流分量小于所述预设阈值，减小对应从机的直流母线电压。
本实施例中以第四逆变器为从机为例，也可以第二逆变器为从机。本实施例中以两台正极逆变器均为主机，两个负极逆变器中有一个为从机。应该理解，也可以两台负极逆变器均为主机，两台正极逆变器中的一台为主机，一台为从机。如图6C所示，两台正极逆变器中包括主机300a和从机300b，两台负极逆变器包括主机400a和主机400b。
以上介绍的双极性光伏***是以4台逆变器为例进行的介绍，可以包括更多的逆变器，下面介绍M为3时，对应6台逆变器的双极性光伏***。
参见图6D，该图为本申请实施例提供的另一种双极性光伏***的示意图。
图6D中的主机包括2台，其中正极逆变器组的主机300a，负极逆变器组的主机400a，正极逆变器组的从机包括2台：从机300b和从机300c。负极逆变器组的从机包括2台：从机400b和从机400c。即6台逆变器包括2台主机好4台从机。
从图6D中可以看出，主机300a、从机300b和从机300c的交流输出端并联在一起，主机400a、从机400b和从机400c的交流输出端并联在一起。
对于图6A-6D几种并联逆变器的环流抑制可以采取与图5类似的方案，在此不再赘述。
当双极性光伏***包括6台逆变器时，除了图6D的实现方案，还有一种参见图6E所示，即6台逆变器中包括4台主机，2台从机。如图6E所示，4台主机分别为：主机300a、主机400a、主机300b、主机300c，2台从机分别为：从机400b和从机400c。
应该理解，图6E仅是一种示意，全部正极逆变器均为主机，负极逆变器组中的2台为从机为例进行的介绍，另外，还可以全部负极逆变器均为主机，正极逆变器中的4台为从机。
下面介绍控制器调节逆变器的直流母线电压的具体实现方式，一种可能的实现方式是对于输入功率恒定的逆变器，即逆变器的输入功率保持不变，控制器需要增加直流母线电压时可以通过减小输出功率来实现，相反，控制器需要减小直流母线电压时可以通过增加输出功率来实现。
以上介绍的是逆变器的输入功率保持不变的情况，还有一种情况是逆变器的输出功率 保持不变，对于输出功率恒定的逆变器，控制器需要增加直流母线电压时可以通过增加输入功率来实现；相反，控制器需要减小直流母线电压时可以通过减小输入功率来实现。以上介绍的均是一对一的控制方式，即针对任意一个需要调节的逆变器均适用。
以上的图5，图6A和图6B均是以正极逆变器组和负极逆变器组共同对应一个变压器T1，其中正极逆变器组连接变压器T1的第一原边绕组，负极逆变器组连接变压器T1的第二原边绕组，第一原边绕组和第二原边绕组共用副边绕组。
另外，正极逆变器组和负极逆变器组可以分别对应独立的变压器。
参见图6F，该图为本申请实施例提供的又一种双极性光伏***的示意图。
图6F中，正极逆变器组对应第一变压器T1A，负极逆变器组对应第二变压器T1B。
本申请实施例中不限定变压器的个数，一个变压器也可以，两个独立的变压器也可以。
另外，以上实施例中均是以并联的各个逆变器对应直流电源DC，本申请实施例中均是以直流电源DC为光伏阵列为了进行的介绍，另外，也可以为风机，也可以为储能电池。
本申请实施例不具体限定逆变器的输入端连接的直流电源的具体形式，下面以应用于光伏发电领域为例介绍一种可能的具体实现方式。
参见图6G，该图为本申请实施例提供的再一种双极性光伏***的示意图。
图6G对应的光伏***可以应用于较大型的光伏电站，逆变器的功率可以比较大，每台逆变器的输入端可以连接对应的汇流箱，汇流箱中可以包括功率变换器，为了增加功率容量，每个汇流箱可以包括多个并联的功率变换器。每个功率变换器的输入端连接对应的光伏阵列PV，图6G中仅是示意性了光伏阵列PV，本申请各个实施例中不具体限定光伏阵列的实现形式，例如可以包括多个光伏组串，各个光伏组串并联在一起。每个光伏组串可以包括串联或串并联的光伏电池板。
第一逆变器300a作为正极逆变器连接对应的正极MPPT汇流箱200a，同理，作为正极逆变器的第三逆变器300b连接对应的正极最大功率点追踪(MPPT，Maximum Power Point Tracking)汇流箱200c。
第二逆变器400a作为负极逆变器连接对应的负极MPPT汇流箱200b，同理，作为负极逆变器的第四逆变器400b连接对应的负极MPPT汇流箱200d。
对于功率等级比较小的光伏***，可以不包括汇流箱，逆变器的输入端直接连接功率变换器，功率变换器的输入端连接对应的光伏阵列。本申请实施例提供的技术方案不限定光伏***的功率大小以及具体的拓扑结构，只要存在并联的逆变器，便可以实现并联的逆变器的输出端的环流抑制。
以上介绍的是双极性光伏***，下面介绍单极性光伏***中多台逆变器并联时的环流抑制方式。对于图2所示的单极光伏***，实际工作时，可以多台逆变器的交流输出端并联在一起，对于单极性光伏***的多台逆变器并联，根据逆变器的直流输入端共正极还是共负极可以分为两种情况，下面分别结合附图进行介绍。
参见图7，该图为本申请实施例提供的一种共负极的单极性光伏***的示意图。
图7仅是以两个逆变器并联为例进行介绍，应该理解，也可以包括更多交流输出端并联在一起的逆变器，例如N个逆变器的交流输出端并联在一起，N为大于等于2的整数， 即N个逆变器的交流输出端并联在一起连接同一个变压器T的原边绕组。
图7所示的第一逆变器1000a的交流输出端和第二逆变器1000b的交流输出端并联在一起，第一逆变器1000a的直流负输入端和第二逆变器1000b的直流负输入端连接在一起，即两个逆变器共直流负极，简称共负极。对于这种连接方式，两个逆变器均是负极逆变器。
对于图7这种交流输出端并联在一起的光伏***，一种环流存在的情况为，两台逆变器的交流输出端通过滤波电感L1、网侧电感L2、共模电感Lcm以及滤波电容Cflt会形成环流回路，即从第一逆变器1000a的交流输出端到第二逆变器1000b的交流输出端，再到第二逆变器1000b的直流输入端，由于第一逆变器1000a的直流负输入端和第二逆变器1000b的直流负输入端连接在一起，因此，从第二逆变器1000b的直流输入端回流到第一逆变器1000a的直流输入端。以上仅是一种环流路径的举例，另外，也可能是从第二逆变器1000b的交流输出端流向第一逆变器1000a的交流输出端，本申请实施例中不做具体限定。
对于图7所示的至少两台逆变器的直流负输入端连接在一起，而交流输出端并联在一起的情况，需要抑制逆变器之间的环流，以免环流影响效率，环流太大时容易引发过流保护。
下面介绍本申请实施例提供的控制方式，控制方式包括两种，一种是将并联的多台逆变器分为主机和从机，即其中一台逆变器为主机，其余逆变器均为从机。例如三台逆变器并联时，一台逆变器为主机，其余两台逆变器为从机。
控制器抑制环流时一种方式是对于主机和从机采取同样的控制方式，另一种是对于主机和从机采取不同的控制方式，例如固定主机的直流母线电压保持不变，即可以控制主机的直流母线电压为预设电压，调节从机的直流母线电压来抑制逆变器之间的环流。
下面介绍共负极环流抑制的第一种方式。
控制器(图中未示出)，具体用于获得每台逆变器的共模输出电流的直流分量，直流分量大于预设阈值时，减小对应逆变器的直流母线电压；直流分量小于预设阈值时，增加对应逆变器的直流母线电压。
需要说明的是，预设阈值可以根据具体的环流抑制需求来设置，例如预设阈值可以设置为0，即直流分量大于0时，控制直流母线电压减小，直流分量小于0时，控制直流母线电压增加。当预设阈值设为0时，可以较好地抑制环流。例如，第一逆变器1000a的直流分量大于0，则减小第一逆变器1000a的直流母线电压，第二逆变器1000b的直流分量小于0，则增加第二逆变器1000b的直流母线电压。应该理解，对于预设阈值设置为0时，即可以判断直流分量的正负，即方向来决定直流母线电压的控制，即判断直流分量是流出逆变器，还是流入逆变器。
本申请各个实施例中的控制方式均是针对单独一台逆变器的控制，即对于第一种方式，主机和所有的从机均采用以上的控制方式，对于每台逆变器，单独检测其输出电流，根据输出电流获得共模输出电流，再从共模输出电流中提取直流分量。当对应的是三相逆变器时，单独检测逆变器的三相输出电流获得共模输出电流，提取共模输出电流的直流分量。
下面介绍共负极环流抑制的第二种方式。
参见图8，该图为图7对应的区分主机和从机的光伏***的示意图。
至少两台逆变器的直流负输入端连接在一起，至少两台逆变器中一个逆变器为主机，其余逆变器为从机；图8中以两台逆变器为例进行介绍，区分主机和从机，其中，即主机1000a和从机1000b，仅对从机1000b进行环流抑制，可以不必调节主机1000a的直流母线电压的大小。
对于每台逆变器对应一个控制器时，仅从机1000b对应的控制器来抑制环流即可。即控制器获得从机1000b的共模输出电流的直流分量，直流分量大于预设阈值时，减小从机1000b的直流母线电压；直流分量小于预设阈值时，增加从机1000b的直流母线电压；主机的控制器可以控制主机1000a的直流母线电压为预设电压。
可以理解的是，对于预设阈值的设置方式，以及直流分量的获取方式可以参见以上实施例中的介绍，在此不再赘述。
下面介绍共正极的多台逆变器并联的光伏***的环流抑制方案。
参见图9，该图为本申请实施例提供的共正极的单极性光伏***的示意图。
N个逆变器的交流输出端并联在一起，N为大于等于2的整数，即N个逆变器的交流输出端并联在一起连接同一个变压器T的原边绕组。图9仅是以两个逆变器并联为例进行介绍。
图9所示的第一逆变器1000a的交流输出端和第二逆变器1000b的交流输出端并联在一起，第一逆变器1000a的直流正输入端和第二逆变器1000b的直流正输入端连接在一起，即两个逆变器共直流正极，简称共正极。对于这种连接方式，两个逆变器均是正极逆变器。
对于图9这种交流输出端并联在一起的光伏***，一种环流存在的情况为，两台逆变器的交流输出端通过滤波电感L1、网侧电感L2、共模电感Lcm以及滤波电容Cflt会形成环流回路，即从第一逆变器1000a的交流输出端到第二逆变器1000b的交流输出端，再到第二逆变器1000b的直流输入端，由于第一逆变器1000a的直流正输入端和第二逆变器1000b的直流正输入端连接在一起，因此，从第二逆变器1000b的直流输入端回流到第一逆变器1000a的直流输入端。以上仅是一种环流路径的举例，另外，也可能是从第二逆变器1000b的交流输出端流向第一逆变器1000a的交流输出端，本申请实施例中不做具体限定。
对于图9所示的至少两台逆变器的直流正输入端连接在一起，而交流输出端并联在一起的情况，需要抑制逆变器之间的环流，以免环流影响效率，环流太大时容易引发过流保护。
对于共正极的并联逆变器，也存在两种抑制环流的方式。下面先结合图9介绍第一种。
第一种抑制环流的方式。
第一种方式不区分主机和从机，即所有并联的逆变器采用相同的环流抑制方式。至少两台逆变器的直流正输入端连接在一起；控制器获得逆变器的共模输出电流的直流分量，直流分量大于预设阈值，增加逆变器的直流母线电压；直流分量小于预设阈值，减小逆变器的直流母线电压。可以看出，对于共正极的逆变器的环流抑制方式与共负极的逆变器的环流抑制方式正好相反。
需要说明的是，预设阈值可以根据具体的环流抑制需求来设置，例如预设阈值可以设置为0，即直流分量大于0时，控制直流母线电压增大，直流分量小于0时，控制直流母线电压减小。当预设阈值设为0时，可以较好地抑制环流。例如，第一逆变器1000a的直流分量大于0，则减小第一逆变器1000a的直流母线电压，第二逆变器1000b的直流分量小于0，则增加第二逆变器1000b的直流母线电压。应该理解，对于预设阈值设置为0时，即可以判断直流分量的正负，即方向来决定直流母线电压的控制，即判断直流分量是流出逆变器，还是流入逆变器。
本申请各个实施例中的控制方式均是针对单独一台逆变器的控制，即对于第一种方式，主机和所有的从机均采用以上的控制方式，对于每台逆变器，单独检测其输出电流，根据输出电流获得共模输出电流，再从共模输出电流中提取直流分量。当对应的是三相逆变器时，单独检测逆变器的三相输出电流获得共模输出电流，提取共模输出电流的直流分量。
下面介绍共负极环流抑制的第二种方式。
参见图10，该图为图9对应的区分主机和从机的光伏***的示意图。
第二种环流抑制方式区分主机和从机，对于主机不调节其直流母线电压，仅调节从机的直流母线电压来抑制主机和从机之间的环流，以及各个从机之间的环流。
至少两台逆变器的直流正输入端连接在一起，至少两台逆变器中一个逆变器为主机，其余逆变器为从机；控制器，具体用于获得从机的共模输出电流的直流分量，直流分量大于预设阈值，增加从机的直流母线电压；直流分量小于预设阈值，减小从机的直流母线电压；控制主机的直流母线电压为预设电压。
图10中以两台逆变器为例进行介绍，区分主机和从机，其中，即主机1000a和从机1000b，仅对从机1000b进行环流抑制，可以不必调节主机1000a的直流母线电压的大小，例如控制主机的直流母线电压为预设电压保持不变，具体可以由主机的控制器来实现。
对于每台逆变器对应一个控制器时，仅从机1000b对应的控制器来抑制环流即可。即控制器获得从机1000b的共模输出电流的直流分量，直流分量大于预设阈值时，增加从机1000b的直流母线电压；直流分量小于预设阈值时，减小从机1000b的直流母线电压；主机的控制器可以控制主机1000a的直流母线电压为预设电压。
可以理解的是，对于预设阈值的设置方式，以及直流分量的获取方式可以参见以上实施例中的介绍，在此不再赘述。
方法实施例
基于以上实施例提供的一种光伏***，本申请实施例还提供一种光伏***的环流抑制方法，下面结合附图进行详细介绍。
参见图11，该图为本申请实施例提供的一种光伏***的环流抑制方法的流程图。
本实施例提供的光伏***的环流抑制方法，应用于如下的光伏***，即包括至少两台逆变器；每台逆变器的直流输入端连接对应的光伏阵列；至少两台逆变器的交流输出端并联在一起；
S1101：获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；
具体可以获得所有逆变器的共模输出电流的直流分量，也可以仅获得其中一部分逆变 器的直流分量，例如对于区分主机和从机的逆变器，可以仅获得从机的共模输出电流的直流分量。
S1102：根据直流分量的大小来调节对应逆变器的直流母线电压，以抑制至少两台逆变器之间的环流。
本实施例提供的方法，对于多台并联的逆变器对应的光伏***，通过检测逆变器各自的共模输出电流的直流分量，根据直流分量的大小来闭环调节逆变器各自的直流母线电压，进而避免并联的逆变器由于直流母线电压的差异造成环流。本实施例提供的技术方案不需要额外增加新的硬件设备来解决环流的技术问题，实施方便简单，成本低。
本申请实施例提供的环流抑制的方法，既可以适用于单极性光伏***中并联的逆变器之间，又可以适用于双极性光伏***中并联的逆变器之间，下面首先结合附图介绍双极性光伏***中并联的逆变器之间的环流抑制方法。
双极性光伏***的具体拓扑结构可以参见以上光伏***实施例中的介绍，在此不再一一赘述。
对于不区分主机和从机的双极性光伏***。
参见图12，该图为本申请实施例提供的另一种光伏***的环流抑制方法的流程图。
本实施例中为了叙述方便，以光伏***包括至少4台逆变器为例进行介绍，即至少两台逆变器包括：正极逆变器组和负极逆变器组，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接第二逆变器的直流正输入端；第三逆变器的直流负输入端连接第四逆变器的直流正输入端；第一逆变器和第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出端并联在一起；
获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
S1201：获得至少两台逆变器中每台逆变器的共模输出电流的直流分量；
S1202：正极逆变器组中的逆变器的直流分量大于预设阈值，减小对应逆变器的直流母线电压；正极逆变器组中的逆变器的直流分量小于预设阈值，增加对应逆变器的直流母线电压；
S1203：负极逆变器组中的逆变器的直流分量大于预设阈值，增加对应逆变器的直流母线电压；负极逆变器组中的逆变器的直流分量小于预设阈值，减小对应逆变器的直流母线电压。
应该理解，S1202与S1203不具有先后顺序。由于正极逆变器组中的逆变器的直流侧的连接方式与负极逆变器组中的逆变器的连接方式不同，因此，负极逆变器组中的逆变器均为负极逆变器，正极逆变器组中的逆变器均为正极逆变器。从S1202和S1203可以看出，对于正极逆变器和负极逆变器的直流母线电压的调节方向相反。
图12对应的是双极性光伏***不区分主机和从机的情况，下面介绍区分主机从机的并联逆变器的环流抑制方法。
参见图13，该图为本申请实施例提供的又一种光伏***的环流抑制方法的流程图。
本实施例中为了叙述方便，以光伏***包括至少4台逆变器为例进行介绍，即至少两台逆变器包括：正极逆变器组和负极逆变器组，正极逆变器组至少包括第一逆变器和第三逆变器，负极逆变器组至少包括第二逆变器和第四逆变器；第一逆变器的直流负输入端连接第二逆变器的直流正输入端；第三逆变器的直流负输入端连接第四逆变器的直流正输入端；第一逆变器和第三逆变器的交流输出端并联在一起，第二逆变器和第四逆变器的交流输出端并联在一起；第一逆变器和第二逆变器中的一台为主机，另一台为从机，第三逆变器和第四逆变器中的一台为主机，另一台为从机；
获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
S1301：控制所有主机的直流母线电压为预设电压；即主机的直流母线电压可以保持不变，不必调节，只调节从机的直流母线电压来抑制多台并联逆变器之间的环流。
S1302：获得从机的共模输出电流的直流分量；
S1303：对于正极逆变器组中的从机的直流分量大于预设阈值，减小对应从机的直流母线电压；正极逆变器组中的从机的直流分量小于预设阈值，增加对应从机的直流母线电压；
S1304：对于负极逆变器组中的从机的直流分量大于预设阈值，增加对应从机的直流母线电压；负极逆变器组中的从机的直流分量小于预设阈值，减小对应从机的直流母线电压。
应该理解，S1302与S1303不具有先后顺序。从S1302和S1303可以看出，对于正极逆变器和负极逆变器的直流母线电压的调节方向相反。
以上介绍的是双极性光伏***的环流抑制方法，下面介绍单极性光伏***的环流抑制方法，单极性光伏***的环流抑制方法基于逆变器的连接关系包括两大类，第一类是针对正极逆变器的环流抑制，第二类是针对负极逆变器的环流抑制。下面先介绍正极逆变器并联时的环流抑制方法。
参见图14，该图为本申请实施例提供的一种单极性光伏***的环流抑制方法的流程图。
本申请实施例提供的环流抑制方法，适用于正极逆变器，即至少两台逆变器的直流负输入端连接在一起；所有逆变器不区分主机和从机，采取同样的控制机制。
获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
S1401：获得至少两台逆变器中每台逆变器的共模输出电流的直流分量；
S1402：直流分量大于预设阈值，减小对应逆变器的直流母线电压；
S1403：直流分量小于预设阈值，增加对应逆变器的直流母线电压。
应该理解，S1402和S1403不区分先后顺序。每台逆变器的控制独立进行，互不影响。每台逆变器检测自身的三相输出电流，根据三相输出电流获得共模输出电流的直流分量，根据直流分量调节直流母线电压，进而抑制环流。
下面介绍单极性光伏***中多台正极逆变器并联但区分主机和从机的情况。
参见图15，该图为本申请实施例提供的另一种单极性光伏***的环流抑制方法的流程图。
本实施例中为了叙述方便，以至少两台逆变器为例进行介绍。即至少两台逆变器的直 流负输入端连接在一起，至少两台逆变器中一个逆变器为主机，其余逆变器为从机；
获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
S1501：控制主机的直流母线电压为预设电压；获得每台从机的共模输出电流的直流分量；
S1502：直流分量大于预设阈值，减小对应从机的直流母线电压；
S1503：直流分量小于预设阈值，增加对应从机的直流母线电压；
需要说明的是，S1502和S1503没有先后顺序关系。
下面介绍单极性光伏***中负极逆变器并联的环流抑制方法。
参见图16，该图为本申请实施例提供的又一种单极性光伏***的环流抑制方法的流程图。
本实施例中为了叙述方便，以至少两台逆变器为例进行介绍，至少两台逆变器的直流正输入端连接在一起；所有并联的逆变器不区分主机和从机，即所有并联的逆变器采取同样的控制策略，各自独立完成电流检测和环流抑制。
获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
S1601：获得每台逆变器的共模输出电流的直流分量；
S1602：直流分量大于预设阈值，增加对应逆变器的直流母线电压；
S1603：直流分量小于预设阈值，减小对应逆变器的直流母线电压。
需要说明的是，S1602和S1603之间不具有先后顺序。
参见图17，该图为本申请实施例提供的再一种单极性光伏***的环流抑制方法的流程图。
本实施例是针对负极逆变器并联在一起的环流抑制方法，并且并联的负极逆变器区分主机和从机。
本实施例中，至少两台逆变器的直流正输入端连接在一起，至少两台逆变器中一个逆变器为主机，其余逆变器为从机；
获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
S1701：控制主机的直流母线电压为预设电压；获得每台从机的共模输出电流的直流分量；应该理解，S1701中的控制主机的直流母线电压与获得从机的直流成分也不具有先后顺序，也可以具有先后顺序，本申请实施例中均不做具体限定。
S1702：直流分量大于预设阈值，增加对应从机的直流母线电压；
S1703：直流分量小于预设阈值，减小对应从机的直流母线电压；
需要说明的是，S1702和S1703不具有先后顺序。
以上各个实施例中获得直流分量的方式可以包括以下两种：
第一种：
获得至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；获得至少一台逆 变器的三相输出电流的平均值作为共模输出电流，从共模输出电流中提取共模输出电流的直流分量；
第二种：
获得至少一台逆变器的三相输出电流各自的直流分量，根据三相输出电流各自的直流分量获得三相输出电流的直流分量平均值作为共模输出电流的直流分量。
以上各个实施例中具体调节直流母线电压的方式包括以下两种：
第一种：
对于输入功率恒定的逆变器，减小输出功率来增加直流母线电压，增加输出功率来减小直流母线电压；
第二种：
对于输出功率恒定的逆变器，增加输入功率来增加直流母线电压，减小输入功率来减小直流母线电压。
本申请以上各个实施例提供的方案，对于正极逆变器采取的控制策略是：当直流分量大于0时，即方向为从逆变器的输出端流出，则说明该逆变器的直流母线电压较高，则需要降低该逆变器的直流母线电压。当直流分量小于0时，即方向为从逆变器的输出端流进逆变器，则说明逆变器的直流母线电压较低，则需要升高该逆变器的直流母线电压。
对于负极逆变器采取的控制策略是：当直流分量大于0时，即方向为从逆变器的输出端流出，则说明该逆变器的直流母线电压较低，则需要升高该逆变器的直流母线电压。当直流分量小于0时，即方向为从逆变器的输出端流进逆变器，则说明该逆变器的直流母线电压较高，需要降低该逆变器的直流母线电压。
本申请实施例提供的技术方案不仅适用于单极性光伏***的多台逆变器并联，也可以适用于双极性光伏***中的多台逆变器并联，由于逆变器的交流输出端并联在一起，当出现环流时，可以抑制环流，从而对逆变器的输出侧实现保护。如果并联的多台逆变器之间不存在电压差则不会存在环流，本申请实施例为了抑制环流，通过调节直流母线电压，来减小或消除各个并联逆变器之间的电压差。
应当理解，在本申请中，“至少一个(项)”是指一个或者多个，“多个”是指两个或两个以上。“和/或”，用于描述关联对象的关联关系，表示可以存在三种关系，例如，“A和/或B”可以表示：只存在A，只存在B以及同时存在A和B三种情况，其中A，B可以是单数或者复数。字符“/”一般表示前后关联对象是一种“或”的关系。“以下至少一项(个)”或其类似表达，是指这些项中的任意组合，包括单项(个)或复数项(个)的任意组合。例如，a，b或c中的至少一项(个)，可以表示：a，b，c，“a和b”，“a和c”，“b和c”，或“a和b和c”，其中a，b，c可以是单个，也可以是多个。
以上所述，以上实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的精神和范围。

Claims (22)

  1. 一种光伏***，其特征在于，包括：控制器和至少两台逆变器；
    每台所述逆变器的直流输入端连接对应的光伏阵列；
    所述至少两台逆变器的交流输出端并联在一起；
    所述控制器，用于获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量，根据所述共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，以抑制所述至少两台逆变器之间的环流。
  2. 根据权利要求1所述的光伏***，其特征在于，所述至少两台逆变器包括：正极逆变器组和负极逆变器组，所述正极逆变器组至少包括第一逆变器和第三逆变器，所述负极逆变器组至少包括第二逆变器和第四逆变器；所述第一逆变器的直流负输入端连接所述第二逆变器的直流正输入端；所述第三逆变器的直流负输入端连接所述第四逆变器的直流正输入端；所述第一逆变器和所述第三逆变器的交流输出端并联在一起，所述第二逆变器和所述第四逆变器的交流输出端并联在一起；
    所述控制器，具体用于获得所述至少两台逆变器中每台逆变器的共模输出电流的直流分量，所述正极逆变器组中的逆变器的所述共模输出电流的直流分量大于预设阈值，减小对应逆变器的直流母线电压；所述正极逆变器组中的逆变器的所述共模输出电流的直流分量小于所述预设阈值，增加对应逆变器的直流母线电压；所述负极逆变器组中的逆变器的所述共模输出电流的直流分量大于预设阈值，增加对应逆变器的直流母线电压；所述负极逆变器组中的逆变器的所述共模输出电流的直流分量小于所述预设阈值，减小对应逆变器的直流母线电压。
  3. 根据权利要求1所述的光伏***，其特征在于，所述至少两台逆变器包括：正极逆变器组和负极逆变器组，所述正极逆变器组至少包括第一逆变器和第三逆变器，所述负极逆变器组至少包括第二逆变器和第四逆变器；所述第一逆变器的直流负输入端连接所述第二逆变器的直流正输入端；所述第三逆变器的直流负输入端连接所述第四逆变器的直流正输入端；所述第一逆变器和所述第三逆变器的交流输出端并联在一起，所述第二逆变器和所述第四逆变器的交流输出端并联在一起；所述第一逆变器和所述第三逆变器中的一台为主机，另一台为从机，所述第二逆变器和所述第四逆变器中的一台为主机，另一台为从机；
    所述控制器，具体用于控制所有所述主机的直流母线电压为预设电压，获得所述从机的共模输出电流的直流分量，对于所述正极逆变器组中的从机的所述共模输出电流的直流分量大于预设阈值，减小对应从机的直流母线电压；所述正极逆变器组中的从机的所述共模输出电流的直流分量小于所述预设阈值，增加对应从机的直流母线电压；对于所述负极逆变器组中的从机的所述共模输出电流的直流分量大于预设阈值，增加对应从机的直流母线电压；所述负极逆变器组中的从机的所述共模输出电流的直流分量小于所述预设阈值，减小对应从机的直流母线电压。
  4. 根据权利要求1所述的光伏***，其特征在于，所述至少两台逆变器包括：正极逆变器组和负极逆变器组，所述正极逆变器组至少包括第一逆变器和第三逆变器，所述负极逆变器组至少包括第二逆变器和第四逆变器；所述第一逆变器的直流负输入端连接所述第 二逆变器的直流正输入端；所述第三逆变器的直流负输入端连接所述第四逆变器的直流正输入端；所述第一逆变器和所述第三逆变器的交流输出端并联在一起，所述第二逆变器和所述第四逆变器的交流输出端并联在一起；所述第一逆变器和所述第三逆变器均为主机，所述第二逆变器和所述第四逆变器中的一台为主机，另一台为从机；或，所述第二逆变器和所述第四逆变器均为主机，所述第一逆变器和所述第三逆变器中的一台为主机，另一台为从机；
    所述控制器，具体用于控制所有所述主机的直流母线电压为预设电压；获得所述从机的共模输出电流的直流分量，所述从机位于所述正极逆变器组中，所述共模输出电流的直流分量大于预设阈值，减小所述从机的直流母线电压，所述共模输出电流的直流分量小于所述预设阈值，增加所述从机的直流母线电压；所述从机位于所述负极逆变器组中，所述共模输出电流的直流分量大于预设阈值，增加所述从机的直流母线电压，所述共模输出电流的直流分量小于所述预设阈值，减小对应从机的直流母线电压。
  5. 根据权利要求1所述的光伏***，其特征在于，所述至少两台逆变器的直流负输入端连接在一起；
    所述控制器，具体用于获得所述至少两台逆变器中每台逆变器的共模输出电流的直流分量，所述共模输出电流的直流分量大于预设阈值，减小对应逆变器的直流母线电压；所述共模输出电流的直流分量小于所述预设阈值，增加对应逆变器的直流母线电压。
  6. 根据权利要求1所述的光伏***，其特征在于，所述至少两台逆变器的直流负输入端连接在一起，所述至少两台逆变器中一个逆变器为主机，其余逆变器为从机；
    所述控制器，具体用于获得每台所述从机的共模输出电流的直流分量，所述共模输出电流的直流分量大于预设阈值，减小对应从机的直流母线电压；所述共模输出电流的直流分量小于所述预设阈值，增加对应从机的直流母线电压；控制所述主机的直流母线电压为预设电压。
  7. 根据权利要求1所述的光伏***，其特征在于，所述至少两台逆变器的直流正输入端连接在一起；
    所述控制器，具体用于获得每台逆变器的共模输出电流的直流分量，所述共模输出电流的直流分量大于预设阈值，增加对应逆变器的直流母线电压；所述共模输出电流的直流分量小于所述预设阈值，减小对应逆变器的直流母线电压。
  8. 根据权利要求1所述的光伏***，其特征在于，所述至少两台逆变器的直流正输入端连接在一起，所述至少两台逆变器中一个逆变器为主机，其余逆变器为从机；
    所述控制器，具体用于获得所述从机的共模输出电流的直流分量，所述共模输出电流的直流分量大于预设阈值，增加所述从机的直流母线电压；所述共模输出电流的直流分量小于所述预设阈值，减小所述从机的直流母线电压；控制所述主机的直流母线电压为预设电压。
  9. 根据权利要求2-8任一项所述的光伏***，其特征在于，所述控制器，还用于获得所述至少一台逆变器的三相输出电流的平均值作为所述共模输出电流，从所述共模输出电流中提取所述共模输出电流的直流分量。
  10. 根据权利要求2-8任一项所述的光伏***，其特征在于，所述控制器，还用于获得所述至少一台逆变器的三相输出电流各自的直流分量，根据所述三相输出电流各自的直流分量获得三相输出电流的直流分量平均值作为所述共模输出电流的直流分量。
  11. 根据权利要求2-9任一项所述的光伏***，其特征在于，所述控制器，具体用于对于输入功率恒定的逆变器，减小输出功率来增加直流母线电压，增加输出功率来减小直流母线电压。
  12. 根据权利要求2-11任一项所述的光伏***，其特征在于，所述控制器，具体用于对于输出功率恒定的逆变器，增加输入功率来增加直流母线电压，减小输入功率来减小直流母线电压。
  13. 根据权利要求1-12任一项所述的光伏***，其特征在于，所述控制器为多个，所述逆变器和所述控制器一一对应。
  14. 一种光伏***的环流抑制方法，其特征在于，所述光伏***包括至少两台逆变器；每台所述逆变器的直流输入端连接对应的光伏阵列；所述至少两台逆变器的交流输出端并联在一起；
    获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；
    根据所述共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，以抑制所述至少两台逆变器之间的环流。
  15. 根据权利要求14所述的方法，其特征在于，所述至少两台逆变器包括：正极逆变器组和负极逆变器组，所述正极逆变器组至少包括第一逆变器和第三逆变器，所述负极逆变器组至少包括第二逆变器和第四逆变器；所述第一逆变器的直流负输入端连接所述第二逆变器的直流正输入端；所述第三逆变器的直流负输入端连接所述第四逆变器的直流正输入端；所述第一逆变器和所述第三逆变器的交流输出端并联在一起，所述第二逆变器和所述第四逆变器的交流输出端并联在一起；
    获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据所述直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
    获得所述至少两台逆变器中每台逆变器的共模输出电流的直流分量；
    所述正极逆变器组中的逆变器的所述共模输出电流的直流分量大于预设阈值，减小对应逆变器的直流母线电压；所述正极逆变器组中的逆变器的所述共模输出电流的直流分量小于所述预设阈值，增加对应逆变器的直流母线电压；所述负极逆变器组中的逆变器的所述共模输出电流的直流分量大于预设阈值，增加对应逆变器的直流母线电压；所述负极逆变器组中的逆变器的所述共模输出电流的直流分量小于所述预设阈值，减小对应逆变器的直流母线电压。
  16. 根据权利要求14所述的方法，其特征在于，所述至少两台逆变器包括：正极逆变器组和负极逆变器组，所述正极逆变器组至少包括第一逆变器和第三逆变器，所述负极逆变器组至少包括第二逆变器和第四逆变器；所述第一逆变器的直流负输入端连接所述第二逆变器的直流正输入端；所述第三逆变器的直流负输入端连接所述第四逆变器的直流正输入端；所述第一逆变器和所述第三逆变器的交流输出端并联在一起，所述第二逆变器和所 述第四逆变器的交流输出端并联在一起；所述第一逆变器和所述第二逆变器中的一台为主机，另一台为从机，所述第三逆变器和所述第四逆变器中的一台为主机，另一台为从机；
    获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据所述直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
    控制所有所述主机的直流母线电压为预设电压；
    获得所述从机的共模输出电流的直流分量；
    对于所述正极逆变器组中的从机的所述共模输出电流的直流分量大于预设阈值，减小对应从机的直流母线电压；所述正极逆变器组中的从机的所述共模输出电流的直流分量小于所述预设阈值，增加对应从机的直流母线电压；对于所述负极逆变器组中的从机的所述共模输出电流的直流分量大于预设阈值，增加对应从机的直流母线电压；所述负极逆变器组中的从机的所述共模输出电流的直流分量小于所述预设阈值，减小对应从机的直流母线电压。
  17. 根据权利要求14所述的方法，其特征在于，所述至少两台逆变器的直流负输入端连接在一起；
    获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据所述共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
    获得所述至少两台逆变器中每台逆变器的共模输出电流的直流分量；
    所述共模输出电流的直流分量大于预设阈值，减小对应逆变器的直流母线电压；
    所述共模输出电流的直流分量小于所述预设阈值，增加对应逆变器的直流母线电压。
  18. 根据权利要求14所述的方法，其特征在于，所述至少两台逆变器的直流负输入端连接在一起，所述至少两台逆变器中一个逆变器为主机，其余逆变器为从机；
    获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据所述共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
    获得每台所述从机的共模输出电流的直流分量，所述共模输出电流的直流分量大于预设阈值，减小对应从机的直流母线电压；所述共模输出电流的直流分量小于所述预设阈值，增加对应从机的直流母线电压；控制所述主机的直流母线电压为预设电压。
  19. 根据权利要求14所述的方法，其特征在于，所述至少两台逆变器的直流正输入端连接在一起；
    获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据所述共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
    获得每台逆变器的共模输出电流的直流分量，所述共模输出电流的直流分量大于预设阈值，增加对应逆变器的直流母线电压；所述共模输出电流的直流分量小于所述预设阈值，减小对应逆变器的直流母线电压。
  20. 根据权利要求14所述的方法，其特征在于，所述至少两台逆变器的直流正输入端连接在一起，所述至少两台逆变器中一个逆变器为主机，其余逆变器为从机；
    获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；根据所述共模输出电流的直流分量的大小来调节对应逆变器的直流母线电压，具体包括：
    获得每台所述从机的共模输出电流的直流分量；
    所述共模输出电流的直流分量大于预设阈值，增加对应从机的直流母线电压；所述共模输出电流的直流分量小于所述预设阈值，减小对应从机的直流母线电压；控制所述主机的直流母线电压为预设电压。
  21. 根据权利要求14-20任一项所述的方法，其特征在于，获得所述至少两台逆变器中至少一台逆变器的共模输出电流的直流分量；
    获得所述至少一台逆变器的三相输出电流的平均值作为所述共模输出电流，从所述共模输出电流中提取所述共模输出电流的直流分量；
    或，
    获得所述至少一台逆变器的三相输出电流各自的直流分量，根据所述三相输出电流各自的直流分量获得三相输出电流的直流分量平均值作为所述共模输出电流的直流分量。
  22. 根据权利要求14-20任一项所述的方法，其特征在于，调节逆变器的直流母线电压，具体包括：
    对于输入功率恒定的逆变器，减小输出功率来增加直流母线电压，增加输出功率来减小直流母线电压；
    对于输出功率恒定的逆变器，增加输入功率来增加直流母线电压，减小输入功率来减小直流母线电压。
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