CN115395561A - Low-voltage ride through control method and system for photovoltaic inverter under weak grid - Google Patents
Low-voltage ride through control method and system for photovoltaic inverter under weak grid Download PDFInfo
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- 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
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- 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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
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- 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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
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- H—ELECTRICITY
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- 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
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- H02J3/381—Dispersed generators
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- 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
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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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
- 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
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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
- 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
- H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
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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
- 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
- H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
- H02M7/5395—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
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- 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
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Abstract
The invention discloses a low-voltage ride through control method and system for a photovoltaic inverter under a weak grid. When a low-penetration fault occurs, adopting a power grid voltage loop and reactive current feedforward control; the power grid voltage ring is used for supporting reactive current required by power grid voltage drop; the reactive current feedforward setting is used for compensating the response speed of the low-penetration reactive current; the total reactive current meets the low-penetration standard through the given amplitude limit of the total reactive current. When the low-pass exits, the given amplitude limit of the total reactive current is gradually reduced along with the recovery of the voltage; after stabilization, the reactive current feed is set to zero, and the total reactive current is set to be limited to the rated current of the inverter. The invention can solve the problem of voltage drop caused by grid-connected operation active current of the inverter under the weak grid, does not need upper-layer scheduling and control loop switching, has simple control algorithm and saves controller resources; and the current is more stable, and the overcurrent protection of the inverter is not easy to be caused.
Description
Technical Field
The invention belongs to the technical field of photovoltaic power generation, and particularly relates to a low-voltage ride through control method and system for a photovoltaic inverter under a weak grid.
Background
With the continuous improvement of new forms of energy photovoltaic permeability, bring the continuous reduction of electric wire netting intensity, the weak electric wire netting condition that the forceful electric power net weakens into the time-varying is increasingly serious.
When the power grid is weak, the increase of active current can cause the reduction of terminal voltage; the traditional photovoltaic inverter usually adopts a reactive power loop, the reactive power is usually zero, and the reactive current cannot be automatically compensated, so that the active power is increased and then reduced, the power is unbalanced, and the system operation is unstable; aiming at a weak power grid, some products can carry out reactive scheduling through upper-layer scheduling to compensate voltage drop caused by active current; when a low-voltage ride-through fault occurs in a power grid, the common method is to remove a power outer loop and only keep a current loop, and the reactive current instruction setting is given by a fault ride-through formula; when the grid fault is cleared, the power loop control method is switched back, current impact may occur in the control loop switching process, the photovoltaic inverter is shut down due to overcurrent protection, and the process is complex and complex to control.
Disclosure of Invention
The invention provides a low-voltage ride through control method and system for a photovoltaic inverter under a weak grid, and aims to solve the problem of control loop switching between grid-connected operation and low-voltage ride through operation at present.
In order to achieve the above purpose, the invention provides a low voltage ride through control method for a photovoltaic inverter under a weak grid, comprising the following steps:
step 1, obtaining a difference value of positive sequence voltage obtained by positive and negative sequence separation of a rated alternating current bus voltage given value and actually measured alternating current bus voltage, and obtaining a first passive current given value by the difference value through a voltage PI controller;
step 2, summing the first reactive current set value and the reactive current feedforward to obtain a total reactive current set value, wherein the total reactive current set value passes through a total reactive current set amplitude limit to obtain a reactive current total set value of a current inner loop;
step 3, making a difference between the reactive current total set value and q-axis component current of the inverter grid-connected current, and obtaining a control voltage q-axis component through the difference value by a current PI regulator;
and 4, carrying out park inverse transformation on the q-axis component of the control voltage by utilizing the phase locking angle of the inverter to obtain a modulation signal, generating a trigger pulse by using a modulation type, and outputting the trigger pulse to an IGBT unit of the inverter for control.
Further, in step 2, the calculation flow of reactive current feedforward and total reactive current given amplitude limiting is as follows:
s1, setting reactive current feedforward to be 0; the reactive current is given to limit as the rated current of the inverter;
s2, judging whether Usp < LVRT _ IN is established or not, wherein Usp is positive sequence voltage obtained by positive and negative sequence separation of actually measured alternating current bus voltage, and LVRT _ IN is a low-penetration set threshold value:
if Usp < LVRT _ IN does not hold, the reactive current feedforward and the given amplitude limit of the reactive current are kept unchanged;
if Usp < LVRT _ IN is established, reactive current feedforward is calculated according to rated current; calculating a total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating-current bus voltage;
s3, judging whether Usp > LVRT _ OUT is true:
if Usp is larger than LVRT _ OUT, reactive current feedforward is calculated according to rated current; calculating the total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating current bus voltage;
when Usp > LVRT _ OUT is established, the total reactive current is given to be limited as the rated current of the inverter, and LVRT _ OUT is a low-pass exit setting threshold value.
Further, in S2, reactive current feed-forward iq2 * The calculation formula of (2) is as follows: iq2 * ＝ξ*I N Wherein, I N And xi is rated current of the inverter, and xi is a compensation coefficient.
Further, in S2, the total reactive current is given a limiting iq * The formula for calculating limit is: iq * _limit＝1.5*(0.9-Usp)*I N ，I N The inverter is rated for current.
Further, in S3, when Usp>LVRT _ OUT is true and has a duration>At low break-through exit state hold time, the total reactive current is given a clipping of I N LVRT _ OUT is a low exit set threshold.
A weak under-grid photovoltaic inverter low voltage ride through control system comprises:
the acquisition module is used for acquiring the actually measured variable values and transmitting the acquired actually measured variable values to the processing module and the display module; the actually measured variable value comprises actually measured alternating current bus voltage and actually measured inverter grid-connected current;
and the processing module is used for generating trigger pulses according to the actually measured variable values and outputting the trigger pulses to the IGBT unit of the inverter so as to control the running state of the inverter.
Further, the processing module comprises:
an initialization module for setting the reactive current feedforward to 0; setting the given amplitude limit of the reactive current as the rated current of the inverter;
the first judging module is used for judging whether Usp < LVRT _ IN is established or not, wherein Usp is positive sequence voltage obtained by positive and negative sequence separation of actually measured alternating current bus voltage, and LVRT _ IN is a low-penetration set threshold value:
if Usp < LVRT _ IN is not true, the reactive current feedforward and the reactive current given amplitude limit are kept unchanged;
if Usp < LVRT _ IN is established, calculating reactive current feedforward according to rated current; calculating the total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating current bus voltage;
a second judging module: for determining whether Usp > LVRT _ OUT holds:
if Usp > LVRT _ OUT is not established, calculating reactive current feedforward according to rated current; calculating the total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating current bus voltage;
when Usp>When LVRT _ OUT is established, the total reactive current is given the amplitude limit as I N LVRT _ OUT is a low exit set threshold.
The computer device comprises a memory and a processor which are electrically connected, wherein a computer program which can run on the processor is stored on the memory, and when the processor executes the computer program, the steps of the weak under-grid photovoltaic inverter low-voltage ride-through control method are realized.
A computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, implements the steps of the weak under-grid photovoltaic inverter low voltage ride through control method described above.
Compared with the prior art, the invention has at least the following beneficial technical effects:
according to the technical scheme, when the grid-connected operation is carried out, the alternating-current bus voltage is adjusted by adopting the power grid voltage loop control, and the voltage drop caused by active current is compensated in real time; when a low-penetration fault occurs, adopting a power grid voltage loop and reactive current feedforward control; the power grid voltage ring is used for supporting reactive current required by power grid voltage drop; the reactive current feedforward setting is used for compensating the response speed of the low-penetration reactive current; whether the total reactive current meets the low-penetration criterion is achieved by a given limiting of the total reactive current. When the low-voltage ride-through exits, the given amplitude limit of the total reactive current is gradually reduced along with the recovery of the voltage; and after the stability is waited, the total reactive current is limited to be the rated current of the inverter. According to the technical scheme, when grid-connected operation is carried out, the grid voltage loop control is adopted, the problem of voltage drop caused by grid-connected operation active current of the inverter under a weak grid is solved, and the upper-layer scheduling is not relied on; the grid-connected operation and the low-voltage ride-through control are unified, no matter under the grid-connected operation or during the low-voltage ride-through, the same set of control strategy is adopted, the switching of a control loop does not exist, the controller resource is saved, the control algorithm is simple, and the realization is easy. When the low-voltage ride through is carried out, the current impact is smaller, the current is more stable, the overcurrent protection of the inverter is not easy to be caused, and the continuous operation of the photovoltaic inverter is ensured.
Furthermore, under the low-penetration state, the reactive current is given to carry out real-time amplitude limiting according to the change of the voltage of the power grid, the total reactive current given amplitude limiting is gradually reduced along with the recovery of the voltage, and the situation that the high penetration is caused due to overhigh voltage is avoided.
Furthermore, the set time is reserved when the low penetration exits, the AC voltage PI control is enabled to be recovered to a normal state, and then the grid-connected operation state is switched to, so that the impact-free control state is realized.
Drawings
Fig. 1 is a block diagram of an implementation of a low-voltage ride through reactive current control method under a weak grid according to an embodiment of the present invention;
fig. 2 is a flow chart of a method for controlling reactive current for low voltage ride through under a weak grid according to an embodiment of the present invention;
FIG. 3 is a three-phase grid voltage waveform diagram;
FIG. 4 is a three-phase grid-connected current waveform diagram;
FIG. 5 is a grid-connected current q-axis component diagram;
FIG. 6 is a schematic diagram of a low voltage ride through reactive current control system under a weak grid according to the present invention;
fig. 7 is a schematic structural diagram of a computer device provided by the present invention.
Detailed Description
In order to make the objects and technical solutions of the present invention clearer and more understandable. The present invention will be described in further detail with reference to the drawings and examples, and the specific examples are provided for illustrative purposes only and are not intended to limit the present invention.
In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified. In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Example 1
As shown in fig. 1 and fig. 2, the method for controlling the low-voltage ride through reactive current under the weak grid of the invention comprises the following steps:
when the grid-connected operation is carried out, the grid voltage loop control is adopted and is used for adjusting the alternating current bus voltage and compensating the voltage drop caused by active current in real time; reactive current feed-forward iq2 * The total reactive current is given a limiting iq for zero * And _limitis the inverter rated current.
When a low-voltage ride-through fault occurs, adopting a power grid voltage loop and reactive current feedforward control; the power grid voltage ring is used for supporting reactive current required by power grid voltage drop; reactive current feed-forward iq2 * The low-penetration reactive current response speed is compensated; setting the amplitude limit iq by the total reactive current * Limit causes the total reactive current to meet the low-penetration criterion.
When the low voltage ride through exits, the control is carried out by adopting the voltage loop control of the power grid, and the total reactive current gives the amplitude limit iq * The limit is gradually reduced along with the recovery of the voltage; after waiting for stabilization, reactive current feed-forward iq2 * The total reactive current is given a limiting iq for zero * And _limitis the inverter rated current.
Referring to fig. 1, a low voltage ride through control method for a photovoltaic inverter under a weak grid includes the following steps:
step 1, setting a rated alternating current bus voltage given value U N Obtaining a difference value with a positive sequence voltage Usp obtained by positive and negative sequence separation of actually measured alternating current bus voltage, and obtaining a first idle current given iq1 through the difference value by a voltage PI controller * ；
Step 2, giving iq1 to the first reactive current * And reactive current feed-forward iq2 * Summing to obtain total reactive current given iq * Total reactive current given iq * By total reactive current given amplitude limit iq * Obtaining a reactive current total set value of a current inner loop by the limit;
step 3, enabling the reactive current total set value and q-axis component current i of the inverter grid-connected current Lq Making a difference, and obtaining a q-axis component of the control voltage by the difference value through a current PI regulator;
step 4, utilizing the phase locking angle theta of the inverter pcc And performing park inverse transformation on the q-axis component of the control voltage to obtain a modulation signal, and generating a trigger pulse PWM signal by the modulation type number through a modulation module SVPWM and outputting the trigger pulse PWM signal to an IGBT unit of the inverter for control.
The operation state detection process is shown in fig. 2, and includes the following steps:
s1, the initial state is a grid-connected running state, and reactive current feedforward iq2 is adopted at the moment * =0; reactive current given amplitude limit iq * _limit＝I N ，I N Rated current for the inverter;
s2, judging whether Usp < LVRT _ IN is established or not, wherein Usp is positive sequence voltage obtained by positive and negative sequence separation of actually measured alternating current bus voltage, and LVRT _ IN is a low-penetration set threshold value:
if Usp<LVRT _ IN is not established and noneWork current feed-forward iq2 * And reactive current given clipping iq * Limit remains unchanged;
if Usp<LVRT _ IN is established, and is judged to enter the low-penetration operation state, at the moment, iq2 * ＝ξ*I N Total reactive current given clipping iq * The formula for limit is: iq * _limit＝1.5*(0.9-Usp)*I N Xi is a compensation coefficient, and xi is more than 0 and less than 1;
s3, judging whether Usp > LVRT _ OUT is established or not:
if Usp>LVRT _ OUT is false, iq2 * ＝ξ*I N ，iq * _limit＝1.5*(0.9-Usp)*I N ；I N The inverter is rated for current.
When Usp>LVRT _ OUT holds and has a duration>At time _ stable, the total reactive current is given a clipping of I N The LVRT _ OUT is a low-penetration exit set threshold, and the time _ stable is low-penetration exit state holding time, can be set in advance, is calculated according to experience or running conditions, and is used for ensuring that the AC voltage PI control is recovered to a normal state and then is switched to a grid-connected running state.
When the grid voltage is restored from the fault state to the normal operating state, from iq * The _limitcalculation formula shows that the amplitude limiting is dynamic amplitude limiting, the reactive current is given according to the change of the voltage of the power grid for real-time amplitude limiting, and iq is carried out along with the recovery of the voltage * The limit becomes smaller and smaller without worrying about the iq2 when the grid voltage recovers * Also at a higher level, resulting in high penetration; with restoration of grid voltage and iq * The limit is limited to the voltage outer ring PI regulator, so that the recovery of the voltage PI controller is accelerated; meanwhile, the low-penetration exit state holding time is set, sufficient time is reserved to ensure that the voltage PI controller is recovered stably, and the controller is not switched.
To verify the validity of this control strategy, the following simulations were performed: the photovoltaic inverter runs at full power (rated power 250 kW), the short-circuit ratio scr =1.5, three-phase symmetrical drop is realized, the drop depth is 50%, and fig. 3, 4 and 5 respectively show three-phase power grid voltage waveform, three-phase power grid current waveform and reactive current q-axis component.
Example 2
Referring to fig. 6, the weak grid low voltage ride through reactive current control system includes an acquisition module, a processing module, and a display module.
The acquisition module is used for acquiring the actually measured variable values and transmitting the acquired actually measured variable values to the processing module and the display module; the actually measured variable value comprises actually measured alternating current bus voltage and actually measured inverter grid-connected current;
the processing module is used for generating trigger pulses according to the measured variable values and outputting the trigger pulses to the IGBT unit of the inverter so as to control the running state of the inverter and transmit the running state of the inverter to the display module;
and the display module is used for displaying the actually measured variable value and the running state of the inverter.
Further, the processing module comprises:
an initialization module for setting the reactive current feedforward to 0; setting the given amplitude limit of the reactive current as the rated current of the inverter;
the first judgment module is used for judging whether Usp < LVRT _ IN is established or not, wherein Usp is positive sequence voltage obtained by separating positive sequence from negative sequence of actually measured alternating current bus voltage, and LVRT _ IN is a low penetration setting threshold value:
if Usp < LVRT _ IN does not hold, the reactive current feedforward and the given amplitude limit of the reactive current are kept unchanged;
if Usp < LVRT _ IN is established, reactive current feedforward is calculated according to rated current; calculating the total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating current bus voltage;
a second judging module: for determining whether Usp > LVRT _ OUT holds:
if Usp is larger than LVRT _ OUT, reactive current feedforward is calculated according to rated current; calculating a total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating-current bus voltage;
when Usp is>When LVRT _ OUT is established, the total reactive current is given a limiting amplitude of I N LVRT _ OUT sets the threshold for low exit.
Example 3
The computer device provided by the present invention, as shown in fig. 7, includes a memory and a processor, which are electrically connected, where the memory stores a computer program that can be executed on the processor, and the processor executes the computer program to implement the steps of the weak under-grid low-voltage ride-through reactive current control method, such as the steps shown in fig. 1.
The computer program may be partitioned into one or more modules/units, stored in the memory and executed by the processor to implement the invention.
The processor may be a Central Processing Unit (CPU), other general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, etc.
The memory may be configured to store the computer program and/or the module, and the processor may implement various functions of the weak underset low voltage ride through reactive current control apparatus/terminal device by running or executing the computer program and/or the module stored in the memory and calling the data stored in the memory.
In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.
The functions, if implemented in software functional units and sold or used as a stand-alone product, may be stored in a non-transitory computer-readable storage medium executable by a processor. Based on such understanding, the technical solution of the present invention or a part thereof which substantially contributes to the prior art may be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (9)
1. A low-voltage ride through control method of a weak under-grid photovoltaic inverter is characterized by comprising the following steps:
step 1, obtaining a difference value of positive sequence voltage obtained by positive and negative sequence separation of a rated alternating current bus voltage given value and actually measured alternating current bus voltage, and obtaining a first passive current given value by the difference value through a voltage PI controller;
step 2, summing the first reactive current set value and the reactive current feedforward to obtain a total reactive current set value, wherein the total reactive current set value passes through a total reactive current set amplitude limit to obtain a reactive current total set value of a current inner loop;
step 3, making a difference between the reactive current total set value and q-axis component current of the inverter grid-connected current, and obtaining a control voltage q-axis component through the difference value by a current PI regulator;
and 4, carrying out park inverse transformation on the q-axis component of the control voltage by using the phase locking angle of the inverter to obtain a modulation signal, generating a trigger pulse by using a modulation type, and outputting the trigger pulse to an IGBT unit of the inverter for control.
2. The method for controlling the low voltage ride through of the photovoltaic inverter under the weak grid according to claim 1, wherein in the step 2, the calculation process of reactive current feedforward and total reactive current given amplitude limiting comprises the following steps:
s1, setting reactive current feedforward as 0; the reactive current is given to limit as the rated current of the inverter;
s2, judging whether Usp < LVRT _ IN is established or not, wherein Usp is positive sequence voltage obtained by positive and negative sequence separation of actually measured alternating current bus voltage, and LVRT _ IN is a low penetration set threshold value:
if Usp < LVRT _ IN does not hold, the reactive current feedforward and the given amplitude limit of the reactive current are kept unchanged;
if Usp < LVRT _ IN is established, calculating reactive current feedforward according to rated current; calculating a total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating-current bus voltage;
s3, judging whether Usp > LVRT _ OUT is established or not:
if Usp > LVRT _ OUT is not established, calculating reactive current feedforward according to rated current; calculating a total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating-current bus voltage;
when Usp > LVRT _ OUT is established, the total reactive current is given to be limited as the rated current of the inverter, and LVRT _ OUT is a low-pass exit setting threshold value.
3. The method for controlling the low voltage ride through of the photovoltaic inverter under the weak grid according to claim 2, wherein in the step S2, the reactive current feedforward iq2 * The calculation formula of (c) is: iq2 * ＝ξ*I N Wherein, I N And xi is the rated current of the inverter, and xi is a compensation coefficient.
4. The method for controlling the low voltage ride through of the photovoltaic inverter under the weak grid according to claim 2, wherein in S2, the total reactive current is given a limiting iq * The formula for limit is: iq * _limit＝1.5*(0.9-Usp)*I N ，I N The inverter is rated for current.
5. The method according to claim 2, wherein in S3, when Usp is used, the method is used>LVRT _ OUT holds and has a duration>When the low-pass exit state is kept for a certain time, the total reactive current is limited to I N LVRT _ OUT sets the threshold for low exit.
6. A photovoltaic inverter low-voltage ride-through control system under weak network is characterized by comprising:
the acquisition module is used for acquiring the actually measured variable values and transmitting the acquired actually measured variable values to the processing module and the display module; the actually measured variable value comprises actually measured alternating current bus voltage and actually measured inverter grid-connected current;
and the processing module is used for generating trigger pulses according to the actually measured variable values and outputting the trigger pulses to the IGBT unit of the inverter so as to control the running state of the inverter.
7. The weak under-grid photovoltaic inverter low voltage ride through control system of claim 6, wherein the processing module comprises:
the initialization module is used for setting the reactive current feedforward to 0; setting the given amplitude limit of the reactive current as the rated current of the inverter;
the first judgment module is used for judging whether Usp < LVRT _ IN is established or not, wherein Usp is positive sequence voltage obtained by separating positive sequence from negative sequence of actually measured alternating current bus voltage, and LVRT _ IN is a low penetration setting threshold value:
if Usp < LVRT _ IN does not hold, the reactive current feedforward and the given amplitude limit of the reactive current are kept unchanged;
if Usp < LVRT _ IN is established, reactive current feedforward is calculated according to rated current; calculating a total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating-current bus voltage;
a second judging module: for determining whether Usp > LVRT _ OUT holds:
if Usp is larger than LVRT _ OUT, reactive current feedforward is calculated according to rated current; calculating the total reactive current given amplitude limit according to positive sequence voltage and rated current obtained by positive and negative sequence separation of actually measured alternating current bus voltage;
when Usp is>When LVRT _ OUT is established, the total reactive current is given a limiting amplitude of I N LVRT _ OUT is a low exit set threshold.
8. A computer device comprising a memory and a processor electrically connected, the memory having stored thereon a computer program operable on the processor, when executing the computer program, performing the steps of the method of any of claims 1-5.
9. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1-5.
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