CN112928931A - MMC sub-module on-off control method, device and system - Google Patents

MMC sub-module on-off control method, device and system Download PDF

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Publication number
CN112928931A
CN112928931A CN201911244027.4A CN201911244027A CN112928931A CN 112928931 A CN112928931 A CN 112928931A CN 201911244027 A CN201911244027 A CN 201911244027A CN 112928931 A CN112928931 A CN 112928931A
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bridge arm
sub
modules
mmc
voltage
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CN112928931B (en
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高源智
汤明杰
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Beijing Goldwind Science and Creation Windpower Equipment Co Ltd
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Beijing Goldwind Science and Creation Windpower Equipment Co Ltd
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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
    • 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
    • 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
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The application provides a submodule on-off control method, device and system of an MMC, and relates to the field of wind power generation. The sub-module on-off control method comprises the following steps: calculating to obtain a bridge arm differential pressure threshold according to the total harmonic content of the conversion equipment comprising the MMC and the average switching frequency of a switching device of a sub-module in each bridge arm of the MMC; for each bridge arm of the MMC, acquiring the voltage of each submodule in the bridge arm in the current control period, and calculating a first difference value, wherein the first difference value is the difference value between the maximum value and the minimum value of the voltage of the submodule in the bridge arm; acquiring the input number N of submodules in the current control period; and controlling the on-off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the differential pressure threshold of the bridge arm and the current direction in the bridge arm. By the aid of the technical scheme, loss of the whole wind generating set can be reduced.

Description

MMC sub-module on-off control method, device and system
Technical Field
The invention belongs to the field of wind power generation, and particularly relates to a submodule on-off control method, device and system of an MMC.
Background
A Modular Multilevel Converter (MMC) is formed by cascading a plurality of Sub-modules (SM). The MMC has the advantages of high electric energy quality, high modularization, strong fault ride-through capability and the like, and is widely applied to various systems and equipment in various scenes, such as a flexible direct-current transmission system, a high-voltage frequency converter, a static reactive compensation system, a power electronic transformer and the like in high-capacity and medium-high voltage power conversion scenes.
The loss of the MMC can affect a system and equipment, and the loss of the SM in the MMC can account for about 90% of the loss of the whole wind generating set. At the present stage, the loss of the MMC is higher, so that the loss of the whole wind generating set is also higher.
Disclosure of Invention
The embodiment of the application provides a submodule on-off control method, a submodule on-off control device and a submodule on-off control system of an MMC, and the loss of the whole wind generating set can be reduced.
In a first aspect, an embodiment of the present application provides a method for controlling on/off of a sub-module of an MMC, including: calculating to obtain a bridge arm differential pressure threshold according to the total harmonic content of the conversion equipment comprising the MMC and the average switching frequency of a switching device of a sub-module in each bridge arm of the MMC; for each bridge arm of the MMC, acquiring the voltage of each submodule in the bridge arm in the current control period, and calculating a first difference value, wherein the first difference value is the difference value between the maximum value and the minimum value of the voltage of the submodule in the bridge arm; acquiring the input number N of submodules in the current control period; and controlling the on-off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the differential pressure threshold of the bridge arm and the current direction in the bridge arm.
In some possible embodiments, the switching loss of the bridge arm corresponding to the bridge arm differential pressure threshold is the minimum switching loss when the total harmonic content is within the preset standard harmonic content range.
In some possible embodiments, obtaining the investment number N of the sub-modules in the current control period includes: and determining the input number N according to the modulation wave of the bridge arm in the current control period and the voltage reference value of the submodule.
In some possible embodiments, controlling the switching on and off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the bridge arm differential pressure threshold, and the current direction in the bridge arm includes: and if the first difference value is larger than the preset pressure difference threshold value, controlling the N sub-modules with the highest voltage or the N sub-modules with the lowest voltage in the bridge arm to be in an input state according to the current direction in the bridge arm.
In some possible embodiments, controlling the N highest-voltage sub-modules or the N lowest-voltage sub-modules in the bridge arm to be in an on state according to the current direction in the bridge arm includes: if the current direction in the bridge arm is the bridge arm charging direction, controlling the N sub-modules with the lowest voltage in the bridge arm to be in the input state; and if the current direction in the bridge arm is the bridge arm discharging direction, controlling the N sub-modules with the highest voltage in the bridge arm to be in the input state.
In some possible embodiments, controlling the switching on and off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the bridge arm differential pressure threshold, and the current direction in the bridge arm includes: if the first difference value is smaller than or equal to the preset pressure difference threshold value, acquiring the number M of the submodules in the input state in the bridge arm in the previous control period; if the second difference is larger than zero, controlling the N-M sub-modules in the bridge arm in the last control period with the lowest voltage or the highest voltage in the bridge arm in the switching-out state to be switched into the switching-in state according to the current direction in the bridge arm, wherein the second difference is the difference between N and M; if the second difference value is equal to zero, controlling the sub-module in the input state in the bridge arm in the previous control period to keep in the input state, and controlling the sub-module in the cut-out state to keep in the cut-out state; and if the second difference is smaller than zero, controlling the lowest voltage or the highest voltage | N-M | submodule in the bridge arm in the previous control period to be switched into the switching-out state according to the current direction in the bridge arm.
In some possible embodiments, controlling the N-M submodules with the lowest voltage or the highest voltage in the bridge arm in the previous control period to switch to the on state according to the current direction in the bridge arm includes: if the current direction in the bridge arm is the bridge arm charging direction, controlling the N-M sub-modules with the lowest voltage in the bridge arm in the switching-out state in the previous control period to be switched into the switching-in state; and if the current direction in the bridge arm is the bridge arm discharging direction, controlling the N-M sub-modules with the highest voltage in the cut-out state in the bridge arm in the previous control period to be switched into the input state.
In some possible embodiments, controlling the lowest-voltage or highest-voltage | N-M | sub-module in the leg in the previous control cycle to switch to the switching-out state according to the current direction in the leg includes: if the current direction in the bridge arm is the charging direction of the bridge arm, controlling the highest voltage | N-M | submodule in the bridge arm in the previous control period to be switched into the switching-out state; and if the current direction in the bridge arm is the discharging direction of the bridge arm, controlling the lowest voltage | N-M | submodule in the bridge arm in the previous control period to be switched into the switching-out state.
In a second aspect, an embodiment of the present application provides an MMC sub-module on-off control apparatus, including: the first calculation module is used for calculating to obtain a bridge arm differential pressure threshold according to the total harmonic content of the conversion equipment comprising the MMC and the average switching frequency of the switching devices of the sub-modules in each bridge arm of the MMC; the second calculation module is used for acquiring the voltage of each submodule in the bridge arm in the current control period for each bridge arm of the MMC, and calculating a first difference value, wherein the first difference value is the difference value between the maximum value and the minimum value of the voltage of the submodule in the bridge arm; the acquisition module is used for acquiring the input number N of the submodules in the current control period; and the control module is used for controlling the on-off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the differential pressure threshold of the bridge arm and the current direction in the bridge arm.
In a third aspect, an embodiment of the present application provides an MMC sub-module on-off control system, including: the pole control equipment is used for calculating to obtain a bridge arm differential pressure threshold according to the total harmonic content of the conversion equipment comprising the MMC and the average switching frequency of the switching devices of the sub-modules in each bridge arm of the MMC, and issuing the bridge arm differential pressure threshold to the valve control equipment; the valve control equipment is used for acquiring the voltage of each submodule in the bridge arm in the current control period for each bridge arm of the MMC, and calculating a first difference value, wherein the first difference value is the difference value between the maximum value and the minimum value of the voltage of the submodule in the bridge arm; acquiring the input number N of the submodules in the current control period; and controlling the on-off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the differential pressure threshold of the bridge arm and the current direction in the bridge arm.
In some possible embodiments, the polar control device and the valve control device are connected through a high-speed serial optical fiber.
The embodiment of the invention provides a submodule on-off control method, a submodule on-off control device and a submodule on-off control system for an MMC (modular multilevel converter). A bridge arm pressure difference threshold value is obtained through calculation according to the total harmonic content of a current conversion device comprising the MMC and the average switching frequency of a switching device of a submodule in each bridge arm of the MMC, wherein the total harmonic content is related to the average switching frequency of the switching device and the loss of the MMC. And controlling the on-off of the submodules of the MMC according to the input number of the submodules required in the current control period, a first difference value between the maximum value and the minimum value of the voltage of the submodules in the bridge arm in the current control period, the calculated bridge arm differential pressure threshold and the current flow direction in the bridge arm. The loss of the MMC is reduced by controlling the on-off of the submodule of the MMC, so that the loss of the whole wind generating set is reduced.
Drawings
The present invention will be better understood from the following description of specific embodiments thereof taken in conjunction with the accompanying drawings, in which like or similar reference characters designate like or similar features.
Fig. 1 is a schematic structural topology diagram of an MMC provided in an embodiment of the present application;
fig. 2 is a flowchart of a sub-module on-off control method for an MMC according to an embodiment of the present disclosure;
fig. 3 is a flowchart of a sub-module on-off control method for an MMC according to another embodiment of the present application;
fig. 4 is a schematic structural diagram of a sub-module on-off control device of an MMC according to an embodiment of the present disclosure;
fig. 5 is a schematic structural diagram of a sub-module on-off control system of an MMC according to an embodiment of the present disclosure.
Detailed Description
Features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but rather covers any modification, replacement or improvement of elements, components or algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.
The embodiment of the application provides a submodule on-off control method, a submodule on-off control device and a submodule on-off control system of an MMC (Modular Multilevel Converter), which can be applied to a conversion device comprising a Modular Multilevel Converter (MMC). Fig. 1 is a schematic structural topology diagram of an MMC according to an embodiment of the present disclosure. As shown in fig. 1, the MMC includes six three-phase arms, which are an upper arm of a first phase, a lower arm of the first phase, an upper arm of a second phase, a lower arm of the second phase, an upper arm of a third phase, and a lower arm of the third phase. The upper and lower bridge arms of each phase are connected through a bridge arm reactor L.
Wherein each bridge arm comprises a plurality of Sub-modules (SM) 11. The sub-module 11 may include more than two switching devices, and the switching devices may be Insulated Gate Bipolar Transistors (IGBTs), which are not limited herein. Each sub-module 11 has three states, a put-in state, a cut-out state and a bypass state. The input state and the output state are states in which the sub-module 11 normally operates. The bypass state is a state in which the sub-module 11 fails.
In each control cycle it is necessary to determine the sub-modules 11 in the switched-in state and the sub-modules 11 in the switched-out state, i.e. the switched-in part sub-modules 11 and/or the switched-out part sub-modules 11. When the voltage of the sub-module 11 changes, the state of the sub-module 11 is changed, for example, the sub-module 11 is switched from the on state to the off state, and the sub-module 11 is switched from the off state to the on state. During the state switching, the switching frequency of the IGBTs in the sub-module 11 affects the switching losses.
The embodiment of the application provides a submodule on-off control method of an MMC, which can ensure that the switching of submodule in two adjacent control periods is as small as possible, and reduce the loss of the MMC, thereby reducing the loss of the whole wind generating set. Fig. 2 is a flowchart of a sub-module on-off control method of an MMC according to an embodiment of the present application. As shown in fig. 2, the sub-module on-off control method of the MMC may include steps S201 to S204.
In step S201, a bridge arm differential pressure threshold is calculated according to the total harmonic content of the commutation device including the MMC and the average switching frequency of the switching device of the sub-module in each bridge arm of the MMC.
The converter equipment including the MMC includes, but is not limited to, a flexible direct current converter valve, a power electronic transformer, a static reactive power compensation device, a high-voltage frequency converter and the like. The bridge arm voltage difference threshold is the difference value of the calculated voltage of the SM with the highest voltage in the bridge arm and the calculated voltage of the SM with the lowest voltage in the bridge arm.
An excessively high switching frequency of a switching device of a sub-module in a bridge arm of the MMC may cause a small harmonic content, but an excessively high switching frequency may also cause a large switching loss. Similarly, too low switching frequency will result in less switching loss, but the power quality of the system in which the converter device is located will be reduced and the harmonic content will also be increased.
In the embodiment of the present application, the differential pressure threshold of the bridge arm may be calculated by using a Harmonic optimization algorithm and a switching loss optimization algorithm according to a Total Harmonic content (THD) of the converter device in which the MMC is located and an average switching frequency of a switching device of the SM in each bridge arm of the MMC. The calculated differential pressure threshold of the bridge arm can enable the total harmonic content of the converter equipment to be within the range of the preset standard harmonic content, and the switching loss can be lower than the preset loss threshold, namely, a balance between the reduction of the total harmonic content and the reduction of the switching loss is achieved. In one example, the calculated switching loss of the bridge arm corresponding to the bridge arm differential pressure threshold is the minimum switching loss when the total harmonic content is within a preset standard harmonic content range. The preset standard harmonic content range may be set according to a specific working scene and a working requirement, and is not limited herein. For example, the predetermined standard harmonic content may be in a range of 2% to 5%.
In step S202, for each bridge arm of the MMC, the voltage of each sub-module in the bridge arm in the current control period is obtained, and a first difference value is calculated.
The first difference is the difference between the maximum value and the minimum value of the voltage of the sub-modules in the bridge arm, namely the difference between the voltage of the sub-module with the highest voltage in the bridge arm in the current control period and the module with the lowest voltage is used as the first difference.
In step S203, the input number N of submodules in the current control cycle is acquired.
The input number N of the submodules in the current control period is the number of the submodules needing to be in the input state in the current control period.
In some examples, the input data N of the sub module in the bridge arm may be determined according to the modulation wave of the bridge arm and the voltage reference value of the sub module in the bridge arm in the current control period.
In step S204, the sub-modules of the MMC are controlled to be turned on or off according to the input number N of the sub-modules, the first difference value, the bridge arm differential pressure threshold, and the current direction in the bridge arm.
Specifically, the specific sub-modules to be switched in or out can be determined by using the switching number N according to the comparison result of the first difference value and the differential pressure threshold of the bridge arm and the current direction in the bridge arm. If the sub-module needing to be put into the current control period is in the put-into state in the last control period, the sub-module does not need to be switched. If the sub-module needing to be switched out in the current control period is in the switching-out state in the last control period, the sub-module does not need to be switched out. And if the submodule needing to be put into the previous control cycle is in the cut-out state in the current control cycle, controlling the submodule to be switched from the cut-out state to the put-in state, namely controlling the submodule to be conducted. And if the submodule needing to be switched out in the current control period is in the switching-in state in the last control period, controlling the submodule to be switched from the switching-in state to the switching-out state, namely controlling the submodule to be switched off.
In the embodiment of the application, the bridge arm pressure difference threshold is obtained by calculating according to the total harmonic content of the converter equipment comprising the MMC and the average switching frequency of the switching device of the sub-module in each bridge arm of the MMC, wherein the total harmonic content is related to the average switching frequency of the switching device and the loss of the MMC. And controlling the on-off of the submodules of the MMC according to the input number of the submodules required in the current control period, a first difference value between the maximum value and the minimum value of the voltage of the submodules in the bridge arm in the current control period, the calculated bridge arm differential pressure threshold and the current flow direction in the bridge arm. The loss of the MMC is reduced by controlling the on-off of the submodule of the MMC, so that the loss of the whole wind generating set is reduced. Moreover, the loss of the MMC can be reduced on the basis that the total harmonic content is within the preset standard harmonic content range, and the balance of low total harmonic content and low MMC loss is achieved.
The following description will be made specifically according to the input number N, the first difference value, the differential pressure threshold of the bridge arm, and the difference in the current direction in the bridge arm. Fig. 3 is a flowchart of a sub-module on-off control method for an MMC according to another embodiment of the present application. Fig. 3 is different from fig. 2 in that step S204 in fig. 2 can be specifically subdivided into steps S2041 to S2045 in fig. 3.
In step S2041, if the first difference is greater than the predetermined differential pressure threshold, the N highest-voltage submodules or the N lowest-voltage submodules in the bridge arm are controlled to be in the on state according to the current direction in the bridge arm.
And the current in the bridge arm is greater than 0, which indicates that the bridge arm is in a charging state, and the current direction is the charging direction of the bridge arm. The current in the bridge arm is less than 0, which indicates that the bridge arm is in a discharging state, and the current direction is the discharging state of the bridge arm.
Specifically, if the current direction in the bridge arm is the bridge arm charging direction, the N submodules with the lowest voltage in the bridge arm are controlled to be in the input state. The submodules in the bridge arm can be arranged according to the arrangement sequence of the voltages from large to small, and N submodules with the lowest voltage are selected to be conducted, so that the N submodules with the lowest voltage are in an input state.
Specifically, if the current direction in the bridge arm is the bridge arm discharging direction, the N sub-modules with the highest voltage in the bridge arm are controlled to be in the switching-in state. The submodules in the bridge arm can be arranged according to the arrangement sequence of the voltages from large to small, and the N submodules with the highest voltage are selected to be conducted, so that the N submodules with the highest voltage are in an input state.
In step S2042, if the first difference is smaller than or equal to the predetermined differential pressure threshold, the number M of the submodules in the previous control cycle bridge arm that are in the input state is obtained.
In step S2043, if the second difference is greater than zero, the N-M submodules in the bridge arm in the previous control period with the lowest voltage or the highest voltage in the switch-out state are controlled to switch to the switch-in state according to the current direction in the bridge arm.
And the second difference is the difference between the input number N of the submodules in the bridge arm in the current control period and the number M of the submodules in the bridge arm in the previous control period in the input state. For convenience of description, a second difference, which is a difference between N and M, is referred to as Δ N, that is, Δ N — M.
If the number delta N is larger than 0, the number delta N of the submodules needing to be in the input state in the bridge arm in the current control period is larger than that of the submodules needing to be in the input state in the bridge arm in the previous control period, and in order to ensure that the states of the submodules in the previous control period are switched as little as possible, the trigger signals for controlling the states of the submodules in the bridge arm are changed as little as possible. And selecting delta N sub-modules in the switching-out state from the bridge arm in the previous control period to switch the sub-modules into the switching-in state. For example, the submodules in the cut-out state may select Δ N with the lowest voltage or the highest voltage to switch to the on state.
Specifically, if the current direction in the bridge arm is the bridge arm charging direction, the N-M sub-modules with the lowest voltage in the bridge arm in the cut-out state in the previous control period are controlled to be switched to the input state. The submodules in the switched-out state in the bridge arm can be arranged according to the arrangement sequence of voltages from large to small, and the Delta N submodules with the lowest voltage are selected to be conducted, so that the Delta N submodules with the lowest voltage are in the switched-in state.
Specifically, if the current direction in the bridge arm is the bridge arm discharging direction, the N-M sub-modules with the highest voltage in the cut-out state in the bridge arm in the previous control period are controlled to be switched to the input state. The submodules in the switching-out state in the bridge arm can be arranged according to the arrangement sequence of voltages from large to small, and the Delta N submodules with the highest voltage are selected to be conducted, so that the Delta N submodules with the highest voltage are in the switching-in state.
In step S2044, if the second difference is equal to zero, the sub-module in the previous control cycle leg in the on state is controlled to maintain the on state, and the sub-module in the off state is controlled to maintain the off state.
And if the delta N is equal to 0, the number of the sub-modules which need to be in the input state in the bridge arm in the current control period is the same as the number of the sub-modules which need to be in the input state in the bridge arm in the previous control period. The state of the sub-modules in the previous control period can be ensured not to be switched, so that the trigger signal for controlling the state of the sub-modules in the bridge arm is not changed.
In step S2045, if the second difference is smaller than zero, the lowest voltage or the highest voltage | N-M | sub-module in the previous control period leg is controlled to switch to the cut-out state according to the current direction in the leg.
If the number delta N is less than 0, the number delta N of the submodules needing to be in the input state in the bridge arm in the current control period is less than that of the submodules needing to be in the input state in the bridge arm in the previous control period, and in order to ensure that the states of the submodules in the previous control period are switched as little as possible, the trigger signals for controlling the states of the submodules in the bridge arm are changed as little as possible. And selecting | Δ N | from the sub-module in the on state in the bridge arm of the previous control period to switch into the off state. For example, the sub-module in the on-state may select | Δ N | or the sub-module in the highest voltage to switch to the off-state. The absolute value of the second difference is | N-M |.
Specifically, if the current direction in the bridge arm is the charging direction of the bridge arm, the highest voltage | N-M | submodule in the bridge arm in the previous control period is controlled to be switched into the switching-out state. The submodules in the on state in the bridge arm can be arranged according to the arrangement sequence of voltages from large to small, and the Delta N submodules with the highest voltage are selected to be disconnected so that the | Delta N | submodule with the highest voltage is in the off state.
Specifically, if the current direction in the bridge arm is the bridge arm discharging direction, the lowest voltage | N-M | submodule in the bridge arm in the previous control period is controlled to be switched into the switching-out state. The sub-modules in the bridge arm that are in the on-state are arranged according to the order of the voltages from large to small, and the | Δ N | sub-module with the lowest voltage is selected for disconnection, so that the | Δ N | sub-module with the lowest voltage is in the off-state.
The trigger signal in the above embodiments may be a pulse signal, and is not limited herein.
For each bridge arm in the MMC, the switching of the states of the multiple sub-modules can be realized by adopting the sub-module on-off control method of the MMC in the above embodiment. The MMC sub-module on-off control method in the embodiment of the application is applicable to a recent level approximation modulation technology, and the switching frequency is optimized on the basis of the recent level approximation modulation technology so as to reduce the switching loss and reduce the total harmonic content.
The embodiment of the application also provides a submodule on-off control device of the MMC. Fig. 4 is a schematic structural diagram of a sub-module on-off control device of an MMC according to an embodiment of the present disclosure. As shown in fig. 4, the sub-module on-off control apparatus 300 of the MMC may include a first calculation module 301, a second calculation module 302, an acquisition module 303, and a control module 304.
The first calculating module 301 is configured to calculate a differential pressure threshold of the bridge arm according to the total harmonic content of the commutation device including the MMC and an average switching frequency of a switching device of a sub-module in each bridge arm of the MMC.
The second calculating module 302 is configured to, for each bridge arm of the MMC, obtain a voltage of each sub-module in the bridge arm in the current control period, and calculate a first difference.
The first difference is the difference between the maximum value and the minimum value of the voltage of the sub-modules in the bridge arm.
An obtaining module 303, configured to obtain the input number N of the submodules in the current control period;
and the control module 304 is used for controlling the on-off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the differential pressure threshold value of the bridge arm and the current direction in the bridge arm.
In the embodiment of the application, the bridge arm pressure difference threshold is obtained by calculating according to the total harmonic content of the converter equipment comprising the MMC and the average switching frequency of the switching device of the sub-module in each bridge arm of the MMC, wherein the total harmonic content is related to the average switching frequency of the switching device and the loss of the MMC. And controlling the on-off of the submodules of the MMC according to the input number of the submodules required in the current control period, a first difference value between the maximum value and the minimum value of the voltage of the submodules in the bridge arm in the current control period, the calculated bridge arm differential pressure threshold and the current flow direction in the bridge arm. Through the break-make of the submodule of control MMC, guarantee to reduce MMC's loss on the basis that total harmonic content is in the standard harmonic content scope of predetermineeing, thereby reduce the loss of wind generating set complete machine.
Specifically, the switching loss of the bridge arm corresponding to the bridge arm differential pressure threshold is the minimum switching loss under the condition that the total harmonic content is within the preset standard harmonic content range.
In some examples, the obtaining module 303 may be specifically configured to: and determining the input number N according to the modulation wave of the bridge arm in the current control period and the voltage reference value of the submodule.
In some examples, the control module 304 may be specifically configured to: and if the first difference value is larger than the preset pressure difference threshold value, controlling the N sub-modules with the highest voltage or the N sub-modules with the lowest voltage in the bridge arm to be in an input state according to the current direction in the bridge arm.
Specifically, the control module 304 is specifically configured to control the N sub-modules with the lowest voltage in the bridge arm to be in an input state if the current direction in the bridge arm is the bridge arm charging direction.
Specifically, the control module 304 is specifically configured to control the N sub-modules with the highest voltage in the bridge arm to be in an input state if the current direction in the bridge arm is the bridge arm discharging direction.
In other examples, the control module 304 may be specifically configured to: if the first difference value is smaller than or equal to the preset pressure difference threshold value, acquiring the number M of the submodules in the input state in the bridge arm in the previous control period; if the second difference is larger than zero, controlling the N-M sub-modules in the bridge arm in the last control period with the lowest voltage or the highest voltage in the bridge arm in the switching-out state to be switched into the switching-in state according to the current direction in the bridge arm, wherein the second difference is the difference between N and M; if the second difference value is equal to zero, controlling the sub-module in the input state in the bridge arm in the previous control period to keep in the input state, and controlling the sub-module in the cut-out state to keep in the cut-out state; and if the second difference is smaller than zero, controlling the lowest voltage or the highest voltage | N-M | submodule in the bridge arm in the previous control period to be switched into the switching-out state according to the current direction in the bridge arm.
Specifically, in the case that the first difference is greater than zero, the control module 304 may be specifically configured to: if the current direction in the bridge arm is the bridge arm charging direction, controlling the N-M sub-modules with the lowest voltage in the bridge arm in the switching-out state in the previous control period to be switched into the switching-in state; and if the current direction in the bridge arm is the bridge arm discharging direction, controlling the N-M sub-modules with the highest voltage in the cut-out state in the bridge arm in the previous control period to be switched into the input state.
In particular, where the first difference is less than zero, the control module 304 may be specifically configured to: if the current direction in the bridge arm is the charging direction of the bridge arm, controlling the highest voltage | N-M | submodule in the bridge arm in the previous control period to be switched into the switching-out state; and if the current direction in the bridge arm is the discharging direction of the bridge arm, controlling the lowest voltage | N-M | submodule in the bridge arm in the previous control period to be switched into the switching-out state.
The application also can provide a submodule on-off control system of the MMC. Fig. 5 is a schematic structural diagram of a sub-module on-off control system of an MMC according to an embodiment of the present disclosure. As shown in fig. 5, the sub-module on-off control system of the MMC may specifically include a pole control device 40 and a valve control device 50.
The sub-module on-off control system of the MMC may include a plurality of pole control devices 40 and a plurality of valve control devices 50, and the number of pole control devices 40 and the number of valve control devices 50 are not limited herein. The polar control apparatus 40 and the valve control apparatus 50 can include a power board, an expansion board, and a communication interface board. The power panel may provide power for operation of the device. The expansion board can operate the sub-module on-off control method of the MMC in the embodiment. The expansion board of the valve control device 50 can generate a trigger signal for controlling the on/off of the sub-module, so as to control the on/off of the sub-module. The communication interface board of the polar control device 40 can implement communication between the polar control device 40 and other devices. The communication interface board of the valve control apparatus 50 can implement communication between the valve control apparatus 50 and other apparatuses.
The polar control apparatus 40 can communicate with the valve control apparatus 50. The pole control device 40 may be configured to calculate a bridge arm differential pressure threshold according to the total harmonic content of the converter device including the MMC and the average switching frequency of the switching device of the sub-module in each bridge arm of the MMC, and issue the bridge arm differential pressure threshold to the valve control device 50.
The valve control device 50 can communicate with the sub-modules 11 of each leg in the MMC. The valve control device 50 may be configured to obtain, for each bridge arm of the MMC, a voltage of each sub-module 11 in the bridge arm in the current control period, and calculate a first difference value, where the first difference value is a difference value between a maximum value and a minimum value of the voltages of the sub-modules 11 in the bridge arm; acquiring the input number N of the submodules 11 in the current control period; and controlling the on-off of the submodule 11 of the MMC according to the input number N of the submodule 11, the first difference value, the differential pressure threshold value of the bridge arm and the current direction in the bridge arm.
Specifically, the switching loss of the bridge arm corresponding to the bridge arm differential pressure threshold is the minimum switching loss under the condition that the total harmonic content is within the preset standard harmonic content range.
In some examples, the valve control device 50 is specifically configured to determine the input number N according to the modulation wave of the bridge arm in the current control cycle and the voltage reference value of the sub-module.
In some embodiments, the valve control device 50 is specifically configured to control the N highest-voltage sub-modules or the N lowest-voltage sub-modules of the bridge arm to be in the on state according to the current direction in the bridge arm if the first difference is greater than the predetermined differential pressure threshold.
Specifically, the valve control device 50 is configured to control the N submodules with the lowest voltage in the bridge arm to be in an input state if the current direction in the bridge arm is the bridge arm charging direction.
Specifically, the valve control device 50 is configured to control the N sub-modules with the highest voltage in the bridge arm to be in an input state if the current direction in the bridge arm is the bridge arm discharging direction.
In other embodiments, the valve control apparatus 50 is particularly useful for: if the first difference value is smaller than or equal to the preset pressure difference threshold value, acquiring the number M of the submodules in the input state in the bridge arm in the previous control period; if the second difference is larger than zero, controlling the N-M sub-modules in the bridge arm in the last control period with the lowest voltage or the highest voltage in the bridge arm in the switching-out state to be switched into the switching-in state according to the current direction in the bridge arm, wherein the second difference is the difference between N and M; if the second difference value is equal to zero, controlling the sub-module in the input state in the bridge arm in the previous control period to keep in the input state, and controlling the sub-module in the cut-out state to keep in the cut-out state; and if the second difference is smaller than zero, controlling the lowest voltage or the highest voltage | N-M | submodule in the bridge arm in the previous control period to be switched into the switching-out state according to the current direction in the bridge arm.
Specifically, when the second difference is greater than zero, the valve control device 50 is configured to control the N-M submodules with the lowest voltage in the switched-out state in the bridge arm in the previous control period to switch to the switched-in state if the current direction in the bridge arm is the bridge arm charging direction; and if the current direction in the bridge arm is the bridge arm discharging direction, controlling the N-M sub-modules with the highest voltage in the cut-out state in the bridge arm in the previous control period to be switched into the input state.
Specifically, in the case that the second difference is smaller than zero, the valve control device 50 is configured to control the largest voltage | N-M | sub-module in the bridge arm in the previous control period to be switched to the switching-out state if the current direction in the bridge arm is the bridge arm charging direction; and if the current direction in the bridge arm is the discharging direction of the bridge arm, controlling the lowest voltage | N-M | submodule in the bridge arm in the previous control period to be switched into the switching-out state.
The valve control device 50 may further obtain other status information such as the temperature of the sub-module of each bridge arm in the MMC, and upload the other status information such as the temperature to the pole control device 40.
In some examples, as shown in fig. 5, the sub-module on-off control system of the MMC may further include a sub-module 11 of each leg of the MMC.
In some examples, as shown in fig. 5, the sub-module on-off control system of the MMC may further include a station control device 60. The station control device 60 may communicate with the pole control device 40. The station control device may be used for monitoring and event recording of an ac switching field, a dc switching plant, a valve hall, a power supply system and other auxiliary systems, and online harmonic monitoring, and the like, but is not limited thereto.
In the above embodiment, the communication between the valve control device 50, the pole control device 40, and the station control device 60 may be wired communication or wireless communication. In some examples, high-speed serial fiber optic connections can be used between the valve control device 50, the pole control device 40, and the station control device 60. Correspondingly, the communication interface board in each device may be specifically a fiber interface board.
It should be clear that the embodiments in this specification are described in a progressive manner, and the same or similar parts in the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. For device embodiments, system embodiments, reference may be made to the description of the method embodiments for their relevance. The present application is not limited to the particular steps and structures described above and shown in the drawings. Those skilled in the art may make various changes, modifications and additions or change the order between the steps after appreciating the spirit of the present application. Also, a detailed description of known process techniques is omitted herein for the sake of brevity.
It will be appreciated by persons skilled in the art that the above embodiments are illustrative and not restrictive. Different features which are present in different embodiments may be combined to advantage. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art upon studying the drawings, the specification, and the claims. In the claims, the term "comprising" does not exclude other means or steps; the indefinite article "a" does not exclude a plurality; the terms "first" and "second" are used to denote a name and not to denote any particular order. Any reference signs in the claims shall not be construed as limiting the scope. The functions of the various parts appearing in the claims may be implemented by a single hardware or software module. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims (10)

1. A submodule on-off control method of an MMC is characterized by comprising the following steps:
calculating to obtain a bridge arm differential pressure threshold according to the total harmonic content of the converter equipment comprising the MMC and the average switching frequency of the switching devices of the sub-modules in each bridge arm of the MMC;
for each bridge arm of the MMC, acquiring the voltage of each submodule in the bridge arm in the current control period, and calculating a first difference value, wherein the first difference value is the difference value between the maximum value and the minimum value of the voltage of the submodules in the bridge arm;
acquiring the input number N of the sub-modules in the current control period;
and controlling the on-off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the differential pressure threshold of the bridge arm and the current direction in the bridge arm.
2. The method of claim 1, wherein the switching loss of the bridge arm corresponding to the bridge arm differential pressure threshold is a minimum switching loss when the total harmonic content is within a preset standard harmonic content range.
3. The method of claim 1, wherein obtaining the invested number N of sub-modules in the current control cycle comprises:
and determining the input number N according to the modulation wave of the bridge arm and the voltage reference value of the submodule in the current control period.
4. The method according to any one of claims 1-3, wherein the controlling of the switching of the sub-modules of the MMC according to the number of inputs N of the sub-modules, the first difference value, the bridge arm differential pressure threshold value, and the current direction in the bridge arm comprises:
and if the first difference value is larger than a preset differential pressure threshold value, controlling the N sub-modules with the highest voltage or the N sub-modules with the lowest voltage in the bridge arm to be in a switching-in state according to the current direction in the bridge arm.
5. The method of claim 4, wherein controlling the N highest voltage sub-modules or the N lowest voltage sub-modules in the bridge arm to be in an on state according to the current direction in the bridge arm comprises:
if the current direction in the bridge arm is the bridge arm charging direction, controlling the N sub-modules with the lowest voltage in the bridge arm to be in an input state;
and if the current direction in the bridge arm is the bridge arm discharging direction, controlling the N sub-modules with the highest voltage in the bridge arm to be in the input state.
6. The method according to any one of claims 1 to 3, wherein the controlling of the switching of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the bridge arm differential pressure threshold value and the current direction in the bridge arm comprises:
if the first difference value is smaller than or equal to a preset pressure difference threshold value, acquiring the number M of the submodules in the input state in the bridge arm in the previous control period;
if the second difference is larger than zero, controlling the N-M sub-modules in the bridge arm in the last control period, which are in the cut-out state and have the lowest voltage or the highest voltage, to be switched into the put-in state according to the current direction in the bridge arm, wherein the second difference is the difference between N and M;
if the second difference value is equal to zero, controlling the sub-modules in the input state in the bridge arm in the previous control period to keep in the input state, and controlling the sub-modules in the cut-out state to keep in the cut-out state;
and if the second difference is smaller than zero, controlling the sub-modules in the bridge arm in the previous control period to be switched into the switching-out state according to the current direction in the bridge arm, wherein the sub-modules are in the switching-in state and have the lowest voltage or the highest voltage.
7. The method according to claim 6, wherein the controlling the N-M submodules with the lowest voltage or the highest voltage in the bridge arm in the last control period to be switched into the on state according to the current direction in the bridge arm comprises:
if the current direction in the bridge arm is the bridge arm charging direction, controlling the N-M sub-modules with the lowest voltage in the bridge arm in the switching-out state in the previous control period to be switched into the switching-in state;
and if the current direction in the bridge arm is the bridge arm discharging direction, controlling the N-M sub-modules with the highest voltage in the cut-out state in the bridge arm in the previous control period to be switched into the switching-in state.
8. The method of claim 6, wherein said controlling said lowest-voltage or highest-voltage | N-M | of said sub-modules in said leg in said previous control period to switch into said switched-out state according to a current direction in said leg comprises:
if the current direction in the bridge arm is the bridge arm charging direction, controlling the sub-modules with the highest voltage in the bridge arm in the input state in the previous control period to be switched into the switching-out state;
and if the current direction in the bridge arm is the bridge arm discharging direction, controlling the sub-modules in the last control period, wherein the voltage of the bridge arm in the input state is the lowest | N-M | to be switched into the switching-out state.
9. The utility model provides a submodule on-off control device of MMC which characterized in that includes:
the first calculation module is used for calculating to obtain a bridge arm differential pressure threshold according to the total harmonic content of the conversion equipment comprising the MMC and the average switching frequency of the switching devices of the sub-modules in each bridge arm of the MMC;
the second calculation module is used for acquiring the voltage of each submodule in the bridge arm in the current control period for each bridge arm of the MMC, and calculating a first difference value, wherein the first difference value is the difference value between the maximum value and the minimum value of the voltage of the submodules in the bridge arm;
the obtaining module is used for obtaining the input number N of the sub-modules in the current control period;
and the control module is used for controlling the on-off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the differential pressure threshold of the bridge arm and the current direction in the bridge arm.
10. The utility model provides a submodule on-off control system of MMC which characterized in that includes:
the pole control equipment is used for calculating to obtain a bridge arm differential pressure threshold according to the total harmonic content of the converter equipment comprising the MMC and the average switching frequency of the switching devices of the sub-modules in each bridge arm of the MMC, and issuing the bridge arm differential pressure threshold to the valve control equipment;
the valve control equipment is used for acquiring the voltage of each submodule in the bridge arm in the current control period for each bridge arm of the MMC, and calculating a first difference value, wherein the first difference value is the difference value between the maximum value and the minimum value of the voltage of the submodules in the bridge arm; and acquiring the input number N of the submodules in the current control period; and controlling the on-off of the sub-modules of the MMC according to the input number N of the sub-modules, the first difference value, the differential pressure threshold of the bridge arm and the current direction in the bridge arm.
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