Control system for a flexible dc transmission converter valve

Abstract

The application discloses a control system of a flexible direct current transmission converter valve, and the system comprises an interface module, a collection module, a filter, a PI controller and a superposition module; wherein the converter valve comprises three-phase bridge arms, each phase bridge arm is divided into an upper bridge arm and a lower bridge arm; the interface module is used for receiving a direct current operation mode and modulation waves of each bridge arm; the collection module is used for obtaining total three-phase currents of the bridge arms; the filter is used for obtaining to-be-suppressed components; the PI controller is used for obtaining oscillation suppression levels opposite to the to-be-suppressed components; and the superposition module is used for obtaining and superimposing modulation waves corresponding to each bridge arm, the oscillation suppression levels and circulating current suppression waves corresponding to each bridge arm, and obtaining reference waves corresponding to each bridge arm. In this way, the reference waves corresponding to each bridge arm of the black start can have a suppression effect, and the tripping risk caused by oscillation in the black start process of the flexible direct current transmission is suppressed. Further, the safety in the black start process of the flexible direct current transmission is improved.

Description

Technical Field

[0001] This application relates to the field of black-start technology for flexible DC transmission, and more specifically, to a control system for a converter valve in flexible DC transmission. Background Technology

[0002] Currently, the flexible DC transmission technology widely used in engineering is based on modular multi-level converters (MMC). The converter valve consists of six arms, each composed of cascaded sub-modules (SMs) of the same number and structure. By controlling the on / off state of the sub-module switching devices, the sub-module can operate in three states: locked, engaged, and disengaged. Each state has two operating modes depending on the current direction, thus allowing the sub-module to operate in six modes, hence the six arms within the converter valve. Furthermore, by controlling the number of cascaded sub-modules in each arm, the three-phase voltage at the connection point between the six arms and the AC system can be made sinusoidal. By controlling the amplitude and phase of this sinusoidal three-phase voltage, the exchange of active and reactive power between the converter and the AC system can be achieved. One of the main functions of the unit control layer is to send modulation commands to the control layer in the converter valve. The modulation commands include the DC operating mode and the modulation wave. Based on the modulation commands and the circulating current suppression wave used to suppress the second harmonic circulating current in the converter valve, the converter valve determines and controls the number of cascaded sub-modules in each bridge arm to realize the exchange of active and reactive power between the converter and the AC system.

[0003] However, during black start-up of flexible DC transmission, after the converter valve is unlocked, the AC voltage on the converter valve side gradually increases under control, generating magnetic flux and excitation current. When there is an oscillating component caused by the operation of the converter transformer in the circuit, it will exacerbate the saturation of the converter transformer, generating a large zero-sequence harmonic current flowing into the neutral point resistance on the valve side, posing a risk of tripping due to neutral point resistance overload protection.

[0004] Therefore, how to suppress the oscillation component during the black start of flexible DC transmission has become a key focus of attention.

[0005] In summary, there is an urgent need for a control system for flexible DC transmission converter valves to suppress oscillation components during the black start process of flexible DC transmission. Summary of the Invention

[0006] In view of this, this application provides a control system for a flexible DC transmission converter valve to suppress oscillation components during the black start process of flexible DC transmission.

[0007] To achieve the above objectives, the following solution is proposed:

[0008] A control system for a flexible DC transmission converter valve includes an interface module, a data acquisition module, a filter, a PI controller, and a superposition module. The converter valve contains three-phase bridge arms, each of which is divided into an upper bridge arm and a lower bridge arm.

[0009] The interface module is used to receive the DC operation mode and the modulation wave corresponding to each bridge arm sent by the unit control layer;

[0010] The acquisition module is used to add the currents of each bridge arm to obtain the total three-phase current of the bridge arm when the DC operation mode is black start mode.

[0011] The filter is used to filter the total three-phase current of the bridge arm to obtain the component to be suppressed;

[0012] The PI controller is used to process the component to be suppressed to obtain an oscillation suppression level opposite to that of the component to be suppressed.

[0013] The superposition module is used to acquire and superimpose the modulation wave corresponding to each bridge arm, the oscillation suppression level, and the circulating suppression wave corresponding to each bridge arm to obtain the reference wave corresponding to each bridge arm.

[0014] Optionally, the acquisition module includes a collection unit and a calculation unit;

[0015] The collection unit is used to collect the current of each bridge arm;

[0016] The calculation unit is used to add the currents of each bridge arm to obtain the total three-phase current of the bridge arm.

[0017] Optionally, the filter includes a filtering module;

[0018] The filtering module is used to perform band-stop filtering on the total electromagnetic wave of the bridge arm to obtain high-frequency components and low-frequency components, and to combine the high-frequency components and low-frequency components into components to be suppressed.

[0019] Optionally, the modulation wave corresponding to each bridge arm is composed of a three-phase upper bridge arm modulation wave and a three-phase lower bridge arm modulation wave, and the circulating current suppression wave corresponding to each bridge arm is composed of a three-phase upper bridge arm circulating current suppression wave and a three-phase lower bridge arm circulating current suppression wave, wherein each modulation wave and each circulating current suppression wave corresponds one-to-one with each bridge arm.

[0020] The overlay module includes a subtractor and an adder;

[0021] The subtractor is used to subtract half of the oscillation suppression level from the sum of the modulation wave corresponding to the lower bridge arm of each phase and the circulating suppression wave corresponding to the lower bridge arm of that phase, so as to obtain the reference wave corresponding to the lower bridge arm of that phase.

[0022] The adder is used to superimpose the modulation wave corresponding to the upper bridge arm of each phase, the circulating suppression wave corresponding to the upper bridge arm of that phase, and half of the oscillation suppression level to obtain the reference wave corresponding to the upper bridge arm of that phase.

[0023] A control system for a flexible DC transmission converter valve includes an interface module, a data acquisition module, a filter, a divider, a first subtractor, a proportional controller, and a superposition module. The converter valve includes three-phase bridge arms, each of which is divided into an upper bridge arm and a lower bridge arm.

[0024] The interface module is used to receive the DC operation mode and the modulation wave corresponding to each bridge arm sent by the unit control layer;

[0025] The acquisition module is used to acquire the current of each bridge arm when the DC operation mode is black start mode, and calculate the difference between the current corresponding to the upper bridge arm of each phase and the current corresponding to the lower bridge arm of the same phase, so as to obtain the current difference of each phase bridge arm.

[0026] The filter is used to perform sliding window filtering on the current difference of each phase bridge arm;

[0027] The divider is used to calculate and obtain the current difference between each phase bridge arm, and the average value after sliding window filtering;

[0028] The first subtractor is used to subtract the average value from the current difference of each phase bridge arm after sliding window filtering to obtain the suppression component corresponding to each phase bridge arm.

[0029] The proportional controller is used to proportionally control the suppression component corresponding to each phase bridge arm to obtain the oscillation suppression level corresponding to each phase bridge arm.

[0030] The superposition module is used to acquire and superimpose the modulation wave corresponding to each bridge arm, the oscillation suppression level corresponding to that bridge arm, and the circulating suppression wave corresponding to that bridge arm to obtain the reference wave corresponding to each bridge arm.

[0031] Optionally, the modulation wave corresponding to each bridge arm is composed of a three-phase upper bridge arm modulation wave and a three-phase lower bridge arm modulation wave, and the circulating current suppression wave corresponding to each bridge arm is composed of a three-phase upper bridge arm circulating current suppression wave and a three-phase lower bridge arm circulating current suppression wave, wherein each modulation wave and each circulating current suppression wave corresponds one-to-one with each bridge arm.

[0032] The superposition module includes an adder and a second subtractor;

[0033] The second subtractor is used to subtract half of the corresponding oscillation suppression level from the sum of the modulation wave corresponding to the lower bridge arm of each phase and the circulating suppression wave corresponding to the lower bridge arm of that phase, so as to obtain the reference wave corresponding to the lower bridge arm of that phase.

[0034] The adder is used to superimpose the modulation wave corresponding to the upper arm of each phase, the circulating suppression wave corresponding to the upper arm of that phase, and half of the oscillation suppression level of that phase to obtain the reference wave corresponding to the upper arm of that phase.

[0035] Optionally, the acquisition module includes a collection unit and a calculation unit;

[0036] The collection unit is used to collect the current of each bridge arm;

[0037] The calculation unit is used to calculate the difference between the current corresponding to the upper bridge arm of each phase and the current corresponding to the lower bridge arm of the same phase, so as to obtain the current difference of each phase bridge arm.

[0038] Optionally, the filter includes a filtering module;

[0039] The filtering module is used to perform sliding window filtering on the current difference of each phase bridge arm.

[0040] Optionally, the divider includes a division module;

[0041] The division module is used to calculate and obtain the current difference between each phase bridge arm and the average value after sliding window filtering.

[0042] Optionally, the proportional controller includes a proportional control module;

[0043] The proportional control module, the proportional controller includes the proportional control module;

[0044] The proportional control module is used to proportionally control the suppression component corresponding to each phase bridge arm to obtain the oscillation suppression level corresponding to each phase bridge arm.

[0045] As can be seen from the above technical solution, the control system of the flexible DC transmission converter valve provided in this application includes an interface module, a data acquisition module, a filter, a PI controller, and a superposition module. This application is only implemented during black start; it cannot be started in non-black start mode to prevent erroneous operation. Therefore, the interface module is used to receive the DC operating mode and the modulation wave corresponding to each bridge arm from the unit control layer. When the DC operating mode is black start mode, the data acquisition module is used to add the currents of each bridge arm to obtain the total three-phase current of the bridge arm. The filter is used to filter the total three-phase current of the bridge arm to obtain the component to be suppressed. Based on this, the component to be suppressed in each bridge arm current is obtained. The PI controller is used to process the component to be suppressed to obtain an oscillation suppression level opposite to the component to be suppressed. Based on this, an additional amount of oscillation suppression opposite to the component to be suppressed is obtained. The superposition module is used to acquire and superimpose the modulation wave corresponding to each bridge arm, the oscillation suppression level, and the circulating current suppression wave corresponding to each bridge arm to obtain the reference wave corresponding to each bridge arm. Thus, by superimposing an additional amount of oscillation suppression opposite to the component to be suppressed onto the modulation wave and circulating current suppression wave corresponding to each bridge arm, a reference wave for black start corresponding to each bridge arm with suppression effect can be obtained, suppressing the tripping risk caused by oscillation during the black start process of flexible DC transmission. Furthermore, this improves the safety during the black start process of flexible DC transmission. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0047] Figure 1 This application discloses a control system for a flexible DC transmission converter valve.

[0048] Figure 2 This is another control system for a flexible DC transmission converter valve disclosed in this application. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] The control system of the flexible DC transmission converter valve provided in this application can suppress oscillations in the reference wave at the connection between each bridge arm and the AC system during the black start of the flexible DC transmission.

[0051] In response to the special situation of AC system power loss, the AC system voltage can be restored through the black start of flexible DC transmission, thus resolving the special circumstances of the AC system. By unlocking the black start function of the converter valve, the connection points between each bridge arm of the converter valve and the AC system, or the primary side of the converter transformer (unloaded), are brought onto the reference wave finally obtained in this application. Subsequently, the AC system voltage can be restored by closing the corresponding AC system switch.

[0052] Next, combine Figure 1 The control system of the flexible DC transmission converter valve of this application is described in detail. For example... Figure 1 As shown, the control system of the flexible DC transmission converter valve consists of an interface module, a data acquisition module, a filter, a PI controller, and a superposition module.

[0053] In actual operation, the interface module, which is one of the components of the control system of the flexible DC transmission converter valve, receives regulation from the unit control layer. The unit control layer can send modulation commands to the control layer in the converter valve under different scenarios. The modulation commands include DC operation mode and modulation wave.

[0054] The DC operation modes can include: power transmission mode, black start mode, static synchronous compensator mode, open circuit test mode, etc.

[0055] The modulation wave can include the modulation wave corresponding to each bridge arm within the converter valve.

[0056] The converter valve contains three phase arms, each of which contains an upper arm and a lower arm. The three phases can be divided into phase A, phase B, and phase C. Therefore, the converter valve can contain phase A upper arm, phase A lower arm, phase B upper arm, phase B lower arm, phase C upper arm, and phase C lower arm.

[0057] Based on this, the modulation waves corresponding to each bridge arm include: the modulation wave corresponding to the upper bridge arm of phase A, the modulation wave corresponding to the lower bridge arm of phase A, the modulation wave corresponding to the upper bridge arm of phase B, the modulation wave corresponding to the lower bridge arm of phase B, the modulation wave corresponding to the upper bridge arm of phase C, and the modulation wave corresponding to the lower bridge arm of phase C.

[0058] The interface module in this application is used to receive the DC operation mode and the modulation wave corresponding to each bridge arm sent by the unit control layer.

[0059] The acquisition module is used to sum the currents of each bridge arm to obtain the total three-phase current of the bridge arm when the DC operation mode is black start mode.

[0060] When summing the currents of the six bridge arms, the acquisition module only adds the currents of the same phase. For example, the six bridge arms may contain the currents of the upper and lower A-phase bridge arms, the upper and lower B-phase bridge arms, the upper and lower C-phase bridge arms, and the lower C-phase bridge arms. The acquisition module adds the A-phase currents of the six bridge arms to obtain the total A-phase current of the bridge arms; it adds the B-phase currents of the six bridge arms to obtain the total B-phase current of the bridge arms; and it adds the C-phase currents of the six bridge arms to obtain the total C-phase current of the bridge arms. Based on this, the total three-phase current of the bridge arms obtained after the converter valves are added is still a three-phase current.

[0061] The converter valve is activated in different modes under different DC operating modes, and the functions it performs are also different. Each DC operating mode has a corresponding function for the converter valve.

[0062] Once the total three-phase current of the bridge arm is obtained, the converter valve outputs the total three-phase current of the bridge arm to the filter.

[0063] A filter is used to filter the total three-phase current of the bridge arm to obtain the component to be suppressed.

[0064] The frequency of the component to be suppressed filtered out by the filter is related to the actual needs. It can filter out the main frequency under normal operation to obtain the component to be suppressed.

[0065] The component to be suppressed filtered out by the filter will be output to the PI controller.

[0066] A PI controller is used to process the component to be suppressed to obtain an oscillation suppression level opposite to that of the component to be suppressed.

[0067] The PI controller performs proportional-integral processing on the component to be suppressed to obtain a level. The frequency of this level is opposite to the frequency of the component to be suppressed, and this level is called the oscillation suppression level.

[0068] The PI controller inputs the oscillation suppression level to the superposition module.

[0069] The superposition module is used to acquire and superimpose the modulation wave corresponding to each bridge arm, the oscillation suppression level, and the circulating suppression wave corresponding to each bridge arm to obtain the reference wave corresponding to each bridge arm.

[0070] Each bridge arm has its corresponding modulation wave, oscillation suppression level, and circulating current suppression wave. The overlay module processes the modulation wave, oscillation suppression level, and circulating current suppression wave of the same bridge arm to obtain the reference wave corresponding to each bridge arm.

[0071] The superposition module, by superimposing the modulation wave, oscillation suppression level and circulating current suppression wave of the same bridge arm, can suppress the oscillation component and second harmonic circulating current in the modulation wave, and obtain a reference wave with suppressed oscillation component and second harmonic circulating current. This allows the reference wave at the connection between each bridge arm in the converter valve and the AC system to better achieve black start.

[0072] As can be seen from the above technical solution, the control system of the flexible DC transmission converter valve provided in this application includes an interface module, a data acquisition module, a filter, a PI controller, and a superposition module. This application is only implemented during black start; it cannot be started in non-black start mode to prevent erroneous operation. Therefore, the interface module is used to receive the DC operating mode and the modulation wave corresponding to each bridge arm from the unit control layer. When the DC operating mode is black start mode, the data acquisition module is used to add the currents of each bridge arm to obtain the total three-phase current of the bridge arm. The filter is used to filter the total three-phase current of the bridge arm to obtain the component to be suppressed. Based on this, the component to be suppressed in each bridge arm current is obtained. The PI controller is used to process the component to be suppressed to obtain an oscillation suppression level opposite to the component to be suppressed. Based on this, an additional amount of oscillation suppression opposite to the component to be suppressed is obtained. The superposition module is used to acquire and superimpose the modulation wave corresponding to each bridge arm, the oscillation suppression level, and the circulating current suppression wave corresponding to each bridge arm to obtain the reference wave corresponding to each bridge arm. In this way, reference waves for black start corresponding to each bridge arm with a suppression effect can be obtained, suppressing the tripping risk caused by oscillations during the black start process of flexible DC transmission. Furthermore, this improves the safety of the flexible DC transmission during black start.

[0073] In some embodiments of this application, the acquisition module may include a collection unit and a calculation unit.

[0074] The collection unit within the acquisition module is used to collect the current of each bridge arm.

[0075] The calculation unit within the acquisition module is used to add the currents of each bridge arm to obtain the total three-phase current of the bridge arm.

[0076] As can be seen from the above technical solution, the acquisition module in this embodiment can include two units, namely a collection unit and a calculation unit. Through the above two units, the total three-phase current of the bridge arm can be better collected and calculated, and the black start of flexible DC transmission can be better realized.

[0077] In some embodiments of this application, the filter may include a filtering module.

[0078] The filtering module is used to perform band-stop filtering on the total three-phase current of the bridge arm to obtain high-frequency and low-frequency components, and to combine the high-frequency and low-frequency components into components to be suppressed.

[0079] In normal operating mode, the frequency is typically 45Hz-55Hz, with a center frequency of 50Hz. Therefore, the total three-phase current of the bridge arm with a frequency of 45Hz-55Hz can be filtered out to avoid affecting normal operation.

[0080] As can be seen from the above technical solution, the filter in this embodiment includes a filtering module. This filtering module can perform band-stop filtering on the total three-phase current of the bridge arm, better filtering out frequencies operating under normal conditions to obtain the components to be suppressed.

[0081] In some embodiments of this application, the PI controller includes a proportional control module.

[0082] The proportional control module is used to perform proportional integration on the component to be suppressed to obtain an oscillation suppression level that is opposite to that of the component to be suppressed.

[0083] In some embodiments of this application, the overlay module may include a subtractor and an adder.

[0084] The subtractor is used to subtract half of the oscillation suppression level from the sum of the modulation wave corresponding to the lower bridge arm of each phase and the circulating suppression wave corresponding to the lower bridge arm of that phase, so as to obtain the reference wave corresponding to the lower bridge arm of that phase.

[0085] Specifically, the converter valve may include an upper bridge arm of phase A, a lower bridge arm of phase A, an upper bridge arm of phase B, a lower bridge arm of phase B, an upper bridge arm of phase C, and a lower bridge arm of phase C.

[0086] At this time, the subtractor can be used to subtract half of the oscillation suppression level from the sum of the modulation wave corresponding to the lower bridge arm of phase A and the circulating suppression wave corresponding to the lower bridge arm of phase A, so as to obtain the reference wave corresponding to the lower bridge arm of phase A.

[0087] The subtractor can be used to subtract half of the oscillation suppression level from the sum of the modulation wave corresponding to the lower bridge arm of phase B and the circulating suppression wave corresponding to the lower bridge arm of phase B, to obtain the reference wave corresponding to the lower bridge arm of phase B.

[0088] The subtractor can be used to subtract half of the oscillation suppression level from the sum of the modulation wave corresponding to the lower arm of phase C and the circulating suppression wave corresponding to the lower arm of phase C, to obtain the reference wave corresponding to the lower arm of phase C.

[0089] An adder is used to superimpose the modulation wave corresponding to the upper bridge arm of each phase, the circulating suppression wave corresponding to the upper bridge arm of that phase, and half of the oscillation suppression level to obtain the reference wave corresponding to the upper bridge arm of that phase.

[0090] At this time, the adder can be used to superimpose the modulation wave corresponding to the upper bridge arm of phase A, the circulating current suppression wave corresponding to the upper bridge arm of phase A, and half of the oscillation suppression level.

[0091] The adder can be used to superimpose the modulation wave corresponding to the upper arm of phase B, the circulating current suppression wave corresponding to the upper arm of phase B, and half of the oscillation suppression level.

[0092] The adder can be used to superimpose the modulation wave corresponding to the upper arm of phase C, the circulating current suppression wave corresponding to the upper arm of phase C, and half of the oscillation suppression level.

[0093] As can be seen from the above technical solution, the superposition module in the embodiment can include an adder and a subtractor. Through the adder and subtractor, the modulation wave, circulating current suppression wave and oscillation suppression level of each bridge arm can be superimposed to obtain the reference wave corresponding to each bridge arm.

[0094] This application also provides another control system for a flexible DC transmission converter valve. This control system comprises an interface module, a data acquisition module, a filter, a divider, a first subtractor, a proportional controller, and a superposition module. Figure 2 As shown.

[0095] The interface module is used to receive the DC operating mode and the corresponding modulation wave of each bridge arm sent by the unit control layer.

[0096] The acquisition module is used to acquire the current of each bridge arm when the DC operation mode is black start mode, and calculate the difference between the current corresponding to the upper bridge arm of each phase and the current corresponding to the lower bridge arm of the same phase, so as to obtain the current difference of each phase bridge arm.

[0097] The acquisition module can calculate the difference between the current corresponding to the upper bridge arm of phase A and the current corresponding to the lower bridge arm of phase A to obtain the current difference of phase A; it can calculate the difference between the current corresponding to the upper bridge arm of phase B and the current corresponding to the lower bridge arm of phase B to obtain the current difference of phase B; and it can calculate the difference between the current corresponding to the upper bridge arm of phase C and the current corresponding to the lower bridge arm of phase C to obtain the current difference of phase C.

[0098] The filter is used to perform sliding window filtering on the current difference of each phase arm.

[0099] The filter can perform sliding window filtering on the current difference of phase A bridge arm; it can perform sliding window filtering on the current difference of phase B bridge arm; and it can perform sliding window filtering on the current difference of phase C bridge arm.

[0100] The divider is used to calculate and obtain the current difference between each phase arm of the bridge, and the average value after sliding window filtering.

[0101] The divider can add the current difference values ​​of phase A bridge arm, phase B bridge arm, and phase C bridge arm after sliding window filtering to obtain the total current difference value, and calculate the ratio between the total current difference value and 3 to obtain the average value after sliding window filtering.

[0102] The first subtractor is used to subtract the average value from the current difference of each phase arm after sliding window filtering to obtain the suppression component corresponding to each phase arm.

[0103] The first subtractor can subtract the average value from the current difference of the A-phase bridge arm after sliding window filtering to obtain the suppression component corresponding to the A-phase bridge arm; it can subtract the average value from the current difference of the B-phase bridge arm after sliding window filtering to obtain the suppression component corresponding to the B-phase bridge arm; and it can subtract the average value from the current difference of the C-phase bridge arm after sliding window filtering to obtain the suppression component corresponding to the C-phase bridge arm.

[0104] The proportional controller is used to proportionally control the suppression component corresponding to each phase bridge arm to obtain the oscillation suppression level corresponding to each phase bridge arm.

[0105] The proportional controller is used to proportionally control the suppression components corresponding to phase A, phase B, and phase C bridge arms, respectively, and obtain the oscillation suppression levels corresponding to phase A, phase B, and phase C bridge arms.

[0106] The superposition module is used to acquire and superimpose the modulation wave, the oscillation suppression level, and the circulating current suppression wave corresponding to each bridge arm to obtain the reference wave corresponding to each bridge arm.

[0107] The superposition module, by superimposing the modulation wave, oscillation suppression level and circulating current suppression wave of the same bridge arm, can suppress the oscillation component and second harmonic circulating current in the modulation wave, and obtain a reference wave with the effect of suppressing the oscillation component and second harmonic circulating current. This allows the reference wave at the connection between each bridge arm in the converter valve and the AC system to better achieve black start.

[0108] As can be seen from the above technical solution, this embodiment provides another system for better realizing the black start of flexible DC transmission. In this embodiment, when obtaining the oscillation suppression level of each phase, it is necessary not only to refer to the components of the current difference after sliding window filtering of the upper and lower bridge arms of each phase, but also to refer to the average value of the current difference after sliding window filtering of each bridge arm. Furthermore, the suppression component corresponding to each phase bridge arm is proportionally controlled to obtain a better oscillation suppression level. After obtaining this oscillation suppression level, the modulation wave corresponding to each bridge arm, the oscillation suppression level corresponding to that bridge arm, and the circulating current suppression wave corresponding to that bridge arm are superimposed to obtain the reference wave for black start of each bridge arm with oscillation suppression and second harmonic circulating current effects. This achieves the suppression of tripping risks caused by oscillation during the black start process of flexible DC transmission. Furthermore, it improves the safety during the black start process of flexible DC transmission.

[0109] In some embodiments of this application, the overlay module consists of an adder and a second subtractor.

[0110] The second subtractor is used to subtract half of the corresponding oscillation suppression level from the sum of the modulation wave corresponding to the lower bridge arm of each phase and the circulating suppression wave corresponding to the lower bridge arm of that phase, so as to obtain the reference wave corresponding to the lower bridge arm of that phase.

[0111] The second subtractor can be used to subtract half of the oscillation suppression level corresponding to the lower bridge arm of phase A from the sum of the modulation wave and the circulating current suppression wave corresponding to the lower bridge arm of phase A to obtain the reference wave corresponding to the lower bridge arm of phase A; subtract half of the oscillation suppression level corresponding to the lower bridge arm of phase B from the sum of the modulation wave and the circulating current suppression wave corresponding to the lower bridge arm of phase B to obtain the reference wave corresponding to the lower bridge arm of phase B; and subtract half of the oscillation suppression level corresponding to the lower bridge arm of phase C from the sum of the modulation wave and the circulating current suppression wave corresponding to the lower bridge arm of phase C to obtain the reference wave corresponding to the lower bridge arm of phase C.

[0112] The adder is used to superimpose the modulation wave corresponding to the upper arm of each phase, the circulating suppression wave corresponding to the upper arm of that phase, and half of the oscillation suppression level of that phase to obtain the reference wave corresponding to the upper arm of that phase.

[0113] The adder can be used to superimpose the modulation wave corresponding to the upper bridge arm of phase A, the circulating current suppression wave corresponding to the upper bridge arm of phase A, and half of the oscillation suppression level corresponding to the upper bridge arm of phase A to obtain the reference wave corresponding to the upper bridge arm of phase A; superimpose the modulation wave corresponding to the upper bridge arm of phase B, the circulating current suppression wave corresponding to the upper bridge arm of phase B, and half of the oscillation suppression level corresponding to the upper bridge arm of phase B to obtain the reference wave corresponding to the upper bridge arm of phase B; and superimpose the modulation wave corresponding to the upper bridge arm of phase C, the circulating current suppression wave corresponding to the upper bridge arm of phase C, and half of the oscillation suppression level corresponding to the upper bridge arm of phase C to obtain the reference wave corresponding to the upper bridge arm of phase C.

[0114] As can be seen from the above technical solution, the superposition module in the embodiment may include an adder and a second subtractor. Through the adder and the second subtractor, the modulation wave, circulating current suppression wave and oscillation suppression level of each bridge arm can be superimposed to obtain the reference wave corresponding to each bridge arm for suppressing low-frequency and high-frequency components.

[0115] In some embodiments of this application, the acquisition module may include a collection unit and a calculation unit.

[0116] The collection unit is used to collect the current of each bridge arm.

[0117] The calculation unit is used to calculate the difference between the current corresponding to the upper bridge arm of each phase and the current corresponding to the lower bridge arm of the same phase, so as to obtain the current difference of each phase bridge arm.

[0118] As can be seen from the above technical solution, the acquisition module in this embodiment can include two units, namely a collection unit and a calculation unit. Through the above two units, the current difference of each phase bridge arm can be better collected and calculated, and the black start of flexible DC transmission can be better realized.

[0119] In some embodiments of this application, the filter includes a filtering module.

[0120] This filtering module is used to perform sliding window filtering on the current difference of each phase bridge arm.

[0121] This filtering module performs sliding window filtering on each current difference.

[0122] During sliding window filtering, the width of the aperture corresponding to each current difference can be consistent.

[0123] As can be seen from the above technical solution, a filtering module has been added in this embodiment. The presence of the filtering module allows the filter to perform sliding window filtering better, thereby achieving black start better.

[0124] In some embodiments of this application, the divider includes a division module; the division module is used to calculate and obtain the current difference between each phase bridge arm and the average value after sliding window filtering.

[0125] In some embodiments of this application, the proportional controller includes a proportional control module; the proportional control module is used to proportionally control the suppression component corresponding to each phase bridge arm to obtain the oscillation suppression level corresponding to each phase bridge arm.

[0126] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0127] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0128] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. The various embodiments of this application can be combined with each other. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control system for a flexible DC transmission converter valve, characterized in that, It includes an interface module, a data acquisition module, a filter, a PI controller, and a superposition module. The converter valve contains three-phase bridge arms, each of which is divided into an upper bridge arm and a lower bridge arm. The interface module is used to receive the DC operation mode and the modulation wave corresponding to each bridge arm sent by the unit control layer; The acquisition module is used to add the currents of each bridge arm to obtain the total three-phase current of the bridge arm when the DC operation mode is black start mode. The filter is used to filter the total three-phase current of the bridge arm to obtain the component to be suppressed; The PI controller is used to process the component to be suppressed to obtain an oscillation suppression level opposite to that of the component to be suppressed. The superposition module is used to acquire and superimpose the modulation wave corresponding to each bridge arm, the oscillation suppression level, and the circulating suppression wave corresponding to each bridge arm to obtain the reference wave corresponding to each bridge arm. The modulation wave corresponding to each bridge arm consists of a three-phase upper bridge arm modulation wave and a three-phase lower bridge arm modulation wave, and the circulating current suppression wave corresponding to each bridge arm consists of a three-phase upper bridge arm circulating current suppression wave and a three-phase lower bridge arm circulating current suppression wave. Each modulation wave and each circulating current suppression wave corresponds one-to-one with each bridge arm. The overlay module includes a subtractor and an adder; The subtractor is used to subtract half of the oscillation suppression level from the sum of the modulation wave corresponding to the lower bridge arm of each phase and the circulating suppression wave corresponding to the lower bridge arm of that phase, so as to obtain the reference wave corresponding to the lower bridge arm of that phase. The adder is used to superimpose the modulation wave corresponding to the upper bridge arm of each phase, the circulating suppression wave corresponding to the upper bridge arm of that phase, and half of the oscillation suppression level to obtain the reference wave corresponding to the upper bridge arm of that phase.

2. The control system for the flexible DC transmission converter valve according to claim 1, characterized in that, The acquisition module includes a collection unit and a calculation unit; The collection unit is used to collect the current of each bridge arm; The calculation unit is used to add the currents of each bridge arm to obtain the total three-phase current of the bridge arm.

3. The control system for the flexible DC transmission converter valve according to claim 1, characterized in that, The filter includes a filtering module; The filtering module is used to perform band-stop filtering on the total three-phase current of the bridge arm to obtain high-frequency components and low-frequency components, and to form the high-frequency components and low-frequency components into components to be suppressed.

4. A control system for a flexible DC transmission converter valve, characterized in that, It includes an interface module, a data acquisition module, a filter, a divider, a first subtractor, a proportional controller, and a superposition module. The converter valve contains three-phase bridge arms, each of which is divided into an upper bridge arm and a lower bridge arm. The interface module is used to receive the DC operation mode and the modulation wave corresponding to each bridge arm sent by the unit control layer; The acquisition module is used to acquire the current of each bridge arm when the DC operation mode is black start mode, and calculate the difference between the current corresponding to the upper bridge arm of each phase and the current corresponding to the lower bridge arm of the same phase, so as to obtain the current difference of each phase bridge arm. The filter is used to perform sliding window filtering on the current difference of each phase bridge arm; The divider is used to calculate and obtain the current difference between each phase bridge arm, and the average value after sliding window filtering; The first subtractor is used to subtract the average value from the current difference of each phase bridge arm after sliding window filtering to obtain the suppression component corresponding to each phase bridge arm. The proportional controller is used to proportionally control the suppression component corresponding to each phase bridge arm to obtain the oscillation suppression level corresponding to each phase bridge arm. The superposition module is used to acquire and superimpose the modulation wave corresponding to each bridge arm, the oscillation suppression level corresponding to the bridge arm, and the circulating suppression wave corresponding to the bridge arm to obtain the reference wave corresponding to each bridge arm. The modulation wave corresponding to each bridge arm consists of a three-phase upper bridge arm modulation wave and a three-phase lower bridge arm modulation wave, and the circulating current suppression wave corresponding to each bridge arm consists of a three-phase upper bridge arm circulating current suppression wave and a three-phase lower bridge arm circulating current suppression wave. Each modulation wave and each circulating current suppression wave corresponds one-to-one with each bridge arm. The superposition module includes an adder and a second subtractor; The second subtractor is used to subtract half of the corresponding oscillation suppression level from the sum of the modulation wave corresponding to the lower bridge arm of each phase and the circulating suppression wave corresponding to the lower bridge arm of that phase, so as to obtain the reference wave corresponding to the lower bridge arm of that phase. The adder is used to superimpose the modulation wave corresponding to the upper arm of each phase, the circulating suppression wave corresponding to the upper arm of that phase, and half of the oscillation suppression level of that phase to obtain the reference wave corresponding to the upper arm of that phase.

5. The control system for the flexible DC transmission converter valve according to claim 4, characterized in that, The acquisition module includes a collection unit and a calculation unit; The collection unit is used to collect the current of each bridge arm; The calculation unit is used to calculate the difference between the current corresponding to the upper bridge arm of each phase and the current corresponding to the lower bridge arm of the same phase, so as to obtain the current difference of each phase bridge arm.

6. The control system for the flexible DC transmission converter valve according to claim 4, characterized in that, The filter includes a filtering module; The filtering module is used to perform sliding window filtering on the current difference of each phase bridge arm.

7. The control system for the flexible DC transmission converter valve according to claim 4, characterized in that, The divider includes a division module; The division module is used to calculate and obtain the current difference between each phase bridge arm and the average value after sliding window filtering.

8. The control system for the flexible DC transmission converter valve according to claim 4, characterized in that, The proportional controller includes a proportional control module; The proportional control module is used to proportionally control the suppression component corresponding to each phase bridge arm to obtain the oscillation suppression level corresponding to each phase bridge arm.

Images