Integrated circuit based on reactive compensation and active filtering

Abstract

The invention discloses an integrated circuit based on reactive compensation and active filtering, and relates to the technical field of electric power, the circuit comprises a valve group module, a first filtering reactor, a second filtering reactor, a third filtering reactor and a power control module, the valve group module comprises a first valve group unit, a second valve group unit and a third valve group unit, wherein the first valve group unit is used for accessing a first phase voltage through the first filter reactor; the second valve group unit is used for accessing a second phase voltage through the second filter reactor; the third valve group unit is used for accessing a third phase voltage through the third filter reactor; the power control module is used for performing reactive compensation on the first phase voltage, the second phase voltage and the third phase voltage according to a reactive compensation control strategy; and the active filtering module is used for carrying out active filtering on the first phase voltage, the second phase voltage and the third phase voltage according to an active filtering control strategy.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to an integrated circuit based on reactive power compensation and active filtering. Background Art

[0002] Offshore wind farms use AC grid-connected access, which is transmitted to onshore substations via submarine cables to achieve grid-connected transmission of offshore wind farms. The use of high-voltage and long-distance submarine cables causes excess charging capacitive reactive power in the wind farm transmission system, and effective means are needed to compensate for reactive power. The distributed capacitance of submarine cable lines cannot be ignored. At the same time, large-scale full-power converters and long-distance AC cables for offshore wind power are widely used on the seabed, which poses a risk of inducing harmonic amplification or harmonic resonance, seriously threatening the safe and stable operation of the wind farm collection network.

[0003] At present, scholars have conducted relevant research on wind farm reactive compensation technology and high-frequency harmonic suppression methods, and have achieved grid-connected operation of related equipment. Most of the research focuses on the suppression of fixed harmonics, but due to the frequent and large changes in the power of the wind farm and the wind farm collection area, the impedance parameters of the system change in real time, and the dynamic changes in the number of high-order harmonics in the wind farm, fixed harmonic control cannot meet the operation and control requirements of offshore wind farms. At the same time, due to the site restrictions and electrical spacing restrictions of offshore wind farm substations, it is impossible to configure the electrical access of reactive compensation and active harmonic equipment at the same time, and the demand for integrated reactive compensation and high-frequency harmonic suppression devices is more urgent.

[0004] This section is intended to provide a background or context to the embodiments of the invention recited in the claims. No admission is made that the description herein is prior art by inclusion in this section. Summary of the invention

[0005] In order to solve at least one problem in the above background technology part, an embodiment of the present invention provides an integrated circuit based on reactive power compensation and active filtering, which has the functions of reactive power compensation and harmonic suppression, and can realize reactive power compensation and harmonic control of offshore wind farms. The circuit includes:

[0006] A valve group module, a first filter reactance, a second filter reactance, a third filter reactance and a power control module, wherein:

[0007] The valve group module includes a first valve group unit, a second valve group unit, and a third valve group unit, wherein:

[0008] The first valve group unit is used to access the first phase voltage through the first filter reactance; the second valve group unit is used to access the second phase voltage through the second filter reactance; the third valve group unit is used to access the third phase voltage through the third filter reactance;

[0009] The power control module is used to perform reactive compensation on the first phase voltage, the second phase voltage and the third phase voltage according to a reactive compensation control strategy; and is used to perform active filtering on the first phase voltage, the second phase voltage and the third phase voltage according to an active filtering control strategy.

[0010] In some optional aspects of this embodiment, the first valve group unit is connected to one end of the first filter reactor, and the other end of the first filter reactor is connected to the first phase voltage input end of the power grid;

[0011] The second valve group unit is connected to one end of the second filter reactor, and the other end of the second filter reactor is connected to the second phase voltage input end of the power grid;

[0012] The third valve group unit is connected to one end of the third filter reactor, and the other end of the third filter reactor is connected to the third phase voltage input end of the power grid.

[0013] In some optional aspects of this embodiment, the first valve group unit, the second valve group unit and the third valve group unit respectively include n valve group circuits connected in sequence.

[0014] In some optional aspects of this embodiment, the valve group circuit includes a capacitor, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a bypass switch, wherein:

[0015] One end of the capacitor is connected to the collector of the first switch tube and the collector of the third switch tube, and the other end of the capacitor is connected to the emitter of the second switch tube and the emitter of the fourth switch tube;

[0016] The emitter of the first switch tube is connected to the collector of the second switch tube, and the emitter of the third switch tube is connected to the collector of the fourth switch tube;

[0017] The gate of the first switch tube, the gate of the second switch tube, the gate of the third switch tube and the gate of the fourth switch tube are respectively connected to the power control module;

[0018] The positive terminal of the bypass switch is connected to the first filter reactor and the emitter of the first switch tube;

[0019] The negative terminal of the bypass switch is connected to the collector of the fourth switch tube and the positive terminal of the bypass switch of the next valve group circuit.

[0020] In some optional aspects of this embodiment, the power control module includes a pulse drive signal generator, which is used to generate a pulse drive signal and output the pulse drive signal to the gate of each switch tube.

[0021] In some optional aspects of this embodiment, the first filter reactor, the second filter reactor and the third filter reactor are all hollow water-cooled reactors.

[0022] In some optional aspects of this embodiment, the reactive power compensation control strategy includes a primary reactive power compensation control sub-strategy, a secondary reactive power compensation control sub-strategy, and a tertiary reactive power compensation control sub-strategy, wherein:

[0023] The primary reactive power compensation control sub-strategy is used to achieve a balance among the first phase current, the second phase current and the third phase current, and suppress the internal circulation of the valve group module;

[0024] The secondary reactive power compensation control sub-strategy is used to achieve a balance among the first phase voltage, the second phase voltage and the third phase voltage;

[0025] The three-level reactive power compensation control sub-strategy is used to achieve internal voltage balance among the first valve group unit, the second valve group unit and the third valve group unit.

[0026] In some optional aspects of this embodiment, on the basis of the primary reactive compensation control sub-strategy, the secondary reactive compensation control sub-strategy and the tertiary reactive compensation control sub-strategy, the reactive compensation control strategy further includes a current tracking control sub-strategy, wherein:

[0027] The current tracking control sub-strategy introduces dq conversion or applies instantaneous reactive power theory;

[0028] The expression of the current tracking control sub-strategy is as follows:

[0029]

[0030] In the formula, I Qref is the target value of reactive power current; I dref is the target value of the DC bus voltage; I d is the control reference value of the d-axis; I q is the control reference value of the q axis; v sd and v sq They are active control component and reactive control component respectively; k1 is the proportional coefficient; k2 is the integral coefficient; T1 is the d-axis time constant and T2 is the q-axis time constant.

[0031] In some optional aspects of this embodiment, the active filtering control strategy includes a phase angle fast detection sub-strategy, wherein:

[0032] The phase angle fast detection sub-strategy is used to determine the phase and angular velocity of the first phase voltage, the second phase voltage and the third phase voltage through a PLL double closed-loop control structure.

[0033] In some optional aspects of this embodiment, the active filtering control strategy further includes a harmonic current compensation control sub-strategy, wherein:

[0034] The harmonic current compensation control sub-strategy is used to offset the load harmonics in the first phase current, the second phase current and the third phase current by outputting harmonic currents that are equal in magnitude and opposite in direction to the first phase current, the second phase current and the third phase current.

[0035] An embodiment of the present invention provides an integrated circuit based on reactive power compensation and active filtering, and proposes an integrated reactive power compensation and active filtering device with a redundant cascade topology architecture. Its topology architecture and design scheme are more convenient for assembly and operation and maintenance, and can greatly improve the operating performance of the equipment. In addition, under the control of the power control module, the integrated device has both reactive power compensation control function and harmonic suppression function, which can realize rapid and accurate regulation of reactive power, and realize reactive power compensation and harmonic control of offshore wind farms. At the same time, accurate suppression of harmonics of different orders can be achieved through rapid detection of full-band harmonics. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0037] Figure 1 It is a schematic diagram of an integrated circuit structure based on reactive power compensation and active filtering in an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of a reactive power compensation control strategy according to an embodiment of the present invention;

[0039] Figure 3 Schematic diagram of active filtering control strategy in an embodiment of the present invention;

[0040] Figure 4 This is the waveform diagram of the frequency phase angle detection of the traditional algorithm;

[0041] Figure 5 This is a frequency phase angle detection waveform diagram with a phase angle fast detection sub-strategy provided based on an embodiment of the present invention. DETAILED DESCRIPTION

[0042] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0043] like Figure 1 As shown, the present application proposes an integrated circuit based on reactive power compensation and active filtering, the circuit comprising a valve group module 1, a first filter reactance L1, a second filter reactance L2, a third filter reactance L3 and a power control module 2, wherein:

[0044] The valve group module 1 includes a first valve group unit 10, a second valve group unit 11, and a third valve group unit 12, wherein:

[0045] The first valve group unit 10 is used to access the first phase voltage through the first filter inductor L1; the second valve group unit 11 is used to access the second phase voltage through the second filter inductor L2; and the third valve group unit 12 is used to access the third phase voltage through the third filter inductor L3.

[0046] It should be understood that the voltage input from the power grid is a three-phase voltage, for example, a first phase voltage input from the A terminal of the power grid, a second phase voltage input from the B terminal of the power grid, and a third phase voltage input from the C terminal of the power grid.

[0047] The power control module 2 is used to perform reactive compensation on the first phase voltage, the second phase voltage and the third phase voltage according to a reactive compensation control strategy; and is used to perform active filtering on the first phase voltage, the second phase voltage and the third phase voltage according to an active filtering control strategy.

[0048] In some optional embodiments of this embodiment, Figure 1 As shown, the first valve group unit 10 is connected to one end of the first filter reactor L1, and the other end of the first filter reactor L1 is connected to the first phase voltage input end (ie, end A) of the power grid;

[0049] The second valve group unit 11 is connected to one end of the second filter reactor L2, and the other end of the second filter reactor L1 is connected to the second phase voltage input end (i.e., end B) of the power grid;

[0050] The third valve group unit 12 is connected to one end of the third filtering inductor L3 , and the other end of the third filtering inductor L3 is connected to the third phase voltage input end (ie, end C) of the power grid.

[0051] In some optional embodiments of this embodiment, Figure 1 As shown, the first valve group unit 10, the second valve group unit 11 and the third valve group unit 12 respectively include n valve group circuits connected in sequence, where n is a natural number greater than or equal to 1, specifically:

[0052] The n valve group circuits connected in sequence in the first valve group unit 10 are SMa1, SMa2, ..., SMan;

[0053] The n valve group circuits connected in sequence in the second valve group unit 11 are SMb1, SMb2, ..., SMbn respectively;

[0054] The n sequentially connected valve group circuits of the third valve group unit 12 are SMc1, SMc2, ... SMcn respectively.

[0055] It should be noted that the circuit structures of the valve group circuits are the same, and all include a capacitor and four switch tubes. Taking SMa1 in the first valve group unit 10 as an example, the structure of the valve group circuit is further described, specifically:

[0056] like Figure 1 As shown, the valve group circuit includes a capacitor C1, a first switch tube SV1, a second switch tube SV2, a third switch tube SV3, a fourth switch tube SV4 and a bypass switch S1, wherein:

[0057] One end of the capacitor C1 is connected to the collector of the first switch tube SV1 and the collector of the third switch tube, and the other end of the capacitor C1 is connected to the emitter of the second switch tube SV2 and the emitter of the fourth switch tube SV4;

[0058] The emitter of the first switch tube SV1 is connected to the collector of the second switch tube SV2, and the emitter of the third switch tube SV3 is connected to the collector of the fourth switch tube SV4;

[0059] The gate of the first switch tube SV1, the gate of the second switch tube SV2, the gate of the third switch tube SV3 and the gate of the fourth switch tube SV4 are respectively connected to the power control module;

[0060] The positive terminal (M terminal) of the bypass switch S1 is connected to the first filter inductor L1 and the emitter of the first switch tube SV1;

[0061] The negative terminal (N terminal) of the bypass switch S1 is connected to the collector of the fourth switch tube SV4 and the positive terminal of the bypass switch of the next valve group circuit.

[0062] In the figure, M represents the positive pole, and N represents the negative pole. The circuit connection method is that the M positive pole of the SMa1 module of the first valve group unit is connected to the first filter inductor, and the N negative pole of the SMa1 module is connected to the positive pole M of the SMa2 module. The first valve group unit is formed by connecting the MN of n SMa modules.

[0063] In some optional embodiments of the present embodiment, the power control module 2 includes a pulse drive signal generator for generating a pulse drive signal and outputting the pulse drive signal to the gate of each switch tube, and each switch tube is turned on and off under the action of the pulse drive signal.

[0064] In this embodiment, the valve group unit module adopts a unified standard style, and according to the modular design, the high voltage level access is achieved by connecting multiple modules in series. The modular design effectively reduces the cost of the device and improves the efficiency of equipment installation and maintenance. At the same time, a bypass switch is added at the connection of each module. If a module fails, the bypass switch can be used to short-circuit the faulty module without affecting the normal operation of the equipment. The filter reactance adopts a hollow water-cooled reactor, which can effectively reduce the heating effect of harmonic current on the reactor and ensure the safe and stable operation of the reactor. At the same time, the reactive compensation and active filtering collaborative controller adopts a high real-time performance DSP+FPGA to operate the control strategy and issue control instructions to realize the operation, monitoring, control and analysis of the entire device.

[0065] In some optional aspects of this embodiment, the reactive power compensation control strategy includes a primary reactive power compensation control sub-strategy, a secondary reactive power compensation control sub-strategy, and a tertiary reactive power compensation control sub-strategy, wherein:

[0066] The primary reactive power compensation control sub-strategy is used to achieve a balance among the first phase current, the second phase current and the third phase current, and suppress the internal circulation of the valve group module;

[0067] The secondary reactive power compensation control sub-strategy is used to achieve a balance among the first phase voltage, the second phase voltage and the third phase voltage;

[0068] The three-level reactive power compensation control sub-strategy is used to achieve internal voltage balance among the first valve group unit, the second valve group unit and the third valve group unit.

[0069] Specifically, reactive power compensation control adopts three-level control, the first level is global DC side voltage balance control, to achieve the balance of ABC three-phase voltage flow and suppress internal circulation. The second level is interphase DC side voltage balance control, to ensure the balance of ABC three-phase DC voltage; the third level is intra-phase DC side voltage balance control, to achieve the balance of each valve group unit module voltage in the phase, to ensure that there is no module overvoltage.

[0070] In some optional aspects of this embodiment, on the basis of the primary reactive compensation control sub-strategy, the secondary reactive compensation control sub-strategy and the tertiary reactive compensation control sub-strategy, the reactive compensation control strategy further includes a current tracking control sub-strategy, wherein:

[0071] On the basis of three-level control, through the direct current control method, the direct control of the current adopts the tracking PWM control technology to feedback control the instantaneous value of the current waveform, among which the tracking PWM control technology can adopt the hysteresis comparison method or the triangle wave comparison method. In the current direct control method of reactive compensation and active filter coordinated control, the dq transformation or the application of instantaneous reactive power theory can be introduced. Since its reference value IQref ,I Pref and feedback value I Q (i.e. I q ), I P (i.e. I d ) are all DC signals in steady state, so current tracking control without steady-state error can be achieved through the PI regulator.

[0072] Depend on Figure 2 It can be concluded that the expression of the current tracking control sub-strategy is as follows:

[0073]

[0074] In the formula, I Qref is the target value of reactive power current; I dref is the target value of the DC bus voltage; I d is the control reference value of the d-axis; I q is the control reference value of the q axis; v sd and v sq They are active control component and reactive control component respectively; k1 is the proportional coefficient; k2 is the integral coefficient; T1 is the d-axis time constant and T2 is the q-axis time constant.

[0075] In addition, Figure 2 middle, I dref is the control reference value of the d-axis, I d The real-time current value on the d-axis obtained after the three-phase current output of the device is transformed by Pack / clack. for Figure 3 The calculated real-time phase angle, i a 、i b 、i c is the instantaneous value of the three-phase current at the equipment grid connection point. apf is the total current at the device end, i pcc is the total current at the grid connection point.

[0076] In addition, I Qref The reactive power current is the target value of the reactive power current. The reactive power of the reactive power compensation device is regulated by issuing manual instructions from the background of the reactive power compensation device or automatic instructions from the station AVC system. dref is the target value of DC bus voltage, u d is the actual value of the DC bus voltage, through u dref -u d To achieve the stability of DC bus voltage and ensure the normal operation of reactive power compensation device. sd 、v sqThey are respectively the active control component and reactive control component of the calculated reactive compensation. The active control component is mainly used to maintain the stability of the DC bus voltage, and the reactive control component can realize reactive compensation and active filtering functions. k1 is the proportional coefficient and k2 is the integral coefficient. The closed-loop tracking control of the control system can be realized through the proportional-integral controller.

[0077] In some optional aspects of this embodiment, the active filtering control strategy includes a phase angle fast detection sub-strategy, wherein:

[0078] The phase angle fast detection sub-strategy is used to determine the phase and angular velocity of the first phase voltage, the second phase voltage and the third phase voltage through a PLL double closed-loop control structure.

[0079] Specifically, in this application, Figure 3 As shown in the figure, in order to eliminate the influence of fundamental negative sequence, harmonic components and voltage phase mutation on fundamental positive sequence voltage frequency and phase detection, an improved PLL phase-locked loop based on generalized integrator is adopted. The PLL based on generalized integration adopts a double closed-loop control structure. First, the three-phase voltage U sabc Then, through Pack transformation, the grid connection point voltage signal is converted from the three-phase stationary coordinate system to the two-phase rotating coordinate system U sαβ Then, through the clack transformation, the two-phase rotating coordinate system is converted to the two-phase stationary coordinate system, and we get use Calculate the phase angle of the power grid. In order to eliminate the influence of the background harmonics of the power grid on the control, the inner loop adopts an improved controller to eliminate the controlled object The harmonic AC signal in the system is increased, and the system bandwidth is increased to improve the dynamic response speed, as follows Figure 3 The dotted box part is shown.

[0080] The outer loop uses a conventional PI controller to regulate because It is a DC signal, and the PI controller can effectively control it to ensure that the positive-sequence fundamental voltage frequency detected by the PI controller is stable, thereby ensuring the measured fundamental positive-sequence voltage phase At the same time, because the detected fundamental voltage positive sequence component angular velocity ω1 is fed back to the resonant controller in real time, it is ensured that the change of grid frequency will not affect the regulation effect of the generalized integral controller. It should be noted that Figure 3 Calculate the phase angle of the power grid Used to implement phase tracking control in the figure.

[0081] After obtaining the full-band voltage phase, the current is decomposed by Fourier, and the amplitude of each harmonic current can be accurately obtained. In addition, the phase and angular velocity at frequencies from the fundamental wave (50Hz) to the 25th harmonic (2500Hz) can be quickly detected, and the amplitude and characteristics of each harmonic in the wind farm can be accurately located, providing a guarantee for the control of the integrated reactive power compensation and active filtering device.

[0082] Figure 4 This is the waveform diagram of the frequency phase angle detection of the traditional algorithm. Figure 5 This is the frequency phase angle detection waveform diagram of the algorithm of this application. Compared with traditional frequency phase angle sampling, the control method proposed in this application can greatly improve the acquisition accuracy and response time.

[0083] In some optional aspects of this embodiment, the active filtering control strategy further includes a harmonic current compensation control sub-strategy, wherein:

[0084] The harmonic current compensation control sub-strategy is used to offset the load harmonics in the first phase current, the second phase current and the third phase current by outputting harmonic currents that are equal in magnitude and opposite in direction to the first phase current, the second phase current and the third phase current.

[0085] Specifically, Figure 2 As shown, by outputting harmonic currents that are equal to the load harmonic current in magnitude and opposite in direction, the load harmonics are offset, so that the current on the system side meets the standard. The implementation method is as follows: the device current is calculated from the reactive compensation current and the active filter current as the harmonic current mode command iapf_i*, iapf_i* is limited to obtain the harmonic current command iapf* of the reactive compensation and active filter cooperative control device, and the harmonic current command iapf* and the active filter output current iapfh are closed-loop controlled to obtain the harmonic modulation wave to control the reactive compensation and active filter cooperative control valve group output harmonic current, thereby achieving effective suppression of harmonic current.

[0086] In the present application, a reactive power compensation and active filtering integrated circuit with a redundant cascade topology is proposed. Its topology and design are easier to assemble, operate and maintain, and can greatly improve the operating performance of the equipment. In addition, the reactive power compensation and active filtering integrated circuit can realize reactive power compensation control function and harmonic suppression function, realize rapid and precise regulation of reactive power, and realize precise suppression of harmonics of different orders through rapid detection of full-band harmonics.

[0087] It can be understood that the above examples are merely examples listed for better understanding of the technical solutions of the embodiments of the present invention, and are not intended to be the sole limitations on the embodiments of the present invention.

[0088] It should be noted that in the description of this application, the terms "upper" and "lower" indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, which are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on this application. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0089] It should also be noted that, in the description of the present application, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the statement "comprise one..." do not exclude the presence of other identical elements in the process, method, article or equipment including the elements.

[0090] In the embodiments of the present application, the singular forms "a", "the", etc. include plural forms and should be broadly understood as "a kind" or "a type" rather than being limited to the meaning of "one"; in addition, the term "said" should be understood to include both singular and plural forms, unless the context clearly indicates otherwise. In addition, the term "according to" should be understood as "at least in part according to...", and the term "based on" should be understood as "at least in part based on...", unless the context clearly indicates otherwise.

[0091] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this disclosure can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of this disclosure can be achieved, and this document is not limited here.

[0092] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. An integrated circuit based on reactive power compensation and active filtering, characterized in that: include: A valve group module, a first filter reactance, a second filter reactance, a third filter reactance and a power control module, wherein: The valve group module includes a first valve group unit, a second valve group unit, and a third valve group unit, wherein: The first valve group unit is used to access the first phase voltage through the first filter reactance; the second valve group unit is used to access the second phase voltage through the second filter reactance; the third valve group unit is used to access the third phase voltage through the third filter reactance; The power control module is used to perform reactive compensation on the first phase voltage, the second phase voltage and the third phase voltage according to a reactive compensation control strategy; and is used to perform active filtering on the first phase voltage, the second phase voltage and the third phase voltage according to an active filtering control strategy.

2. The circuit according to claim 1, characterized in that The first valve group unit is connected to one end of the first filter reactor, and the other end of the first filter reactor is connected to the first phase voltage input end of the power grid; The second valve group unit is connected to one end of the second filter reactor, and the other end of the second filter reactor is connected to the second phase voltage input end of the power grid; The third valve group unit is connected to one end of the third filter reactor, and the other end of the third filter reactor is connected to the third phase voltage input end of the power grid.

3. The circuit according to claim 2, characterized in that The first valve group unit, the second valve group unit and the third valve group unit respectively include n valve group circuits connected in sequence.

4. The circuit according to claim 3, characterized in that The valve group circuit includes a capacitor, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a bypass switch, wherein: One end of the capacitor is connected to the collector of the first switch tube and the collector of the third switch tube, and the other end of the capacitor is connected to the emitter of the second switch tube and the emitter of the fourth switch tube; The emitter of the first switch tube is connected to the collector of the second switch tube, and the emitter of the third switch tube is connected to the collector of the fourth switch tube; The gate of the first switch tube, the gate of the second switch tube, the gate of the third switch tube and the gate of the fourth switch tube are respectively connected to the power control module; The positive terminal of the bypass switch is connected to the first filter reactor and the emitter of the first switch tube; The negative terminal of the bypass switch is connected to the collector of the fourth switch tube and the positive terminal of the bypass switch of the next valve group circuit.

5. The circuit according to claim 4, characterized in that The power control module includes a pulse drive signal generator, which is used to generate a pulse drive signal and output the pulse drive signal to the gate of each switch tube.

6. The circuit according to claim 1, characterized in that The first filter reactor, the second filter reactor and the third filter reactor are all hollow water-cooled reactors.

7. The circuit according to claim 1, characterized in that The reactive power compensation control strategy includes a primary reactive power compensation control sub-strategy, a secondary reactive power compensation control sub-strategy and a tertiary reactive power compensation control sub-strategy, wherein: The primary reactive power compensation control sub-strategy is used to achieve a balance among the first phase current, the second phase current and the third phase current, and suppress the internal circulation of the valve group module; The secondary reactive power compensation control sub-strategy is used to achieve a balance among the first phase voltage, the second phase voltage and the third phase voltage; The three-level reactive power compensation control sub-strategy is used to achieve internal voltage balance among the first valve group unit, the second valve group unit and the third valve group unit.

8. The circuit according to claim 7, characterized in that On the basis of the primary reactive compensation control sub-strategy, the secondary reactive compensation control sub-strategy and the tertiary reactive compensation control sub-strategy, the reactive compensation control strategy further includes a current tracking control sub-strategy, wherein: The current tracking control sub-strategy introduces dq conversion or applies instantaneous reactive power theory; The expression of the current tracking control sub-strategy is as follows: In the formula, I Qref is the target value of reactive power current; I dref is the target value of the DC bus voltage; I d is the control reference value of the d-axis; I q is the control reference value of the q axis; v sd and v sq They are active control component and reactive control component respectively; k1 is the proportional coefficient; k2 is the integral coefficient; T1 is the d-axis time constant and T2 is the q-axis time constant.

9. The circuit according to claim 7, characterized in that The active filter control strategy includes a phase angle fast detection sub-strategy, wherein: The phase angle fast detection sub-strategy is used to determine the phase and angular velocity of the first phase voltage, the second phase voltage and the third phase voltage through a PLL double closed-loop control structure.

10. The circuit according to claim 9, characterized in that The active filtering control strategy also includes a harmonic current compensation control sub-strategy, wherein: The harmonic current compensation control sub-strategy is used to offset the load harmonics in the first phase current, the second phase current and the third phase current by outputting harmonic currents that are equal in magnitude and opposite in direction to the first phase current, the second phase current and the third phase current.

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