Self-voltage-stabilizing control method for three-phase four-bridge-arm series flexible interconnection switch

Abstract

The invention provides a direct-current self-voltage-stabilizing control method for a three-phase four-bridge-arm series flexible interconnection switch, which is applied to a power distribution network connected with two three-phase alternating-current sources, and the two three-phase alternating-current sources respectively form a first-end network side and a second-end network side of the power distribution network. Comprising the steps that power grid multi-dimensional electrical state parameter sets of a first end grid side and a second end grid side are collected, and the power grid multi-dimensional electrical state parameter sets comprise electrical state parameters and line structure parameters; based on the multi-dimensional electrical state parameter set of the power grid, determining a series voltage vector control parameter; and determining a pulse width modulation signal of a fourth bridge arm of the inverter based on the series voltage vector control parameter. Following control of an existing three-phase four-bridge-arm inverter is fully utilized, the active power dispatching size between feeder lines can be controlled, self-voltage-stabilizing control can be carried out on the direct-current side without other power electronic equipment or a direct-current source, the voltage-withstanding requirement for devices is lowered, the number of the devices is reduced, and the stability and economical efficiency of the system are improved.

Description

Technical Field

[0001] The present application relates to the field of power control technology, and in particular to a self-stabilizing voltage control method for a three-phase four-bridge-arm series-type flexible interconnected switch. Background Art

[0002] With the rapid development of power electronics and active distribution network technologies in recent years, distribution network soft open points (SOPs) have attracted widespread attention due to their advantages, including more flexible power flow regulation, faster response, reduced loop impact, and longer operating life. SOPs have the ability to improve the overall power flow distribution, feeder voltage levels, and accommodate distributed power generation in low-voltage distribution networks, thereby enhancing grid reliability. Currently, SOPs can be broadly divided into two categories: parallel and series. The primary topology of parallel devices is a back-to-back AC-DC-AC converter. By adjusting the port control strategy, they enable free power flow between adjacent feeders and isolate faults. However, when a parallel structure regulates power, full power flows through the device itself, resulting in large capacity, a large number of components, and high device tolerance requirements for parallel equipment.

[0003] In contrast, series SOPs offer advantages in terms of cost and volume. While achieving the same power regulation capability as parallel SOPs, the series-type equipment itself only needs to bear a small portion of the power to control high power flows. Consequently, series-type SOPs, with their advantages of requiring less equipment capacity, lower device voltage ratings, and lower costs and losses, have become a focus of current research.

[0004] The current series SOP control mainly focuses on precise power flow control. For example, the patent (application number 202510234084.3, titled "Control Method for Three-Phase Decoupled Series Power Flow Control Equipment") analyzes the power flow control method of the series four-bridge SOP with three-phase independent active and reactive power decoupling. Its topology is as follows: Figure 1 As shown in Figure 1, the proposed control method does not have a self-stabilizing function, and the DC side still needs to use a stable DC source or an additional voltage-stabilizing port for voltage control. Therefore, the existing series-type four-arm SOP control method in the prior art cannot simultaneously meet the dual requirements of DC side voltage stability control and power flow regulation. Summary of the Invention

[0005] In order to overcome the above technical defects, the present application provides a self-stabilizing voltage control method for a three-phase four-bridge-arm series-type flexible interconnected switch. To achieve the above purpose, the present application is implemented according to the following technical solutions: The present application provides a DC self-stabilizing voltage control method for a three-phase four-bridge-arm series-type flexible interconnected switch, which is applied to a distribution network connected to two three-phase AC sources, wherein the two three-phase AC sources respectively constitute a first end network side and a second end network side of the distribution network, including: Collecting a multi-dimensional electrical state parameter set of the power grid at the first end network side and the second end network side, wherein the multi-dimensional electrical state parameter set of the power grid includes electrical state parameters and line structure parameters; Determining series voltage vector control parameters based on the multi-dimensional electrical state parameter set of the power grid; Based on the series voltage vector control parameter, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

[0006] Optionally, the electrical state parameters include three-phase voltage amplitudes and three-phase voltage phases, the line structure parameters include three-phase line resistance and three-phase line inductance; the series voltage vector control parameters include series reference output initial voltage amplitude and series reference output initial voltage phase; and determining the series voltage vector control parameters based on the multi-dimensional electrical state parameter set of the power grid includes: Determining a series reference output initial voltage phase based on the three-phase voltage amplitude, the three-phase voltage phase, the three-phase line resistance, and the three-phase line inductance; Based on the series reference output initial voltage phase, the series reference output initial voltage amplitude is determined.

[0007] Optionally, determining the pulse width modulation signal of the fourth bridge arm of the inverter based on the voltage vector control parameter includes: Collect the actual value of DC voltage; Get the DC voltage target value; Performing proportional integration on the difference between the actual DC voltage value and the target DC voltage value, and outputting a phase change value; Subtracting the series reference output initial voltage phase from the phase change value to obtain a series output reference voltage phase; A pulse width modulation signal of a fourth bridge arm of the inverter is determined based on the series output reference voltage phase and the series reference output initial voltage amplitude.

[0008] Optionally, determining the pulse width modulation signal of the fourth bridge arm of the inverter based on the series output reference voltage phase and the series reference output initial voltage amplitude includes: Performing a sinusoidal calculation on the series output reference voltage phase to output a sinusoidal value of the series reference output voltage phase; determining a pulse width modulation signal of the fourth bridge arm of the inverter based on the sinusoidal value of the series reference output voltage phase and the series reference output initial voltage amplitude.

[0009] Optionally, determining the pulse width modulation signal of the fourth bridge arm of the inverter based on the series reference output voltage phase sine value and the series reference output initial voltage amplitude includes: Multiplying the series reference output voltage phase sine value and the series reference output initial voltage amplitude to obtain a three-phase reference output voltage vector; Based on the three-phase reference output voltage vector, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

[0010] Optionally, determining the pulse width modulation signal of the fourth bridge arm of the inverter based on the three-phase reference output voltage vector includes: Collect the actual three-phase output voltage; Performing proportional-integral feedback on the difference between the three-phase actual output voltage and the three-phase reference output voltage vector to obtain a current feedback value; Based on the current feedback amount, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

[0011] Optionally, determining the pulse width modulation signal of the fourth bridge arm of the inverter based on the current feedback amount includes: Collect the inverter filter capacitor current; Performing proportional feedback control on the difference between the current feedback amount and the inverter filter capacitor current to obtain a modulated voltage signal; Based on the modulated voltage signal, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

[0012] Optionally, determining a pulse width modulation signal of a fourth bridge arm of the inverter based on the modulation voltage signal includes: Comparing the waveform of the modulated voltage signal with the triangular wave to obtain a pulse width modulation signal of the three-phase bridge arm of the inverter; Based on the pulse width modulation signal of the three-phase bridge arm of the inverter, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

[0013] Optionally, determining the pulse width modulation signal of the fourth bridge arm of the inverter based on the pulse width modulation signal of the three-phase bridge arm of the inverter includes: Decoupling the pulse width modulation signal of the three-phase bridge arm of the inverter through the fourth bridge arm to obtain a modulation voltage of the fourth bridge arm; The modulation voltage of the fourth bridge arm is compared with the triangular wave, and a pulse width modulation signal of the fourth bridge arm of the inverter is output.

[0014] This application has the following beneficial effects: The method proposed in this application makes full use of the following control of the existing three-phase four-leg inverter, can control the active power scheduling between feeders, and can perform self-voltage control on the DC side without the need for other power electronic equipment or DC sources, thereby reducing the voltage resistance requirements of the devices and the number of devices, thereby improving the stability and economy of the system.

[0015] In addition to the above-described purposes, features and advantages, the present application also has other purposes, features and advantages. The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings: Figure 1 This is a schematic diagram of the topological structure applied to the power flow control method of the series-type four-bridge-arm SOP three-phase independent active and reactive decoupling provided in the background technology of this application; Figure 2 This is a flow chart of a DC self-stabilizing voltage control method for a three-phase four-bridge-arm series-type flexible interconnected switch provided in an embodiment of the present application; Figure 3 Schematic diagram of the topological structure applied to the DC self-stabilizing control method for three-phase four-bridge-arm series-type flexible interconnected switches provided in an embodiment of the present application; Figure 4 This is the circuit equivalent model of the power on the 1-end network side flowing to the 2-end network side through the SF-SOP under the grid-connected working condition in the embodiment of the present application; Figure 5 : This is a vector diagram of the SF-SOP single-phase output circuit in an embodiment of the present application; Figure 6 Schematic diagram of the DC capacitor control principle in an embodiment of the present application; Figure 6 (a) is a schematic diagram of capacitor discharge, Figure 6 (b) is a schematic diagram of DC side balance, Figure 6 (c) is a schematic diagram of capacitor charging; Figure 7 This is the waveform diagram of the DC voltage and the substation voltage of SF-SOP under simulated conditions during the experimental simulation phase in the embodiment of the present application; Figure 7 (a) is the waveform diagram of the comparison of the phase a voltage on the grid side of ports 1 and 2. Figure 7 (b) is the DC side voltage of SF-SOP; Figure 8 This is the voltage and current waveform diagram of the three-phase device of SF-SOP under simulation conditions in the experimental simulation stage of the embodiment of the present application. Figure 8 (a) is the waveform of the output voltage of SF-SOP series connection. Figure 8 (b) is the waveform of the output current of SF-SOP series connection; Figure 9 This is the experimental simulation stage of the embodiment of the present application, the SF-SOP three-phase power grid transmission flow waveform under simulation conditions, Figure 9 (a) is the waveform of the active power output of SF-SOP itself. Figure 9 (b) is the waveform of the transmission power in the SF-SOP area; Figure 10 This is a topological diagram of the existing flexible interconnection switch connected to the power grid during the experimental simulation phase of the embodiment of the present application. Figure 10 (a) Back-to-back power inverter equipment topology diagram; Figure 10 (b) is the topology diagram of the three-phase H-bridge structure flexible interconnection equipment; Figure 11 The experimental simulation stage in the embodiment of this application is a simulation waveform diagram of the output voltage and current of three flexible interconnect switches in series under the same simulation conditions. Figure 11 (a) is the simulation waveform of the output voltage of back-to-back SOP series; Figure 11 (b) is the simulated waveform of the output current of back-to-back SOP series; Figure 11 (c) is the simulation waveform of the output voltage of the three-phase H-bridge in series; Figure 11 (d) is the simulation waveform of the output current of the three-phase H-bridge in series; Figure 11 (e) is the simulated waveform of the SF-SOP series output voltage of this application; Figure 11 (f) is the simulated waveform of the SF-SOP series output current of this application; Figure 12 The experimental simulation stage in the embodiment of this application is a simulation waveform diagram of the DC side voltage and the transmission power of the substation under the same simulation conditions for three types of flexible interconnected switches. Figure 12 (a) is the simulation waveform of the DC side voltage of the back-to-back SOP; Figure 12 (b) is the simulated waveform of the transmission power in the back-to-back area; Figure 12 (c) is the simulation waveform of the DC side voltage of the three-phase H-bridge; Figure 12 (d) is the simulated waveform of the power transmitted in the three-phase H-bridge area; Figure 12 (e) is the simulated waveform of the DC side voltage of the SF-SOP of this application; Figure 12 (f) is the simulated waveform of the transmission power of the SF-SOP area of ​​this application. DETAILED DESCRIPTION

[0017] The embodiments of the present application are described in detail below with reference to the accompanying drawings, but the present application can be implemented in many different ways as defined and covered by the claims.

[0018] Therefore, in order to solve the above problems, Figure 2 As shown, the present application proposes a DC self-stabilizing voltage control method for a three-phase four-leg series flexible interconnected switch, including: Step S201: collecting a multi-dimensional electrical state parameter set of the power grid at the first end network side and the second end network side, wherein the multi-dimensional electrical state parameter set of the power grid includes electrical state parameters and line structure parameters; The method proposed in this application is applied to Figure 3 The topology shown is a distribution network connecting two three-phase AC sources. The two three-phase AC sources respectively constitute the first end network side 1 (hereinafter referred to as the 1-end network side) and the second end network side 2 (hereinafter referred to as the 2-end network side) of the distribution network. DN1 represents the three-phase AC source substation on the 1-end network side; DN2 represents the three-phase AC source substation on the 2-end network side. R 1—x 、 R 2—x ( x =a, b, c represents the three-phase resistance of a, b, c) and L 1—x 、 L 2—x Respectively represent the resistance and inductance of the three-phase line a, b, and c between the 1st and 2nd terminals; i 12 Indicates the feeder current between the grid side of terminals 1 and 2; u sx Indicates the SF-SOP three-phase series output voltage, U dc is the actual value of DC voltage.

[0019] When performing the calculation, it is first necessary to collect the multi-dimensional electrical state parameter set of the power grid on the first end network side and the second end network side. The multi-dimensional electrical state parameter set of the power grid includes electrical state parameters and line structure parameters; the electrical state parameters include three-phase voltage amplitude and three-phase voltage phase. and three-phase voltage phase (i=1, 2 indicates ports 1 and 2); line structure parameters include three-phase line resistance R1-x, R2-x (x=a, b, c indicates phases a, b, c) and three-phase line inductance L1-x, L2-x.

[0020] Step S202: determining series voltage vector control parameters based on the multi-dimensional electrical state parameter set of the power grid; After obtaining the above parameters, corresponding calculations need to be performed to determine the series voltage vector control parameters. The series voltage vector control parameters include the series reference output initial voltage amplitude and the series reference output initial voltage phase. The calculation process of step S202 and step S203 is described in detail: First, based on the three-phase voltage amplitude, three-phase voltage phase, three-phase line resistance and three-phase line inductance, the series reference output initial voltage phase is determined. The calculation process is as follows: Taking phase a as an example, the circuit equivalent model of the flexible interconnection switch of SF-SOP under grid-connected working conditions is as follows: Figure 4 As shown, represents the impedance set of the three-phase line a, b, and c between the network side of terminals 1 and 2, which is calculated by the line inductance and resistance using formula (1); and Respectively represent the grid-side output voltage amplitude and phase; the power flow control equipment is equivalent to a controlled voltage source , is its actual output voltage amplitude, is its actual output voltage phase.

[0021] like Figure 5 As shown, and Represent the single-phase voltage vectors of the substations 1 and 2 respectively, Establish a coordinate system for the real axis; Indicates the phase difference of the voltage in the substation area; Indicates the voltage drop caused by line impedance; Represents the single-phase output voltage vector of SF-SOP; represents the line current vector; Indicates the line current phase; Represents the single-phase output voltage phase of SF-SOP, where and The phase difference is 90°. If the output voltage amplitude of the grid side of terminal 1 is greater than the output voltage amplitude of the grid side of terminal 2, it will cause a larger line voltage , and thus cause significant line current , the flexible interconnection switch will provide a reverse potential to offset the voltage sag of DN2, or the grid-side output voltage phase of terminal 1 will lead the grid-side output voltage phase of terminal 2, and the power will flow from terminal 1 to terminal 2. Similarly, the conditions for power flowing from terminal 2 to terminal 1 only need to be opposite.

[0022] like Figure 6 As shown, the DC capacitor adjusts the DC voltage by charging and discharging. In order to stabilize the DC voltage, the output voltage of the SF-SOP needs to be orthogonal to the line circuit.

[0023] Based on Figure 5The equivalent circuit model shown in the figure can be used to calculate the power transmission size of the power grid. The reactive power flows from the grid-side output voltage with high amplitude to the grid-side output voltage with low amplitude, and the active power flows from the grid-side output voltage with advanced phase to the grid-side output voltage with lagging phase. When connected to the grid, the grid-side output active power flows from high frequency to low frequency. The power of each node in the distribution network under the grid-connected conditions is calculated as follows.

[0024] First, based on the equivalent circuit model, we calculate: (1) Where, is the imaginary unit, is the grid angular frequency, and are the actual output voltage amplitude and phase of SF-SOP respectively; Represents the line impedance set between the network side of terminals 1 and 2, including and , Indicates the impedance phase of the distribution network line; Then, combined with formula (1), the active power injected from the 1-end network side to the 2-end network side is obtained: Or the active power injected from the 2-end network side to the 1-end network side for: (2) Subsequently, when the phase difference between the series output voltage and the line current is 90°, the DC side voltage can remain stable. Combining formula (1) and formula (2), the following formula (3) can be obtained: (3) Substituting the above collected data into formula (3), the initial voltage phase of the series reference output is calculated .

[0025] Then the series reference output initial voltage phase Substitute the above collected data into the following formula (4) to calculate the initial voltage amplitude of the series reference output : (4) Step S203: determining a pulse width modulation signal of the fourth bridge arm of the inverter based on the series voltage vector control parameter.

[0026] The specific calculation process for determining the pulse width modulation (PWM) signal of the fourth bridge arm of the inverter is as follows: At this time, the SF-SOP initial voltage control instruction needs to be corrected. The following calculations need to be performed to collect the actual value of the DC voltage. and obtain the DC voltage target value , then the difference between the actual DC voltage value and the target DC voltage value is proportionally integrated and the phase change value is output .

[0027] Then Input limiting link, ensure that the SF-SOP series output voltage changes within a certain phase range, to prevent the transition correction from causing the series output voltage and line current phase difference of 90 degrees to fail, causing DC side voltage instability. Then the series reference output initial voltage phase and phase change value The series reference output voltage phase is obtained by subtracting Then the output voltage phase is adjusted according to the series reference. and the series reference output initial voltage amplitude , to determine the pulse width modulation signal of the fourth bridge arm of the inverter.

[0028] The series reference output voltage phase Perform sine calculation and output the series reference output voltage phase sine value, and then calculate the series reference output voltage phase sine value and the series reference output initial voltage amplitude. , to determine the pulse width modulation signal of the fourth bridge arm of the inverter.

[0029] The phase sine value of the series reference output voltage and the initial voltage amplitude of the series reference output voltage are Multiply them together to get the three-phase reference output voltage vector ( x =a, b, c represents the three phases a, b, and c of the inverter). Then, the pulse width modulation signal of the fourth bridge arm of the inverter is determined according to the three-phase reference output voltage vector.

[0030] After determining the three-phase reference output voltage vector, it is necessary to track the three-phase four-bridge arm reference voltage command. The implementation process is as follows: Collect the actual three-phase output voltage , then the actual three-phase output voltage and the three-phase reference output voltage vector The difference between the two is subjected to proportional integral feedback control to obtain the current feedback value. , and then according to the current feedback , to determine the pulse width modulation signal of the fourth bridge arm of the inverter.

[0031] At this time, the inverter filter capacitor current is collected , then the inverter filter capacitor current and current feedback The difference between the two is proportional feedback controlled to obtain the modulated voltage signal , and then determine the pulse width modulation signal of the fourth bridge arm of the inverter according to the modulation voltage signal.

[0032] The modulated voltage signal The waveform of the inverter is compared with the triangular wave to obtain the pulse width modulation signal of the three-phase bridge arm of the inverter, and then the pulse width modulation signal of the fourth bridge arm of the inverter is determined according to the pulse width modulation signal of the three-phase bridge arm of the inverter.

[0033] The pulse width modulation signal of the inverter three-phase bridge arm is decoupled and calculated through the fourth bridge arm to obtain the modulation voltage of the fourth bridge arm. , the modulation voltage of the fourth bridge arm is compared with the triangular wave, and the pulse width modulation signal of the fourth bridge arm of the inverter is output.

[0034] The PWM generation method in this application adopts the method of comparing the modulation wave with the triangle wave. Regarding the PI adjustment value of this application, The larger the value, the smaller the equivalent inductance of each phase of the flexible loop equipment. However, from the perspective of feedback control, Too large, it will easily cause shock, so Choose moderately.

[0035] Experimental simulation This application builds a novel three-phase, four-leg series-connected flexible switch model in the MATLAB / Simulink simulation platform to verify the effectiveness and correctness of the control method proposed in this application. The simulation parameters are shown in Table 1.

[0036] Table 1 Simulation parameters ; In order to simulate the actual working state of the new three-phase four-bridge-arm series flexible interconnected switch and verify the effectiveness of the control method of this application, this application fully considers the dynamic fluctuation of the active power transmitted on the grid side. Figure 7 As shown, the voltage amplitude of station 1 is 311V, the initial phase is 0°, and the voltage amplitude of port 2 is 280V, the initial phase is 15°.

[0037] In addition, if Figure 8 As shown in the figure, the current waveform of the line and the output voltage waveform of SF-SOP. SF-SOP can change the output voltage according to the voltage control method and control requirements of the device, so as to better control the active power of the line and the stability of the DC side voltage.

[0038] Under the simulation conditions, the three-phase load is uneven. 70kW active power is transmitted from phase a of port 1 to port 2, 50kW active power is transmitted from phase c, and 60kW active power is transmitted from phase b of port 2 to port 1. The measured line active power and SF-SOP's own output power are as follows: Figure 9 shown.

[0039] To further verify the stability and superiority of the three-phase four-bridge-arm series flexible interconnected switch of this application, three schemes are compared below. ① Scheme 1: Based on a four-bridge-arm back-to-back power electronic device, such as Figure 10 (a) As shown; ②Scheme 2: Based on a three-phase H-bridge structure device, such as Figure 10 (b) As shown; ③ In this application, a three-phase four-bridge-arm series-connected flexible interconnected switch with self-stabilizing voltage capability, such as Figure 2 As shown; For ease of comparison and discussion, the above schemes were implemented under the following conditions: the AC side's normal operating voltage amplitude is 311V, the three-phase voltages are phase-shifted by 120°, the DC side voltage is stabilized at 800V, the initial phase of the grid voltage at port 2 leads that of port 1 by 15°, and the voltage amplitudes are the same. Each phase transmits 70 / -60 / 50 kW of active power. A comparison of this application with existing schemes is shown in Table 2.

[0040] Table 2 ; The comparison results in Table 2 show that the parallel SOP uses two three-phase isolation transformers in the substation, while the series SOP uses three single-phase isolation transformers. The output voltage of the parallel SOP is determined by the substation bus voltage, while the output voltage of the series SOP is calculated based on the compensation voltage. The compensation voltage is often lower than the bus voltage, so the output voltage of the parallel SOP is higher than that of the series SOP. The passive components of the four-leg parallel back-to-back SOP include 6 filter inductors, 6 filter capacitors, and 1 DC capacitor, and the power electronic components include 16 IGBTs. The passive components of the three-phase H-bridge SOP include 3 filter inductors, 3 filter capacitors, and 3 DC capacitors, and the power electronic components include 12 IGBTs. The passive components of the SF-SOP include 4 filter inductors, 3 filter capacitors, and 1 DC capacitor. The SF-SOP has fewer components, a smaller system size, lower capacity, and lower cost. Therefore, compared with existing SOPs, the SF-SOP can significantly reduce the required and number of components, reducing the capacity and cost of the device itself. Furthermore, the present invention achieves self-stabilization of the DC side without the need for an external DC source, and achieves excellent voltage stabilization. Therefore, compared to the prior art, the present invention can achieve self-stabilization without the need for other power electronic devices or DC sources, reducing the number and requirements of components, and further reducing the size and investment cost of series-connected equipment.

[0041] In order to further verify the advantages of the proposed device, this application conducts simulation verification of four-arm parallel back-to-back SOP, three-phase H-bridge SOP and SF-SOP. The simulation parameters are set according to the comparison conditions. The output voltage, line current, DC side voltage and active power transmission size of the back-to-back SOP, three-phase H-bridge SOP and SF-SOP are as follows: Figure 11-12 shown.

[0042] Simulation experiments show that when controlling the same power, the line current of the three SOPs is consistent, but the output voltage of the series SOP is much lower than that of the parallel SOP, and the DC side stability is slower than that of the SF-SOP. Therefore, the capacity of the series SOP is smaller than that of the parallel SOP, and the SF-SOP has stronger DC side stability. While the SF-SOP and the three-phase H-bridge SOP have the same control capabilities, the three-phase H-bridge SOP has more components than the SF-SOP, resulting in a larger device size and lower utilization. At the same time, the single-phase DC side control has secondary ripple. Therefore, the SF-SOP has better DC side control and is more advantageous in terms of size and cost.

[0043] In summary, the method proposed in this application makes full use of the following control of the existing three-phase four-leg inverter, can control the active power scheduling size between feeders, and the DC side does not require other power electronic equipment or DC sources to perform self-voltage control, reducing the voltage resistance requirements of the devices and reducing the number of devices, thereby improving the stability and economy of the system.

[0044] The foregoing description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A DC self-stabilizing voltage control method for three-phase four-bridge-arm series-connected flexible switches, applied to a distribution network connected to two three-phase AC sources, the two three-phase AC sources forming the first and second network ends of the distribution network, respectively. include: Collecting a multi-dimensional electrical state parameter set of the power grid at the first end network side and the second end network side, wherein the multi-dimensional electrical state parameter set of the power grid includes electrical state parameters and line structure parameters; Determining series voltage vector control parameters based on the multi-dimensional electrical state parameter set of the power grid; Based on the series voltage vector control parameter, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

2. The method according to claim 1, characterized in that The electrical state parameters include three-phase voltage amplitudes and three-phase voltage phases, the line structure parameters include three-phase line resistance and three-phase line inductance; the series voltage vector control parameters include series reference output initial voltage amplitude and series reference output initial voltage phase; and determining the series voltage vector control parameters based on the multi-dimensional electrical state parameter set of the power grid includes: Determining a series reference output initial voltage phase based on the three-phase voltage amplitude, the three-phase voltage phase, the three-phase line resistance, and the three-phase line inductance; Based on the series reference output initial voltage phase, the series reference output initial voltage amplitude is determined.

3. The method according to claim 2, characterized in that The step of determining a pulse width modulation signal of a fourth bridge arm of the inverter based on the voltage vector control parameter includes: Collect the actual value of DC voltage; Get the DC voltage target value; Performing proportional integration on the difference between the actual DC voltage value and the target DC voltage value, and outputting a phase change value; Subtracting the series reference output initial voltage phase from the phase change value to obtain a series output reference voltage phase; A pulse width modulation signal of a fourth bridge arm of the inverter is determined based on the series output reference voltage phase and the series reference output initial voltage amplitude.

4. The method according to claim 3, characterized in that The step of determining a pulse width modulation signal of a fourth bridge arm of the inverter based on the series output reference voltage phase and the series reference output initial voltage amplitude includes: Performing a sine calculation on the series output reference voltage phase to output a sine value of the series reference output voltage phase; A pulse width modulation signal of a fourth bridge arm of the inverter is determined based on the series reference output voltage phase sine value and the series reference output initial voltage amplitude.

5. The method according to claim 4, characterized in that The step of determining a pulse width modulation signal of a fourth bridge arm of the inverter based on the series reference output voltage phase sine value and the series reference output initial voltage amplitude comprises: Multiplying the series reference output voltage phase sine value and the series reference output initial voltage amplitude to obtain a three-phase reference output voltage vector; Based on the three-phase reference output voltage vector, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

6. The method according to claim 5, characterized in that The step of determining a pulse width modulation signal of a fourth bridge arm of the inverter based on the three-phase reference output voltage vector comprises: Collect the actual three-phase output voltage; Performing proportional-integral feedback on the difference between the three-phase actual output voltage and the three-phase reference output voltage vector to obtain a current feedback value; Based on the current feedback amount, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

7. The method according to claim 6, characterized in that Determining the pulse width modulation signal of the fourth bridge arm of the inverter based on the current feedback amount includes: Collect the inverter filter capacitor current; Performing proportional feedback control on the difference between the current feedback amount and the inverter filter capacitor current to obtain a modulated voltage signal; Based on the modulated voltage signal, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

8. The method according to claim 7, characterized in that Determining a pulse width modulation signal of a fourth bridge arm of the inverter based on the modulation voltage signal includes: Comparing the waveform of the modulated voltage signal with the triangular wave to obtain a pulse width modulation signal of the three-phase bridge arm of the inverter; Based on the pulse width modulation signal of the three-phase bridge arm of the inverter, a pulse width modulation signal of the fourth bridge arm of the inverter is determined.

9. The method according to claim 8, characterized in that The step of determining the pulse width modulation signal of the fourth bridge arm of the inverter based on the pulse width modulation signal of the three-phase bridge arm of the inverter includes: Decoupling the pulse width modulation signal of the three-phase bridge arm of the inverter through the fourth bridge arm to obtain a modulation voltage of the fourth bridge arm; The modulation voltage of the fourth bridge arm is compared with the triangular wave, and a pulse width modulation signal of the fourth bridge arm of the inverter is output.

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