VSG fault current limiting control strategy based on reactive deviation integral feedback

Abstract

This application provides a VSG fault current limiting control strategy based on reactive power deviation integral feedback, including: constructing a reactive power deviation integral feedback control branch between the reactive power droop control output and the voltage command generation in the VSG reactive power loop; determining an integral feedback compensation value based on reactive power deviation control based on the reactive power deviation integral feedback control branch; and limiting the short-circuit current amplitude based on the integral feedback compensation value. The strategy proposed in this application, by introducing reactive power deviation integral feedback compensation control during fault periods, can equivalently adjust the reactive power droop coefficient and voltage command value, effectively reducing the fault current amplitude during fault periods and providing reactive power support for the system.

Description

Technical Field

[0001] This application relates to the field of network control technology, and in particular to a VSG fault current limiting control strategy based on reactive power deviation integral feedback. Background Technology

[0002] Virtual Synchronous Generators (VSGs) can simulate the rotational inertia and damping characteristics of synchronous machines, significantly improving the voltage and frequency support capabilities of distribution networks, and are now widely used in distributed renewable energy grid integration. However, VSG converters are essentially still power electronic devices, and their current overload capacity is far lower than that of traditional synchronous generators. When a voltage dip fault occurs on the distribution network side, the voltage difference between the converter output voltage and the grid voltage increases sharply, inducing a significant fault current surge. Due to limitations in the current withstand capability and heat capacity of semiconductor devices, VSG converters are highly susceptible to overcurrent operation during transient processes, even leading to device burnout due to overcurrent. VSG overcurrent problems have become one of the major challenges restricting the safe and stable operation of high-proportion power electronics connected to the distribution network.

[0003] Existing research has extensively explored transient power angle stability during faults, such as frequency stability or transient power angle dynamics. However, compared to frequency stability or transient power angle dynamics, the abnormal increase in fault current caused by voltage dips on the distribution network side remains one of the significant challenges in the transient operation of VSGs. However, the aforementioned studies only investigated the transient stability of VSGs during faults, neglecting the fault current limiting issue. Summary of the Invention

[0004] This application provides a VSG fault current limiting control strategy based on reactive power deviation integral feedback. To solve the above-mentioned technical problems, this application adopts the following technical method: Firstly, this application provides a VSG fault current limiting control strategy based on reactive power deviation integral feedback, including: In the reactive power droop control output and voltage command generation in the VSG reactive power loop, a reactive power deviation integral feedback control branch is constructed; Based on the reactive power deviation integral feedback control branch, determine the integral feedback compensation value based on reactive power deviation control; Based on the integral feedback compensation value, the short-circuit current amplitude is limited.

[0005] Optionally, determining the integral feedback compensation value based on the reactive power deviation control based on the reactive power deviation integral feedback control branch includes: Based on the reactive power deviation integral feedback control branch, the compensation coefficient based on reactive power deviation integral feedback is determined. Based on the compensation coefficient, the integral feedback compensation value based on reactive power deviation control is determined.

[0006] Optionally, determining the integral feedback compensation value based on the compensation coefficient for reactive power deviation control includes: Obtain the grid voltage reference value and VSG historical voltage command value; Based on the grid voltage reference value, the VSG historical voltage command value, and the compensation coefficient, the integral feedback compensation value based on reactive power deviation control is determined.

[0007] Optionally, limiting the short-circuit current amplitude based on the integral feedback compensation value includes: Obtain the rated voltage amplitude of the VSG; The current voltage command value of the VSG is determined based on the rated voltage amplitude of the VSG and the integral feedback compensation value. Based on the current voltage command value of the VSG, the short-circuit current amplitude is limited.

[0008] Optionally, limiting the short-circuit current amplitude based on the current VSG voltage command value includes: Obtain the virtual power angle of the VSG; The short-circuit current amplitude is limited based on the virtual power angle of the VSG and the current voltage command value of the VSG.

[0009] Optionally, limiting the short-circuit current amplitude based on the virtual power angle of the VSG and the current voltage command value of the VSG includes: Based on the virtual power angle of the VSG and the current voltage command value of the VSG, the synthesized voltage command value is determined; Based on the synthesized voltage command value, the PWM modulation signal is determined; Based on the PWM modulation signal, adjust the amplitude of the VSG output voltage; The short-circuit current amplitude is limited based on the output voltage amplitude of the VSG.

[0010] Secondly, this application also provides a computer system, comprising: Memory is used to store instructions that can be executed by the processor; A processor for executing the instructions to implement the method as described in any of the first aspects.

[0011] Thirdly, this application also provides a computer-readable medium storing computer program code that, when executed by a processor, implements the method as described in any of the first aspects.

[0012] This application has the following beneficial effects: The strategy proposed in this application, by introducing reactive power deviation integral feedback compensation control during fault periods, can effectively adjust the reactive power droop coefficient and voltage command value, thereby effectively reducing the fault current amplitude during fault periods and providing reactive power support for the system. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the VSG main circuit structure provided in an embodiment of this application; Figure 2 This is a block diagram of the VSG power loop control structure provided in an embodiment of this application; Figure 3 VSG phase plane diagrams with different droop coefficients kq provided for embodiments of this application; Figure 4 Equivalent circuit diagram of VSG grid connection provided in the embodiments of this application; Figure 5 Voltage and current vector diagrams before and after a fault provided in this application embodiment; Figure 6 The voltage and current vector diagrams before and after reactive power loop adjustment provided in the embodiments of this application; Figure 7 A flowchart illustrating the VSG fault current limiting control strategy based on reactive power deviation integral feedback provided in this application embodiment; Figure 8 A block diagram of the VSG reactive power loop control strategy for fault current limiting provided in this application embodiment; Figure 9 Block diagram of the VSG reactive power loop control strategy for fault current limiting provided in this application embodiment Figure 10 A comparison diagram of the transient processes of different VSG control strategies under the condition of voltage drop to 0.7 pu provided in the embodiments of this application; Figure 10 (a) is a waveform diagram under traditional VSG control; Figure 10 (b) The VSG waveform diagram under reactive power deviation integral compensation control; Figure 11 A comparison diagram of the transient processes of different VSG control strategies under the condition of voltage drop to 0.65 pu provided in the embodiments of this application; Figure 11 (a) is a waveform diagram under traditional VSG control; Figure 11 (b) is the VSG waveform diagram under reactive power deviation integral compensation control. Detailed Implementation

[0014] To facilitate understanding by those skilled in the art, the present application will be further described below in conjunction with embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present application.

[0015] To facilitate understanding of the technical solution of this application, its background is briefly explained below: VSG basic principle: The main circuit structure diagram of the VSG-controlled photovoltaic inverter is as follows: Figure 1 As shown in the figure, and These are the inductance and capacitance of the filter, respectively; , and These are the inverter's output current, the grid connection point (PCC) voltage, and the grid-side voltage, respectively. This is the DC side voltage value; Line reactance; PWM stands for pulse width modulation; This is the synthesized voltage command value; and After dq transformation, it is decomposed into , , and Q1~Q6 are switching transistors.

[0016] VSG power loop control structure as follows Figure 2 As shown. The control equations for its active and reactive power loops are shown in equations (1) and (2), respectively: (1) (2) In the formula: and These are the VSG's active power reference value and actual output value, respectively. and These are the actual and reference values ​​of the virtual rotor angular velocity of the VSG, respectively. and These are the reference value and the actual output value of the inverter's reactive power, respectively. This is the reactive power-voltage droop factor. For virtual rotational inertia, The damping coefficient; This is a virtual work angle; and These are the VSG rated voltage amplitude and voltage command value, respectively.

[0017] Transient work angle characteristics: Active power transferred between VSG and the power grid and reactive power As shown in equations (3) and (4) respectively: (3) (4) In the formula: and These are the VSG output voltage and the mains voltage, respectively. This refers to the line reactance.

[0018] Combining equations (2) and (4), the voltage command value of VSG can be obtained as follows: (5) Substituting equations (5) and (3) into equation (1), we get: (6) The plot was drawn according to equation (6) in Different times The VSG phase plane diagram with the values ​​is as follows Figure 3 As shown in the figure. It can be seen from the figure that, with... As the voltage drops, the VSG transitions from transient stability to transient instability, and its transient stability gradually decreases. This is because, under voltage dips on the distribution network side, the amplitude difference between the VSG output voltage and the grid voltage increases, leading to a gradual increase in output reactive power. According to the reactive power droop characteristic, reactive power is inversely proportional to output voltage; therefore, reducing the voltage drop... This will enhance the reactive power droop characteristic, further reducing the VSG output voltage. Combined with the analysis of equation (3), it can be seen that the decrease in output voltage will affect the amplitude of the VSG's output active power, thereby affecting its power angle characteristics and transient stability. Therefore, when analyzing the transient characteristics of the VSG, the reactive power loop and its droop coefficient must be fully considered. The impact.

[0019] Fault current characteristic analysis: When a voltage dip fault occurs on the distribution network side, the equivalent circuit diagram of VSG grid connection is as follows: Figure 4 As shown in the figure, This refers to the VSG short-circuit current. and These are the VSG output voltage vector value and the grid voltage vector value during the fault period, respectively.

[0020] The output voltage and current of VSG satisfy the following circuit equation: (7) From equation (7), the VSG short-circuit current can be obtained as: (8) In the formula, This represents the VSG short-circuit current vector value.

[0021] Figure 5 This is a voltage and current vector diagram before and after the fault. (The diagram shows the vector diagrams before and after the fault.) , and These represent the power angles under different fault voltages. As shown in the figure, when a voltage dip occurs on the distribution network side, the vector difference between the VSG output voltage and the grid voltage continuously increases, and the power angle changes from... Change to This leads to a continuous increase in the short-circuit current of the VSG. Therefore, by improving the transient power angle stability of the VSG and adjusting its output voltage amplitude during the fault duration, the short-circuit current amplitude can be effectively limited to ensure the safe and stable operation of the VSG inverter during the fault.

[0022] When a voltage dip occurs on the distribution network side, the VSG will exhibit current over-limit behavior. Therefore, short-circuit current limiting is necessary to ensure the safe and stable operation of the VSG inverter. Although the aforementioned power angle control can effectively improve the transient stability performance of the VSG and reduce the fault current amplitude to some extent, the fault current amplitude will increase significantly under severe voltage dips on the distribution network side. Power angle control alone is insufficient to meet the current limiting requirements of the VSG inverter under fault conditions.

[0023] Figure 6 This is a voltage-current vector diagram before and after reactive power loop adjustment. Figure 6 Analysis shows that the angle and magnitude difference between the VSG's output voltage vector and the grid voltage vector determine the short-circuit current magnitude of the VSG during the fault duration phase. If the fault dip and power angle remain constant, introducing voltage compensation values ​​into the reactive power loop further compensates for the VSG's output voltage under fault dip conditions, adjusting the voltage vector difference between the VSG and the grid, effectively limiting the magnitude of the short-circuit current during the fault duration phase.

[0024] Based on the above analysis, in order to solve the technical problems raised in the background, such as Figure 7 As shown, this application proposes a VSG fault current limiting control strategy based on reactive power deviation integral feedback, including: S101: Construct a reactive power deviation integral feedback control branch between the reactive power droop control output and the voltage command generation in the reactive power loop of the VSG. like Figure 8 As shown in the diagram, the VSG reactive power loop control strategy block diagram for fault current limiting constructs a reactive power deviation integral feedback control branch between the reactive power droop control output and the voltage command generation in the VSG reactive power loop.

[0025] This branch integrates the reactive power deviation signal and uses the resulting compensation as a voltage regulation component. This component is then superimposed on the voltage regulation generated by the original reactive power droop control at the voltage command generation node, thus jointly affecting the voltage command value of the VSG.

[0026] The integral element takes the reactive power deviation as the integral object, and its implementation can be carried out by continuous integration or equivalent discrete integration, specifically by the integral module in the digital controller or processor.

[0027] S102: Based on the reactive power deviation integral feedback control branch, determine the integral feedback compensation value based on reactive power deviation control; During the fault persistence phase, the reactive power deviation integral feedback control branch can be used to derive the value obtained by integrating the deviation of the VSG input, multiplying the integral value by the compensation coefficient based on the reactive power deviation integral feedback, and then multiplying it by the grid voltage reference value. and VSG historical voltage command value The difference between them constitutes the compensation term, which is the integral feedback compensation value based on reactive power deviation control. Then, this compensation term is fed back to the reactive power control loop, from which the improved reactive power loop control equation can be obtained: (9) In the formula, This is the integral feedback compensation value based on reactive power deviation control; The compensation coefficient is based on the reactive power deviation integral feedback. For the Laplace operator; This is the reference value for the grid voltage.

[0028] Compensation coefficient based on reactive power deviation integral feedback The determination process is as follows Figure 9 As shown, combined with Figure 9 The simulation process shows that by sampling the deviation between the reactive power reference value and the actual output value, and integrating the reactive power deviation signal, a corresponding compensation amount is obtained. This compensation amount is further superimposed with the deviation between the actual voltage output and the voltage command value, and the resulting composite amount participates in the voltage command generation process as a compensation term of the reactive power control loop.

[0029] Among them, the compensation coefficient These are key parameters derived from the established governing equations and equivalent relationships. Mathematical derivation shows that, with... The increase in reactive power deviation integral feedback affects the voltage command reference value. The regulatory effect is enhanced, which is equivalent to the voltage command reference value. The decrease. Therefore, The upper limit of the value must guarantee the equivalent voltage command reference value. It can provide sufficient voltage compensation to ensure that the output current can be effectively reduced during faults and to provide reactive power support for the VSG system.

[0030] By combining and rearranging equation (9), we can obtain: (10) Comparing equations (2) and (10), it can be seen that the reactive power deviation integral feedback current limiting control can achieve an equivalent adjustment of the reactive power droop coefficient. and voltage command reference value for: (11) (12) As can be seen from the analysis of equation (10), compared with the current limiting methods in existing studies, the strategy proposed in this application can effectively adjust the reactive power droop coefficient and voltage command value without freezing the reactive power loop. While limiting the amplitude of VSG fault current, it can also provide reactive power voltage support for the distribution network.

[0031] S103: Based on the integral feedback compensation value, limit the short-circuit current amplitude.

[0032] Then, the rated voltage amplitude and integral feedback compensation value of the VSG are calculated to determine the current voltage command value of the VSG. The current voltage command value of the VSG and the virtual power angle of the VSG are used to determine the synthesized voltage value. Based on the synthesized voltage value, the PWM modulation signal is determined. Then, the output voltage amplitude of the VSG is adjusted according to the PWM modulation signal, thereby limiting the short-circuit current amplitude.

[0033] Simulation verification: To verify the correctness of the theoretical analysis and the effectiveness of the proposed control strategy, a system was built in Matlab / Simulink. Figure 1 The VSG grid-connected simulation model is shown below. The simulation parameters are shown in Table 1.

[0034] Table 1 Simulation Parameters ; The grid-connected inverter initially operates in a stable state. At 1 second, the grid voltage experiences a voltage drop, which lasts for 0.8 seconds. The following simulation compares the traditional VSG control and the VSG inverter with the proposed control strategy under the voltage drop to 0.7 pu condition.

[0035] The grid-connected inverter initially operates in a stable state. At 1 second, the grid voltage experiences a voltage drop, which lasts for 0.8 seconds. The following simulation compares the traditional VSG control and the VSG inverter with the proposed control strategy under the voltage drop to 0.7 pu condition.

[0036] Figure 10 A comparison of transient waveforms for different VSG control strategies when the grid voltage drops to 0.7 pu. Figure 10(a) is a waveform diagram under traditional VSG control. It can be seen from the figure that the current of the traditional VSG increases to 1.75pu during the fault process. Figure 10 (b) The waveform diagram of VSG under reactive power deviation integral compensation control shows that the control can reduce the current to 1.48pu during the fault period, which meets the requirements for safe grid-connected operation.

[0037] The grid-connected inverter initially operates in a stable state. At 1 second, the grid voltage experiences a voltage drop, which lasts for 0.8 seconds. A simulation comparison will be performed here between the traditional VSG control and the VSG inverter with the control strategy proposed in this application under the voltage drop condition of 0.65 pu.

[0038] Figure 11 A comparison of transient waveforms for different VSG control strategies when the grid voltage drops to 0.65 pu. Figure 11 (a) is a waveform diagram under traditional VSG control. It can be seen from the figure that the current of the traditional VSG increases to 2.21 pu during the fault process. Figure 11 (b) is the VSG waveform diagram under reactive power deviation integral compensation control. It can be seen that the control can reduce the current to 2.1pu during the fault, effectively reducing the fault current amplitude, thus demonstrating the effectiveness of the control strategy.

[0039] In summary, the strategy proposed in this application, by introducing reactive power deviation integral feedback compensation control during fault periods, can effectively adjust the reactive power droop coefficient and voltage command value, thereby effectively reducing the fault current amplitude during fault periods and providing reactive power support for the system.

[0040] In some embodiments, this application also provides a computer system including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0041] This application also provides a computer-readable storage medium for storing a computer program. This computer-readable storage medium can be applied to a computer device, and the computer program causes the computer device to execute the corresponding processes in the methods described above in the embodiments of this application; for brevity, further details are omitted here.

[0042] The above embodiments are preferred implementations of this application. In addition, this application can be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this application.

[0043] To facilitate understanding by those skilled in the art of the improvements made by this application compared to the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this application.

Claims

1. A VSG fault current limiting control strategy based on reactive power deviation integral feedback, characterized in that, include: In the reactive power droop control output and voltage command generation in the VSG reactive power loop, a reactive power deviation integral feedback control branch is constructed; Based on the reactive power deviation integral feedback control branch, determine the integral feedback compensation value based on reactive power deviation control; Based on the integral feedback compensation value, the short-circuit current amplitude is limited.

2. The strategy according to claim 1, characterized in that, The determination of the integral feedback compensation value based on the reactive power deviation control branch includes: Based on the reactive power deviation integral feedback control branch, the compensation coefficient based on reactive power deviation integral feedback is determined. Based on the compensation coefficient, the integral feedback compensation value based on reactive power deviation control is determined.

3. The strategy according to claim 2, characterized in that, The determination of the integral feedback compensation value based on the compensation coefficient for reactive power deviation control includes: Obtain the grid voltage reference value and VSG historical voltage command value; Based on the grid voltage reference value, the VSG historical voltage command value, and the compensation coefficient, the integral feedback compensation value based on reactive power deviation control is determined.

4. The strategy according to claim 3, characterized in that, The limitation of short-circuit current amplitude based on the integral feedback compensation value includes: Obtain the rated voltage amplitude of the VSG; The current voltage command value of the VSG is determined based on the rated voltage amplitude of the VSG and the integral feedback compensation value. Based on the current voltage command value of the VSG, the short-circuit current amplitude is limited.

5. The strategy according to claim 4, characterized in that, The step of limiting the short-circuit current amplitude based on the current VSG voltage command value includes: Obtain the virtual power angle of the VSG; The short-circuit current amplitude is limited based on the virtual power angle of the VSG and the current voltage command value of the VSG.

6. The strategy according to claim 5, characterized in that, The limitation of short-circuit current amplitude based on the virtual power angle of the VSG and the current voltage command value of the VSG includes: Based on the virtual power angle of the VSG and the current voltage command value of the VSG, the synthesized voltage command value is determined; Based on the synthesized voltage command value, the PWM modulation signal is determined; Based on the PWM modulation signal, adjust the amplitude of the VSG output voltage; The short-circuit current amplitude is limited based on the output voltage amplitude of the VSG.

7. A computer system, characterized in that, include: Memory is used to store instructions that can be executed by the processor; A processor for executing the instructions to implement the strategy as described in any one of claims 1 to 6.

8. A computer-readable medium, characterized in that, The system stores computer program code that, when executed by a processor, implements the strategy as described in any one of claims 1 to 6.

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