Impedance Measurement Method and System for New Energy Power Stations Based on Cascaded H-Bridge SVG

Abstract

This invention discloses a method and system for impedance measurement of renewable energy power plants based on cascaded H-bridge SVG, comprising: connecting the SVG to the power system in a direct parallel connection to act as a current source outputting inductive or capacitive reactive current into the power system; controlling the output signal of the control loop to superimpose an adjustable disturbance current component into the output reactive current, thereby injecting a disturbance measurement signal into the power system; measuring the voltage and current response of the power system based on the injected disturbance measurement signal, and calculating the impedance of the renewable energy power plant. This invention can complete the impedance measurement of renewable energy power plants without adding new equipment and ensures measurement accuracy.

Description

Technical Field

[0001] This invention relates to the field of new energy grid connection, specifically to a method and system for measuring the impedance of new energy power stations based on cascaded H-bridge SVG. Background Technology

[0002] In recent years, with the increasing application of new energy sources such as wind power and photovoltaics in the power system, power electronic equipment such as converters are also being used more and more widely in the power system. However, under the "dual high" trend of high proportion of new energy and high proportion of power electronic equipment, the stability problem of the power system has become increasingly prominent.

[0003] Impedance analysis is an important method for stability analysis of power systems. Its physical meaning is clear and its analytical method is simple, and it has been applied in the analysis of multiple renewable energy grid-connected systems. Obtaining the impedance characteristics of the power system is a crucial step in impedance analysis, which mainly considers two aspects: establishing a mathematical model and injecting disturbances to measure impedance. Impedance measurement has received extensive research attention due to its timeliness and accuracy.

[0004] Currently, existing impedance measurement technologies and equipment are mostly geared towards low-voltage, low-power new energy power generation and microgrid systems. However, in new energy power plants, factors such as high voltage and large capacity require the addition of new power electronic equipment when measuring impedance characteristics, introducing new stability influencing factors and resulting in problems of high measurement complexity and low measurement accuracy.

[0005] Therefore, to solve the above problems, there is a need for a method and system for impedance measurement of new energy power stations based on cascaded H-bridge SVG, which can utilize the cascaded H-bridge SVG already installed in the new energy power station for impedance measurement without adding new equipment, thus ensuring measurement accuracy. Summary of the Invention

[0006] In view of this, the purpose of this invention is to overcome the defects in the prior art and provide a method and system for measuring the impedance of new energy power stations based on cascaded H-bridge SVG, which can complete the impedance measurement of new energy power stations without adding new equipment and ensure measurement accuracy.

[0007] The impedance measurement method for new energy power stations based on cascaded H-bridge SVG of the present invention includes the following steps:

[0008] The SVG is connected to the power system in a direct parallel connection to act as a current source and output inductive or capacitive reactive current into the power system.

[0009] The output signal of the control loop is controlled to superimpose an adjustable disturbance current component into the output reactive current, thereby realizing the injection of disturbance measurement signal into the power system.

[0010] The voltage and current response of the power system is measured based on the injected disturbance measurement signal, and the impedance of the new energy power station is calculated.

[0011] Furthermore, the injection of disturbance measurement signals into the power system is implemented, specifically including:

[0012] An open-loop disturbance injection module is connected in parallel to the control signal output of the cascaded H-bridge SVG control loop, in response to the control signal s output by the SVG. a s b s c The disturbance control signal s is superimposed on each of the above. a3 s b3 s c3 At the same time, the disturbance amplitude coefficient K is set. r And adjust the frequency f of the given disturbance measurement signal. p A disturbance component of 1–1000 Hz is generated in the bridge arm current to complete the disturbance measurement signal injection based on the cascaded H-bridge SVG; wherein, the disturbance amplitude coefficient K r Take 3% to 10% of the steady-state amplitude of the fundamental control signal.

[0013] Furthermore, by decoupling the disturbance measurement signal, the impedance of the new energy power station is calculated, specifically including:

[0014] By injecting current at the frequency of the disturbance measurement signal and current at the coupling frequency, the frequency f of the disturbance measurement signal is obtained. p Impedance Z of the new energy power station SAfp It can be represented as:

[0015]

[0016] In equation (4), V fp2 Generated by disturbance coupling current, V fp2 This can be viewed as a disturbance coupling current passing through a companion impedance at frequency f. p The effect of the following on the voltage is due to the accompanying impedance being a reflection of the coupling frequency on the frequency f. p Due to the influence of [various factors], the accompanying impedance at the same frequency is constant. Therefore, equation (4) can be transformed into:

[0017]

[0018] When a coupling frequency current is injected, we have:

[0019]

[0020] Combining equations (5) and (6), the impedance of the new energy power station is obtained as follows:

[0021]

[0022] Among them, V fp The voltage component at the measured frequency at the direct-drive wind farm port when the first disturbance measurement signal is injected; I fp The current component at the measured frequency at the direct-drive wind farm port when the first disturbance measurement signal is injected; I fo The current component at the coupling frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; Z AAfp To characterize the coupling frequency versus frequency f p The accompanying impedance of the effect; The voltage component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the coupling frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected.

[0023] Furthermore, to achieve decoupling of the disturbance measurement signal, two disturbance injection methods are implemented, specifically including:

[0024] For disturbance measurement signals below 100Hz, the frequency of the disturbance measurement signal input to the open-loop disturbance injection module is set to f. p The output current of the cascaded H-bridge SVG is the measured current I. sfp and coupling current I sfo After completing the first perturbation injection, the set frequency is then changed from f. p Change its coupling frequency f o The new SVG output current is obtained as the measured current I. sfp * and coupling current I sfo * ;

[0025] For disturbance measurement signals of 100Hz and above, the coupling signal is changed to negative sequence injection. Due to the nonlinear control loop inside the SVG, the frequency of the disturbance measurement signal is set to f. p and f o At that time, two pairs of linearly independent measurement signals will be output respectively, thereby decoupling the calculation of the disturbance response.

[0026] An impedance measurement system for new energy power stations based on cascaded H-bridge SVG includes an SVG access unit, a signal injection unit, and an impedance calculation unit;

[0027] The SVG access unit is used to connect the SVG to the power system in a direct parallel connection manner, and output inductive or capacitive reactive current into the power system as a current source.

[0028] The signal injection unit is used to control the output signal of the control loop, so that an adjustable disturbance current component is superimposed on the output reactive current, thereby realizing the injection of disturbance measurement signal of the power system.

[0029] The impedance calculation unit is used to measure the voltage and current response of the power system based on the injected disturbance measurement signal, and to calculate the impedance of the new energy power station.

[0030] Furthermore, the injection of disturbance measurement signals into the power system is implemented, specifically including:

[0031] An open-loop disturbance injection module is connected in parallel to the control signal output of the cascaded H-bridge SVG control loop, in response to the control signal s output by the SVG. a s b s c The disturbance control signal s is superimposed on each of the above. a3 s b3 s c3 At the same time, the disturbance amplitude coefficient K is set. r And adjust the frequency f of the given disturbance measurement signal. p A disturbance component of 1–1000 Hz is generated in the bridge arm current to complete the disturbance measurement signal injection based on the cascaded H-bridge SVG; wherein, the disturbance amplitude coefficient K r Take 3% to 10% of the steady-state amplitude of the fundamental control signal.

[0032] Furthermore, by decoupling the disturbance measurement signal, the impedance of the new energy power station is calculated, specifically including:

[0033] By injecting current at the frequency of the disturbance measurement signal and current at the coupling frequency, the frequency f of the disturbance measurement signal is obtained. p Impedance Z of the new energy power station SAfp It can be represented as:

[0034]

[0035] In equation (4), V fp2 Generated by disturbance coupling current, V fp2 This can be viewed as a disturbance coupling current passing through a companion impedance at frequency f. p The effect of the following on the voltage is due to the accompanying impedance being a reflection of the coupling frequency on the frequency f. p Due to the influence of [various factors], the accompanying impedance at the same frequency is constant. Therefore, equation (4) can be transformed into:

[0036]

[0037] When a coupling frequency current is injected, we have:

[0038]

[0039] Combining equations (5) and (6), the impedance of the new energy power station is obtained as follows:

[0040]

[0041] Among them, V fp The voltage component at the measured frequency at the direct-drive wind farm port when the first disturbance measurement signal is injected; I fp The current component at the measured frequency at the direct-drive wind farm port when the first disturbance measurement signal is injected; I fo The current component at the coupling frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; Z AAfp To characterize the coupling frequency versus frequency f p The accompanying impedance of the effect; The voltage component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the coupling frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected.

[0042] Furthermore, to achieve decoupling of the disturbance measurement signal, two disturbance injection methods are implemented, specifically including:

[0043] For disturbance measurement signals below 100Hz, the frequency of the disturbance measurement signal input to the open-loop disturbance injection module is set to f. p The output current of the cascaded H-bridge SVG is the measured current I. sfp and coupling current I sfo After completing the first perturbation injection, the set frequency is then changed from f. p Change its coupling frequency f o The new SVG output current is obtained as the measured current I. sfp * and coupling current I sfo * ;

[0044] For disturbance measurement signals of 100Hz and above, the coupling signal is changed to negative sequence injection. Due to the nonlinear control loop inside the SVG, the frequency of the disturbance measurement signal is set to f. p and f o At that time, two pairs of linearly independent measurement signals will be output respectively, thereby decoupling the calculation of the disturbance response.

[0045] The beneficial effects of this invention are as follows: The present invention discloses a method and system for measuring the impedance of a new energy power station based on a cascaded H-bridge SVG. By considering the SVG as a current source that outputs inductive or capacitive reactive current into the system when it is directly connected in parallel to the power system, and by controlling the output signal of its control loop, an adjustable disturbance current component is superimposed on the output reactive current to realize the injection of disturbance measurement signal into the power system. Then, based on the injected disturbance current, the voltage and current response of the system is measured, and finally the impedance characteristics of the new energy power station are calculated. This invention achieves the impedance measurement of a new energy power station without adding new equipment and ensures measurement accuracy. Attached Figure Description

[0046] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0047] Figure 1 This is a schematic diagram of disturbance measurement signal injection based on cascaded H-bridge SVG according to the present invention;

[0048] Figure 2 This is a schematic diagram of the open-loop disturbance injection module based on cascaded H-bridge SVG of the present invention;

[0049] Figure 3 This is a schematic diagram for verifying the disturbance output signal of the present invention;

[0050] Figure 4 This is a schematic diagram of the voltage response of the disturbance measurement current and the disturbance coupling current in the system according to the present invention;

[0051] Figure 5 This is a flowchart of the impedance measurement process based on a cascaded H-bridge SVG according to the present invention.

[0052] Figure 6 This is a schematic diagram for verifying the impedance measurement results of the present invention. Detailed Implementation

[0053] The present invention will be further described below with reference to the accompanying drawings, as shown in the figures:

[0054] The impedance measurement method for new energy power stations based on cascaded H-bridge SVG of the present invention includes:

[0055] in accordance with Figure 1A schematic diagram of disturbance measurement signal injection based on a cascaded H-bridge SVG is presented. When the SVG is connected to the power system, it is directly connected in parallel, thus it can be considered as a current source outputting inductive or capacitive reactive current into the system. By controlling the output signal of its control loop, an adjustable disturbance current component is superimposed on the output reactive current, achieving disturbance measurement signal injection into the power system. Subsequently, the voltage and current responses of the power system are measured based on the injected disturbance current, and finally, the impedance characteristics of the renewable energy power station are calculated.

[0056] Among them, SVG (Static Synchronous Compensator) is a reactive power compensation device used in power systems. SVG is usually composed of cascaded H-bridge inverters and is used to adjust the reactive power in the power system to maintain voltage stability, improve system efficiency and reduce grid losses.

[0057] In this embodiment, the injection of disturbance measurement signals into the power system specifically includes:

[0058] An open-loop disturbance injection module is connected in parallel to the control signal output of the cascaded H-bridge SVG control loop, such as... Figure 2 As shown, in the original output control signal s a s b s c Superimposed disturbance control signal s a3 s b3 s c3 At the same time, the disturbance amplitude coefficient K is set. r Take 3% to 10% of the steady-state amplitude of the fundamental control signal and adjust the frequency f of the given disturbance measurement signal. p A disturbance component of 1–1000 Hz is generated in the bridge arm current to complete the disturbance measurement signal injection based on the cascaded H-bridge SVG. Signal verification is as follows. Figure 3 As shown.

[0059] In this embodiment, when calculating the impedance characteristics of the renewable energy power station, the voltage response V is measured at the port of the renewable energy power station. fp It consists of two parts: one part is generated by the measuring current, and the other part is generated by the coupling current. The frequency f of the disturbance measurement signal... p The impedance characteristics under the condition are only related to the measured current I fp and the voltage response V generated by the measured current fp1 Therefore, under dual asymmetric control, the measured signal contains signal coupling, and the coupling principle is as follows: Figure 4 As shown, it is necessary to decouple the measurement signal to improve measurement accuracy.

[0060] Therefore, based on the above, a signal decoupling method under dual asymmetric control is designed. This method involves decoupling the disturbance measurement signal to calculate the impedance of the new energy power station. Specifically, this includes:

[0061] By injecting current at the frequency of the disturbance measurement signal and current at the coupling frequency, the frequency f of the disturbance measurement signal is obtained. p The impedance Z of the new energy power station SAfp It can be represented as:

[0062]

[0063] And V in the formula fp2 The effect of coupling current on the voltage at the measured frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; V fp2 Generated by the disturbance coupling current, it can be viewed as the disturbance coupling current passing through a companion impedance at frequency f. p The effect of the following on the voltage is due to the accompanying impedance being a reflection of the coupling frequency on the frequency f. p Due to the influence of [various factors], the associated impedance at the same frequency is constant. Therefore, equation (4) can be transformed into [the following equation].

[0064]

[0065] When a coupling frequency current is injected, there is

[0066]

[0067] Combining equations (5) and (6), the impedance of the new energy power station is obtained as follows:

[0068]

[0069] In the formula, V fp The voltage component at the measured frequency at the direct-drive wind farm port when the first disturbance measurement signal is injected; I fp The current component at the measured frequency at the direct-drive wind farm port when the first disturbance measurement signal is injected; I fo The current component at the coupling frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; Z AAfp To characterize the coupling frequency versus frequency f p The accompanying impedance of the effect; The voltage component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the coupling frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the measured frequency at the direct-drive wind farm port when the second disturbance measurement signal is injected. V foThe voltage component at the coupling frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; The voltage component at the coupling frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected.

[0070] In this embodiment, to satisfy the decoupling of the disturbance measurement signal mentioned above, the open-loop disturbance injection module needs to provide two nonlinear disturbance signal outputs for the power system. Therefore, two disturbance injection methods are set for impedance measurement:

[0071] Firstly, for disturbance measurement signals below 100Hz, the frequency of the disturbance measurement signal input to the module is set to f. p The output current of the cascaded H-bridge SVG is the measured current I. sfp and coupling current I sfo This completes the first perturbation injection. Next, the set frequency is changed from f... p Change its coupling frequency f o The new SVG output current is obtained as the measured current I. sfp * and coupling current I sfo * .

[0072] For disturbance measurement signals of 100Hz and above, the coupling signal is changed to negative sequence injection. Due to the nonlinear control loop inside the SVG, the frequency of the disturbance measurement signal is set to f. p and f o At that time, two pairs of linearly independent measurement signals will be output separately, thereby decoupling the disturbance response for calculation, and finally measuring the impedance characteristics of the new energy power station. The specific flowchart is as follows. Figure 5 As shown.

[0073] The present invention also relates to a new energy power station impedance measurement system based on cascaded H-bridge SVG. The system can be understood as a system that implements the above-mentioned new energy power station impedance measurement method based on cascaded H-bridge SVG. The system includes an SVG access unit, a signal injection unit, and an impedance calculation unit.

[0074] The SVG access unit is used to connect the SVG to the power system in a direct parallel connection manner, and output inductive or capacitive reactive current into the power system as a current source.

[0075] The signal injection unit is used to control the output signal of the control loop, so that an adjustable disturbance current component is superimposed on the output reactive current, thereby realizing the injection of disturbance measurement signal of the power system.

[0076] The impedance calculation unit is used to measure the voltage and current response of the power system based on the injected disturbance measurement signal, and to calculate the impedance of the new energy power station.

[0077] The impedance measurement method and system for new energy power stations based on cascaded H-bridge SVG of this invention enables impedance measurement of new energy power stations without adding new equipment, while ensuring measurement accuracy. Figure 6 The schematic diagram showing the impedance measurement results demonstrates that the impedance calculated by this invention is in excellent agreement with the actual measured value, further verifying that the impedance calculated by this invention has high accuracy.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring the impedance of a new energy power station based on a cascaded H-bridge SVG, characterized in that: Includes the following steps: The SVG is connected to the power system in a direct parallel connection to act as a current source and output inductive or capacitive reactive current into the power system. The output signal of the control loop is controlled to superimpose an adjustable disturbance current component into the output reactive current, thereby realizing the injection of disturbance measurement signal into the power system. The voltage and current response of the power system is measured based on the injected disturbance measurement signal, and the impedance of the new energy power station is calculated. The impedance of the new energy power station is calculated by decoupling the disturbance measurement signal, specifically including: By injecting current at the frequency of the disturbance measurement signal and current at the coupling frequency, the frequency f of the disturbance measurement signal is obtained. p impedance of new energy power stations It can be represented as: (4) In equation (4), V fp2 Generated by disturbance coupling current, This can be viewed as a disturbance coupling current passing through a companion impedance at frequency f. p The effect of the following on the voltage is due to the accompanying impedance being a reflection of the coupling frequency on the frequency f. p Due to the influence of [various factors], the accompanying impedance at the same frequency is constant. Therefore, equation (4) can be transformed into: (5) When a coupling frequency current is injected, we have: (6) Combining equations (5) and (6), the impedance of the new energy power station is obtained as follows: in, The voltage component at the measured frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; The current component at the measured frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; The current component at the coupling frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; To characterize the coupling frequency versus frequency f p The accompanying impedance of the effect; The voltage component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the coupling frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected.

2. The impedance measurement method for new energy power stations based on cascaded H-bridge SVG according to claim 1, characterized in that: To achieve the injection of disturbance measurement signals into the power system, specifically including: An open-loop disturbance injection module is connected in parallel to the control signal output of the cascaded H-bridge SVG control loop, in response to the control signal s output by the SVG. a s b s c The disturbance control signal s is superimposed on each of the above. a3 s b3 s c3 At the same time, the disturbance amplitude coefficient K is set. r And adjust the frequency f of the given disturbance measurement signal. p A disturbance component of 1~1000Hz is generated in the bridge arm current to complete the disturbance measurement signal injection based on the cascaded H-bridge SVG; wherein, the disturbance amplitude coefficient K r Take 3% to 10% of the steady-state amplitude of the fundamental control signal.

3. The impedance measurement method for new energy power stations based on cascaded H-bridge SVG according to claim 1, characterized in that: To achieve decoupling of the disturbance measurement signal, two disturbance injection methods are implemented, specifically including: For disturbance measurement signals below 100Hz, the frequency of the disturbance measurement signal input to the open-loop disturbance injection module is set to f. p The output current of the cascaded H-bridge SVG is the measured current I. sfp and coupling current I sfo After completing the first perturbation injection, the set frequency is then changed from f. p Change its coupling frequency f o The new SVG output current is obtained as the measured current I. sfp * and coupling current I sfo * ; For disturbance measurement signals of 100Hz and above, the coupling signal is changed to negative sequence injection. Due to the nonlinear control loop inside the SVG, the frequency of the disturbance measurement signal is set to f. p and f o At that time, two pairs of linearly independent measurement signals will be output respectively, thereby decoupling the calculation of the disturbance response.

4. An impedance measurement system for new energy power stations based on cascaded H-bridge SVG, characterized in that: Includes an SVG access unit, a signal injection unit, and an impedance calculation unit; The SVG access unit is used to connect the SVG to the power system in a direct parallel connection manner, and output inductive or capacitive reactive current into the power system as a current source. The signal injection unit is used to control the output signal of the control loop, so that an adjustable disturbance current component is superimposed on the output reactive current, thereby realizing the injection of disturbance measurement signal of the power system. The impedance calculation unit is used to measure the voltage and current response of the power system based on the injected disturbance measurement signal, and calculate the impedance of the new energy power station. The impedance of the new energy power station is calculated by decoupling the disturbance measurement signal, specifically including: By injecting current at the frequency of the disturbance measurement signal and current at the coupling frequency, the frequency f of the disturbance measurement signal is obtained. p impedance of new energy power stations It can be represented as: (4) In equation (4), V fp2 Generated by disturbance coupling current, This can be viewed as a disturbance coupling current passing through a companion impedance at frequency f. p The effect of the following on the voltage is due to the accompanying impedance being a reflection of the coupling frequency on the frequency f. p Due to the influence of [various factors], the accompanying impedance at the same frequency is constant. Therefore, equation (4) can be transformed into: (5) When a coupling frequency current is injected, we have: (6) Combining equations (5) and (6), the impedance of the new energy power station is obtained as follows: in, The voltage component at the measured frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; The current component at the measured frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; The current component at the coupling frequency at the port of the direct-drive wind farm when the first disturbance measurement signal is injected; To characterize the coupling frequency versus frequency f p The accompanying impedance of the effect; The voltage component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the coupling frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected; The current component at the measured frequency at the port of the direct-drive wind farm when the second disturbance measurement signal is injected.

5. The impedance measurement system for new energy power stations based on cascaded H-bridge SVG according to claim 4, characterized in that: To achieve the injection of disturbance measurement signals into the power system, specifically including: An open-loop disturbance injection module is connected in parallel to the control signal output of the cascaded H-bridge SVG control loop, in response to the control signal s output by the SVG. a s b s c The disturbance control signal s is superimposed on each of the above. a3 s b3 s c3 At the same time, the disturbance amplitude coefficient K is set. r And adjust the frequency f of the given disturbance measurement signal. p A disturbance component of 1~1000Hz is generated in the bridge arm current to complete the disturbance measurement signal injection based on the cascaded H-bridge SVG; wherein, the disturbance amplitude coefficient K r Take 3% to 10% of the steady-state amplitude of the fundamental control signal.

6. The impedance measurement system for new energy power stations based on cascaded H-bridge SVG according to claim 4, characterized in that: To achieve decoupling of the disturbance measurement signal, two disturbance injection methods are implemented, specifically including: For disturbance measurement signals below 100Hz, the frequency of the disturbance measurement signal input to the open-loop disturbance injection module is set to f. p The output current of the cascaded H-bridge SVG is the measured current I. sfp and coupling current I sfo After completing the first perturbation injection, the set frequency is then changed from f. p Change its coupling frequency f o The new SVG output current is obtained as the measured current I. sfp * and coupling current I sfo * ; For disturbance measurement signals of 100Hz and above, the coupling signal is changed to negative sequence injection. Due to the nonlinear control loop inside the SVG, the frequency of the disturbance measurement signal is set to f. p and f o At that time, two pairs of linearly independent measurement signals will be output respectively, thereby decoupling the calculation of the disturbance response.

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