Cascaded H-bridge-based simulation line impedance control method for power grid simulator

Abstract

The invention discloses a power grid simulator simulation line impedance characteristic control method based on a cascaded H bridge, belongs to the technical field of power grid simulator control, and is suitable for a line impedance characteristic simulation system. The control method comprises the steps of firstly calculating active power and reactive power of a power grid simulator, then calculating through a VSG algorithm to obtain an output voltage instruction, and finally adding a virtual complex impedance based on generalized second-order differential on the basis of an original voltage and current double-closed-loop feedback control system to realize a simulation function of system line impedance. The generalized second-order differential function keeps the phase lead compensation differential effect on a specific frequency range, and eliminates the inherent high-frequency noise amplification effect of a traditional differential function. According to the control method, the dynamic performance of the system can be effectively improved, the output signal ripple is small, and the control speed is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid simulator control, and in particular relates to a power grid simulator simulation line impedance control method based on a cascaded H-bridge. Background Art

[0002] With the increase in the penetration rate of distributed power generation systems, the demand for power quality and grid adaptability test platforms for new energy power generation systems such as photovoltaic and wind power is increasing. They need to be connected to the grid through long-distance transmission and distribution lines. At this time, the system line impedance will not only change the impedance characteristics of the grid, but also affect the working performance of the grid-connected converter. Therefore, in order to more realistically simulate the actual grid situation and detect and simulate the line impedance of a single-machine system, it is very meaningful for the grid simulator to use the line impedance simulation function to conduct simulation experiments.

[0003] At present, there are two ideas for impedance simulation in existing research: introducing virtual impedance in control and adjusting virtual impedance parameters to simulate impedance. Another idea is to improve the main circuit topology or control method to simulate impedance, such as the Chinese invention patent application publication "A control method, control device and power grid simulator" (publication number CN CN116819210A), "Weak power grid simulator and line impedance simulation method of series active H-bridge converter" (publication number CN 117239825A) and "Power grid simulator control method with wide frequency domain simulation function of transmission line impedance" (publication number CN118068125A), among which:

[0004] The "A Control Method, Control Device and Grid Simulator for a Grid Simulator" published on September 29, 2023 uses an improved voltage and current dual closed-loop control strategy to control the grid simulator. It reduces the difference between the grid mirror simulated by the grid simulator and the actual grid by simulating line impedance and the frequency fluctuation characteristics of the synchronous power supply. It does not require the addition of additional power electronic equipment, thus reducing costs. However, the integral controller involved in the patent control loop brings about a phase lag problem.

[0005] The "Weak Grid Simulator and Line Impedance Simulation Method of Series Active H-Bridge Converter" published on December 5, 2023 achieves the purpose of accurately simulating line impedance by controlling the active H-bridge converter connected in series in the main topology. However, the impedance command of this method is obtained based on the harmonic current extraction control, resulting in many harmonic components;

[0006] The "Grid Simulator Control Method with Wide-Frequency Domain Simulation Function of Transmission Line Impedance" published on May 24, 2024 constructs a transmission line with complex parameters into a distributed parameter circuit model through a transmission line model. The simulated line impedance has high accuracy, but the multi-order linear approximation method used in the transmission line model is relatively complex, and the control performance is greatly affected by the parameters.

[0007] In summary, the prior art has deficiencies, specifically:

[0008] 1. The integral controller involved in the control loop brings about phase lag problem;

[0009] 2. Most of the existing analog inductive impedance characteristics use traditional differential links, which will cause high-frequency harmonic interference;

[0010] 3. Among the control methods of power grid simulators for simulating line impedance characteristics, there is little research on dynamic stability performance and improvement measures. Summary of the invention

[0011] The technical problem to be solved by the present invention is to overcome the limitations of the above-mentioned various technical solutions, and to solve the phase lag problem corresponding to the integral link and improve the harmonic compensation performance. The present invention proposes a line impedance control method of a power grid simulator based on a cascaded H-bridge.

[0012] The object of the present invention is achieved in this way. The present invention provides a method for simulating line impedance control of a power grid simulator based on a cascaded H-bridge, wherein the power grid simulator includes a cascaded H-bridge module, a filter inductor, an AC filter capacitor and a load, wherein the cascaded H-bridge module is composed of N identical single-phase H-bridges in cascade, and its output end is connected in parallel with the AC side filter capacitor, the load is connected in parallel to the other side of the AC side filter capacitor, and the filter inductor is connected to the connection line between the output end of the cascaded H-bridge module and the positive electrode of the AC side filter capacitor; any one of the N single-phase H bridges is recorded as a single-phase H bridge i, i=1, 2, 3...N; the input end of the single-phase H bridge i is connected in parallel with a DC source; each single-phase H bridge i includes 4 switch tubes, which are respectively recorded as switch tubes S i-1 , switch tube S i-2 , switch tube S i-3 And switch tube S i-4 , where the switch tube S i-1 The collector and switch tube S i-3 The collectors are connected to the DC positive bus of the DC source, and the emitters are connected to the switch tube S i-2 The collector and switch tube S i-4 The collector of the switch tube S i-2 The emitter and switch tube S i-4 The emitters are connected to the negative DC bus of the DC source respectively;

[0013] The steps of the control method are as follows:

[0014] The current of the sampled current filter inductor is recorded as the bridge arm side inductor current i L , sample the voltage at the AC filter capacitor and record it as the filter capacitor voltage u c , sample the current at the load and record it as load current i o ;

[0015] The sampled filter capacitor voltage u c After a delay of 90°, an imaginary axis component u orthogonal to it is obtained. c_90 , the sampled load current i o After a delay of 90°, an imaginary axis component i orthogonal to it is obtained. o_90 ; u in the two-phase stationary coordinate system c ,u c_90 After synchronous rotating coordinate transformation, the filter capacitor voltage dq component U is obtained cd , U cq , i in the two-phase stationary coordinate system o ,i o_90 After synchronous rotation coordinate transformation, the load current dq component I is obtained od , I oq ; According to the dq component of the filter capacitor voltage U cd , U cq and the load current dq component I od , I oq Calculate the active power P and reactive power Q of the power grid simulator;

[0016] According to the calculated active power P and the given active power command P 0 And the given active power command P 0 Rated angular frequency ω 0 , the output angular frequency ω of the power grid simulator is obtained through the power angle control equation, and the output phase θ of the power grid simulator control is obtained by integrating ω;

[0017] According to the calculated reactive power Q and the given reactive power command Q 0 , given reactive power command Q 0 Rated voltage U 0 , the voltage amplitude control equation is used to obtain the output voltage amplitude command U of the power grid simulator c_ref ;

[0018] According to the power grid simulator, the output phase θ and the power grid simulator output voltage amplitude command U c_ref , calculate the output voltage command u of the cascaded H-bridge module c_ref ;

[0019] The inductive impedance is simulated by the controller G(s), and the virtual complex impedance Z based on controller 1 is introduced. v ; According to the introduced virtual complex impedance Z v , output voltage command u c_ref 、Filter capacitor voltage u c and load current i o , the output current command signal i is obtained through the voltage control equation ref ; According to the output current command signal i ref , the inductor current i on the bridge arm side L and load current i o , output voltage command u c_ref , the modulation signal u is obtained through the current control equation * ;

[0020] According to the modulation signal u * , based on the phase shift modulation method, with the switch tube S l-1 The driving signal As a benchmark, generate N single-phase H-bridge switch tubes S i-1 , switch tube S i-2 , switch tube S i-3 , switch tube S i-4 The corresponding driving signal Drive signal Drive signal and drive signal

[0021] Preferably, the power angle control equation is:

[0022]

[0023] Among them, m is the power angle control droop coefficient, J is the simulated virtual moment of inertia, and s is the Laplace operator.

[0024] Preferably, the voltage amplitude control equation is:

[0025] U c_ref =U 0 +n(Q 0 -Q)

[0026] Where n is the reactive power-voltage droop coefficient.

[0027] Preferably, the controller G(s) is a generalized second-order differentiator, and its expression is:

[0028]

[0029] Wherein, s is the Laplace operator, K is the proportional coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and ω is the angular frequency of the generalized second-order differential transfer function G(s).

[0030] Preferably, the virtual complex impedance Z v is a virtual complex impedance containing a purely inductive component, and its expression is:

[0031]

[0032] Where K is the proportionality coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and L v is the virtual inductance corresponding to the power grid simulator.

[0033] Preferably, the virtual complex impedance Z in step 6 is v is a virtual complex impedance containing resistive and inductive components, and its expression is:

[0034]

[0035] Where K is the proportionality coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and L v is the virtual inductance corresponding to the power grid simulator, R v is the virtual resistance corresponding to the power grid simulator.

[0036] Preferably, the voltage control equation and the current control equation are respectively:

[0037]

[0038] Among them, s is the Laplace operator, K p1 is the proportional coefficient of the first PI controller corresponding to the power grid simulator, K i1 is the integral coefficient of the first PI controller corresponding to the power grid simulator, K p2 is the proportional coefficient of the second PI controller corresponding to the power grid simulator, K i2 is the integral coefficient of the second PI controller corresponding to the power grid simulator.

[0039] Preferably, the content of the phase shift modulation method is as follows:

[0040] Drive signal Drive signal Drive signal Drive signal The frequency is f s ; Make the switch tube S i-1 With switch tube Si-2 Complementary conduction, switch tube S i-3 With switch tube S i-4 Complementary conduction;

[0041] The N switch tubes S i-1 The switch tube S l-1 The switch tubes other than the switch tube are denoted as switch tube S j-1 , and the switch tube S j-1 The driving signal is recorded as the driving signal Drive signal Lag behind the drive signal The lag time is T 1 , Lag behind the drive signal The lag time is T 1 , Drive signal Lag behind the drive signal The lag time is T 2 , driving signal Lag behind the drive signal The lag time is T 2 ,

[0042] Preferably, the calculation formulas for the active power P and reactive power Q of the power grid simulator are respectively:

[0043] P = 0.5 (U cq I oq +U cd I od )

[0044] Q=0.5(U cd I oq -U cq I od ).

[0045] Preferably, the output voltage instruction u of the cascaded H-bridge module c_ref The calculation formula is:

[0046] u c_ref =U c_ref sin(θ).

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1. The generalized second-order differential function in the present invention has a phase lead compensation effect in a specific frequency range, which can make up for the phase lag caused by the integral link, thereby increasing the phase margin and improving the dynamic stability performance of the system;

[0049] 2. Compared with the common differential link, the generalized second-order differential function in the present invention not only retains the phase lead compensation differential effect in a specific frequency range, but also eliminates the high-frequency noise amplification effect inherent in the traditional differential function, thereby improving the reliability of the system;

[0050] 3. The power grid simulator control method based on generalized second-order differential simulated line impedance adopted by the present invention has good output dynamic performance and fast control speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a topological diagram of the power grid simulator of the present invention.

[0052] Figure 2 It is a control block diagram of the present invention.

[0053] Figure 3 The output voltage waveform is obtained by simulating the cascaded H-bridge module of the present invention by using a generalized second-order differentiator to simulate a pure inductive component.

[0054] Figure 4 The output voltage waveform is obtained by simulating the cascaded H-bridge module of the present invention by using a generalized second-order differentiator to simulate the resistive and inductive components.

[0055] Figure 5 The output voltage waveform is obtained by simulating the resistive component of the cascaded H-bridge module of the present invention using a traditional differential control method.

[0056] Figure 6 The output voltage waveform is obtained by simulating the inductive component of the cascaded H-bridge module of the present invention using a traditional differential control method.

[0057] Figure 7 It is a simplified diagram of the control method of the present invention. DETAILED DESCRIPTION

[0058] The preferred embodiments of the present invention are described in further detail below in conjunction with the accompanying drawings.

[0059] Figure 1 is the topological diagram of the power grid simulator of the present invention. Figure 1 It can be seen that the power grid simulator includes a cascaded H-bridge module, a filter inductor, an AC filter capacitor and a load, wherein the cascaded H-bridge module is composed of N identical single-phase H-bridges in cascade, and its output end is connected in parallel with the AC side filter capacitor, the load is connected in parallel to the other side of the AC side filter capacitor, and the filter inductor is connected to the line connecting the output end of the cascaded H-bridge module and the positive electrode of the AC side filter capacitor. Any one of the N single-phase H bridges is denoted as single-phase H bridge i, i=1, 2, 3...N. The input end of the single-phase H bridge i is connected in parallel with a DC source. Each single-phase H bridge i includes 4 switching tubes, which are respectively denoted as switch tubes Si-1 , switch tube S i-2 , switch tube S i-3 And switch tube S i-4 , where the switch tube S i-1 The collector and switch tube S i-3 The collectors are connected to the DC positive bus of the DC source, and the emitters are connected to the switch tube S i-2 The collector and switch tube S i-4 The collector of the switch tube S i-2 The emitter and switch tube S i-4 The emitters are respectively connected to the DC negative bus of the DC source.

[0060] Depend on Figure 1 It can be seen that a DC side filter capacitor is connected in parallel between each single-phase H bridge i and the DC source.

[0061] exist Figure 1 In, V i is the DC voltage of the single-phase H bridge i, C i is the capacitance of the DC side filter capacitor of the single-phase H bridge i, L is the inductance of the filter inductor, C is the capacitance of the AC filter capacitor, R L Specifically, the parameters in this embodiment are as follows: N = 12, that is, the cascaded H-bridge module is composed of 12 single-phase H-bridges, and the DC voltage V of each single-phase H-bridge is i The corresponding cascade H-bridge module DC voltage is 1130V, the corresponding cascade H-bridge module DC voltage is equivalent to 13560V, the output AC phase voltage effective value is 10000V / 50Hz, the rated capacity is 1GW, L=0.6627mH, C=3.12μF, the sampling frequency f s is 12kHz, so the sampling period T s =83.3μs.

[0062] Figure 2 is a control block diagram of the present invention, Figure 7 is a schematic diagram of the control method of the present invention, comprising Figure 2 and Figure 7 It can be seen that the steps of the line impedance control method of the power grid simulator based on the cascade H-bridge of the present invention are as follows:

[0063] Step 1: Sample the current flowing through the filter inductor and record it as the bridge arm side inductor current i L , sample the voltage at the AC filter capacitor and record it as the filter capacitor voltage u c , sample the current at the load and record it as load current i o .

[0064] Step 2: Calculate the filter capacitor voltage u obtained in step 1 c After a delay of 90°, an imaginary axis component u orthogonal to it is obtained. c_90, for the load current i obtained in step 1 o After a delay of 90°, an imaginary axis component i orthogonal to it is obtained. o_90 ; u in the two-phase stationary coordinate system c ,u c_90 After synchronous rotating coordinate transformation, the filter capacitor voltage dq component U is obtained cd , U cq , i in the two-phase stationary coordinate system o ,i o_90 After synchronous rotation coordinate transformation, the load current dq component I is obtained od , I oq ; According to the filter capacitor voltage dq component U cd , U cq and the load current dq component I od , I oq The active power P and reactive power Q of the power grid simulator are calculated.

[0065] In this embodiment, the calculation formulas for the active power P and reactive power Q of the power grid simulator are:

[0066] P = 0.5 (U cq I oq +U cd I od )

[0067] Q=0.5(U cd I oq -U cq I od ).

[0068] Step 3: Based on the active power P obtained in step 2 and the given active power command P 0 And the given active power command P 0 Rated angular frequency ω 0 , the power grid simulator output angular frequency ω is obtained through the power angle control equation, and the power grid simulator control output phase θ is obtained by integrating ω.

[0069] In this embodiment, the power angle control equation is:

[0070]

[0071] Among them, m is the power angle control droop coefficient, J is the simulated virtual moment of inertia, and s is the Laplace operator.

[0072] The active power droop curve relationship in the power angle control equation includes three coefficients. The power angle control droop coefficient m represents the slope of the droop curve. The value is taken as follows: when the active power changes by 100%, the frequency changes within 0.5Hz. The given active power command P 0and the corresponding rated angular frequency ω 0 It represents the position relationship of the droop curve, mainly considering that the output active power of the new energy grid-connected inverter is P 0 When , its output frequency is large. In this embodiment, J=0.06kg·m 2 To ensure that the energy does not flow to the DC side during control operation, the active power command value is P 0 =1MW, the corresponding rated angular frequency is ω 0 =314.1593rad / s.

[0073] Step 4: Based on the reactive power Q obtained in step 2 and the given reactive power command Q 0 , given reactive power command Q 0 Rated voltage U 0 , the voltage amplitude control equation is used to obtain the output voltage amplitude command U of the power grid simulator c_ref .

[0074] In this embodiment, the voltage amplitude control equation is:

[0075] U c_ref =U 0 +n(Q 0 -Q)

[0076] Where n is the reactive power-voltage droop coefficient.

[0077] The reactive power-voltage droop coefficient n is set according to the principle that when the reactive power changes by 100%, the voltage amplitude changes within 2%; the given reactive power command Q 0 And the corresponding rated output capacitor voltage U 0 It represents the position relationship of the droop curve, mainly considering that the reactive power output of the new energy grid-connected inverter is Q 0 When, its output voltage is large.

[0078] In this embodiment, Q 0 =0,U 0 =10000V.

[0079] Step 5: Control the output phase θ of the power grid simulator obtained in step 3 and the output voltage amplitude instruction U of the power grid simulator obtained in step 4. c_ref , calculate the output voltage command u of the cascaded H-bridge module c_ref .

[0080] In this example, the output voltage instruction u of the cascaded H-bridge module is c_ref The calculation formula is:

[0081] uc_ref =U c_ref sin(θ).

[0082] Step 6: The inductive impedance is simulated by the controller G(s) and a virtual complex impedance Z based on the controller G(s) is introduced. v ; According to the introduced virtual complex impedance Z v , output voltage command u c_ref 、Filter capacitor voltage u c and load current i o , the output current command signal i is obtained through the voltage control equation ref ; According to the output current command signal i ref , the inductor current i on the bridge arm side L and load current i o , output voltage command u c_ref , the modulation signal u is obtained through the current control equation * .

[0083] In this embodiment, the generalized second-order differentiator expression is:

[0084]

[0085] Wherein, s is the Laplace operator, K is the proportional coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and ω is the angular frequency of the generalized second-order differential transfer function G(s).

[0086] In this embodiment, F=0.32, K=1.

[0087] In this embodiment, the virtual complex impedance Z v is a virtual complex impedance containing a purely inductive component, and its expression is:

[0088]

[0089] Where K is the proportionality coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and L v is the virtual inductance corresponding to the power grid simulator.

[0090] In this embodiment, L v =80mH, the calculated analog voltage theoretical value u v =i o Z v =2512V;

[0091] In this embodiment, the virtual complex impedance Z v is a virtual complex impedance containing resistive and inductive components, and its expression is:

[0092]

[0093] Where K is the proportionality coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and L v is the virtual inductance corresponding to the power grid simulator, R v is the virtual resistance corresponding to the power grid simulator.

[0094] In this embodiment, R v =20Ω, L v =80mH, the calculated analog voltage theoretical value is u v =i o Z v =3212V

[0095] In this embodiment, the voltage control equation and the current control equation are respectively:

[0096]

[0097] Among them, s is the Laplace operator, K p1 is the proportional coefficient of the first PI controller corresponding to the power grid simulator, K i1 is the integral coefficient of the first PI controller corresponding to the power grid simulator, K p2 is the proportional coefficient of the second PI controller corresponding to the power grid simulator, K i2 is the integral coefficient of the second PI controller corresponding to the power grid simulator.

[0098] In this embodiment, K p1 is 1, K i1 50,K p2 is 0.8, K i2 is 50.

[0099] Step 7: According to the modulation signal u * , based on the phase shift modulation method, with the switch tube S l-1 The driving signal As a benchmark, generate N single-phase H-bridge switch tubes S i-1 , switch tube S i-2 , switch tube S i-3 , switch tube S i-4 The corresponding driving signal Drive signal Drive signal and drive signal

[0100] In this embodiment, the content of the phase shift modulation method is as follows:

[0101] Drive signal Drive signal Drive signal Drive signal The frequency is f s ; Make the switch tube S i-1 With switch tube S i-2 Complementary conduction, switch tube S i-3 With switch tube S i-4 Complementary conduction;

[0102] The N switch tubes S i-1 The switch tube S l-1 The switch tubes other than the switch tube are denoted as switch tube S j-1 , and the switch tube S j-1 The driving signal is recorded as the driving signal Drive signal Lag behind the drive signal The lag time is T 1 , Lag behind the drive signal The lag time is T 1 , Drive signal Lag behind the drive signal The lag time is T 2 , driving signal Lag behind the drive signal The lag time is T 2 ,

[0103] In this embodiment, T 1 =41.67(i-1)μs, T 2 =41.67(i+11)μs.

[0104] In order to demonstrate the technical effect of the present invention, the invention was simulated.

[0105] Figure 3 The output voltage waveform is obtained by simulating the pure inductive component of the cascaded H-bridge module of the present invention using a generalized second-order differentiator. Figure 4 The output voltage waveform is obtained by simulating the resistive and inductive components of the cascaded H-bridge module of the present invention using a generalized second-order differentiator. The resistive and inductive components refer to the virtual complex impedance Z in step 6. v is a virtual complex impedance containing resistive and inductive components. Figure 3It can be seen that the inductive simulation voltage leads the load voltage by 1 / 4 cycle, the response time is within 0.02s, and the pure inductive and resistive inductive simulation voltage components at power frequency are 2443.5 and 3213.97 respectively. Compared with the theoretical values, it can be proved that this control method can achieve high-precision simulation at specific sub-frequency; at the same time, the THD is 0.61% and 1.13% respectively, proving that the generalized second-order differentiator can filter out high-order harmonics.

[0106] In order to verify the advantages of the control method based on generalized second-order differential, the cascaded H-bridge module is used to simulate the resistive and inductive components based on the traditional differential control method, and the simulation waveform based on the generalized second-order differentiator to simulate the impedance characteristics is compared with the simulation waveform based on the pure differential control unit, while the topology and control system parameters remain consistent. Figure 5 The output voltage waveform is obtained by simulating the resistive component of the cascaded H-bridge module of the present invention using the traditional differential control method. Figure 6 The output voltage waveform is obtained by simulating the inductive component of the cascaded H-bridge module of the present invention using the traditional differential control method. The THDs are 40.83% and 20.34% respectively. It can be seen that the generalized second-order differentiator eliminates the high-frequency noise amplification effect inherent in the traditional differential function and effectively improves the dynamic performance of the system.

Claims

1. A method for simulating line impedance control based on a power grid simulator of a cascaded H-bridge, wherein the power grid simulator comprises a cascaded H-bridge module, a filter inductor, an AC filter capacitor and a load, wherein the cascaded H-bridge module is composed of N identical single-phase H-bridges in cascade, wherein the output end thereof is connected in parallel with the AC side filter capacitor, the load is connected in parallel with the other side of the AC side filter capacitor, and the filter inductor is connected to the line connecting the output end of the cascaded H-bridge module and the positive electrode of the AC side filter capacitor; any one of the N single-phase H-bridges is denoted as a single-phase H-bridge i, i=1, 2, 3…N; the input end of the single-phase H-bridge i is connected in parallel with a DC source; and each single-phase H-bridge i comprises four switch tubes, which are denoted as switch tubes S and S, respectively. i-1 , switch tube S i-2 , switch tube S i-3 And switch tube S i-4 ,in, Switching tube S i-1 The collector and switch tube S i-3 The collectors are connected to the DC positive bus of the DC source, and the emitters are connected to the switch tube S i-2 The collector and switch tube S i-4 The collector of the switch tube S i-2 The emitter and switch tube S i-4 The emitters are connected to the negative DC bus of the DC source respectively; Characterized in that the control method comprises the following steps: The current of the sampled current filter inductor is recorded as the bridge arm side inductor current i L , sample the voltage at the AC filter capacitor and record it as the filter capacitor voltage u c , sample the current at the load and record it as load current i o ; The sampled filter capacitor voltage u c After a delay of 90°, an imaginary axis component u orthogonal to it is obtained. c_90 , the sampled load current i o After a delay of 90°, an imaginary axis component i orthogonal to it is obtained. o_90 ; u in the two-phase stationary coordinate system c ,u c_90 After synchronous rotating coordinate transformation, the filter capacitor voltage dq component U is obtained cd , U cq , i in the two-phase stationary coordinate system o ,i o_90 After synchronous rotation coordinate transformation, the load current dq component I is obtained od , I oq ; According to the filter capacitor voltage dq component U cd , U cq and the load current dq component I od , I oq Calculate the active power P and reactive power Q of the power grid simulator; According to the calculated active power P, the given active power command P0 and the rated angular frequency ω0 at the given active power command P0, the power grid simulator output angular frequency ω is obtained through the power angle control equation, and the power grid simulator control output phase θ is obtained by integrating ω; According to the calculated reactive power Q, the given reactive power command Q0, and the rated voltage U0 at the given reactive power command Q0, the output voltage amplitude command U of the power grid simulator is obtained through the voltage amplitude control equation. c_ref ; According to the power grid simulator, the output phase θ and the power grid simulator output voltage amplitude command U c_ref , calculate the output voltage command u of the cascaded H-bridge module c_ref ; The inductive impedance is simulated by the controller G(s), and the virtual complex impedance Z based on the controller G(s) is introduced. v ; According to the introduced virtual complex impedance Z v , output voltage command u c_ref 、Filter capacitor voltage u c and load current i o , the output current command signal i is obtained through the voltage control equation ref ; According to the output current command signal i ref , the inductor current i on the bridge arm side L and load current i o , output voltage command u c_ref , the modulation signal u is obtained through the current control equation * ; According to the modulation signal u * , based on the phase shift modulation method, with the switch tube S 1-1 The driving signal As a benchmark, generate N single-phase H-bridge switch tubes S i-1 , switch tube S i-2 , switch tube S i-3 , switch tube S i-4 The corresponding driving signal Drive signal Drive signal and drive signal 2. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The expression of the power angle control equation is: Among them, m is the power angle control droop coefficient, J is the simulated virtual moment of inertia, and s is the Laplace operator.

3. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The voltage amplitude control equation is expressed as: U c_ref =U0+n(Q0-Q) Where n is the reactive power-voltage droop coefficient.

4. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The controller G(s) is a generalized second-order differentiator, and its expression is: Wherein, s is the Laplace operator, K is the proportional coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and ω is the angular frequency of the generalized second-order differential transfer function G(s).

5. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The virtual complex impedance Z v is a virtual complex impedance containing a purely inductive component, and its expression is: Where K is the proportionality coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and L v is the virtual inductance corresponding to the power grid simulator.

6. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The virtual complex impedance Z v is a virtual complex impedance containing resistive and inductive components, and its expression is: Where K is the proportionality coefficient of the generalized second-order differential transfer function G(s), F is the quality factor of the generalized second-order differential transfer function G(s), and L v is the virtual inductance corresponding to the power grid simulator, R v is the virtual resistance corresponding to the power grid simulator.

7. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The voltage control equation and the current control equation are respectively: Among them, s is the Laplace operator, K p1 is the proportional coefficient of the first PI controller corresponding to the power grid simulator, K i1 is the integral coefficient of the first PI controller corresponding to the power grid simulator, K p2 is the proportional coefficient of the second PI controller corresponding to the power grid simulator, K i2 is the integral coefficient of the second PI controller corresponding to the power grid simulator.

8. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The content of the phase shift modulation method is as follows: Drive signal Drive signal Drive signal Drive signal The frequency is f s ; Make the switch tube S i-1 With switch tube S i-2 Complementary conduction, switch tube S i-3 With switch tube S i-4 Complementary conduction; The N switch tubes S i-1 The switch tube S 1-1 The switch tubes other than the switch tube are denoted as switch tube S j-1 , and the switch tube S j-1 The driving signal is recorded as the driving signal j=2,...N;driving signal Lag behind the drive signal The lag time is T1, Lag behind the drive signal The lag time is T1, Drive signal Lag behind the drive signal The lag time is T2, the driving signal Lag behind the drive signal The lag time is T2, 9. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The calculation formulas for the active power P and reactive power Q of the power grid simulator are: P=0.5(U cq AND oq +U cd AND od ) Q=0.5(U cd I oq -U cq I od )。 10. The method for controlling line impedance of a power grid simulator based on a cascaded H-bridge according to claim 1, characterized in that: The output voltage instruction u of the cascaded H-bridge module c_ref The calculation formula is: in c_ref =U c_ref sin(θ).

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