A control method for simulating impedance of an AC power supply grid

Abstract

This invention discloses a control method for simulating grid impedance in AC power supply. The user sets the equivalent circuit structure of the virtual impedance through a controller. The controller samples the output current at the filter's downstream end in real time, calculates the voltage drop across the equivalent circuit of the virtual impedance in real time, and superimposes this voltage drop onto the basic setpoint of the output voltage to form the final setpoint of the output voltage. A closed-loop regulator controls the AC power supply output voltage to track this setpoint in real time. This control method for simulating grid impedance in AC power supply can achieve the function of simulating grid impedance. Because it is calculated in the time domain, the simulated impedance has a wide frequency band and fast calculation speed, resulting in high real-time performance.

Description

Technical Field

[0001] This invention relates to the field of AC power supply, and more particularly to a method for controlling AC power supply to simulate grid impedance. Background Technology

[0002] With the increasing proportion of new energy sources in the power grid and the large-scale grid connection of power electronic equipment, the power quality of the power grid is deteriorating, posing a significant challenge to its stability. To ensure grid reliability, new energy grid-connected power generation equipment needs to undergo grid adaptability and power quality testing using a multi-functional AC power supply to simulate the grid environment before grid connection. Generally, the multi-functional AC power supply should be able to output grid voltages under conditions including grid imbalance, flicker, and harmonics, to examine the grid imbalance adaptability, flicker adaptability, and harmonic adaptability of the grid-connected power generation equipment. Simultaneously, the AC power supply also needs to simulate grid impedance to assess the adaptability of the grid-connected power generation equipment under different grid impedance environments.

[0003] Chinese invention patent 201510541756.1 discloses a power grid simulator with precise harmonic voltage and virtual impedance control. Its virtual impedance calculation first involves decomposing the current using a Fast Fourier Transform (FFT), and then calculating the corresponding virtual impedance voltage divider for each harmonic in the frequency domain. This method cannot decompose non-integer harmonics. When the current contains interharmonics, the virtual impedance voltage divider calculation is inaccurate; when the current contains non-periodic signals, the FFT calculation has a large error; and because the FFT calculation is computationally intensive, its real-time performance is poor, which also introduces errors. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a control method for simulating grid impedance using an AC power supply. The AC power supply includes a controller and a voltage generator. The method comprises the following steps:

[0005] The controller is used to set the AC power supply's output voltage reference value V. gSet and virtual impedance Z gSim The equivalent circuit structure and parameters;

[0006] The controller samples the output current I of the load device in real time. g And calculate the output current in real time at the virtual impedance Z. gSim The voltage drop ΔV on the equivalent circuit ZSim ;

[0007] The AC power supply output voltage reference value V gSet Subtract the voltage drop ΔV across the virtual impedance ZSim The reference value V of the AC power supply output voltage is obtained. gRef ;

[0008] The actual output voltage V of the voltage generator in the AC power supply is controlled by a closed-loop regulator. g Real-time tracking of the output voltage reference value V gRef .

[0009] Preferably, the virtual impedance Z gSim The equivalent circuit includes the virtual inductance L. gSim ; or the virtual impedance Z gSim The equivalent circuit includes the virtual resistance R. gSim With virtual inductance L gSim The virtual resistance R gSim With virtual inductance L gSim Connected together; or the virtual impedance Z gSim The equivalent circuit includes the virtual inductance L. gSim and virtual capacitance C gSim The virtual inductance L gSim With virtual capacitance C gSim Connected together; or the virtual impedance Z gSim The equivalent circuit includes the virtual resistance R. gSim Virtual inductance L gSim and virtual capacitance C gSim The virtual resistance R gSim Virtual inductance L gSim and virtual capacitance C gSim Connected together.

[0010] Preferably, the calculated output current is at the virtual impedance Z gSim The voltage drop ΔV on the equivalent circuit ZSim The virtual impedance Z is calculated in real time using a time-domain calculation method. gSim The equivalent circuit voltage drop ΔV ZSim .

[0011] Preferably, the calculated output current is at the virtual impedance Z gSim The voltage drop ΔV on the equivalent circuit ZSim This includes calculating the voltage drop ΔV across the virtual resistor. RSim The voltage drop ΔV across the virtual inductor LSim and the voltage drop ΔV across the virtual capacitor CSim ;

[0012] The voltage drop ΔV across the virtual resistor RSim The voltage drop ΔV across the virtual inductor LSim The voltage drop ΔV across the virtual capacitor CSim After superposition, the virtual impedance Z is obtained. gSim The voltage drop ΔV on the equivalent circuit ZSim .

[0013] Preferably, the voltage drop ΔV across the calculated virtual resistor is... RSim This includes calculating the proportional value of the output current.

[0014] Preferably, the voltage drop ΔV across the calculated virtual inductor is... Lsim This includes calculating the differential value of the output current, which is performed using a second-order tracking differentiator or its discrete differential form.

[0015] Preferably, the voltage drop ΔV across the virtual capacitor is calculated. Csim This includes calculating the integral value of the output current, which is performed using a high-pass filter.

[0016] Preferably, the closed-loop regulator adopts dual closed-loop control of voltage outer loop and current inner loop; the voltage outer loop controller takes the output voltage reference value as a given value and the actual output voltage value as feedback to generate the output current reference value; the current inner loop controller takes the output current reference value as a given value and the actual output current value as feedback, the output voltage reference value is used as a feedforward component, the output value of the current inner loop controller is subtracted, and the decoupling component is superimposed to generate the wave quantity, which is then modulated by PWM to generate the PWM switching quantity.

[0017] Preferably, the internal voltage outer loop controller of the closed-loop regulator adopts a PI controller superimposed with a repetitive controller.

[0018] After using the above method, the output voltage reference value V of the AC power supply is set through the controller. gSet and virtual impedance Z gSim The equivalent circuit structure and parameters; the controller samples the output current I of the load device in real time. g And calculate the output current in real time at the virtual impedance Z. gSim The voltage drop ΔV on the equivalent circuit ZSim The AC power supply output voltage reference value V gSet Subtract the voltage drop ΔV across the virtual impedance ZSim The reference value V of the AC power supply output voltage is obtained. gRef The actual output voltage V of the voltage generator in the AC power supply is controlled by a closed-loop regulator. g Real-time tracking of the output voltage reference value V gRef This AC power supply control method for simulating grid impedance can realize the function of simulating grid impedance. Because its virtual impedance voltage drop is calculated in the time domain, the frequency band of the simulated impedance is wide, and the calculation speed is fast and the real-time performance is high. Attached Figure Description

[0019] Figure 1This is a diagram of the AC power supply structure for the AC power supply control method for simulating grid impedance according to the present invention.

[0020] Figure 2 The control method for simulating grid impedance of AC power supply in this invention uses a unit current with a noise signal frequency of 50Hz and a waveform diagram of the differential value of the current obtained by the differential method.

[0021] Figure 3 In the AC power supply simulation grid impedance control method of the present invention, the Bode plot of the transfer function of the second-order tracking differentiator (ξ=1, ω=104rad / s) is used to calculate the differential value of the current.

[0022] Figure 4 The control method for simulating grid impedance of AC power supply in this invention uses a unit current with a noise signal frequency of 50Hz and the waveform of the current differential value obtained by using a second-order tracking differentiator.

[0023] Figure 5 The control block diagram for the output voltage and output current of the AC power supply simulating grid impedance control method of the present invention adopts dual closed-loop control. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0025] Example 1

[0026] This embodiment discloses a method for controlling an AC power supply to simulate grid impedance. The AC power supply includes a controller and a voltage generator. The method includes the following steps:

[0027] The controller is used to set the AC power supply's output voltage reference value V. gSet And the virtual impedance Z of the power grid gSim The equivalent circuit structure and parameters;

[0028] The controller samples the output current I of the load device in real time. g And calculate the output current I in real time. g In the virtual impedance Z gSim The voltage drop ΔV on the equivalent circuit ZSim ;

[0029] The AC power supply output voltage reference value V gSet Subtract the voltage drop ΔV across the virtual impedance ZSim The reference value V of the AC power supply output voltage is obtained. gRef ;

[0030] The actual output voltage V of the voltage generator in the AC power supply is controlled by a closed-loop regulator. g Real-time tracking of the output voltage reference value V gRef .

[0031] In this embodiment, the virtual impedance Z gSim The equivalent circuit includes the virtual inductance L. gSim ; or the virtual impedance Z gSim The equivalent circuit includes the virtual resistance R. gSim With virtual inductance L gSim The virtual resistance R gSim With virtual inductance L gSim Connected together; or the virtual impedance Z gSim The equivalent circuit includes the virtual inductance L. gSim and virtual capacitance C gSim The virtual inductance L gSim With virtual capacitance C gSim Connected together; or the virtual impedance Z gSim The equivalent circuit includes the virtual resistance R. gSim Virtual inductance L gSim and virtual capacitance C gSim The virtual resistance R gSim Virtual inductance L gSim and virtual capacitance C gSim Connected together.

[0032] The calculated output current is at the virtual impedance Z. gSim The voltage drop ΔV on the equivalent circuit ZSim The virtual impedance Z is calculated in real time using a time-domain calculation method. gSim The equivalent circuit voltage drop ΔV ZSim .

[0033] In this embodiment, the calculated output current is based on the virtual impedance Z. gSim The voltage drop ΔV on the equivalent circuit ZSim This includes calculating the voltage drop ΔV across the virtual resistor. RSim The voltage drop ΔV across the virtual inductor LSim and the voltage drop ΔV across the virtual capacitor CSim The voltage drop ΔV across the virtual resistor is calculated. RSim This includes calculating the proportional value of the output current, and calculating the voltage drop ΔV across the virtual inductor. Lsim This includes calculating the differential value of the output current, which is performed using a second-order tracking differentiator or its discretized difference form. The calculation also includes calculating the voltage drop ΔV across the virtual capacitor. CsimThis includes calculating the integral value of the output current, which is performed using a high-pass filter.

[0034] The voltage drop ΔV across the virtual resistor RSim The voltage drop ΔV across the virtual inductor LSim The voltage drop ΔV across the virtual capacitor CSim After superposition, the virtual impedance Z is obtained. gSim The voltage drop ΔV on the equivalent circuit ZSim .

[0035] Example 2

[0036] This embodiment discloses a virtual impedance control method for a three-phase AC power supply, wherein the AC power supply includes a controller and a voltage generator, and the control method includes the following steps:

[0037] The controller calculates the reference value of the three-phase output voltage of the AC power supply based on the three-phase voltage amplitude, frequency and phase set by the user.

[0038]

[0039] Among them, V Aset V Bset V Cset θ is the set amplitude of the ABC three-phase output voltage. Aset θ Bset θ Cset For the set phase of the ABC three-phase output voltage, f set To set the frequency, V gSetA V gSetB V gSetC This is the instantaneous value of the three-phase output reference voltage.

[0040] Furthermore, the user sets the structure and parameters of the equivalent circuit for the virtual impedance through the controller:

[0041] In this embodiment, the virtual impedance equivalent circuit includes a virtual resistance R. gSim Virtual inductance L gSim and virtual capacitance C gSim The virtual resistance R gSim Virtual inductance L gSim Virtual capacitor C gSim and series connection.

[0042] Furthermore, the controller samples the three-phase output current of the load device in real time and calculates the three-phase virtual impedance Z. gSim The voltage drop ΔV in the equivalent circuit ZSim To ensure the virtual impedance has wide-band characteristics, a time-domain calculation method is used to calculate the three-phase virtual impedance Z in real time. gSimThe equivalent circuit voltage drop ΔV ZSim :

[0043]

[0044] Among them, R gSim To set the value of the virtual resistance in the virtual impedance, L gSim C represents the inductance value of the virtual inductance in the virtual impedance. gSim i represents the capacitance value in the virtual impedance; gA i gB i gC The three-phase output current of the AC power supply; ΔV ZSimA ΔV ZSimB ΔV ZSimC This represents the instantaneous value of the three-phase virtual impedance voltage drop.

[0045] Virtual impedance Z in the time domain gSim Calculating the inductor voltage drop in the equivalent circuit requires obtaining the differential of the current, which is generally done directly using the finite difference method:

[0046]

[0047] Where T is the sampling period of the discrete system.

[0048] However, in practical applications, current signals experience significant interference. Directly using the differential method to calculate the derivative amplifies the high-frequency noise in the original signal, making it almost unusable. Figure 2 The figure shows a unit current with a frequency of 50Hz containing a noisy signal, and the differential value of the current obtained using the finite difference method.

[0049] A second-order tracking differentiator is used to obtain the differential component of the current, and its transfer function is as follows:

[0050]

[0051] Where ξ is the damping ratio and ω is the Nyquist angular frequency of the control system, the second-order tracking differentiator has basically the same characteristics as the pure differentiator in the low-frequency range, while it has a significant noise suppression capability in the high-frequency range.

[0052] like Figure 3 As shown, Figure 3 In the AC power supply simulation grid impedance control method of this invention, the Bode plot of the transfer function of a second-order tracking differentiator (ξ=1, ω=104rad / s) is used to calculate the differential value of the current. It can be seen that the characteristics of the second-order differentiator are basically consistent with those of the ideal differentiator in the low-frequency range.

[0053] like Figure 4 As shown, Figure 4The control method for simulating grid impedance of AC power supply in this invention uses a unit current with a noise signal frequency of 50Hz and the waveform of the current differential value obtained by using a second-order tracking differentiator.

[0054] Then, using the bilinear transformation method, the transfer function of the second-order tracking differentiator is discretized according to the control period T:

[0055]

[0056] In this embodiment, the virtual impedance Z gSim The calculation of the capacitor voltage drop in the equivalent circuit requires the current integral. To prevent the integration from introducing a DC component, a high-pass filter is added. In this embodiment, a first-order high-pass filter is used. The current integral transfer function is as follows:

[0057]

[0058] Similarly, using the bilinear transformation method, the current integral transfer function with high-pass filtering is discretized according to the control period T:

[0059]

[0060] Substituting the differential component G(z) of the three-phase output current (see Equation ②) and the integral component H(z) of the three-phase output current (see Equation ③) into the three-phase virtual impedance Z gSim The equivalent circuit voltage drop ΔV ZSim (See equation ①) to obtain the three-phase virtual impedance voltage drop:

[0061]

[0062] Furthermore, the AC power supply output voltage reference value V gSet Subtract the voltage drop ΔV across the virtual impedance ZSim The reference value V of the AC power supply output voltage is obtained. gRef :

[0063]

[0064] Among them, V gRefA V gRefB and V gRefC This is the reference value for the three-phase output voltage.

[0065] Furthermore, the actual output voltage V of the voltage generator in the AC power supply is controlled by a closed-loop regulator. g Real-time tracking of the output voltage reference value V gRef .

[0066] Example 3

[0067] Please see Figure 5This embodiment is based on Embodiment 2, "controlling the actual output voltage V of the voltage generator in the AC power supply through a closed-loop regulator". g Real-time tracking of the output voltage reference value V gRef Specifically, it includes:

[0068] The controller employs dual closed-loop control with an outer voltage looper and an inner current looper, such as... Figure 5 As shown. The three-phase voltage reference values ​​are transformed using coordinates to obtain the output voltage dq-axis reference values:

[0069]

[0070] The actual output voltage of the AC power supply is detected, and the coordinate transformation of the three-phase actual voltage is also performed to obtain the actual value of the output voltage on the dq axis:

[0071]

[0072] The actual output current of the AC power supply is detected, and the coordinate transformation of the three-phase actual current is also performed to obtain the actual value of the output current on the dq axis:

[0073]

[0074] The voltage outer loop controller uses the output voltage dq axis reference value as the setpoint and the actual output voltage dq axis value as the feedback. The output current dq axis reference value is used. Because the voltage setpoint contains high frequency components, in order to improve the controller performance, the voltage outer loop controller uses a PI controller and simultaneously superimposes a repetitive controller.

[0075]

[0076] Among them, V gRefd V gRefq V is a value given by the output voltage dq axis reference value. gd V gq The value is fed back based on the actual value of the output voltage dq axis.

[0077] The inner current loop controller takes the output current dq-axis reference value as a given value and the actual output current dq-axis value as feedback. The PWM waveform is generated by subtracting the output value of the inner current loop controller from the feedforward component of the output voltage dq-axis reference value and adding the decoupling component.

[0078]

[0079] Where L is the actual internal resistance of the AC power supply, and I Refd and I Refq I is a value given by the output current dq axis reference value. d I qV is the value fed back with the actual value of the output current dq axis. gRefd V gRefq ωLI is the value of the feedforward component with the output voltage dq-axis reference value as the reference value. q and ωLI d For decoupling components.

[0080] Furthermore, the PWM waveform is fed into the PWM modulation module to generate a three-phase PWM switching signal.

[0081] Furthermore, since the voltage and current setpoints contain high-frequency components, in order to improve the performance of the controller, the aforementioned voltage outer loop controller and current inner loop controller adopt a PI parallel repetitive controller.

[0082] It should be understood that the above are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the patent. Any equivalent structural or procedural transformations made using the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A control method of an AC power supply simulating impedance of a power grid, characterized by, The AC power supply includes a controller and a voltage generator, and the method includes the following steps: setting, by the controller, an output voltage reference value of the ac power supply V gSet and a virtual impedance of the power grid Z gSim equivalent circuit structure and parameters The controller samples the output current of the load device in real time. I g The output current is calculated in real time using a time-domain calculation method. I g In the virtual impedance Z gSim The voltage drop Δ on the equivalent circuit V ZSim The voltage drop Δ across the virtual resistor V RSim The voltage drop Δ across the virtual inductor V LSim and the voltage drop Δ on the virtual capacitor V CSim After superposition, the virtual impedance is obtained. Z gSim The voltage drop Δ on the equivalent circuit V ZSim ; The AC power supply output voltage reference value V gSet Subtract the voltage drop Δ across the virtual impedance V ZSim The reference value of the output voltage of the AC power supply is obtained. V gRef ; The actual output voltage of the voltage generator in the AC power supply is controlled by a closed-loop regulator. V g Real-time tracking of the output voltage reference value V gRef .

2. The control method for simulating grid impedance of AC power supply according to claim 1, characterized in that, The virtual impedance Z gSim The equivalent circuit includes virtual resistance. R gSim Virtual inductance L gSim and virtual capacitance C gSim The virtual resistor R gSim Virtual inductance L gSim and virtual capacitance C gSim Connected together.

3. The control method for simulating grid impedance of AC power supply according to claim 1, characterized in that, Calculate the voltage drop Δ across the virtual resistor. V RSim This includes calculating the proportional value of the output current.

4. The control method for simulating grid impedance of AC power supply according to claim 1, characterized in that, The voltage drop Δ on the virtual inductor is calculated. V Lsim This includes calculating the differential value of the output current, which is performed using a second-order tracking differentiator or its discrete differential form.

5. The control method for simulating grid impedance of AC power supply according to claim 1, characterized in that, The voltage drop Δ across the virtual capacitor is calculated. V Csim This includes calculating the integral value of the output current, which is performed using a high-pass filter.

6. The control method for simulating grid impedance of AC power supply according to claim 1, characterized in that, The closed-loop regulator adopts dual closed-loop control with an outer voltage loop and an inner current loop; the outer voltage loop controller generates an output current reference value by taking the output voltage reference value as a given value and taking the actual output voltage value as feedback. The current inner loop controller takes the output current reference value as a given value and the actual output current value as feedback. The output voltage reference value is used as a feedforward component. The output value of the current inner loop controller is subtracted from the output value of the current inner loop controller and the decoupling component is added to generate the wave quantity. After PWM modulation, the PWM switching quantity is generated.

7. The method for controlling AC power supply impedance simulating grid impedance according to claim 6, characterized in that, The closed-loop regulator's internal voltage outer loop controller employs a PI controller superimposed with a repetitive controller.

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