Repeat adaptive based cascaded grid simulator inverter side control method

Abstract

The application discloses a kind of based on repeated self-adapting cascade type power grid simulator inverter side control method, comprising: acquisition output voltage and output current;The output voltage is subtracted from given signal to obtain error voltage;Error voltage is inputted repeated controller to obtain first control signal, and first control signal is added to given signal to obtain the reference voltage of self-adapting control;Self-adapting control reference voltage, output voltage, output circuit input self-adapting controller and carry out self-adapting processing, obtain second control signal;Output current is inputted feedforward compensator and is compensated, and compensated control signal is obtained;Compensated control signal and second control signal are added to obtain third control signal;Third control signal is modulated to obtain SPWM pulse of the SPWM pulse of control cascade type power grid simulator inverter side output voltage.The application is based on voltage outer loop repeated control to realize no static error tracking, and harmonic tracking capability is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a control method for the inverter side of a cascaded grid simulator based on repeated self-adaptation. BACKGROUND

[0002] With large-scale grid connection of distributed power generation systems, the grid puts forward higher performance requirements for new energy grid-connected equipment. As the core equipment for simulating various operating conditions of the grid, the grid simulator is used to test the grid adaptability of new energy grid-connected equipment. In order to accurately simulate the characteristics of the grid, the grid simulator needs to have good output waveform quality, which requires the grid simulator to have a small steady-state error and strong anti-disturbance ability under various operating conditions. The current main control methods are:

[0003] PI control: simple to implement, but the system stability margin is low and cannot achieve zero steady-state error tracking.

[0004] Proportional-resonant control: can achieve high gain at the resonance point and realize zero steady-state error tracking, but a proportional-resonant controller can only be used for one frequency, and multiple proportional-resonant controllers need to be designed if the reference signal has multiple frequencies, which increases the design workload and system complexity.

[0005] Deadbeat control: fast dynamic response, but requires high accuracy of the mathematical model of the controlled object and cannot suppress load disturbances.

[0006] Sliding mode variable structure control: has strong robustness, but the sampling of the system and the determination of the sliding surface will affect the control performance and easily cause high-frequency chattering.

[0007] Repetitive control: can achieve zero steady-state error tracking, but has poor dynamic performance and the first given signal period after disturbance is equivalent to open-loop control.

[0008] State feedback + repetitive control: optimizes the dynamic performance of a single repetitive controller, but relies too much on the accuracy of the parameters of the controlled object.

[0009] PI + repetitive control: optimizes the dynamic performance of a single repetitive controller, but cannot achieve high-order harmonic tracking.

[0010] The above control methods all have deficiencies and cannot balance robustness, response speed, anti-interference ability and harmonic tracking ability, making it difficult to ensure the quality of the output waveform. SUMMARY

[0011] The purpose of the present application is to overcome the deficiencies of the prior art and provide a control method for a cascaded grid simulator based on repeated self-adaptation, so as to ensure that the output voltage waveform of the entire grid simulator has high steady-state accuracy, strong dynamic performance and anti-load disturbance ability.

[0012] The technical scheme for achieving the object of the present application is a control method for the inverter side of a cascaded grid simulator based on repeated self-adaptation, and the specific steps are as follows:

[0013] The output voltage and the output current of the inverter side of the cascaded grid simulator are collected.

[0014] The output voltage of the inverter side of the cascaded grid simulator is subtracted from a given signal to obtain an error voltage.

[0015] The error voltage is input into a repeated controller to obtain a first control signal, and the first control signal is added to the given signal to obtain a reference voltage controlled by self-adaptation.

[0016] The reference voltage controlled by self-adaptation, the output voltage of the inverter side of the cascaded grid simulator, and the output circuit are input into an adaptive controller for adaptive processing to obtain a second control signal.

[0017] The output current is input into a feedforward compensator for compensation to obtain a compensated control signal.

[0018] The compensated control signal is added to the second control signal to obtain a third control signal.

[0019] The third control signal is subjected to SPWM modulation to obtain an SPWM pulse for controlling the output voltage of the inverter side of the cascaded grid simulator.

[0020] Preferably, the output voltage and the output current of the cascaded grid simulator are collected by a voltage sampling circuit and a current sampling circuit, respectively.

[0021] Preferably, the repeated controller is specifically as follows:

[0022]

[0023] In the formula, S(z) is a compensator, N is the number of samples in one reference signal period, Q(z) is a zero-phase-shift low-pass filter, and z is the Z-transform time domain.

[0024] Preferably, the compensator is specifically as follows:

[0025] S(z)=k r z k c(z)

[0026] z k is a lead element, k r is a proportional coefficient, and c(z) is a second-order low-pass filter.

[0027] And the compensator S(z) satisfies |Q(z)-H(z)S(z)|<1, and H(z) is the discrete-domain closed-loop transfer function of the inverter side of the cascaded grid simulator.

[0028] Preferably, the discrete-domain closed-loop transfer function of the inverter side of the cascaded grid simulator is specifically:

[0029]

[0030] wherein a1(z) is obtained by bilinear transformation of a1(s) in the adaptive controller, a2(z) is obtained by bilinear transformation of a2(s) in the adaptive controller, and P(z) is obtained by zero-order holder transformation of P(s) = 1 / (LCs 2 + rCs + 1) of the controlled object.

[0031] Preferably, the adaptive control law adopted by the adaptive controller is:

[0032] u2 = a1(s)v o + a2(s)v ref + a3(s)i o

[0033] wherein v ref is the reference signal of the adaptive control, v o is the output voltage of the inverter side of the cascaded grid simulator, i o is the output current of the inverter side of the cascaded grid simulator, and a1(s), a2(s), and a3(s) satisfy:

[0034]

[0035] wherein k, k1, and p are control parameters, is the estimated value of the filter capacitor C, is the estimated value of the filter inductor L, is the estimated value of the equivalent resistance r.

[0036] Preferably, the control parameters k, k1, and p are calculated by pole placement method, and satisfy:

[0037]

[0038] wherein ζ r and ω r are the desired damping ratio and natural frequency, respectively.

[0039] Preferably, and satisfy

[0040]

[0041] wherein γ c , γ L , and γ ris the self-defined adaptive gain, i L is the inductance current, i dL is the ideal control current, i c is the capacitance current, e v is the voltage tracking deviation, e i is the current deviation, C , L , r are the lower limits of self-defined C, L, r respectively, are the upper limits of self-defined C, L, r respectively, and Proj(·) is a projection algorithm.

[0042] Compared with the prior art, the present application has the following advantages: the present application realizes zero static error tracking based on voltage outer loop repetitive control, improves harmonic tracking ability, and improves anti-disturbance and dynamic response ability through adaptive current inner loop control and feedforward compensation control, and can compensate for unknown parameters of the system; the present application adopts double-loop compound control based on repetitive adaptation, and can output high-quality AC voltage waveforms meeting laboratory requirements. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is the structure topology of the inverter side of the cascaded grid simulator provided in the embodiment of the present application.

[0044] Figure 2 is the structure block diagram of the inverter side of the cascaded grid simulator provided in the embodiment of the present application.

[0045] Figure 3 is the inner loop structure block diagram of the inverter side of the cascaded grid simulator provided in the embodiment of the present application.

[0046] Figure 4 is the repetitive control structure block diagram.

[0047] Figure 5 is the design scheme of the inverter side of the cascaded grid simulator provided in the embodiment of the present application.

[0048] Figure 6 is the system output voltage error and output current simulation waveform when the load is suddenly changed in the embodiment.

[0049] Figure 7 is the FFT analysis of the output voltage simulation waveform in the embodiment under no-load condition. DETAILED DESCRIPTION

[0050] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0051] As an embodiment, a cascaded grid simulator inverter side control method based on repetitive adaptation, the topology structure of the cascaded grid simulator inverter side is as shown in Figure 1As shown, the cascade grid simulator includes two DC power supplies, two inverter circuits, LC filters and a device under test.

[0052] The control method comprises:

[0053] The output voltage and the output current of the inverter side of the cascade grid simulator are collected.

[0054] Specifically, the output voltage and the output current of the cascade grid simulator are collected by a voltage sampling circuit and a current sampling circuit respectively.

[0055] The output voltage v o of the inverter side of the cascade grid simulator is subtracted from a given signal v r to obtain an error voltage v e , wherein the given signal is a composite signal including a fundamental wave, low-order harmonics and high-order harmonics.

[0056] The error voltage v e is input into a repetitive controller to obtain a first control signal u1, and the first control signal is added to the given signal v r to obtain a reference voltage v ref of adaptive control.

[0057] In a further embodiment, a repetitive controller is designed to implement outer-loop repetitive control for improving the steady-state accuracy of the system output voltage. Considering the one-step delay and zero-order hold caused by sampling and calculation, the inner-loop adaptive control and the control object are discretized to obtain a discrete-domain closed-loop transfer function of the inverter side of the cascade grid simulator only considering the adaptive control light load:

[0058]

[0059] In the formula,

[0060] In a further embodiment, the repetitive controller is used to improve the steady-state accuracy of the inverter side of the cascade grid simulator, and the repetitive controller includes an inner model and a compensator, as shown in Figure 4 The repetitive controller specifically comprises:

[0061]

[0062] In the formula, S(z) is a compensator designed for the inner-loop closed-loop transfer function H(z), N is the sampling number of one reference signal period, and Q(z) is a zero-phase-shift low-pass filter, and the expression is:

[0063]

[0064] Specifically, the compensator S(z) of the repetitive controller is repeated, so that the low frequency band of the frequency characteristic of H(z)S(z) has the characteristics of zero gain change and zero phase shift change, specifically:

[0065] S(z) = k r z k c(z)

[0066] z k is a lead element for compensating phase lag, k r is a proportional coefficient, and c(z) is a second-order low-pass filter for improving the attenuation capability of the system to high-frequency components.

[0067] On the basis of meeting the zero gain and zero phase shift of the low frequency band of the frequency characteristic of H(z)S(z), the compensator S(z) is adjusted to make |Q(z)-H(z)S(z)|<1, so as to form a stable repetitive adaptive-based cascade-type grid simulator inverter-side control method.

[0068] Specifically, the repetitive control module is based on the voltage error signal v e to obtain the first control signal u1, u1=G rc (z)v e .

[0069] The reference voltage v ref of the adaptive control, the output voltage of the cascade-type grid simulator inverter side, and the output circuit input adaptive controller are adaptively processed to obtain the second control signal u2;

[0070] In a further embodiment, the main circuit structure block diagram of the cascade-type grid simulator inverter side is as shown in Figure 2 , and the adaptive control module is designed based on this. The design of the inner loop adaptive control precedes the design of the outer loop repetitive control module, so the reference signal of the adaptive control is first set to the preset reference signal v r , i.e., v ref =v r . The adaptive controller adopts the adaptive control law as shown in Figure 3 :

[0071] u2=a1(s)v o +a2(s)v ref +a3(s)i o

[0072] wherein v ref is the reference signal of the adaptive control, v o is the output voltage of the cascade-type grid simulator inverter side, v i is the second control signal, i o is the output current of the cascade-type grid simulator inverter side, and a1(s), a2(s), and a3(s) satisfy

[0073]

[0074] where k, k1 and p are control parameters, is the estimated value of filter inductance L, is the estimated value of filter inductance L, is the estimated value of equivalent resistance r, whose update law is and satisfies

[0075]

[0076] where γ c , γ L and γ r are adaptive gains, i L is inductance current, i dL is ideal control current, which can be calculated by , i c is capacitance current, e v is voltage tracking error, which can be calculated by v = v o - v ref , e i is current error, which can be calculated by i = i L - i dL , Proj(·) is projection algorithm, whose calculation method is

[0077]

[0078] The control parameters k, k1 and p are calculated by pole placement method, which satisfies:

[0079]

[0080] where ζ r and ω r are desired damping ratio and natural frequency, respectively, which can be taken as ζ r = 0.8 and ω r = 4000 rad / s.

[0081] The output current is input to the feedforward compensator for compensation to obtain a compensated control signal;

[0082] To improve the ability of the control system of the inverter side of the cascaded grid simulator to overcome load disturbance, an output current feedforward compensation loop is added, and a feedforward compensator

[0083] G0(s) = Ls + k1

[0084] Further, the output current io The control signal u3 after compensation by the feedforward compensator is:

[0085] u3=G0(s)i o .

[0086] The third control signal u is obtained by adding the compensated control signal u3 and the second control signal u2. r ;

[0087] The third control signal is subjected to SPWM modulation to obtain an SPWM pulse for controlling the output voltage of the inverter side of the cascaded power grid simulator.

[0088] Further, the driving signal of the inverter full-bridge IGBT is obtained by a bipolar carrier phase-shift SPWM algorithm.

[0089] A simulation model is built based on MATLAB / Simulink and simulation verification is performed. Figure 6 The simulation waveforms of the system output voltage error and output current are given for the load mutation. The dynamic response performance of the system is tested under the condition of a nonlinear load. When the reference wave is a fundamental wave, the simulation waveforms of the system from no-load to nonlinear load and then to no-load show that the application can not only realize zero static error tracking, but also has good anti-load disturbance and dynamic response capability. Figure 7 FFT analysis of the output voltage simulation waveforms for the no-load condition is given. The given signal contains a fundamental wave, 3rd, 5th, 7th, 9th and 11th harmonics, wherein the harmonic amplitudes are all 5% of the fundamental wave amplitude, and the expression is: ref =U m (sin(ωt)+5%sin(3ωt)+5%sin(5ωt)+5%sin(7ωt)+5%sin(9ωt)+5%sin(11ωt)). It can be seen from the figure that the application has good harmonic tracking performance.

[0090] The above embodiments are only examples and do not represent a limitation on the scope of the application. These embodiments can be implemented in various other ways, and various omissions, substitutions, changes can be made without departing from the technical idea of the application.

Claims

1. A cascaded grid simulator inverter-side control method based on repetitive adaptive control, characterized in that, The specific steps are as follows: Collect the output voltage and output current on the inverter side of the cascaded power grid simulator; The error voltage is obtained by subtracting the output voltage of the inverter side of the cascaded power grid simulator from the given signal. The error voltage is input to the repetitive controller to obtain the first control signal, and the first control signal is added to the given signal to obtain the reference voltage for adaptive control. The reference voltage for adaptive control, the output voltage of the inverter side of the cascaded power grid simulator, and the output circuit are input into the adaptive controller for adaptive processing to obtain the second control signal. The output current is input into the feedforward compensator for compensation to obtain the compensated control signal; The compensated control signal is added to the second control signal to obtain the third control signal; The third control signal is SPWM modulated to obtain the SPWM pulse for controlling the output voltage of the inverter side of the cascaded power grid simulator.

2. The inverter-side control method for a cascaded power grid simulator based on repetitive adaptive control according to claim 1, characterized in that, The output voltage and output current of the cascaded power grid simulator are collected through voltage sampling circuit and current sampling circuit, respectively.

3. The inverter-side control method for a cascaded power grid simulator based on repetitive adaptive control according to claim 1, characterized in that, The repetitive controller is specifically: In the formula, S(z) is the compensator, N is the number of samplings in one reference signal period, Q(z) is the zero-phase-shift low-pass filter, and z is the Z-transform time domain.

4. The inverter-side control method for a cascaded power grid simulator based on repetitive adaptive control according to claim 3, characterized in that, The compensator is specifically: S(z)=k r z k c(z) z k As an advanced stage, k r Here, c(z) is the scaling factor, and c(z) is a second-order low-pass filter. Furthermore, the compensator S(z) makes |Q(z)-H(z)S(z)|<1, and H(z) is the discrete domain closed-loop transfer function of the inverter side of the cascaded power grid simulator.

5. The inverter-side control method for a cascaded power grid simulator based on repetitive adaptive control according to claim 4, characterized in that, The discrete-domain closed-loop transfer function of the inverter side in the cascaded power grid simulator is as follows: In the formula, a1(z) is obtained by discretization of a1(s) in the adaptive controller using the bilinear transform method, a2(z) is obtained by discretization of a2(s) in the adaptive controller using the bilinear transform method, and P(z) is obtained by the controlled object P(s) = 1 / (LCs) 2 The zero-order hold transform method is used to discretize the signal, where C is the filter capacitor, L is the filter inductor, a1(s) is the output voltage feedback controller, and a2(s) is the reference signal controller.

6. The inverter-side control method for a cascaded power grid simulator based on repetitive adaptive control according to claim 1, characterized in that, The adaptive control law used by the adaptive controller is: u2=a1(s)v o +a2(s)v ref +a3(s)i o Among them, v ref For adaptive control, v o For the inverter-side output voltage of the cascaded power grid simulator, i o Let a1(s) be the output current of the inverter side of the cascaded power grid simulator, a2(s) be the output voltage feedback controller, a3(s) be the reference signal controller, and a3(s) be the output current feedback controller. a1(s), a2(s), and a3(s) satisfy the following: In the formula, k, k1, and ρ are all control parameters. This is an estimated value for the filter capacitor C. This is an estimated value for the filter inductance L. This is an estimate of the equivalent resistance r.

7. The inverter-side control method for a cascaded power grid simulator based on repetitive adaptive control according to claim 6, characterized in that, The control parameters k, k1, and ρ are calculated using the pole placement method and satisfy the following: Where ζ r ω r These represent the desired damping ratio and the natural frequency, respectively.

8. The inverter-side control method for a cascaded power grid simulator based on repetitive adaptive control according to claim 6, characterized in that, and satisfy In the formula, γ c γ L and γ r For custom adaptive gain, i L For inductor current, i dL For ideal control current, i c For capacitor current, e v For voltage tracking deviation, e i For current deviation, C , L , r These are the custom lower bounds for C, L, and r, respectively. These are the upper limits of custom C, L, and r, respectively, and Proj(·) represents the projection algorithm.

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