Single-phase rectifier symmetric control method adaptive to grid frequency fluctuation

Abstract

This invention discloses a symmetrical control method for a single-phase rectifier that adapts to grid frequency fluctuations. A symmetrical phase-locked loop (PLL) introduces a complex phase angle to construct a completely symmetrical phase and amplitude tracking loop. Combined with an orthogonal signal generator based on the generalized inverse Park transform, the system can quickly restore the orthogonality of the virtual orthogonal signal when the grid frequency fluctuates. A symmetrical current control algorithm based on the generalized inverse Park transform employs a symmetrical structure similar to the PLL to suppress frequency coupling components introduced by the current control loop. A symmetrical DC voltage control algorithm based on per-unit filtered complex power constructs filtered complex power by combining the DC-side load power feedback value. The per-unit power reference and power feedback are obtained by introducing the square of the voltage amplitude at the grid common coupling point and the square of the filtered actual grid voltage amplitude. Identical proportional-integral controllers are used to adjust active and reactive power separately, thereby simultaneously achieving symmetrical control of DC voltage and reactive power.

Description

Technical Field

[0001] This invention belongs to the field of power system grid-connected converter control, and relates to a symmetrical control method for a single-phase rectifier that adapts to grid frequency fluctuations, especially to frequency coupling suppression and frequency adaptive symmetrical control of a single-phase voltage source rectifier under weak grid conditions. Background Technology

[0002] In recent years, the large-scale grid connection of renewable energy sources such as photovoltaics and wind power has led to a continuous increase in the penetration rate of power electronic converters. Single-phase voltage source rectifiers, due to their high efficiency and strong controllability, have been widely used in new energy distributed generation, industrial DC power supply, rail transit traction, and new energy vehicle charging and distribution.

[0003] However, in weak grid scenarios, the asymmetric structure of traditional converter control schemes can induce frequency coupling effects: when a frequency of f is injected into the AC side... p When the voltage is disturbed, the grid-connected current is divided by f p In addition to producing a synchronous response at f, it will also be at f p Coupled components are excited at ±2f1 (f1 is the grid fundamental frequency). If grid impedance is considered, the system will change from a single-input single-output model to an infinite-dimensional multi-input multi-output model, which greatly increases the difficulty of impedance modeling and stability analysis, and may cause subsynchronous or supersynchronous oscillations.

[0004] The root cause of frequency coupling lies in the asymmetrical structure of the d-q axes in traditional control schemes: DC bus voltage control only regulates the dynamics of the d-axis current, and the phase-locked loop (PLL) based on the synchronous reference frame only regulates the dynamics of the q-axis voltage, resulting in coupling components at the frequencies of ω−2ω1, ω, and ω+2ω1. Furthermore, traditional quadrature signal generators designed based on fixed frequencies cannot maintain the orthogonality of the virtual signal when the grid frequency deviates, leading to a sharp deterioration in coupling suppression. Existing symmetrical control schemes for three-phase converters rely on three-phase symmetry and cannot be directly applied to single-phase systems; existing methods for single-phase inverters only consider the frequency coupling effect caused by the PLL and fail to address the frequency coupling suppression problem when DC bus voltage control and the PLL coexist in the rectifier. Summary of the Invention

[0005] To address the above problems, this invention provides a symmetrical control method for a single-phase rectifier that adapts to grid frequency fluctuations. Its core lies in a symmetrical phase-locked loop (PLL) based on generalized inverse Park transform, a symmetrical current control algorithm, and a symmetrical DC voltage control algorithm based on per-unit filtered complex power. This method simultaneously eliminates the frequency coupling effect introduced by DC bus voltage control and the PLL at the control architecture level, and also exhibits frequency adaptability when the grid frequency fluctuates within the range of 48–52 Hz. The specific steps of this invention for a symmetrical control method for a single-phase rectifier that adapts to grid frequency fluctuations are as follows:

[0006] S1, Establish the generalized Park transform and generalized inverse Park transform based on the complex phase angle, and apply them to the grid-connected common coupling point voltage u. pcc A symmetric phase-locked loop algorithm based on the generalized inverse Park transform is applied to extract θ, which reflects the voltage phase at the common coupling point. d and voltage amplitude deviation θ q This forms the complex phase angle θ dq = θ d + jθ q The specific process of the symmetric phase-locked loop algorithm based on the generalized inverse Park transform is as follows:

[0007] S1.1, Define the complex phase angle and establish the generalized Park transform and the generalized inverse Park transform:

[0008] Define the complex phase angle θ dq = θ d + jθ q , where the real part θ d Let θ be the phase angle of the power grid, and its imaginary part be θ. q This is used to characterize the deviation of the voltage amplitude at the grid-connected common coupling point from the nominal value V1. Based on this complex phase angle, the formulas for the generalized Park transform and the generalized inverse Park transform are:

[0009] (1);

[0010] In the formula X dq =X d +jX q X αβ =X α +jX β .

[0011] S1.2, the grid-connected common coupling point voltage u pcc As the α-axis component u α The β-axis virtual orthogonal voltage signal u is generated from the dq-axis voltage signal using the generalized inverse Park transform. β For the complex voltage vector u αβ = u α + ju β Applying the generalized Park transform and passing it through a low-pass filter G LPFu (s) After filtering, the voltage component u in the dq-axis rotating coordinate system is obtained. dq = u d + ju q :

[0012] (2);

[0013] (3);

[0014] In the formula, s represents the Laplace operator, ω u This indicates the cutoff angular frequency of the low-pass filter.

[0015] S1.3, convert the d-axis and q-axis voltages u d and u q Using the exact same proportional-integral controller G PLL (s) = k p1 + k i1 The d-axis directional angular frequency ω is obtained by adjusting the angular frequency by / s, with reference values ​​V1 and 0 respectively. d and q-axis orientation angular frequency ω q :

[0016] (4);

[0017] (5);

[0018] In the formula k p1 k represents the proportional coefficient of the phase-locked loop proportional-integral controller. i1 This represents the integral coefficient of the phase-locked loop proportional-integral controller; ω1 represents the rated angular frequency of the power grid, and V1 represents the rated voltage amplitude of the power grid.

[0019] The d- and q-axis oriented voltages ω d ω q After integration, the angle θ required in the generalized Park transform is obtained. d and θ q :

[0020] (6);

[0021] In the formula, dt represents the infinitesimal variable with time t as the variable;

[0022] S2, for DC bus voltage u dc and AC side reactive power Q ac By applying a symmetrical DC voltage control algorithm based on per-unit filtered complex power, the dq-axis oriented AC current reference value i is obtained. d,ref and i q,ref The specific process of the symmetrical DC voltage control algorithm based on per-unit filtered complex power is as follows:

[0023] S2.1, using the generalized inverse Park transform, a virtual orthogonal voltage signal u on the β axis is generated from the dq-axis voltage signal. β , and the voltage u at the common coupling point of the grid pcc (i.e. u α ) constitutes the voltage complex vector u αβ = u α+ ju β Similarly, virtual orthogonal current signals i are generated. β , and grid-connected current i g (i.e. i α ) constitutes the complex vector of current i αβ = i α + ji β 。;

[0024] S2.2, Calculation considering low-pass filter G L (s) DC-side active power feedback value P fdc and AC side reactive power feedback value Q fac The specific process is as follows:

[0025] Calculate the reactive power Q on the AC side ac Instantaneous power P of inductor Lf and the square of the AC side voltage amplitude v p 2 :

[0026] (7);

[0027] In the formula, L f d(x) / dt represents the value of the AC side filter inductance, and d(x) / dt represents the derivative with respect to the variable x.

[0028] Calculate the reactive power Q on the AC side ac Instantaneous power P of inductor Lf and the square of the AC side voltage amplitude v p 2 Low-pass filter value:

[0029] (8);

[0030] In the formula, s represents the Laplace operator, and R dc C represents the DC-side load resistance value. dc Q represents the value of the DC-side filter capacitor. fac P fLf and V fp They represent Q respectively ac P Lf and v p 2 The low-pass filter value.

[0031] Neglecting power losses in power electronic switches, the instantaneous power balance between the AC and DC sides of the main circuit yields the following:

[0032] (9);

[0033] In the formula i g =iα Consider the active power P on the DC side of the low-pass filter. fdc The expression is as follows:

[0034] (10);

[0035] Substituting equation (9) into equation (10) yields:

[0036] (11);

[0037] S2.3, Calculate the complex power reference value by combining the DC-side load power feedback value. and the complex power feedback value of the filter :

[0038] (12);

[0039] In the formula, U dc,ref Q is the reference value for DC voltage. ref For AC reactive power reference value, u dc This is the sampled value of the DC bus voltage. The complex power reference value is obtained by converting the AC voltage amplitude. and the complex power feedback value of the filter Perform per-unit scaling and filter complex power. The complex reference value i of the dq-axis current is obtained after proportional-integral adjustment. dq,ref :

[0040] (13);

[0041] (14);

[0042] Where k pdc k represents the proportional coefficient of a DC voltage proportional-integral regulator. idc i represents the integral coefficient of the DC voltage proportional-integral regulator. d,ref and i q,ref These are the d-axis directional current reference values ​​and the q-axis directional current reference values, respectively.

[0043] S3, based on the extracted complex phase angle θ dq The current reference i obtained from the symmetrical DC voltage control algorithm dq,ref The system applies a symmetrical current control algorithm based on the generalized inverse Park transform to perform closed-loop control of the grid-connected current, outputting a PWM modulated reference voltage signal v. α,ref The specific process of the symmetric current control algorithm based on the generalized inverse Park transform is as follows:

[0044] S3.1, the grid-connected current i g As the α-axis component i αUsing the generalized inverse Park transform, a virtual orthogonal current signal i on the β axis is generated from the dq-axis current signal. β For the complex vector of current i αβ = i α + ji β The dq-axis current components i are obtained by applying the generalized Park transform. dq = i d + ji q ;

[0045] (15);

[0046] S3.2, dq axis current i d and i q Respectively with current reference i d,ref and i q,ref After the difference is calculated, each is processed by an identical proportional-integral controller G. ci (s) Adjustment to obtain the dq-axis voltage reference v dq,ref :

[0047] (16);

[0048] (17);

[0049] In the formula, k pi k represents the proportional coefficient of the current proportional-integral controller. ii Indicates the integral coefficient of the current proportional-integral controller;

[0050] S3.3, Finally, regarding v dq,ref The αβ-axis voltage reference is obtained by applying the generalized inverse Park transform, taking only the α-axis component v. α,ref As a modulation signal, it drives the H-bridge rectifier to operate:

[0051] (18).

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] 1. This invention simultaneously eliminates the frequency coupling effect introduced by the phase-locked loop and the DC bus voltage control circuit;

[0054] 2. Since the frequency coupling effect is eliminated, the single-phase rectifier can be directly modeled as a simple and accurate single-input single-output admittance model, thereby simplifying controller design and stability analysis.

[0055] 3. The adaptive orthogonal signal generator based on the generalized inverse Park transform has frequency adaptability. When the power grid frequency fluctuates, the system can quickly restore the orthogonality of the virtual orthogonal signal.

[0056] 4. This invention is implemented entirely within the controller, requiring no additional hardware, and is simple to implement, exhibiting good metastable performance. Attached Figure Description

[0057] Figure 1 The main circuit structure diagram of the single-phase grid-connected rectifier according to an embodiment of the present invention;

[0058] Figure 2 DSP control block diagram of the control system according to an embodiment of the present invention;

[0059] Figure 3 Control algorithm block diagram of the control system of this invention embodiment;

[0060] Figure 4 Block diagram of the symmetric phase-locked loop algorithm based on the generalized inverse Park transform in this invention embodiment;

[0061] Figure 5 Block diagram of a symmetrical DC voltage control algorithm based on per-unit filtered complex power in an embodiment of the present invention;

[0062] Figure 6 Block diagram of the symmetric current control algorithm based on the generalized inverse Park transform in this invention embodiment;

[0063] Figure 7 Flowchart of the control algorithm in this invention embodiment;

[0064] Figure 8 The grid current FFT analysis diagram for verifying the frequency coupling suppression effect in this embodiment of the invention;

[0065] Figure 9 Simulation waveform diagram of the present invention during a step change in power grid frequency. Detailed Implementation

[0066] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0067] This invention provides a symmetrical control method for a single-phase rectifier that adapts to grid frequency fluctuations. It proposes a three-module collaborative control scheme: a symmetrical phase-locked loop based on the generalized inverse Park transform, symmetrical current control based on the generalized inverse Park transform, and symmetrical DC voltage control based on per-unit filtered complex power. This scheme eliminates the frequency coupling dynamics introduced by the asymmetrical control structure of the single-phase grid-connected rectifier, thereby reducing the difficulty of converter modeling, controller design, and stability analysis. The orthogonal signal generator based on the generalized inverse Park transform in this control method has frequency adaptability, enabling the system to quickly restore the orthogonality of the virtual orthogonal signal when the grid frequency fluctuates.

[0068] like Figure 1 As shown, a single-phase grid-connected rectifier includes a grid power supply ug Equivalent impedance of the power grid L g / R g Input filter inductor L f Series resistor R f H-bridge rectifier circuit, output DC side capacitor C dc and load resistance R dc The AC side of the H-bridge circuit passes through the input filter inductor L. f It is then connected to the power grid, with a DC load connected to the DC side. The voltage at the grid connection point of common coupling is u. pcc The grid current is i g The DC bus voltage is u dc .

[0069] Figure 2 The diagram shows the DSP control block diagram of the control system of the present invention. The main circuit in the diagram includes the single-phase grid-connected rectifier, which is the embodiment of the present invention. The control circuit includes a sampling and conditioning circuit, a controller, and a drive circuit.

[0070] The first part of the sampling circuit on the left is responsible for sampling and conditioning the current of the grid-side inductor, while the second part on the left is responsible for sampling and conditioning the voltage at the common coupling point. The controller is responsible for important tasks such as controller calculation and modulation, and transmits each PWM switching signal to the drive circuit to achieve the purpose of controlling each switch.

[0071] Figure 3 This is an overall block diagram of the control system of the present invention. The converter control in this invention employs a single-phase rectifier symmetrical control method adapted to grid frequency fluctuations.

[0072] Figure 4 , Figure 5 , Figure 6 The following is a block diagram illustrating the implementation of the symmetrical phase-locked loop based on the generalized inverse Park transform, the symmetrical current control algorithm, and the symmetrical DC voltage control algorithm based on per-unit filtered complex power in this invention. First, the generalized Park transform and generalized inverse Park transform based on the complex phase angle are established, and the grid-connected common coupling point voltage u... pcc A symmetric phase-locked loop algorithm based on the generalized inverse Park transform is applied to extract θ, which reflects the voltage phase at the grid common coupling point. d and voltage amplitude deviation θ q This forms the complex phase angle θ dq = θ d + jθ q The specific process of the symmetric phase-locked loop algorithm based on the generalized inverse Park transform is as follows:

[0073] Define the complex phase angle and establish the generalized Park transform and the generalized inverse Park transform:

[0074] Define the complex phase angle θ dq= θ d + jθ q , where the real part θ d Let θ be the phase angle of the power grid, and its imaginary part be θ. q This is used to characterize the deviation of the voltage amplitude at the grid-connected common coupling point from the nominal value V1. Based on this complex phase angle, the formulas for the generalized Park transform and the generalized inverse Park transform are:

[0075] (1);

[0076] In the formula X dq =X d +jX q X αβ =X α +jX β .

[0077] The grid-connected common coupling point voltage u pcc As the α-axis component u α The β-axis virtual orthogonal voltage signal u is generated from the dq-axis voltage signal using the generalized inverse Park transform. β For the complex voltage vector u αβ = u α + ju β Applying the generalized Park transform and passing it through a low-pass filter G LPFu (s) After filtering, the voltage component u in the dq-axis rotating coordinate system is obtained. dq = u d + ju q :

[0078] (2);

[0079] (3);

[0080] In the formula, s represents the Laplace operator, ω u This indicates the cutoff angular frequency of the low-pass filter.

[0081] The d-axis and q-axis voltages u d and u q Using the exact same proportional-integral controller G PLL (s) = k p1 + k i1 The d-axis directional angular frequency ω is obtained by adjusting the angular frequency by / s, with reference values ​​V1 and 0 respectively. d and q-axis orientation angular frequency ω q :

[0082] (4);

[0083] (5);

[0084] In the formula k p1 k represents the proportional coefficient of the phase-locked loop proportional-integral controller. i1 This represents the integral coefficient of the phase-locked loop proportional-integral controller; ω1 represents the rated angular frequency of the power grid, and V1 represents the rated voltage amplitude of the power grid.

[0085] The d- and q-axis oriented voltages ω d ω q After integration, the angle θ required in the generalized Park transform is obtained. d and θ q :

[0086] (6);

[0087] In the formula, dt represents the infinitesimal variable with time t as the variable;

[0088] For DC bus voltage u dc and AC side reactive power Q ac By applying a symmetrical DC voltage control algorithm based on per-unit filtered complex power, the dq-axis oriented AC current reference value i is obtained. d,ref and i q,ref The specific process of the symmetrical DC voltage control algorithm based on per-unit filtered complex power is as follows:

[0089] Using the generalized inverse Park transform, a virtual orthogonal voltage signal u on the β axis is generated from the dq-axis voltage signal. β , and the voltage u at the common coupling point of the grid pcc (i.e. u α ) constitutes the voltage complex vector u αβ = u α + ju β Similarly, virtual orthogonal current signals i are generated. β , and grid-connected current i g (i.e. i α ) constitutes the complex vector of current i αβ = i α + ji β 。;

[0090] Calculation considering low-pass filter G L (s) DC-side active power feedback value P fdc and AC side reactive power feedback value Q fac The specific process is as follows:

[0091] Calculate the reactive power Q on the AC side ac Instantaneous power P of inductor Lf and the square of the AC side voltage amplitude v p 2 :

[0092] (7);

[0093] In the formula, L f d(x) / dt represents the value of the AC side filter inductance, and d(x) / dt represents the derivative with respect to the variable x.

[0094] Calculate the reactive power Q on the AC side ac Instantaneous power P of inductor Lf and the square of the AC side voltage amplitude v p 2 Low-pass filter value:

[0095] (8);

[0096] In the formula, s represents the Laplace operator, and R dc C represents the DC-side load resistance value. dc Q represents the value of the DC-side filter capacitor. fac P fLf and V fp They represent Q respectively ac P Lf and v p 2 The low-pass filter value.

[0097] Neglecting power losses in power electronic switches, the instantaneous power balance between the AC and DC sides of the main circuit yields the following:

[0098] (9);

[0099] In the formula i g =i α Consider the active power P on the DC side of the low-pass filter. fdc The expression is as follows:

[0100] (10);

[0101] Substituting equation (9) into equation (10) yields:

[0102] (11);

[0103] Calculate the complex power reference value by combining the DC-side load power feedback value. and the complex power feedback value of the filter :

[0104] (12);

[0105] In the formula, U dc,refQ is the reference value for DC voltage. ref For AC reactive power reference value, u dc This is the sampled value of the DC bus voltage. The complex power reference value is obtained by converting the AC voltage amplitude. and the complex power feedback value of the filter Perform per-unit scaling and filter complex power. The complex reference value i of the dq-axis current is obtained after proportional-integral adjustment. dq,ref :

[0106] (13);

[0107] (14);

[0108] Where k pdc k represents the proportional coefficient of a DC voltage proportional-integral regulator. idc i represents the integral coefficient of the DC voltage proportional-integral regulator. d,ref and i q,ref These are the d-axis directional current reference values ​​and the q-axis directional current reference values, respectively.

[0109] Based on the extracted complex phase angle θ dq The current reference i obtained from the symmetrical DC voltage control algorithm dq,ref The system applies a symmetrical current control algorithm based on the generalized inverse Park transform to perform closed-loop control of the grid-connected current, outputting a PWM modulated reference voltage signal v. α,ref The specific process of the symmetric current control algorithm based on the generalized inverse Park transform is as follows:

[0110] The grid-connected current i g As the α-axis component i α Using the generalized inverse Park transform, a virtual orthogonal current signal i on the β axis is generated from the dq-axis current signal. β For the complex vector of current i αβ = i α + ji β The dq-axis current components i are obtained by applying the generalized Park transform. dq =i d + ji q ;

[0111] (15);

[0112] dq axis current i d and i q Respectively with current reference i d,ref and i q,ref After the difference is calculated, each is processed by an identical proportional-integral controller G. ci (s) Adjustment to obtain the dq-axis voltage reference vdq,ref :

[0113] (16);

[0114] (17);

[0115] In the formula, k pi k represents the proportional coefficient of the current proportional-integral controller. ii Indicates the integral coefficient of the current proportional-integral controller;

[0116] Finally, regarding v dq,ref The αβ-axis voltage reference is obtained by applying the generalized inverse Park transform, taking only the α-axis component v. α,ref As a modulation signal, it drives the H-bridge rectifier to operate:

[0117] (18);

[0118] According to the rectifier voltage modulation signal v a,ref The rectifier uses a unipolar or bipolar modulation strategy to control the operation of four switches S1, S2, S3, and S4 to synthesize the rectifier output voltage.

[0119] Figure 7 This is a flowchart of the overall control algorithm in an embodiment of the present invention.

[0120] Figure 8 This is a verification diagram of the frequency coupling suppression effect of the present invention. Injections with amplitudes of 0.1V1 and frequencies of f were respectively used. p The voltage disturbances are 55 Hz and 115 Hz. Under a 55 Hz disturbance, the conventional asymmetric control strategy generates large coupling current components at 45 Hz and 155 Hz; under a 115 Hz disturbance, it generates large coupling current components at 15 Hz and 215 Hz. With the control strategy proposed in this invention, when a 55 Hz voltage disturbance is injected, the grid-side current i... g Almost no frequency coupling components were generated at 45 Hz and 155 Hz; when a voltage disturbance was injected at 115 Hz, the grid-side current i g Almost no frequency coupling components were generated at 15 Hz and 215 Hz. This result demonstrates that the present invention can effectively cut off the harmonic coupling path and has a very significant suppressive effect on frequency coupling.

[0121] Figure 9This study verifies the performance of the symmetric phase-locked loop (PLL) based on the generalized inverse Park transform in this invention under a step change in grid frequency. At t = 1.0 s, when the grid frequency steps from 50 Hz to 52 Hz, the PLL quickly locks in the new phase and frequency, and the output signal exhibits no significant low-frequency oscillation ripple; the virtual signal rapidly recovers its orthogonality. This result fully verifies the frequency adaptive characteristics of the PLL based on the generalized inverse Park transform. The system also demonstrates good performance under the condition of a grid frequency step change from 50 Hz to 48 Hz.

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A symmetrical control method for a single-phase rectifier adapting to power grid frequency fluctuations, characterized in that, A symmetric control architecture based on the generalized inverse Park transform and per-unit scaling for power reference and power feedback are adopted. The specific steps are as follows: S1, Establish the generalized Park transform and generalized inverse Park transform based on the complex phase angle, and apply them to the grid-connected common coupling point voltage u. pcc A symmetric phase-locked loop algorithm based on the generalized inverse Park transform is applied to extract θ, which reflects the voltage phase at the common coupling point. d and voltage amplitude deviation θ q This forms the complex phase angle θ dq = θ d + jθ q ; S2, for DC bus voltage u dc and AC side reactive power Q ac By applying a symmetrical DC voltage control algorithm based on per-unit filtered complex power, the dq-axis oriented AC current reference value i is obtained. d,ref and i q,ref ; S3, based on the extracted complex phase angle θ dq The current reference i obtained from the symmetrical DC voltage control algorithm dq,ref A symmetrical current control algorithm based on the generalized inverse Park transform is applied to perform closed-loop control of the grid-connected current, outputting a PWM modulated reference voltage signal v. α,ref .

2. The symmetrical control method for a single-phase rectifier adapting to power grid frequency fluctuations according to claim 1, characterized in that, The specific process of the symmetric phase-locked loop algorithm based on the generalized inverse Park transform is as follows: S1.1, Define the complex phase angle and establish the generalized Park transform and the generalized inverse Park transform: Define the complex phase angle θ dq = θ d + jθ q , where the real part θ d Let θ be the phase angle of the power grid, and its imaginary part be θ. q Used to characterize the deviation between the voltage amplitude at the grid-connected common coupling point and the nominal value V1; based on this complex phase angle, the formulas for the generalized Park transform and the generalized inverse Park transform are: （1）； X in the formula dq =X d +jX q , X αβ =X α +jX β ; S1.2, the grid-connected common coupling point voltage u pcc As the α-axis component u α The β-axis virtual orthogonal voltage signal u is generated from the dq-axis voltage signal using the generalized inverse Park transform. β For the complex voltage vector u αβ = u α + ju β Applying the generalized Park transform and passing it through a low-pass filter G LPFu (s) After filtering, the voltage component u in the dq-axis rotating coordinate system is obtained. dq = u d + ju q : （2）； （3）； In the formula, s represents the Laplace operator, ω u This indicates the cutoff angular frequency of the low-pass filter; S1.3, convert the d-axis and q-axis voltages u d and u q Using the exact same proportional-integral controller G PLL (s) = k p1 + k i1 The d-axis directional angular frequency ω is obtained by adjusting the angular frequency by / s, with reference values ​​V1 and 0 respectively. d and q-axis orientation angular frequency ω q : （4）； （5）； In the formula k p1 k represents the proportional coefficient of the phase-locked loop proportional-integral controller. i1 This represents the integral coefficient of the phase-locked loop proportional-integral controller; ω1 represents the rated angular frequency of the power grid, and V1 represents the rated voltage amplitude of the power grid. d-axis and q-axis oriented voltage ω d ω q After integration, the angle θ required in the generalized Park transform is obtained. d and θ q : （6）； In the formula, dt represents the infinitesimal variable with time t as the variable.

3. The symmetrical control method for a single-phase rectifier adapting to power grid frequency fluctuations according to claim 1, characterized in that, The specific process of the symmetrical DC voltage control algorithm based on per-unit filtered complex power is as follows: S2.1, using the generalized inverse Park transform, a virtual orthogonal voltage signal u on the β axis is generated from the dq-axis voltage signal. β , and the voltage u at the common coupling point of the grid pcc Constitutes the complex voltage vector u αβ = u α + ju β Similarly, virtual orthogonal current signals i are generated. β , and grid-connected current i g Constructing the complex vector of current i αβ = i α + ji β ; S2.2, Calculation considering low-pass filter G L (s) DC-side active power feedback value P fdc and AC side reactive power feedback value Q fac The specific process is as follows: Calculate the reactive power Q on the AC side ac Instantaneous power P of inductor Lf and the square of the AC side voltage amplitude v p 2 : （7）； In the formula, L f d(x) / dt represents the value of the AC side filter inductance, and d(x) / dt represents the derivative with respect to the variable x. Calculate the reactive power Q on the AC side ac Instantaneous power P of inductor Lf and the square of the AC side voltage amplitude v p 2 Low-pass filter value: （8）； In the formula, s represents the Laplace operator, and R dc C represents the DC-side load resistance value. dc Q represents the value of the DC-side filter capacitor. fac P fLf and V fp They represent Q respectively ac P Lf and v p 2 The low-pass filter value; Ignoring power losses from power electronic switches; the instantaneous power balance between the AC and DC sides of the main circuit yields the following: （9）； In the formula i g =i α Considering the active power P on the DC side of the low-pass filter fdc The expression is as follows: （10）； Substituting equation (9) into equation (10), we get: （11）； S2.3, Calculate the complex power reference value by combining the DC-side load power feedback value. and the filter complex power feedback value : （12）； In the formula, U dc,ref Q is the reference value for DC voltage. ref For AC reactive power reference value, u dc The DC bus voltage is sampled; the complex power reference value is obtained by converting the AC voltage amplitude. and the filter complex power feedback value Perform per-unit scaling and filter complex power. The complex reference value i of the dq-axis current is obtained after proportional-integral adjustment. dq,ref : （13）； （14）； Where k pdc k represents the proportional coefficient of a DC voltage proportional-integral regulator. idc i represents the integral coefficient of the DC voltage proportional-integral regulator. d,ref and i q,ref These are the d-axis directional current reference values ​​and the q-axis directional current reference values, respectively.

4. The symmetrical control method for a single-phase rectifier adapting to power grid frequency fluctuations according to claim 1, characterized in that, The specific process of the symmetric current control algorithm based on the generalized inverse Park transform is as follows: S3.1, the grid-connected current i g As the α-axis component i α Using the generalized inverse Park transform, a virtual orthogonal current signal i on the β axis is generated from the dq-axis current signal. β For the complex vector of current i αβ = i α + ji β The dq-axis current components i are obtained by applying the generalized Park transform. dq = i d + ji q ; （15）； S3.2, dq axis current i d and i q Respectively with current reference i d,ref and i q,ref After the difference is calculated, each is processed by an identical proportional-integral controller G. ci (s) Adjustment to obtain the dq-axis voltage reference v dq,ref : （16）； （17）； In the formula, k pi k represents the proportional coefficient of the current proportional-integral controller. ii Indicates the integral coefficient of the current proportional-integral controller; S3.3, Finally, regarding v dq,ref The αβ-axis voltage reference is obtained by applying the generalized inverse Park transform, taking only the α-axis component v. α,ref As a modulation signal, it drives the H-bridge rectifier to operate: （18）。

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