Control method and device for three-phase AC system

Abstract

The present invention provides a three-phase AC system and a control method thereof, the method comprising: receiving an output signal of the three-phase AC system, and obtaining a characteristic value of the output signal according to the output signal; performing virtual synchronous machine control on the inverter according to the characteristic value to obtain a fundamental wave potential; extracting harmonic components in the output signal, and obtaining an error signal according to the harmonic components and a reference value of the harmonic components; controlling the error signal to obtain a harmonic compensation potential; obtaining a control potential by superimposing the harmonic compensation potential with the fundamental wave potential; obtaining a pulse signal by modulating the control potential, and obtaining a switching signal of the inverter according to the pulse signal. The technical solution of the embodiment of the present invention can suppress the harmonic components in the output signal of the three-phase AC system under the control of a virtual synchronous machine.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a control method and device for a three-phase alternating current system. Background Art

[0002] At present, grid-connected inverters using power electronic equipment are put into the power grid in large quantities. The dynamic response of the inverter is fast but the rotational inertia is small, which is not conducive to the stability of the power grid.

[0003] Synchronous generators can maintain the stability of grid voltage and frequency. Grid-connected inverters with virtual synchronous machine performance can simulate the inertia and damping characteristics of synchronous generators, provide transient power support when the load changes suddenly, and maintain the stability of grid frequency. However, virtual synchronous machines have no measures to suppress the harmonic content of output current when they are connected to the grid, and no measures to suppress the harmonics of output voltage when they are off-grid and have asymmetric and nonlinear loads. The amplitude and frequency of the output voltage will deviate from the rated value.

[0004] If the virtual synchronous machine needs to be actually operated, harmonic control needs to be added to ensure that the output current quality of the virtual synchronous machine meets the standards when it is connected to the grid, and that the output voltage quality meets the standards when it is off-grid and with different loads.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] The purpose of the present disclosure is to provide a control method and device for a three-phase AC system, thereby overcoming one or more problems caused by limitations and defects of related technologies at least to a certain extent.

[0007] According to a first aspect of the present invention, a control method for a three-phase AC system is provided, wherein the three-phase AC system comprises an inverter and a filtering unit, wherein the inverter is coupled to a power grid through the filtering unit, and the control method comprises: step 1: receiving an output signal of the three-phase AC system, and obtaining a characteristic value of the output signal according to the output signal; step 2: performing virtual synchronous machine control on the inverter according to the characteristic value to obtain a fundamental wave potential; step 3: extracting harmonic components from the output signal, and obtaining an error signal according to the harmonic components and a reference value of the harmonic components; step 4: controlling the error signal to obtain a harmonic compensation potential; step 5: obtaining a control potential by superimposing the harmonic compensation potential with the fundamental wave potential; step 6: obtaining a pulse signal by modulating the control potential, and obtaining a switching signal of the inverter according to the pulse signal.

[0008] In some embodiments, when the three-phase AC system operates in a grid-connected mode and controls the harmonic current in the inverter output current, step 3 includes: performing a coordinate transformation on the inverter output current to obtain a current signal, performing a low-pass filter on the current signal to obtain a fundamental current, and subtracting the fundamental current from the current signal to obtain a harmonic current; and setting a reference value of the harmonic current to zero to obtain the error signal.

[0009] In some embodiments, when the three-phase AC system operates in a grid-connected mode and controls the harmonic current in the inverter output current, step 3 includes: performing coordinate transformation on the inverter output current to obtain a current signal, performing low-pass filtering on the current signal to obtain a fundamental current, and subtracting the fundamental current from the current signal to obtain a harmonic current; performing coordinate transformation on the harmonic current in multiple coordinate systems to obtain harmonic currents corresponding to the multiple coordinate systems, setting the harmonic current reference value in each of the coordinate systems to zero, and obtaining the error signal in each of the coordinate systems.

[0010] In some embodiments, when the three-phase AC system operates in an off-grid mode and controls the harmonic voltage in the output voltage of the three-phase AC system, step 3 includes: performing coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, performing low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtracting the fundamental voltage from the voltage signal to obtain a harmonic voltage; and setting a reference value of the harmonic voltage to zero to obtain the error signal.

[0011] In some embodiments, when the three-phase AC system operates in an off-grid mode and controls the harmonic voltage in the output voltage of the three-phase AC system, step 3 includes: performing coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, performing low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtracting the fundamental voltage from the voltage signal to obtain a harmonic voltage; performing coordinate transformation on the harmonic voltage in multiple coordinate systems to obtain harmonic voltages corresponding to the multiple coordinate systems, setting the harmonic voltage reference value in each of the coordinate systems to zero, and obtaining the error signal in each of the coordinate systems.

[0012] In some embodiments, step 4 includes: performing coordinate transformation of the error signal in multiple coordinate systems to obtain the error signal in each of the coordinate systems; in each of the coordinate systems, performing closed-loop control on the error signal in each of the coordinate systems to obtain potential instructions corresponding to the multiple coordinate systems; performing coordinate transformation on the potential instructions to obtain multiple harmonic potentials in a two-phase stationary coordinate system; adding the multiple harmonic potentials in the two-phase stationary coordinate system and performing two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0013] In some embodiments, step 4 includes: performing closed-loop control on the error signal in each of the coordinate systems to obtain potential instructions corresponding to the multiple coordinate systems; performing coordinate transformation on the potential instructions to obtain multiple harmonic potentials in a two-phase stationary coordinate system; adding the multiple harmonic potentials in the two-phase stationary coordinate system and performing a two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0014] In some embodiments, step 4 includes: performing coordinate transformation on the error signal to obtain an error signal in a two-phase stationary coordinate system; inputting the error signal in the two-phase stationary coordinate system into multiple control modules for closed-loop control to obtain multiple harmonic potentials in the two-phase stationary coordinate system; adding the multiple harmonic potentials in the two-phase stationary coordinate system and performing a two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0015] In some embodiments, the plurality of control modules include a PR control module and two R control modules, wherein the PR control module outputs a negative sequence harmonic potential, and the two R control modules output a 5th harmonic potential and a 7th harmonic potential, respectively.

[0016] According to a second aspect of the present invention, a control device for a three-phase AC system is provided, wherein the three-phase AC system comprises an inverter and a filtering unit, wherein the inverter is coupled to a power grid through the filtering unit, and the control device comprises: a first calculation unit, for receiving an output signal of the three-phase AC system, and obtaining a characteristic value of the output signal according to the output signal; a first control unit, for performing virtual synchronous machine control on the inverter to obtain a fundamental wave potential; an error acquisition unit, for extracting harmonic components from the output signal, and obtaining an error signal according to the harmonic components and a reference value of the harmonic components; an error adjustment unit, for controlling the error signal to obtain a harmonic compensation potential; a second calculation unit, for obtaining a control potential by superimposing the harmonic compensation potential with the fundamental wave potential; and a modulation unit, for obtaining a pulse signal by modulating the control potential, and obtaining a switching signal of the inverter according to the pulse signal.

[0017] In some embodiments, when the three-phase AC system operates in a grid-connected mode, the harmonic current in the inverter output current is controlled; the error acquisition unit includes: a harmonic current acquisition module, used to perform coordinate transformation on the inverter output current to obtain a current signal, perform low-pass filtering on the current signal to obtain a fundamental current, and subtract the fundamental current from the current signal to obtain a harmonic current; a current reference value setting module, used to set the reference value of the harmonic current to zero to obtain the error signal.

[0018] In some embodiments, when the three-phase AC system operates in a grid-connected mode, the harmonic current in the inverter output current is controlled; the error acquisition unit includes: a harmonic current acquisition module, used to perform coordinate transformation on the inverter output current to obtain a current signal, perform low-pass filtering on the current signal to obtain a fundamental current, and subtract the fundamental current from the current signal to obtain a harmonic current; a current reference value setting module, used to perform coordinate transformation on the harmonic current in multiple coordinate systems to obtain harmonic currents corresponding to the multiple coordinate systems, set the harmonic current reference value in each of the coordinate systems to zero, and obtain the error signal in each of the coordinate systems.

[0019] In some embodiments, when the three-phase AC system operates in an off-grid mode, the harmonic voltage in the inverter output voltage is controlled; the error acquisition unit includes: a harmonic voltage acquisition module, which is used to perform coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, perform low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtract the fundamental voltage from the voltage signal to obtain a harmonic voltage; a voltage reference value setting module, which is used to set the reference value of the harmonic voltage to zero to obtain the error signal.

[0020] In some embodiments, when the three-phase AC system operates in off-grid mode, the harmonic voltage in the inverter output voltage is controlled; the error acquisition unit includes: a harmonic voltage acquisition module, which is used to perform coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, perform low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtract the fundamental voltage from the voltage signal to obtain a harmonic voltage; a voltage reference value setting module, which is used to perform coordinate transformation on the harmonic voltage in multiple coordinate systems to obtain harmonic voltages corresponding to the multiple coordinate systems, set the harmonic voltage reference value in each of the coordinate systems to zero, and obtain the error signal in each of the coordinate systems.

[0021] In some embodiments, the error adjustment unit includes: a first coordinate transformation module, used to perform coordinate transformation of the error signal in multiple coordinate systems to obtain the error signal in each of the coordinate systems; a harmonic control module, used to perform closed-loop control of the error signal in each of the coordinate systems to obtain potential instructions corresponding to the multiple coordinate systems; a second coordinate transformation module, used to perform coordinate transformation of the potential instructions to obtain multiple harmonic potentials in a two-phase stationary coordinate system; a first calculation module, used to add the multiple harmonic potentials in the two-phase stationary coordinate system and then perform a two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0022] In some embodiments, the error adjustment unit includes: a harmonic control module, which is used to perform closed-loop control on the error signal in each of the coordinate systems to obtain potential instructions corresponding to the multiple coordinate systems; a third coordinate transformation module, which is used to perform coordinate transformation on the potential instructions to obtain multiple harmonic potentials in the two-phase stationary coordinate system; and a second calculation module, which is used to add the multiple harmonic potentials in the two-phase stationary coordinate system and then perform a two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0023] In some embodiments, the error adjustment unit includes: a fourth coordinate transformation module, used to perform coordinate transformation on the error signal to obtain an error signal in a two-phase stationary coordinate system; multiple control modules, respectively used to perform closed-loop control on the error signal in the two-phase stationary coordinate system to obtain multiple harmonic potentials in the two-phase stationary coordinate system; a third calculation module, used to add the multiple harmonic potentials in the two-phase stationary coordinate system and then perform a two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0024] In some embodiments, the plurality of control modules include a PR control module and two R control modules, wherein the PR control module outputs a negative sequence harmonic potential, and the two R control modules output a 5th harmonic potential and a 7th harmonic potential, respectively.

[0025] In the technical solution of the embodiment of the present invention, the harmonic compensation potential is superimposed on the fundamental wave potential to obtain the control potential, and the control potential is modulated to obtain the switching signal of the inverter, thereby realizing virtual synchronous machine control and suppressing the harmonic components in the output signal of the three-phase AC system.

[0026] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0028] Figure 1 A flow chart schematically showing a control method for a three-phase AC system according to an embodiment of the present invention;

[0029] Figure 2 A schematic diagram schematically shows the principle of a three-phase AC system according to an embodiment of the present invention;

[0030] Figure 3A block diagram schematically illustrates a first computing unit according to an embodiment of the present invention;

[0031] Figure 4 A block diagram schematically illustrates a first control unit according to an embodiment of the present invention;

[0032] Figure 5a A control flow chart of harmonic current according to an embodiment of the present invention is schematically shown;

[0033] Figure 5b Schematically shown Figure 5a A schematic diagram of the control architecture corresponding to the control flow in FIG.

[0034] Figure 6 A control flow chart of harmonic current according to another embodiment of the present invention is schematically shown;

[0035] Figure 7a A control flow chart of harmonic current according to another embodiment of the present invention is schematically shown;

[0036] Figure 7b Schematically shown Figure 7a A schematic diagram of the control architecture corresponding to the control flow in FIG.

[0037] Figure 8a A control flow chart of harmonic voltage according to another embodiment of the present invention is schematically shown;

[0038] Figure 8b Schematically shown Figure 8a A schematic diagram of the control architecture corresponding to the control flow in FIG.

[0039] Fig. 9 A control flow chart of harmonic voltage according to another embodiment of the present invention is schematically shown;

[0040] Fig.10 A schematic diagram schematically showing a control structure of harmonic voltage according to another embodiment of the present invention;

[0041] Fig.11 A schematic diagram schematically shows the principle of a three-phase AC system according to another embodiment of the present invention;

[0042] Fig.12 A flowchart schematically illustrating the method for island determination according to an embodiment of the present invention;

[0043] Fig.13 A block diagram schematically showing a first control unit and a fourth control unit of an embodiment of the present invention;

[0044] Fig.14 A block diagram schematically showing a first control unit and a fourth control unit of another embodiment of the present invention;

[0045] Fig.15 A schematic diagram schematically shows the principle of a three-phase AC system according to another embodiment of the present invention;

[0046] Fig.16 A block diagram schematically showing a first control unit and a fifth control unit according to an embodiment of the present invention;

[0047] Fig.17 A block diagram schematically shows a control device for a three-phase AC system according to an embodiment of the present invention.

[0048] Fig.18 A block diagram schematically shows a fourth control unit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the present invention will be more comprehensive and complete and fully convey the concept of the example embodiments to those skilled in the art.

[0050] In addition, the described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present invention. However, those skilled in the art will appreciate that the technical solution of the present invention can be practiced without one or more of the specific details, or other methods, components, devices, steps, etc. may be adopted. In other cases, known methods, devices, implementations or operations are not shown or described in detail to avoid blurring various aspects of the present invention.

[0051] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities may be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0052] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0053] The present invention provides a control method and device for a three-phase AC system, so as to achieve harmonic suppression of the three-phase AC system under the control of a virtual synchronous machine, and ensure that the output power quality meets the standard.

[0054] The three-phase AC system includes a control device, an inverter and a filter unit. The control device is electrically connected to the inverter, and the inverter is coupled to the power grid or load through the filter unit. The control device controls the switching operation of the inverter to adjust the output signal of the three-phase system. Figure 1 The following is a flow chart of the steps of the control method executed by the control device. Figure 1 As shown, the control method includes:

[0055] Step S1, receiving an output signal of a three-phase AC system, and obtaining a characteristic value of the output signal according to the output signal.

[0056] Step S2, performing virtual synchronous machine control on the inverter according to the characteristic value to obtain the fundamental wave potential.

[0057] Step S3, extracting the harmonic component in the output signal, and obtaining an error signal according to the harmonic component and the harmonic component reference value.

[0058] Step S4, controlling the error signal to obtain harmonic compensation potential.

[0059] Step S5, obtaining the control potential by superimposing the harmonic compensation potential on the fundamental wave potential.

[0060] Step S6, obtaining a pulse signal by modulating the control potential, and obtaining a switching signal of the inverter according to the pulse signal.

[0061] The inverter is subjected to virtual synchronous machine control to obtain the fundamental potential, the harmonic components in the output signal including the fundamental negative sequence component are extracted, the harmonic components are subtracted from zero to obtain the error signal, the error is subjected to closed-loop control to obtain the harmonic compensation potential, and the fundamental potential and the harmonic compensation potential are added to obtain the control potential. The control potential is modulated by SVPWM (space vector pulse width modulation) or SPWM (sinusoidal pulse width modulation) to obtain a switching signal to control the switching operation of the inverter. The technical solution of this embodiment performs virtual synchronous machine control on the inverter so that the inverter simulates the inertia and damping characteristics of the synchronous motor to maintain the stability of the grid voltage and frequency; and harmonic regulation is added to suppress the harmonic components in the output signal of the three-phase AC system.

[0062] Figure 2 It is a schematic diagram of the principle of a three-phase AC system. Figure 2 As shown, the three-phase AC system is coupled to the power grid through a main contactor, and the three-phase AC system is also electrically connected to a load. The three-phase system includes an inverter 201, an LC filter and a control device, and the control device samples the output current I abc And the output voltage U of the three-phase AC system abc The control device includes a first calculation unit 202 , a first control unit 203 , a regulating unit, a second calculation unit 206 and a modulation unit 207 .

[0063] The first calculation unit 202 samples the output signal of the three-phase AC system, that is, the output current I of the inverter 201 abc And the output voltage U of the three-phase AC system abc , to output the inverter's active power P, reactive power Q, and output voltage U abc The first control unit 203 performs virtual synchronous machine (VSG) control on the inverter to obtain the fundamental wave potential E abc The regulating unit includes a second control unit 204 and a third control unit 205, wherein the second control unit 204 receives the output current I abc and angle signal θ to output harmonic compensation potential E iabc , suppressing harmonic currents in the inverter output current including fundamental negative sequence current; the third control unit 205 receives the output voltage U of the three-phase AC system abc and angle signal θ to output harmonic compensation potential E uabc , suppressing the harmonic voltages in the output voltage of the three-phase AC system including the fundamental negative sequence voltage.

[0064] The control device further includes a selection unit 208, which selects to perform harmonic current control and output the harmonic compensation potential E according to the operation mode of the three-phase AC system. iabc , or choose to perform harmonic voltage control and output harmonic compensation potential E uabc Specifically, when the three-phase AC system operates in the grid-connected mode, the selection unit switches to the second control unit 204 to output the harmonic compensation potential E iabc , suppressing harmonic current; when the three-phase AC system operates in off-grid mode with an asymmetric or nonlinear load, the selection unit switches into the third control unit 205, outputting the harmonic compensation potential E uabc , suppressing harmonic voltage. The second calculation unit 206 is an adder, which adds the harmonic compensation potential and the fundamental potential to obtain the control potential E abc '. The modulation unit 207 controls the potential E abc 'Modulate to obtain a pulse signal, and obtain a switching signal of the inverter according to the pulse signal, wherein the modulation method can be SVPWM and SPWM, etc.

[0065] For a three-phase AC system based on virtual synchronous machine control, when connected to the grid, harmonic current is extracted, and harmonic current closed-loop control is performed to ensure that the output current quality meets the standard and the output voltage is clamped by the grid voltage. When operating off-grid with asymmetric and nonlinear loads, harmonic voltage is extracted, and harmonic voltage closed-loop control is performed to ensure that the output voltage quality meets the standard. The three-phase AC system and control method proposed in the present invention can simultaneously achieve the performance of the virtual synchronous machine itself and the control performance of the connected and off-grid.

[0066] Figure 3 for Figure 2 An exemplary schematic diagram of the first computing unit 202 in FIG. Figure 3 As shown, the first calculation unit 202 includes a phase lock 2021, a coordinate converter 2022, an integrator 2023 and a calculator 2024. The first calculation unit samples the output current I abc And the output voltage U abc The phase-locked device 2021 outputs the voltage U abc Phase locking is performed to obtain the amplitude U and angular frequency ω. Integrator 2023 integrates the angular frequency ω to obtain an angle signal θ. Coordinate converter 2022 respectively converts the output current I abc And the output voltage U abc Perform 2r / 3s (two-phase rotating / three-phase stationary) coordinate transformation to obtain the d-axis voltage U d , q-axis voltage U q , d-axis current I d and q-axis current I q The calculator 2024 calculates the d-axis voltage U d , q-axis voltage U q , d-axis current I d and q-axis current I q , calculate the active power P and reactive power Q of the three-phase AC system.

[0067] Figure 4 for Figure 2 The control block diagram corresponding to the first control unit 203 is the control block diagram of the virtual synchronous machine. Figure 4 As shown, the first control unit performs virtual synchronous machine control of the inverter, and performs droop control on the output voltage amplitude U and angular frequency ω according to the power angle characteristics to obtain the reactive power given Q * And the active power given P * The calculated active power P and reactive power Q are used as power feedback for VSG control; the active power regulation uses inertia and damping control to obtain the output angular frequency ω E , the angular frequency is integrated to obtain the angle signal θ E ; Reactive power regulation uses PI closed-loop control to output the potential amplitude E; according to the potential amplitude E and the angle signal θ EThe three-phase AC potential E is obtained abc , E abc It is the fundamental positive sequence output potential, referred to as the fundamental potential.

[0068] When the three-phase AC system operates in the grid-connected mode, the harmonic current of the inverter output current is controlled. Therefore, in step S3, the output signal corresponds to the output current, and the harmonic component corresponds to the harmonic current; the harmonic current in the output current of the inverter 201 is extracted, and the harmonic current error signal is obtained according to the harmonic current reference value, and the error signal is adjusted to obtain the harmonic compensation potential.

[0069] Figure 5a This is a flow chart of the control steps of harmonic current in grid-connected mode. Figure 5b for Figure 5a The control architecture corresponding to the control process. Specifically, Figure 5a As shown, step S3 may include the following sub-steps:

[0070] Step S311, the output current I abc The current signal is obtained by performing 3s / 2r (three-phase stationary / two-phase rotating) coordinate transformation, and the fundamental current is obtained by low-pass filtering the current signal. The harmonic current is obtained by subtracting the fundamental current from the current signal. Among them, the current signal is actually the d-axis current I of the output current in the dq coordinate system. d and q-axis current I q .

[0071] Step S312, setting the harmonic current reference value to zero to obtain an error signal, wherein the error signal is essentially the difference between the harmonic current and zero, that is, the error signal is obtained by subtracting the harmonic current from zero.

[0072] Step S4 may include the following sub-steps:

[0073] Step S411, the error signal is subjected to coordinate transformation of multiple coordinate systems to obtain an error signal in each coordinate system. For example, the harmonic current error signal is subjected to Park transformation of multiple coordinate systems to obtain error signals in multiple coordinate systems.

[0074] Step S412, performing closed-loop control on the error signal in each coordinate system to obtain potential instructions corresponding to multiple coordinate systems.

[0075] Step S413, coordinate transformation is performed on the potential instructions of multiple coordinate systems to obtain multiple harmonic potentials in the two-phase stationary coordinate system. For example, Inpark transformation is performed on the potential instructions in multiple coordinate systems to obtain multiple harmonic potentials in the two-phase stationary coordinate system, wherein the angular frequencies of the multiple harmonic potentials are different.

[0076] Step S414, adding up the multiple harmonic potentials of the two-phase stationary coordinate system and performing 2s / 3s (two-phase stationary / three-phase stationary) coordinate transformation to obtain the harmonic compensation potential.

[0077] Please refer to Figure 5a and 5b , including coordinate converters 1TR1 to 1TR12, low-pass filters LPF and current regulators 2TR1 to 2TR5. The coordinate converter 1TR1 receives the output current I abc and angle signal θ, and the output current I abc The d-axis current signal I is obtained by transforming the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq (3s / 2r coordinate transformation). d and the q-axis current signal I q In another embodiment, the coordinate transformer 1TR1 receives the output current I abc and angle signal θ, and the output current I abc First, it is transformed from the three-phase stationary coordinate system abc to the two-phase stationary coordinate system αβ (3s / 2s coordinate transformation), and then transformed from the two-phase stationary coordinate system αβ to the two-phase rotating coordinate system dq (2s / 2r coordinate transformation). d and I q Filter and extract the fundamental current I df and I qf , using the total current signal I d and I q Subtract the fundamental current I df and I qf Get the harmonic current I dh and I qh The given value of harmonic current is 0, and the feedback value of harmonic current is I dh and I qh , and get the error signal I de and I qe .

[0078] The coordinate converter 1TR2 converts the harmonic current error signal I de and I qe After the transformation from the positive sequence rotating coordinate system to the negative sequence rotating coordinate system, the dq axis component I of the error signal in the negative sequence coordinate system is obtained. de2 and I qe2 The current regulator 2TR1 can be a proportional-integral regulator. The current regulator 2TR1 has a proportional-integral regulator for the dq axis component I de2 and I qe2 Perform proportional integral (PI) closed-loop regulation to obtain the potential command E in the negative sequence coordinate system d2 and E q2The coordinate converter 1TR3 converts the negative sequence potential command E according to the angle -θ. d2 and E q2 After the transformation from the negative-sequence rotating coordinate system to the two-phase stationary coordinate system, the negative-sequence potential E in the two-phase stationary coordinate system is obtained. α2 and E β2 It should be noted that the present invention needs to suppress the negative sequence component in the output current, that is, harmonic control includes control of the negative sequence component, and the frequency of the actual negative sequence component is also ω, for example, 50HZ, which is the fundamental negative sequence component.

[0079] The coordinate converter 1TR4 converts the harmonic current error signal I de and I qe After the transformation from the positive sequence rotating coordinate system to the positive sequence fifth order rotating coordinate system, the dq axis component I of the harmonic current error in the positive sequence fifth order coordinate system is obtained. de4 and I qe4 The current regulator 2TR2 can be an integral regulator. The current regulator 2TR2 is an integral regulator for the dq axis component I de4 and I qe4 Perform integral (I) closed-loop regulation to obtain the potential command E in the positive sequence 5th coordinate system d4 and E q4 The coordinate converter 1TR5 converts the positive sequence 5th potential command E according to the angle 5θ. d4 and E q4 After the transformation from the positive sequence fifth-order rotating coordinate system to the two-phase stationary coordinate system, the positive sequence fifth-order harmonic potential E in the two-phase stationary coordinate system is obtained. α4 and E β4 .

[0080] The coordinate converter 1TR6 converts the harmonic current error signal I de and I qe After the transformation from the positive sequence rotating coordinate system to the negative sequence 5th order rotating coordinate system, the dq axis component I of the error signal in the negative sequence 5th order coordinate system is obtained. de5 and I qe5 The current regulator 2TR3 can be an integral regulator. The current regulator 2TR3 is for the dq axis component I de5 and I qe5 Perform integral (I) closed-loop regulation to obtain the potential command E in the negative sequence 5th coordinate system d5 and E q5 The coordinate converter 1TR7 converts the negative sequence 5th potential command E to -5θ. d5 and E q5 After the transformation from the negative sequence fifth harmonic rotating coordinate system to the two-phase stationary coordinate system, the negative sequence fifth harmonic potential E in the two-phase stationary coordinate system is obtained. α5 and E β5 .

[0081] The coordinate converter 1TR8 converts the harmonic current error signal I de and I qe After the transformation from the positive sequence rotating coordinate system to the positive sequence 7th rotating coordinate system, the dq axis component I of the error signal in the positive sequence 7th coordinate system is obtained. de6 and I qe6 The current regulator 2TR4 can be an integral regulator. The current regulator 2TR4 is an integral regulator for the dq axis component I de6 and I qe6 Perform integral (I) closed-loop regulation to obtain the potential command E in the positive sequence 7th coordinate system d6 and E q6 The coordinate converter 1TR9 converts the positive sequence 7th potential command E according to the angle 7θ. d6 and E q6 After the transformation from the positive sequence 7th rotating coordinate system to the two-phase stationary coordinate system, the positive sequence 7th harmonic potential E in the two-phase stationary coordinate system is obtained. α6 and E β6 .

[0082] The coordinate converter 1TR10 converts the harmonic current error signal I de and I qe After the transformation from the positive sequence rotating coordinate system to the negative sequence 7th rotating coordinate system, the dq axis component I of the harmonic current error in the negative sequence 7th coordinate system is obtained. de7 and I qe7 The current regulator 2TR5 can be an integral regulator. The current regulator 2TR5 has an integral regulator for the dq axis component I de7 and I qe7 Perform integral (I) closed-loop regulation to obtain the potential command E in the negative sequence 7th coordinate system d7 and E q7 The coordinate converter 1TR11 converts the negative sequence 7th potential command E to -7θ. d7 and E q7 After the transformation from the negative-sequence seventh-order rotating coordinate system to the two-phase stationary coordinate system, the negative-sequence seventh-order harmonic potential E in the two-phase stationary coordinate system is obtained. α7 and E β7 .

[0083] Add the negative sequence potential and each harmonic potential to obtain the total harmonic potential E in the two-phase stationary coordinate system. hα and E hβ The coordinate converter 1TR12 converts the harmonic potential E in the two-phase stationary coordinate system hα and E hβ The harmonic compensation potential E is obtained by transforming the two-phase stationary coordinate system to the three-phase stationary coordinate system. habc . Harmonic compensation potential E habc With fundamental potential E abc Add up to get the control potential.

[0084] Figure 6 is another control step flow chart of harmonic current in grid-connected mode, specifically, as follows: Figure 6 As shown, step S3 may include the following sub-steps:

[0085] Step S321, perform 3s / 2r (three-phase stationary / two-phase rotating) coordinate transformation on the output current to obtain a current signal, perform low-pass filtering on the current signal to obtain a fundamental current, and subtract the fundamental current from the current signal to obtain a harmonic current. The current signal is essentially the d-axis current Id and the q-axis current Iq of the output current in the dq coordinate system.

[0086] Step S322: perform coordinate transformation of multiple coordinate systems on the harmonic current to obtain harmonic currents corresponding to the multiple coordinate systems. For example, perform Park transformation of multiple coordinate systems on the harmonic current to obtain harmonic currents in multiple coordinate systems.

[0087] Step S323, setting the harmonic current reference value in each coordinate system to zero, and obtaining an error signal in each coordinate system. The error signal in each coordinate system is essentially the difference between the harmonic current in each coordinate system and zero, that is, zero minus the harmonic current to obtain the error signal.

[0088] Step S4 may include the following sub-steps:

[0089] Step S421, performing closed-loop control on the error signal in each coordinate system to obtain potential instructions corresponding to multiple coordinate systems.

[0090] Step S422: coordinate transformation is performed on the potential command to obtain multiple harmonic potentials in the two-phase stationary coordinate system. For example, the potential command in each coordinate system is subjected to Inpark transformation to obtain harmonic potentials, including negative sequence potentials.

[0091] Step S423, adding up the multiple harmonic potentials in the two-phase stationary coordinate system and performing a 2s / 3s (two-phase stationary / three-phase stationary) coordinate transformation to obtain a harmonic compensation potential.

[0092] visible, Figure 5a In the process, the harmonic current reference value is first set to zero to obtain an error signal, the error signal is subjected to coordinate transformation to obtain error transformation signals in multiple coordinate systems, and the error transformation signal in each coordinate system is subjected to closed-loop regulation to output a potential compensation signal. Figure 6 In the method, the harmonic current is first transformed into coordinates to obtain harmonic current transformation signals in multiple coordinate systems, the reference value of the harmonic current transformation signal in each coordinate system is set to zero to obtain an error signal in each coordinate system, and the error signal in each coordinate system is closed-loop regulated to output a potential compensation signal.

[0093] Figure 6 The control architecture corresponding to the control process in Figure 5b Similar, the difference is: get the dq axis component I of the harmonic current dh and I qh After that, the dq axis component I dh and I qh Input coordinate converters 1TR2, 1TR4, 1TR6, 1TR8 and 1TR10. Coordinate converter 1TR2 converts the harmonic current I dh and I qh After the transformation from the positive sequence rotating coordinate system to the negative sequence rotating coordinate system, the dq axis component I of the harmonic current in the negative sequence coordinate system is obtained. dh2 and I qh2 In the negative sequence coordinate system, the harmonic current set value is 0, and the harmonic current feedback value is I dh2 and I qh2 , we can get the dq axis component I of the error signal in the negative sequence coordinate system de2 and I qe2 The coordinate converter 1TR4 converts the harmonic current I dh and I qh After the transformation from the positive sequence rotating coordinate system to the positive sequence 5th rotating coordinate system, the dq axis component I of the harmonic current in the positive sequence 5th coordinate system is obtained. dh4 and I qh4 In the positive sequence 5th coordinate system, the harmonic current set value is 0, and the harmonic current feedback value is I dh4 and I qh4 , and obtain the dq-axis component I of the harmonic current error in the positive sequence 5th coordinate system de4 and I qe4 The coordinate converter 1TR6 converts the harmonic current I dh and I qh After the transformation from the positive sequence rotating coordinate system to the negative sequence 5th rotating coordinate system, the dq axis component I of the harmonic current in the negative sequence 5th coordinate system is obtained. dh5 and I qh5 In the negative sequence 5th coordinate system, the harmonic current set value is 0, and the harmonic current feedback value is I dh5 and I qh5 , we get the dq axis component I of the error signal in the negative sequence 5th coordinate system de5 and I qe5 The coordinate converter 1TR8 converts the harmonic current I dh and I qh After the transformation from the positive sequence rotating coordinate system to the positive sequence 7th rotating coordinate system, the dq axis component I of the harmonic current in the positive sequence 7th coordinate system is obtained. dh6 and I qh6 In the positive sequence 7th coordinate system, the harmonic current set value is 0, and the harmonic current feedback value is I dh6 and Iqh6 , the dq-axis component I of the harmonic current error in the positive sequence 7th coordinate system is obtained de6 and I qe6 The coordinate converter 1TR10 converts the harmonic current I dh and I qh After the transformation from the positive sequence rotating coordinate system to the negative sequence 7th rotating coordinate system, the dq axis component I of the harmonic current in the negative sequence 7th coordinate system is obtained. dh7 and I qh7 In the negative sequence 7th coordinate system, the harmonic current set value is 0, and the harmonic current feedback value is I dh7 and I qh7 , we get the dq axis component I of the error signal in the negative sequence 7th coordinate system de7 and I qe7 For other similar parts, please refer to Figure 5b The description is not repeated here.

[0094] It should be noted that the above-mentioned multiple coordinate systems include a negative sequence coordinate system, a positive and negative fifth order coordinate system, and a positive and negative seventh order coordinate system, so as to achieve the effect of suppressing negative sequence current, positive and negative fifth order harmonic current, and positive and negative seventh order harmonic current, but the present invention is not limited to this and may also include coordinate systems of other frequencies.

[0095] Figure 7a Another control step flow chart of harmonic current in grid-connected mode is shown in FIG. Figure 7b for Figure 7a The control architecture corresponding to the control flow in Figure 5a compared to, Figure 7a The following is a detailed description of the differences, and the same parts can be found in step S4. Figure 5a .

[0096] Step S4 may include the following sub-steps:

[0097] Step S451, performing coordinate transformation on the error signal to obtain an error signal in a two-phase stationary coordinate system.

[0098] Step S452, inputting the error signal in the two-phase stationary coordinate system into a plurality of control modules to perform closed-loop control, thereby obtaining a plurality of harmonic potentials in the two-phase stationary coordinate system;

[0099] Step S453, adding up the multiple harmonic potentials in the two-phase stationary coordinate system and performing a 2s / 3s (two-phase stationary / three-phase stationary) coordinate transformation to obtain the harmonic compensation potential.

[0100] Among them, Figure 7bAs shown, multiple control modules include a PR (proportional resonance) control module and two R (resonance) control modules, wherein the PR control module outputs a negative-sequence potential, i.e., the frequency of the negative-sequence potential is ω, for example, 50HZ, and the two R control modules respectively output the 5th harmonic potential and the 7th harmonic potential, i.e., the frequencies of the harmonic potential are 5ω and 7ω, for example, 250HZ and 350HZ.

[0101] Please refer to Figure 7a and Figure 7b , including coordinate converters 3TR1 to 3TR3, low-pass filters LPF and current regulators 4TR1 to 4TR3. Among them, the current regulators 4TR1 to 4TR3 are PR control modules and two R control modules respectively. The coordinate converter 3TR1 receives the output current I abc and angle signal θ, and the output current I abc The d-axis current signal I is obtained by transforming the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq (3s / 2r coordinate transformation). d and the q-axis current signal I q In another embodiment, the coordinate transformer 3TR1 receives the output current I abc and angle signal θ, and the output current I abc First, it is transformed from the three-phase stationary coordinate system abc to the two-phase stationary coordinate system αβ (3s / 2s coordinate transformation), and then transformed from the two-phase stationary coordinate system αβ to the two-phase rotating coordinate system dq (2s / 2r coordinate transformation). d and I q Filter and extract the fundamental current I df and I qf , using the total current signal I d and I q Subtract the fundamental current I df and I qf Get the dq axis component I of the harmonic current dh and I qh The given value of harmonic current is 0, and the feedback value of harmonic current is I dh and I qh , and get the error signal I de and I qe .

[0102] The coordinate converter 3TR2 converts the harmonic current error signal I de and I qe After Inpark coordinate transformation, the αβ axis component I of the harmonic current error in the two-phase stationary coordinate system is obtained. αe and I βe The current regulator 4TR1 can be a proportional resonant (PR) regulator. The current regulator 4TR1 is Iαe and I βe Perform PR closed-loop regulation to obtain the negative sequence potential E in the two-phase stationary coordinate system. α2 and E β2 , where the resonant frequency of PR regulation is ω, for example, 50HZ. The current regulator 4TR2 can be a resonant regulator. The current regulator 4TR2 regulates I in the two-phase stationary coordinate system. αe and I βe Perform R closed-loop regulation to obtain the fifth harmonic potential E in the two-phase stationary coordinate system. α5 and E β5 , where the resonant frequency of the resonant regulation is 5ω. The current regulator 4TR3 can be the resonant regulator for the I αe and I βe Perform R closed-loop regulation to obtain the 7th harmonic potential E in the two-phase stationary coordinate system. α7 and E β7 , where the resonant frequency of the resonance adjustment is 7ω.

[0103] Add the negative sequence potential and each harmonic potential to obtain the total harmonic potential E in the two-phase stationary coordinate system. hα and E hβ The coordinate converter 3TR3 converts the harmonic potential E in the two-phase stationary coordinate system hα and E hβ The harmonic compensation potential E is obtained by transforming the two-phase stationary coordinate system to the three-phase stationary coordinate system. habc . Harmonic compensation potential E habc With fundamental potential E abc Add up to get the control potential.

[0104] In other embodiments, Figure 7b The control block diagram in can also be changed to: Get the dq axis component I of the harmonic current dh and I qh After that, it is first input into the coordinate converter 3TR2 for Inpark transformation to obtain the αβ axis component I of the harmonic current in the two-phase stationary coordinate system. αh and I βh The given value of harmonic current is 0, and the feedback value is I αh and I βh , and obtain the error signal I in the two-phase stationary coordinate system αe and I βe , for I in the two-phase stationary coordinate system αe and I βe Closed-loop regulation is performed to obtain various harmonic potentials in a two-phase stationary coordinate system, wherein the frequencies of the various harmonic potentials are different.

[0105] When the three-phase AC system operates in off-grid mode, especially with asymmetric or nonlinear loads, harmonic voltage control is activated and harmonic current control is shielded. Therefore, in step S3, the output signal corresponds to the output voltage, and the harmonic component corresponds to the harmonic voltage; the harmonic voltage in the output voltage of the inverter 201 is extracted, and the harmonic voltage error signal is obtained according to the harmonic voltage reference value, and the error signal is adjusted to obtain the harmonic compensation potential.

[0106] The three-phase AC system operates in off-grid mode, also known as operating in island mode.

[0107] Figure 8a The control flow chart of harmonic voltage in off-grid mode is as follows: Figure 8b for Figure 8a The control architecture corresponding to the control flow in . Specifically, Figure 8a As shown, step S3 may include the following sub-steps:

[0108] Step S331, perform 3s / 2r (three-phase stationary / two-phase rotating) coordinate transformation on the output voltage to obtain a voltage signal, perform low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtract the fundamental voltage from the voltage signal to obtain a harmonic voltage. The voltage signal is essentially the d-axis voltage U of the output voltage in the dq coordinate system. d and q-axis voltage U q .

[0109] Step S332, setting the harmonic voltage reference value to zero to obtain an error signal, wherein the error signal is essentially the difference between the harmonic voltage and zero, that is, the error signal is obtained by subtracting the harmonic voltage from zero.

[0110] Step S4 may include the following sub-steps:

[0111] Step S431, the error signal is subjected to coordinate transformation of multiple coordinate systems to obtain an error signal in each coordinate system. For example, the error signal is subjected to Park transformation to obtain error signal components of multiple coordinate systems, so as to perform closed-loop control on the error signal components in each coordinate system.

[0112] Step S432, performing closed-loop control on the error signal in each coordinate system to obtain potential instructions corresponding to multiple coordinate systems.

[0113] Step S433, respectively transform the potential instructions of multiple coordinate systems to obtain multiple harmonic potentials in the two-phase stationary coordinate system; for example, respectively perform Inpark transformation on the potential instructions in each coordinate system to obtain multiple harmonic potentials in the two-phase stationary coordinate system, wherein the angular frequencies of the multiple harmonic potentials are different.

[0114] Step S434, adding up the multiple harmonic potentials of the two-phase stationary coordinate system and performing a 2s / 3s (two-phase stationary / three-phase stationary) coordinate transformation to obtain the harmonic compensation potential.

[0115] Please refer to Figure 8a and Figure 8b , including coordinate converters 5TR1 to 5TR12, low-pass filters LPF and voltage regulators 6TR1 to 6TR5. The coordinate converter 5TR1 receives the output voltage U abc and angle signal θ, and the output voltage U abc The d-axis voltage signal U is obtained by transforming the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq (3s / 2r coordinate transformation). d and q-axis voltage signal U q In another embodiment, the coordinate converter 5TR1 receives the output voltage U abc and angle signal θ, and the output voltage U abc First, it is transformed from the three-phase stationary coordinate system abc to the two-phase stationary coordinate system αβ (3s / 2s coordinate transformation), and then transformed from the two-phase stationary coordinate system αβ to the two-phase rotating coordinate system dq (2s / 2r coordinate transformation). d and U q Filter and extract the fundamental voltage U df and U qf , using the total voltage signal U d and U q Subtract the fundamental voltage U df and U qf Get the harmonic voltage U dh and U qh The given value of harmonic voltage is 0, and the feedback value of harmonic voltage is U dh and U qh , and get the error signal U de and U qe .

[0116] The coordinate converter 5TR2 converts the error signal U to de and U qe After the transformation from the positive sequence rotating coordinate system to the negative sequence rotating coordinate system, the dq axis component U of the error signal in the negative sequence coordinate system is obtained. de2 and U qe2 The voltage regulator 6TR1 can be a proportional-integral regulator. The voltage regulator 6TR1 is sensitive to the dq axis component U de2 and U qe2 Perform proportional integral (PI) closed-loop regulation to obtain the potential command E in the negative sequence coordinate system d2 and E q2 The coordinate converter 5TR3 converts the negative sequence potential command E according to the angle -θ.d2 and E q2 After the transformation from the negative-sequence rotating coordinate system to the two-phase stationary coordinate system, the negative-sequence potential E in the two-phase stationary coordinate system is obtained. α2 and E β2 It should be noted that the present invention needs to suppress the negative sequence component in the output voltage, that is, harmonic control includes control of the negative sequence component, and the frequency of the actual negative sequence component is also ω, for example, 50HZ, which is the fundamental negative sequence component.

[0117] The coordinate converter 5TR4 converts the harmonic voltage error signal U de and U qe After the transformation from the positive sequence rotating coordinate system to the positive sequence fifth order rotating coordinate system, the dq axis component U of the harmonic voltage error in the positive sequence fifth order coordinate system is obtained. de4 and U qe4 The voltage regulator 6TR2 can be an integral regulator. The voltage regulator 6TR2 is de4 and U qe4 Perform integral (I) closed-loop regulation to obtain the potential command E in the positive sequence 5th coordinate system d4 and E q4 The coordinate converter 5TR5 converts the positive sequence 5th potential command E according to the angle 5θ. d4 and E q4 After the transformation from the positive sequence fifth-order rotating coordinate system to the two-phase stationary coordinate system, the positive sequence fifth-order harmonic potential E in the two-phase stationary coordinate system is obtained. α4 and E β4 .

[0118] The coordinate converter 5TR6 converts the harmonic voltage error signal U into de and U qe After the transformation from the positive sequence rotating coordinate system to the negative sequence 5th order rotating coordinate system, the dq axis component U of the error signal in the negative sequence 5th order coordinate system is obtained. de5 and U qe5 The voltage regulator 6TR3 can be an integral regulator. The voltage regulator 6TR3 is de5 and U qe5 Perform integral (I) closed-loop regulation to obtain the potential command E in the negative sequence 5th coordinate system d5 and E q5 The coordinate converter 5TR7 converts the negative sequence 5th potential command E to -5θ. d5 and E q5 After the transformation from the negative sequence fifth harmonic rotating coordinate system to the two-phase stationary coordinate system, the negative sequence fifth harmonic potential E in the two-phase stationary coordinate system is obtained. α5 and E β5 .

[0119] The coordinate converter 5TR8 converts the harmonic voltage error signal U de and U qe After the transformation from the positive sequence rotating coordinate system to the positive sequence 7th rotating coordinate system, the dq axis component U of the error signal in the positive sequence 7th coordinate system is obtained. de6 and U qe6 The voltage regulator 6TR4 can be an integral regulator. The voltage regulator 6TR4 is effective for the dq axis component U de6 and U qe6 Perform integral (I) closed-loop regulation to obtain the potential command E in the positive sequence 7th coordinate system d6 and E q6 The coordinate converter 5TR9 converts the positive sequence 7th potential command E according to the angle 7θ. d6 and E q6 After the transformation from the positive sequence 7th rotating coordinate system to the two-phase stationary coordinate system, the positive sequence 7th harmonic potential E in the two-phase stationary coordinate system is obtained. α6 and E β6 .

[0120] The coordinate converter 5TR10 converts the harmonic voltage error signal U into de and U qe After the transformation from the positive sequence rotating coordinate system to the negative sequence 7th rotating coordinate system, the dq axis component U of the harmonic voltage error in the negative sequence 7th coordinate system is obtained. de7 and U qe7 The voltage regulator 6TR5 can be an integral regulator. The voltage regulator 6TR5 is sensitive to the dq axis component U de7 and U qe7 Perform integral (I) closed-loop regulation to obtain the potential command E in the negative sequence 7th coordinate system d7 and E q7 The coordinate converter 5TR11 converts the negative sequence 7th potential command E to -7θ. d7 and E q7 After the transformation from the negative-sequence seventh-order rotating coordinate system to the two-phase stationary coordinate system, the negative-sequence seventh-order harmonic potential E in the two-phase stationary coordinate system is obtained. α7 and E β7 .

[0121] Add the negative sequence potential and each harmonic potential to obtain the total harmonic potential E in the two-phase stationary coordinate system. hα and E hβ The coordinate converter 5TR12 converts the harmonic potential E in the two-phase stationary coordinate system hα and E hβ The harmonic compensation potential E is obtained by transforming the two-phase stationary coordinate system to the three-phase stationary coordinate system. habc . Harmonic compensation potential E habc With fundamental potential E abc Add up to get the control potential.

[0122] Fig. 9 FIG. 1 is another flow chart of control steps of harmonic voltage in off-grid mode. Specifically, Fig. 9 As shown, step S3 may include the following sub-steps:

[0123] Step S341, perform 3s / 2r coordinate transformation on the output voltage to obtain a voltage signal, perform low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtract the fundamental voltage from the voltage signal to obtain a harmonic voltage. The voltage signal is essentially the d-axis current Id and the q-axis current Iq of the output current in the dq coordinate system.

[0124] Step S342: perform coordinate transformation of multiple coordinate systems on the harmonic voltage to obtain harmonic voltages corresponding to the multiple coordinate systems. For example, perform Park transformation of multiple coordinate systems on the harmonic voltage to obtain harmonic voltages in multiple coordinate systems.

[0125] Step S343, setting the reference value of the harmonic voltage component in each coordinate system to zero, and obtaining an error signal in each coordinate system. The error signal in each coordinate system is actually the difference between the harmonic voltage and zero in each coordinate system, that is, zero minus the harmonic voltage to obtain the error signal.

[0126] Step S4 may include the following sub-steps:

[0127] Step S441, performing closed-loop control on the error signal in each coordinate system to obtain potential instructions corresponding to multiple coordinate systems;

[0128] Step S442: coordinate transformation is performed on the potential command to obtain multiple harmonic potentials in the two-phase stationary coordinate system. For example, the potential command in each coordinate system is subjected to Inpark transformation to obtain harmonic potentials, including negative sequence potentials.

[0129] Step S443, adding up the multiple harmonic potentials in the two-phase stationary coordinate system and performing a 2s / 3s (two-phase stationary / three-phase stationary) coordinate transformation to obtain the harmonic compensation potential.

[0130] visible, Figure 8a and Fig. 9 The difference between the steps in Figure 8a In each step, the harmonic voltage reference value is first set to zero to obtain an error signal, the error signal is subjected to coordinate transformation to obtain error transformation signals in multiple coordinate systems, and the error transformation signal in each coordinate system is subjected to closed-loop regulation to output a potential compensation signal. Fig. 9In each step, the harmonic voltage is first transformed into coordinates to obtain harmonic voltage transformation signals in multiple coordinate systems, the reference value of the harmonic voltage transformation signal in each coordinate system is set to zero to obtain the error signal in each coordinate system, and the error signal in each coordinate system is closed-loop regulated to output the potential compensation signal. Both methods can ultimately obtain the harmonic compensation potential.

[0131] Fig. 9 The control architecture corresponding to the control process in Figure 8b Similar, the difference is: get the dq axis component U of the harmonic voltage dh and U qh After that, directly convert the dq axis component U dh and U qh Input coordinate converters 5TR2, 5TR4, 5TR6, 5TR8 and 5TR10. Coordinate converter 5TR2 converts the harmonic voltage U dh and U qh After the transformation from the positive sequence rotating coordinate system to the negative sequence rotating coordinate system, the dq axis component U of the harmonic voltage in the negative sequence coordinate system is obtained. dh2 and U qh2 In the negative sequence coordinate system, the harmonic voltage set value is 0, and the harmonic voltage feedback value is U dh2 and U qh2 , we can get the dq axis component U of the error signal in the negative sequence coordinate system de2 and U qe2 The coordinate converter 5TR4 converts the harmonic voltage U dh and U qh After the transformation from the positive sequence rotating coordinate system to the positive sequence 5th rotating coordinate system, the dq axis component U of the harmonic voltage in the positive sequence 5th coordinate system is obtained. dh4 and U qh4 In the positive sequence 5th coordinate system, the harmonic voltage set value is 0, and the harmonic voltage feedback value is U dh4 and U qh4 , and obtain the dq-axis component U of the harmonic voltage error in the positive sequence 5th coordinate system de4 and U qe4 The coordinate converter 5TR6 converts the harmonic voltage U dh and U qh After the transformation from the positive sequence rotating coordinate system to the negative sequence 5th rotating coordinate system, the dq axis component U of the harmonic voltage in the negative sequence 5th coordinate system is obtained. dh5 and U qh5 In the negative sequence 5th coordinate system, the harmonic voltage set value is 0, and the harmonic voltage feedback value is U dh5 and U qh5 , we get the dq axis component U of the error signal in the negative sequence 5th coordinate system de5 and U qe5The coordinate converter 5TR8 converts the harmonic voltage U dh and U qh After the transformation from the positive sequence rotating coordinate system to the positive sequence 7th rotating coordinate system, the dq axis component U of the harmonic voltage in the positive sequence 7th coordinate system is obtained. dh6 and U qh6 In the positive sequence 7th coordinate system, the harmonic voltage set value is 0, and the harmonic voltage feedback value is U dh6 and U qh6 , the dq-axis component U of the harmonic voltage error in the positive sequence 7th coordinate system is obtained de6 and U qe6 The coordinate converter 5TR10 converts the harmonic voltage U dh and U qh After the transformation from the positive sequence rotating coordinate system to the negative sequence 7th rotating coordinate system, the dq axis component U of the harmonic voltage in the negative sequence 7th coordinate system is obtained. dh7 and U qh7 In the negative sequence 7th coordinate system, the harmonic voltage set value is 0, and the harmonic voltage feedback value is U dh7 and U qh7 , the dq-axis component U of the harmonic voltage error in the negative sequence 7th coordinate system is obtained de7 and U qe7 For other similar parts, please refer to Figure 8b The description is not repeated here.

[0132] It should be noted that the above-mentioned multiple coordinate systems include a negative sequence coordinate system, a positive and negative fifth order coordinate system, and a positive and negative seventh order coordinate system, so as to achieve the effect of suppressing negative sequence voltage, positive and negative fifth order harmonic voltage, and positive and negative seventh order harmonic voltage, but the present invention is not limited to this and may also include coordinate systems of other frequencies.

[0133] Fig.10 Another control architecture for harmonic voltage in off-grid mode. Figure 8a compared to, Fig.10 The corresponding step S4 in the control flow is different. Only the differences are described in detail below. For the same parts, please refer to Figure 8a .

[0134] Step S4 may include the following sub-steps:

[0135] Step S451, performing coordinate transformation on the error signal to obtain an error signal in a two-phase stationary coordinate system.

[0136] Step S452 , inputting the error signal in the two-phase stationary coordinate system into a plurality of control modules to perform closed-loop control, thereby obtaining a plurality of harmonic potentials in the two-phase stationary coordinate system.

[0137] Step S453, adding up the multiple harmonic potentials in the two-phase stationary coordinate system and performing a 2s / 3s (two-phase stationary / three-phase stationary) coordinate transformation to obtain the harmonic compensation potential.

[0138] Among them, Fig.10 As shown, multiple control modules include a PR (proportional resonance) control module and two R (resonance) control modules, wherein the PR control module outputs a negative-sequence potential, i.e., the frequency of the negative-sequence potential is ω, for example, 50HZ, and the two R control modules respectively output the 5th harmonic potential and the 7th harmonic potential, i.e., the frequencies of the harmonic potential are 5ω and 7ω, for example, 250HZ and 350HZ.

[0139] Please refer to Fig.10 , including coordinate converters 7TR1 to 7TR3, low-pass filters LPF and voltage regulators 8TR1 to 8TR3. The coordinate converter 7TR1 receives the output voltage U abc and angle signal θ, and the output voltage U abc The d-axis voltage signal U is obtained by transforming the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq (3s / 2r coordinate transformation). d and q-axis voltage signal U q In another embodiment, the coordinate converter 7TR1 receives the output voltage U abc and angle signal θ, and the output voltage U abc First, it is transformed from the three-phase stationary coordinate system abc to the two-phase stationary coordinate system αβ (3s / 2s coordinate transformation), and then transformed from the two-phase stationary coordinate system αβ to the two-phase rotating coordinate system dq (2s / 2r coordinate transformation). d and U q Filter and extract the fundamental voltage U df and U qf , using the total voltage signal U d and U q Subtract the fundamental voltage U df and U qf Get the dq axis component U of the harmonic voltage dh and U qh The given value of harmonic voltage is 0, and the feedback value of harmonic voltage is U dh and U qh , and get the error signal U de and U qe .

[0140] The coordinate converter 7TR2 converts the harmonic voltage error signal U into de and U qe After Inpark coordinate transformation, the αβ axis component U of the error signal in the two-phase stationary coordinate system is obtained. αe and Uβe The voltage regulator 8TR1 can be a proportional resonant (PR) regulator. The voltage regulator 8TR1 is used for U αe and U βe Perform PR closed-loop regulation to obtain the negative sequence potential E in the two-phase stationary coordinate system. α2 and E β2 , where the resonant frequency of PR regulation is ω, for example, 50HZ. The voltage regulator 8TR2 can be a resonant regulator. The voltage regulator 8TR2 is U in the two-phase stationary coordinate system. αe and U βe Perform R closed-loop regulation to obtain the fifth harmonic potential E in the two-phase stationary coordinate system. α5 and E β5 , where the resonant frequency of the resonant regulation is 5ω. The voltage regulator 8TR3 can be a resonant regulator. The voltage regulator 8TR3 is U in the two-phase stationary coordinate system. αe and U βe Perform R closed-loop regulation to obtain the 7th harmonic potential E in the two-phase stationary coordinate system. α7 and E β7 , where the resonant frequency of the resonance adjustment is 7ω.

[0141] Add the negative sequence potential and each harmonic potential to obtain the total harmonic potential E in the two-phase stationary coordinate system. hα and E hβ The coordinate converter 7TR3 converts the harmonic potential E in the two-phase stationary coordinate system hα and E hβ The harmonic compensation potential E is obtained by transforming the two-phase stationary coordinate system to the three-phase stationary coordinate system. habc . Harmonic compensation potential E habc With fundamental potential E abc Add up to get the control potential.

[0142] In other embodiments, Fig.10 The control block diagram in can also be modified as follows: The dq axis component U of the harmonic voltage is obtained dh and U qh After that, it is first input to the coordinate converter 7TR2 for Inpark transformation to obtain the αβ axis component U of the harmonic voltage in the two-phase stationary coordinate system. αh and U βh The given value of harmonic voltage is 0, and the feedback value is U αh and U βh , and obtain the error signal U in the two-phase stationary coordinate system αe and U βe , for U in the two-phase stationary coordinate system αe and U βe Perform closed-loop regulation to obtain the harmonic potentials of the two-phase stationary coordinate system. For other similar parts, please refer to Fig.10 The description of the steps is not repeated here. For the specific step flow chart, please refer to Fig. 9 , I will not go into details here.

[0143] Fig.11 Another schematic diagram of the three-phase AC system. Figure 2 The three-phase AC system shown in Fig.11 The three-phase AC system shown in the figure has an island detection function added. Fig.11 As shown, the control device in the three-phase AC system further includes a fourth control unit 209, which is electrically connected to the first control unit 203 and is used to implement island detection. The first control unit includes a droop control, and the output of the fourth control unit 209 is superimposed on at least one given value of the droop control.

[0144] Fig.12 The flowchart of the steps of the island determination method is as follows: Fig.12 As shown, the island determination method includes:

[0145] Step A1, obtaining the output voltage U of the three-phase AC system abc The parameter M and its corresponding steady-state value M within a certain duration 0 .

[0146] Step A2: according to the parameter M and the steady-state value M 0 Get interference signal.

[0147] Step A3, superimposing the interference signal on at least one given value of the droop control.

[0148] Step A4, detecting the parameter M after adding the interference signal, when the parameter M is greater than the upper limit or less than the lower limit, it is determined that an island occurs.

[0149] In step A1, the output voltage U abc The parameter M is the voltage amplitude U or the voltage angular frequency ω, which can be obtained by Figure 3 The phase-locked device in the output voltage U abc Phase lock is performed to obtain the steady-state value M 0 The parameter M is obtained by filtering for a duration, and the duration can be set according to the actual situation. Specifically, when the parameter M is the voltage amplitude U, the steady-state value M 0 Corresponding to U 0 , which can be obtained by filtering the voltage amplitude U for a duration, and can be corresponded to the average value of the voltage amplitude within the duration; when the parameter M is the angular frequency ω, the steady-state value M 0 Corresponding to ω 0 , which can be obtained by filtering the angular frequency ω over a duration, can correspond to the average value of the angular frequency over the duration.

[0150] Step A2 further comprises the sub-steps of:

[0151] Step A21, compare steady-state value M 0 and parameter M.

[0152] Step A22, when the steady-state value M 0 When it is not equal to parameter M, an increment δ is added to parameter M to obtain a new parameter M'.

[0153] Step A23, calculate the steady-state value M 0 The error with the new parameter M' is negated to obtain the interference signal.

[0154] Among them, when the steady-state value M 0 When it is greater than the parameter M, the increment δ is negative and the steady-state value M 0 The error with the new parameter M' is positive, the interference signal is negative, and the reverse disturbance is superimposed on the droop control setting. abc Clamped by the power grid, the real-time parameter M will not change or change slightly, the given change of the droop control is small, and the reverse disturbance effect is not obvious. If an island occurs, the given droop control is superimposed with the reverse disturbance, and the real-time parameter M decreases, then the absolute value of the interference signal increases, the reverse disturbance increases, and the real-time parameter M further decreases, eventually reaching the lower limit value, and an island is determined.

[0155] On the other hand, when the steady-state value M 0 When it is less than the parameter M, the increment δ is positive and the steady-state value M 0 The error with the new parameter M' is negative, the interference signal is positive, and a positive disturbance is superimposed on the droop control setting. abc Clamped by the power grid, the real-time parameter M will not change or change slightly, the given value of the droop control will change slightly, and the positive disturbance effect will not be obvious. If an island occurs, the given value of the droop control is superimposed with the positive disturbance, and the real-time parameter M increases, then the interference signal increases, the positive disturbance increases, and the real-time parameter M increases further, eventually reaching the upper limit value, and an island is determined.

[0156] The inverter is subjected to virtual synchronous machine control, which includes droop control. The droop control includes an angular frequency setting and a voltage amplitude setting. When the parameter M is the voltage amplitude U, the interference signal is superimposed on the voltage setting of the droop control. When the parameter M is the angular frequency ω, the interference signal is superimposed on the angular frequency setting of the droop control.

[0157] Fig.13 is a control block diagram corresponding to the first control unit and the fourth control unit. Fig.13 As shown, the fourth control unit 209 obtains the angular frequency ω of the inverter output voltage, and filters the angular frequency ω to obtain a steady-state value ω of the angular frequency 0, can be understood as the average value of the angular frequency over a duration. Compare ω and ω 0 , when the two are not equal, increase or decrease ω by an increment Δω to obtain ω', 0 The interference signal is obtained by negating the error with ω' and injected into the frequency setting of the droop control. If an island occurs, the disturbance superimposed on the frequency setting of the droop control will cause the grid angular frequency to deviate from the rated value and reach the upper or lower limit, thus determining an island.

[0158] like Fig.13 As shown, the increment Δω can be positive or negative. 0 When it is greater than ω, the increment Δω is negative, then ω 0 The error with ω' is negated to get the interference signal ω is , superimposed on the frequency given ω * Obviously, the interference signal ω is is a negative value, which is equivalent to superimposing a small frequency reverse disturbance on the frequency setting of the droop control. 0 When it is less than ω, the increment Δω is positive, then ω 0 The error with ω' is negated to get the interference signal ω is , superimposed on the frequency given ω * Obviously, the interference signal ω is is a positive value, which is equivalent to superimposing a small frequency positive disturbance on the frequency setting of the droop control. Δω takes a small value. In this embodiment, Δω is ±0.01Hz, but the present invention is not limited to this. For example, ω 0 is 50HZ, when ω is 51HZ, Δω is 0.01Hz, ω' is 51.01HZ, ω 0 The error with ω' is -1.01HZ. At this time, the interference signal ω is is 1.01HZ; when ω is 49HZ, Δω is -0.01Hz, ω' is 48.99HZ, ω 0 The error with ω' is 1.01HZ. At this time, the interference signal ω is It is -1.01HZ.

[0159] When 0 When it is greater than ω, the interference signal ω is is a negative value, the frequency setting of droop control is ω * A small negative frequency disturbance is superimposed on the output voltage U abc Clamped by the power grid, its angular frequency ω will not change or change slightly. If an island occurs, the real-time angular frequency ω will gradually decrease due to negative feedback, and the disturbance frequency ω is The absolute value of will gradually increase, and the frequency setting of the droop control after the disturbance is superimposed will gradually decrease, and finally reach the lower frequency limit, and it is judged that an island occurs.

[0160] When 0 When it is less than ω, the interference signal ω is is a positive value, the frequency setting of droop control is ω * A small frequency positive disturbance is superimposed on the output voltage U abc Clamped by the power grid, its angular frequency ω will not change or change slightly. If an island occurs, the real-time angular frequency ω will gradually increase due to the positive feedback effect, and the disturbance frequency ω is It will gradually increase, and the frequency setting of the droop control after the disturbance is superimposed will gradually increase, and finally reach the upper frequency limit, and it is judged that an island occurs.

[0161] Fig.14 is another control block diagram corresponding to the first control unit and the fourth control unit. Fig.14 As shown, the fourth control unit 209 obtains the voltage amplitude U of the inverter output voltage, and filters the voltage amplitude U to obtain the steady-state value U of the voltage amplitude 0 , which can be understood as the average value of the voltage amplitude within a certain duration. Compare U and U 0 , when the two are not equal, increase or decrease U by an increment ΔU to obtain U', and 0 The error with U' is inverted to obtain the interference signal, which is injected into the voltage setting of the droop control. If an island occurs, the disturbance superimposed on the voltage setting of the droop control will cause the grid voltage to deviate from the rated value and reach the upper or lower limit, thus determining an island.

[0162] like Fig.14 As shown, the increment ΔU can be positive or negative. 0 When it is greater than U, the increment ΔU is negative, then U 0 The error with U' is negated to get the interference signal U is , superimposed on the voltage given by U * Obviously, the interference signal U is is a negative value, which is equivalent to superimposing a small voltage reverse disturbance on the voltage setting of the droop control. 0 When it is less than U, the increment ΔU is positive, then U 0 The error with U' is negated to get the interference signal U is , superimposed on the voltage given by U * Obviously, the interference signal U is is a positive value, which is equivalent to superimposing a small positive disturbance of voltage on the voltage setting of droop control. ΔU takes a small value. In this embodiment, ΔU is ±0.1V, but the present invention is not limited to this. For example, U 0 is 200V, when U is 201V, ΔU is 0.1V, U' is 201.1V, U 0The error with U' is -1.1V. At this time, the interference signal U is is 1.1V; when U is 199V, ΔU is -0.1V, U' is 198.9V, U 0 The error with U' is 1.1V. At this time, the interference signal U is is -1.1V.

[0163] WhenU 0 When it is greater than U, the interference signal U is is a negative value, the voltage setting U * A small negative voltage disturbance is superimposed on the output voltage U abc Clamped by the power grid, its voltage U will not change or change slightly. If an island occurs, the real-time voltage U will gradually decrease due to negative feedback, and the disturbance voltage U is The absolute value of will gradually increase, and the voltage setting of the droop control after the disturbance is superimposed will gradually decrease, and finally reach the voltage lower limit, and it is judged that an island occurs.

[0164] WhenU 0 When it is less than U, the interference signal U is is a positive value, the voltage setting U for droop control * A small positive disturbance of voltage is superimposed on the output voltage. abc Clamped by the power grid, its voltage U will not change or change slightly. If an island occurs, the real-time voltage U will gradually increase due to the positive feedback effect, and the disturbance voltage U is It will gradually increase, and the voltage setting of the droop control after the disturbance is superimposed will gradually increase, and finally reach the voltage upper limit, and it is judged that an island occurs.

[0165] The island detection method disclosed in the present invention is simple and has accurate judgment results. By superimposing a positive or reverse interference signal on the voltage setting or frequency setting of the virtual synchronous machine droop control, the voltage or angular frequency is subjected to a continuous small-amplitude positive disturbance or negative disturbance, and the voltage amplitude and angular frequency after the disturbance are compared with the threshold value. When the voltage amplitude and angular frequency are greater than the upper limit value or less than the lower limit value, an island is detected. The present invention can quickly identify the island phenomenon, the result is accurate, the interference signal is small, and the stable operation of the AC system is not affected; the disturbance signal is directly superimposed on the droop setting of the virtual synchronous machine control, and the implementation method is simple.

[0166] like Fig.15As shown, the three-phase AC system may further include a fifth control unit 210, so that the virtual synchronous machine (VSG) of the three-phase AC system may have a secondary voltage and frequency regulation function when operating off-grid. When the virtual synchronous machine is operating off-grid, the load may cause the frequency and amplitude of the voltage to change, causing the output voltage and frequency to deviate from the rated value. By adding closed-loop control of the secondary voltage regulation and the secondary frequency regulation, the voltage amplitude and frequency may be adjusted to the rated voltage amplitude and frequency.

[0167] Specifically, the angular frequency ω of the output voltage is PI-regulated according to the rated frequency to obtain a first given value, and the frequency given value ω of the virtual synchronous machine control is * Add the first given value to obtain a new frequency reference value; perform PI adjustment on the output voltage amplitude U according to the output voltage rated value to obtain the second given value, the voltage given value U of the virtual synchronous machine control * Add the second given value to obtain a new voltage reference value.

[0168] like Fig.16 As shown, the secondary voltage regulation is given as the rated voltage U N * , the output voltage amplitude U is used as feedback, and after PI regulation, the output secondary voltage regulation is given by ΔU 2 * This voltage setting is different from the voltage setting U of the voltage droop control. * The sum is taken as the new voltage setting for droop control. After closed-loop control, the voltage amplitude can be adjusted to the rated voltage amplitude U N * .

[0169] The secondary frequency modulation is given as the rated frequency ω N * , the output voltage angular frequency ω is used as feedback, and after PI regulation, the output secondary frequency is given by Δω 2 * This frequency setting is the same as the frequency setting of the frequency droop control ω * The sum is taken as the new frequency setting for droop control. After closed-loop control, the voltage frequency can be adjusted to the rated frequency ω N * .

[0170] In addition, when the front-end power grid is restored and the virtual synchronous machine needs to automatically synchronize with the power grid and reconnect to the grid, the given value of the secondary voltage and frequency regulation is the amplitude U of the front-end power grid. g and angular frequency ω g .

[0171] It should be noted that the three-phase AC system can also include Fig.11 The fourth control unit 209 and the fifth control unit 210 in the grid-connected system can perform island detection, and the grid-connected system can perform secondary voltage and frequency regulation.

[0172] In the control method of the three-phase AC system in the embodiment of the present invention, the harmonic components in the output signal of the three-phase AC system including the fundamental negative sequence component are extracted, and the harmonic component error signal is obtained according to the harmonic component reference value, and then the harmonic compensation potential is obtained; the harmonic compensation potential is added to the fundamental potential and then modulated to obtain a pulse signal, which can simultaneously realize the performance of the virtual synchronous machine itself in mitigating the frequency change of the power grid and the harmonic control performance of grid connection and off-grid connection. It can also have the functions of island detection and secondary voltage and frequency regulation.

[0173] The following introduces an apparatus embodiment of the present invention, which can be used to execute the above-mentioned real-time message processing method of the present invention.

[0174] like Fig.17 As shown, an embodiment of the present invention provides a control device 700 for a three-phase AC system. The three-phase AC system includes an inverter and a filter unit. The inverter is coupled to a power grid through the filter unit. Specifically, the control device includes:

[0175] The first calculation unit 710 is used to receive an output signal of the three-phase AC system and obtain a characteristic value of the output signal according to the output signal.

[0176] The first control unit 720 is used to perform virtual synchronous machine control on the inverter to obtain fundamental wave potential.

[0177] The error acquisition unit 730 is used to extract the harmonic component in the output signal and obtain an error signal according to the harmonic component and the harmonic component reference value.

[0178] The error adjustment unit 740 is used to control the error signal to obtain the harmonic compensation potential.

[0179] The second calculation unit 750 is used to obtain the control potential by superimposing the harmonic compensation potential on the fundamental wave potential.

[0180] The modulation unit 760 is used to obtain a pulse signal by modulating the control potential, and obtain a switching signal of the inverter according to the pulse signal.

[0181] In the technical solution of the embodiment of the present invention, the harmonic components of the output signal are extracted to perform closed-loop control of the harmonic components to obtain the harmonic compensation potential. The harmonic compensation potential and the fundamental wave potential are added to obtain the control potential and the inverter is controlled according to the control potential. The inertia and damping characteristics of the virtual synchronous machine can be realized, and the harmonic components in the output signal of the three-phase AC system can be suppressed.

[0182] The error acquisition unit and the error adjustment unit correspond to Figure 2 The adjustment unit in .

[0183] When the three-phase AC system is running in grid-connected mode, the second control unit is switched on to control the harmonic current of the inverter output current and shield the third control unit. Figure 5a In the steps, the error acquisition unit includes the following modules:

[0184] The harmonic current acquisition module is used to perform 3s / 2r coordinate transformation on the output current of the inverter to obtain a current signal, perform low-pass filtering on the current signal to obtain a fundamental current, and subtract the fundamental current from the current signal to obtain a harmonic current. In some embodiments, it includes a coordinate transformer, a filter, and a subtractor. The coordinate transformer performs 3s / 2r coordinate transformation according to the angle signal θ, or performs 3s / 2s coordinate transformation first and then 2s / 2r coordinate transformation. The current signal includes a d-axis current signal I d and the q-axis current signal I q .

[0185] The current reference value setting module is used to set the harmonic current reference value to zero to obtain an error signal. In some embodiments, it includes a subtractor to achieve zero minus the harmonic current.

[0186] The error adjustment unit 740 may include the following modules:

[0187] The first coordinate transformation module is used to transform the error signal into multiple coordinate systems to obtain the error signal in each coordinate system. In some embodiments, it includes multiple coordinate transformers.

[0188] The harmonic control module is used to perform closed-loop control on the error signal in each coordinate system to obtain potential instructions corresponding to multiple coordinate systems. In some embodiments, it includes multiple current regulators.

[0189] The second coordinate transformation module is used to transform the potential instruction to obtain multiple harmonic potentials of the two-phase stationary coordinate system. In some embodiments, it includes multiple coordinate transformers.

[0190] The first calculation module is used to add multiple harmonic potentials of the two-phase stationary coordinate system and then perform two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0191] In another embodiment, to implement the above steps Figure 6The step in the error acquisition unit includes the following modules: a harmonic current acquisition module and a current reference value setting module. The harmonic current acquisition module is similar in structure and function to the harmonic current acquisition module of the above embodiment. The current reference value setting module is used to transform the harmonic current into multiple coordinate systems, obtain the harmonic current corresponding to the multiple coordinate systems, set the harmonic current reference value in each coordinate system to zero, and obtain the error signal in each of the coordinate systems. In some embodiments, it includes multiple coordinate transformers and multiple subtractors. For details, please refer to Figure 6 The description is not repeated here.

[0192] The error adjustment unit 740 may include:

[0193] The harmonic control module is used to perform closed-loop control on the error signal in each coordinate system to obtain potential instructions corresponding to multiple coordinate systems.

[0194] The third coordinate transformation module is used to perform coordinate transformation on the potential instruction to obtain multiple harmonic potentials in a two-phase stationary coordinate system.

[0195] The second calculation module is used to add up multiple harmonic potentials in the two-phase stationary coordinate system and then perform two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0196] In this embodiment, to achieve the above steps Figure 7a In the step, the error adjustment unit 740 may further include:

[0197] The fourth coordinate transformation module is used to perform coordinate transformation on the error signal to obtain the error signal in a two-phase stationary coordinate system.

[0198] The multiple control modules are respectively used to perform closed-loop control on the error signal in the two-phase stationary coordinate system to obtain multiple harmonic potentials in the two-phase stationary coordinate system.

[0199] The third calculation module is used to add up multiple harmonic potentials of the two-phase stationary coordinate system and then perform two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0200] The multiple control modules include a PR control module and two R control modules, wherein the PR control module outputs a negative sequence potential, and the two R control modules output a 5th harmonic potential and a 7th harmonic potential respectively.

[0201] When the three-phase AC system operates in an off-grid mode, the third control unit is switched on to control the harmonic voltage of the inverter output voltage and shield the second control unit.

[0202] To achieve Figure 8a In the step, the error acquisition unit may include:

[0203] The harmonic voltage acquisition module is used to perform coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, perform low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtract the fundamental voltage from the voltage signal to obtain a harmonic voltage. In some embodiments, it includes a coordinate transformer, a filter, and a subtractor. The coordinate transformer performs a 3s / 2r coordinate transformation according to the angle signal θ, or first performs a 3s / 2s coordinate transformation and then a 2s / 2r coordinate transformation. The voltage signal includes a d-axis voltage signal U d and q-axis voltage signal U q .

[0204] The voltage reference value setting module is used to set the reference value of the harmonic voltage to zero to obtain an error signal.

[0205] In this embodiment, the error adjustment unit 740 may further include:

[0206] The first coordinate transformation module is used to perform coordinate transformation of the error signal in multiple coordinate systems to obtain an error signal in each coordinate system.

[0207] The harmonic control module is used to perform closed-loop control on the error signal in each coordinate system to obtain potential instructions corresponding to multiple coordinate systems. In some embodiments, it includes multiple voltage regulators.

[0208] The second coordinate transformation module is used to perform coordinate transformation on the potential instruction to obtain multiple harmonic potentials of a two-phase stationary coordinate system.

[0209] The first calculation module is used to add multiple harmonic potentials of the two-phase stationary coordinate system and then perform two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0210] To achieve Fig. 9 In the step, the error acquisition unit may include:

[0211] The harmonic voltage acquisition module is used to perform coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, perform low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtract the fundamental voltage from the voltage signal to obtain the harmonic voltage.

[0212] The voltage reference value setting module is used to transform the harmonic voltage into multiple coordinate systems, obtain the harmonic voltage corresponding to the multiple coordinate systems, set the harmonic voltage reference value in each coordinate system to zero, and obtain the error signal in each coordinate system.

[0213] The error adjustment unit 740 may include:

[0214] The harmonic control module is used to perform closed-loop control in each coordinate system and obtain potential instructions corresponding to multiple coordinate systems.

[0215] The third coordinate transformation module is used to perform coordinate transformation on the potential instruction to obtain multiple harmonic potentials in a two-phase stationary coordinate system.

[0216] The second calculation module is used to add up multiple harmonic potentials in the two-phase stationary coordinate system and then perform two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0217] To achieve Fig.10 The error adjustment unit 740 may further include:

[0218] The fourth coordinate transformation module is used to perform coordinate transformation on the error signal to obtain the error signal in a two-phase stationary coordinate system.

[0219] The multiple control modules are respectively used to perform closed-loop control on the error signal in the two-phase stationary coordinate system to obtain multiple harmonic potentials in the two-phase stationary coordinate system.

[0220] The third calculation module is used to add up multiple harmonic potentials of the two-phase stationary coordinate system and then perform two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

[0221] The multiple control modules include a PR control module and two R control modules, wherein the PR control module outputs a negative sequence potential, and the two R control modules output a 5th harmonic potential and a 7th harmonic potential respectively.

[0222] Please refer to the above description for details, which will not be repeated here for simplicity.

[0223] The control device of the three-phase AC system of the present invention extracts the harmonic components in the output signal of the three-phase AC system, performs closed-loop control on the harmonic components to obtain the harmonic compensation potential; superimposes the harmonic compensation potential on the fundamental wave potential of the virtual synchronous machine control output to obtain the control potential, modulates the control potential to obtain the switching signal of the inverter, realizes the virtual synchronous machine control, and suppresses the harmonic components in the output signal of the three-phase AC system at the same time.

[0224] The three-phase AC system of the present invention also has an island detection function, which is used to determine whether the three-phase AC system is operating in a grid-connected mode or an off-grid mode. The corresponding control device also includes a fourth control unit for performing island detection. To implement the island detection method of the present invention, for example Figure 12-14 The fourth control unit 800 includes: a parameter acquisition module 810, an interference signal acquisition module 820, an interference signal injection module 830 and a judgment module 840, please refer to Fig.18 .

[0225] Parameter acquisition module, used to obtain the output voltage U of the three-phase AC system abc The parameter M and its corresponding steady-state value M within a certain duration0 For example, it is coupled to the first calculation unit to receive the output voltage U abc The amplitude U or angular frequency ω; and the steady-state value U of the parameter is obtained through a filter 0 or 0 The interference signal acquisition module, according to the parameter M and the steady-state value M 0 Get the interference signal. Specifically, compare the steady-state value and the parameter. When the two are not equal, obtain the new parameter M' by superimposing an increment δ on the parameter M. The interference signal is obtained by inverting the error between the steady-state value and the new parameter. The interference signal injection module is used to superimpose the interference signal on the given droop control. Specifically, when the parameter M is the voltage amplitude, the interference signal is superimposed on the voltage given by the droop control; when the parameter is the angular frequency, the interference signal is superimposed on the angular frequency given by the droop control. The judgment module detects the parameters after the interference signal is added in real time and compares them with the threshold. When the parameter exceeds the threshold, it is determined that an island occurs. For example, when the interference signal is added to the angular frequency given ω * When the angular frequency ω of the output voltage is detected in real time and compared with the threshold value; when the interference signal is added to the given amplitude U * When the output voltage amplitude U is detected in real time, it is compared with the threshold.

[0226] To implement the island detection method in the present invention, the interference signal acquisition module further includes: a comparison submodule, which is used to compare the steady-state value and the parameter; a superposition submodule, when the steady-state value and the parameter are not equal, a new parameter is obtained by superimposing an increment on the parameter; a calculation submodule, which is used to obtain the error between the steady-state value and the new parameter, and invert the error to obtain the interference signal.

[0227] Since the functional modules of the control device for a three-phase AC system of the exemplary embodiment of the present invention correspond to the steps of the exemplary embodiment of the control method for a three-phase AC system described above, for details not disclosed in the embodiment of the device of the present invention, please refer to the embodiment of the control method for a three-phase AC system of the present invention described above.

[0228] The control device of the three-phase AC system with VSG function described above can be a computer solution based on the method flow of the present invention, that is, a software architecture, which can be applied to the control system of VSG. The above device is the processing process corresponding to the method flow.

[0229] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0230] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A control method for a three-phase AC system, the three-phase AC system comprising an inverter and a filter unit, the inverter being coupled to a power grid through the filter unit, characterized in that: The control method comprises: Step 1: receiving an output signal of the three-phase AC system, and obtaining a characteristic value of the output signal according to the output signal; Step 2: Performing virtual synchronous machine control on the inverter according to the characteristic value to obtain fundamental wave potential; Step 3: extracting the harmonic component in the output signal, and obtaining an error signal according to the harmonic component and the harmonic component reference value; Step 4: Control the error signal to obtain harmonic compensation potential; Step 5: Obtaining a control potential by superimposing the harmonic compensation potential with the fundamental wave potential; Step 6: Obtain a pulse signal by modulating the control potential, and obtain a switching signal of the inverter according to the pulse signal.

2. The control method of the three-phase AC system according to claim 1, characterized in that: When the three-phase AC system operates in the grid-connected mode and controls the harmonic current in the inverter output current, the step 3 includes: Performing coordinate transformation on the inverter output current to obtain a current signal, performing low-pass filtering on the current signal to obtain a fundamental current, and subtracting the fundamental current from the current signal to obtain a harmonic current; The reference value of the harmonic current is set to zero to obtain the error signal.

3. The control method of the three-phase AC system according to claim 1, characterized in that: When the three-phase AC system operates in the grid-connected mode and controls the harmonic current in the inverter output current, the step 3 includes: Performing coordinate transformation on the inverter output current to obtain a current signal, performing low-pass filtering on the current signal to obtain a fundamental current, and subtracting the fundamental current from the current signal to obtain a harmonic current; The harmonic current is subjected to coordinate transformation of multiple coordinate systems to obtain harmonic currents corresponding to the multiple coordinate systems, and a reference value of the harmonic current in each of the coordinate systems is set to zero to obtain the error signal in each of the coordinate systems.

4. The control method of the three-phase AC system according to claim 1, characterized in that: When the three-phase AC system operates in an off-grid mode, the harmonic voltage in the output voltage of the three-phase AC system is controlled, and step 3 includes: Performing coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, performing low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtracting the fundamental voltage from the voltage signal to obtain a harmonic voltage; The reference value of the harmonic voltage is set to zero to obtain the error signal.

5. The control method of the three-phase AC system according to claim 1, characterized in that: When the three-phase AC system operates in an off-grid mode, the harmonic voltage in the output voltage of the three-phase AC system is controlled, and step 3 includes: Performing coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, performing low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtracting the fundamental voltage from the voltage signal to obtain a harmonic voltage; The harmonic voltage is subjected to coordinate transformation of multiple coordinate systems to obtain harmonic voltages corresponding to the multiple coordinate systems, and a reference value of the harmonic voltage in each of the coordinate systems is set to zero to obtain the error signal in each of the coordinate systems.

6. The control method of the three-phase AC system according to claim 2 or 4, characterized in that: The step 4 comprises: Performing coordinate transformation of the error signal in multiple coordinate systems to obtain the error signal in each coordinate system; Performing closed-loop control on the error signal in each of the coordinate systems to obtain potential instructions corresponding to the plurality of coordinate systems; Performing coordinate transformation on the potential command to obtain multiple harmonic potentials of a two-phase stationary coordinate system; The harmonic compensation potential is obtained by adding the multiple harmonic potentials of the two-phase stationary coordinate system and performing a two-phase stationary / three-phase stationary coordinate transformation.

7. The control method of the three-phase AC system according to claim 3 or 5, characterized in that: The step 4 comprises: Performing closed-loop control on the error signal in each of the coordinate systems to obtain potential instructions corresponding to the multiple coordinate systems; Performing coordinate transformation on the potential instruction to obtain a plurality of harmonic potentials in a two-phase stationary coordinate system; The harmonic compensation potential is obtained by adding the multiple harmonic potentials in the two-phase stationary coordinate system and performing a two-phase stationary / three-phase stationary coordinate transformation.

8. The control method of the three-phase AC system according to claim 2 or 4, characterized in that: The step 4 comprises: Performing coordinate transformation on the error signal to obtain an error signal in a two-phase stationary coordinate system; Inputting the error signal in the two-phase stationary coordinate system into a plurality of control modules to perform closed-loop control, thereby obtaining a plurality of harmonic potentials in the two-phase stationary coordinate system; The harmonic compensation potential is obtained by adding the multiple harmonic potentials of the two-phase stationary coordinate system and performing a two-phase stationary / three-phase stationary coordinate transformation.

9. The control method of the three-phase AC system according to claim 8, characterized in that: The multiple control modules include a PR control module and two R control modules, wherein the PR control module outputs a negative sequence harmonic potential, and the two R control modules output a 5th harmonic potential and a 7th harmonic potential respectively.

10. A control device for a three-phase AC system, the three-phase AC system comprising an inverter and a filter unit, the inverter being coupled to a power grid via the filter unit, characterized in that: The control device comprises: a first calculation unit, configured to receive an output signal of the three-phase AC system and obtain a characteristic value of the output signal according to the output signal; A first control unit, configured to perform virtual synchronous machine control on the inverter according to the characteristic value to obtain a fundamental wave potential; An error acquisition unit, used for extracting the harmonic component in the output signal, and obtaining an error signal according to the harmonic component and a harmonic component reference value; An error adjustment unit, used for controlling the error signal to obtain a harmonic compensation potential; a second calculation unit, configured to obtain a control potential by superimposing the harmonic compensation potential on the fundamental wave potential; The modulation unit is used to obtain a pulse signal by modulating the control potential, and obtain a switching signal of the inverter according to the pulse signal.

11. The control device for a three-phase AC system according to claim 10, characterized in that: When the three-phase AC system operates in a grid-connected mode, the harmonic current in the inverter output current is controlled; the error acquisition unit includes: A harmonic current acquisition module, used for performing coordinate transformation on the inverter output current to obtain a current signal, performing low-pass filtering on the current signal to obtain a fundamental current, and subtracting the fundamental current from the current signal to obtain a harmonic current; The current reference value setting module is used to set the reference value of the harmonic current to zero to obtain the error signal.

12. The control device for a three-phase AC system according to claim 10, characterized in that: When the three-phase AC system operates in a grid-connected mode, the harmonic current in the inverter output current is controlled; the error acquisition unit includes: A harmonic current acquisition module, used for performing coordinate transformation on the inverter output current to obtain a current signal, performing low-pass filtering on the current signal to obtain a fundamental current, and subtracting the fundamental current from the current signal to obtain a harmonic current; The current reference value setting module is used to transform the harmonic current into multiple coordinate systems, obtain the harmonic current corresponding to the multiple coordinate systems, set the harmonic current reference value in each coordinate system to zero, and obtain the error signal in each coordinate system.

13. The control device for a three-phase AC system according to claim 10, characterized in that: When the three-phase AC system operates in an off-grid mode, the harmonic voltage in the inverter output voltage is controlled; the error acquisition unit includes: A harmonic voltage acquisition module, used for performing coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, performing low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtracting the fundamental voltage from the voltage signal to obtain a harmonic voltage; The voltage reference value setting module is used to set the reference value of the harmonic voltage to zero to obtain the error signal.

14. The control device for a three-phase AC system according to claim 10, characterized in that: When the three-phase AC system operates in an off-grid mode, the harmonic voltage in the inverter output voltage is controlled; the error acquisition unit includes: A harmonic voltage acquisition module, used for performing coordinate transformation on the output voltage of the three-phase AC system to obtain a voltage signal, performing low-pass filtering on the voltage signal to obtain a fundamental voltage, and subtracting the fundamental voltage from the voltage signal to obtain a harmonic voltage; The voltage reference value setting module is used to transform the harmonic voltage into multiple coordinate systems to obtain the harmonic voltage corresponding to the multiple coordinate systems, set the harmonic voltage reference value in each coordinate system to zero, and obtain the error signal in each coordinate system.

15. The control device for a three-phase AC system according to claim 11 or 13, characterized in that: The error adjustment unit comprises: A first coordinate transformation module, used for performing coordinate transformation of the error signal in multiple coordinate systems to obtain the error signal in each coordinate system; A harmonic control module, used for performing closed-loop control on the error signal in each of the coordinate systems to obtain potential instructions corresponding to the plurality of coordinate systems; A second coordinate transformation module, used for performing coordinate transformation on the potential instruction to obtain a plurality of harmonic potentials of a two-phase stationary coordinate system; The first calculation module is used for adding the multiple harmonic potentials of the two-phase stationary coordinate system and then performing two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

16. The control device for a three-phase AC system according to claim 12 or 14, characterized in that: The error adjustment unit comprises: A harmonic control module, used for performing closed-loop control on the error signal in each of the coordinate systems to obtain potential instructions corresponding to the multiple coordinate systems; A third coordinate transformation module, used for performing coordinate transformation on the potential instruction to obtain a plurality of harmonic potentials in a two-phase stationary coordinate system; The second calculation module is used for adding the multiple harmonic potentials in the two-phase stationary coordinate system and then performing two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

17. The control device for a three-phase AC system according to claim 11 or 13, characterized in that: The error adjustment unit comprises: A fourth coordinate transformation module, used for performing coordinate transformation on the error signal to obtain an error signal in a two-phase stationary coordinate system; A plurality of control modules are respectively used to perform closed-loop control on the error signal in the two-phase stationary coordinate system to obtain a plurality of harmonic potentials in the two-phase stationary coordinate system; The third calculation module is used to add the multiple harmonic potentials of the two-phase stationary coordinate system and then perform two-phase stationary / three-phase stationary coordinate transformation to obtain the harmonic compensation potential.

18. The control device for a three-phase AC system according to claim 17, characterized in that: The multiple control modules include a PR control module and two R control modules, wherein the PR control module outputs a negative sequence harmonic potential, and the two R control modules output a 5th harmonic potential and a 7th harmonic potential respectively.

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