Synchronous rotation coordinate transformation method and system for three-phase asymmetric system

Abstract

The invention provides a synchronous rotation coordinate transformation method and system for a three-phase asymmetric system, and the method comprises the steps: collecting an instantaneous voltage value of a common grid connection point, and defining an a axis in a three-phase rotation coordinate system as a reference A axis; based on the reference A axis, the output voltage and the output current of the grid-forming inverter are converted from a three-phase static coordinate system to a three-phase synchronous rotating coordinate system; a voltage reference value is obtained based on the voltage reference values of the coordinate axes A, B and C under the three-phase synchronous rotating coordinate system, and a current reference value is obtained through a voltage PI link of the voltage reference value; calculating a difference value between the current reference value and the A, B and C coordinate axis components under the three-phase synchronous rotating coordinate system to obtain voltage carriers under the A, B and C coordinate axes under the three-phase synchronous rotating coordinate system; and based on the voltage carrier wave, inversely transforming the voltage carrier wave into a three-phase static coordinate system through a three-phase synchronous rotating coordinate system to obtain a three-phase sine carrier wave, thereby completing the synchronous rotating coordinate transformation method for the three-phase asymmetric system.

Description

Technical Field

[0001] The present invention relates to the field of renewable energy power generation systems, and in particular to a synchronous rotating coordinate transformation method and system for a three-phase asymmetric system. Background Art

[0002] With the rapid development of renewable energy generation, DC transmission and AC microgrid systems, the degree of power electronics in power systems is constantly improving. This change poses new challenges to traditional power system fault analysis methods, especially in the context of high power electronics. In addition, with the extension of transmission and distribution lines and the asymmetry of their line impedance, accurate analysis of power systems under three-phase asymmetric conditions has become more complex and urgent. At present, scholars at home and abroad have shown great interest in the analysis methods under three-phase asymmetric conditions.

[0003] Although in the prior art, as shown in the invention patent with authorization number CN110943446B, methods for small signal modeling of three-phase grid-connected inverters in a synchronous rotating coordinate system have been developed, these methods mainly construct models in an orthogonal rotating coordinate system, and their analysis and modeling processes are relatively complex, and may not be efficient or accurate enough when dealing with the analysis of voltage and current under three-phase asymmetric conditions. Summary of the invention

[0004] The present invention proposes a novel coordinate transformation method, which aims to provide a more simplified and efficient analysis tool for the special working conditions of three-phase asymmetric power systems. This method is particularly suitable for power systems with a high degree of power electronics, and can handle the analysis challenges brought about by the instability of renewable energy generation, the complexity of long-distance DC transmission, and the dynamics of microgrids. In addition, the present invention also includes corresponding control means to improve the stability and efficiency of the system. Through the present invention, the analysis process of the power system under asymmetric working conditions can be significantly simplified, and the accuracy and efficiency of the analysis can be improved, so as to better cope with the challenges of modern power systems:

[0005] Step S1, collecting the instantaneous voltage value of the common grid connection point, and defining the a-axis in the three-phase rotating coordinate system as the reference A-axis;

[0006] Step S2: based on the reference A axis, transform the output voltage and output current of the grid-type inverter from the three-phase stationary coordinate system to the three-phase synchronous rotating coordinate system;

[0007] Step S3, obtaining a voltage reference value based on the voltage reference values ​​of the A, B, and C axes in the three-phase synchronous rotating coordinate system, and obtaining a current reference value by passing the voltage reference value through a voltage PI link;

[0008] Step S4, calculating the difference between the current reference value and the A, B, and C coordinate axis components in the three-phase synchronous rotating coordinate system, and obtaining the voltage carrier under the A, B, and C coordinate axes in the three-phase synchronous rotating coordinate system;

[0009] Step S5: Based on the voltage carrier, the three-phase synchronous rotating coordinate system is inversely transformed into the three-phase stationary coordinate system to obtain a three-phase sinusoidal carrier, thereby completing the synchronous rotating coordinate transformation method for the three-phase asymmetric system.

[0010] Optionally, in step S2, based on the reference A axis, the process of transforming the output voltage and output current of the grid-type inverter from the three-phase stationary coordinate system to the three-phase synchronous rotating coordinate system specifically includes:

[0011] Assume that the phase difference between axis A and axis a is ωt, and the phase quantity U a The angle difference from the A axis is always Any point V in the three-phase stationary coordinate system abc =[V a , V b , V c ] T The projection to the three-phase synchronous rotating coordinate system is V ABC =[V A , V B , V C ] T ,The formula for transforming the three-phase stationary coordinate system to the three-phase synchronous rotating coordinate system is:

[0012]

[0013] Where Γ represents the abc To V ABC The transformation matrix of .

[0014] Optionally, in step S3, the voltage reference value is obtained based on the voltage reference values ​​of the A, B, and C axes in the three-phase synchronous rotating coordinate system, and the current reference value is obtained based on the voltage reference value through the voltage PI link, specifically including:

[0015]

[0016] Among them, E ref,A 、E ref,B and E ref,C They represent the voltage reference value input of the A, B, and C axes in the three-phase synchronous rotating coordinate system respectively, E represents the voltage reference value of the reactive power-voltage control output, and δ is the synchronous power angle value of the active power-power angle control output.

[0017] Optionally, in step S5, based on the voltage carrier, the three-phase synchronous rotating coordinate system is inversely transformed into a three-phase stationary coordinate system to obtain the content of the three-phase sinusoidal carrier, which specifically includes:

[0018] V abc =Γ -1 V ABC .

[0019] The present invention also discloses a synchronous rotating coordinate transformation system for a three-phase asymmetric system, the system comprising:

[0020] A data acquisition module is used to collect the instantaneous voltage value of the common grid connection point and define the a-axis in the three-phase rotating coordinate system as the reference A-axis;

[0021] A coordinate conversion module, used for converting the output voltage and output current of the grid-type inverter from a three-phase stationary coordinate system to a three-phase synchronous rotating coordinate system based on a reference A axis;

[0022] A current reference acquisition module is used to obtain a voltage reference value based on the voltage reference values ​​of the A, B, and C coordinate axes in the three-phase synchronous rotating coordinate system, and obtain a current reference value by passing the voltage reference value through a voltage PI link;

[0023] A voltage carrier calculation module is used to calculate the difference between the current reference value and the A, B, and C coordinate axis components in the three-phase synchronous rotating coordinate system to obtain the voltage carrier under the A, B, and C coordinate axes in the three-phase synchronous rotating coordinate system;

[0024] The rotating coordinate transformation module is used to transform the voltage carrier through the three-phase synchronous rotating coordinate system to the three-phase stationary coordinate system to obtain the three-phase sinusoidal carrier, thus completing the synchronous rotating coordinate transformation method for the three-phase asymmetric system.

[0025] Optionally, the workflow of the coordinate conversion module specifically includes:

[0026] Assume that the phase difference between axis A and axis a is ωt, and the phase quantity U a The angle difference from the A axis is always Any point V in the three-phase stationary coordinate system abc =[V a , V b , V c ] T The projection to the three-phase synchronous rotating coordinate system is V ABC =[V A , V B , V C ] T ,The formula for transforming the three-phase stationary coordinate system to the three-phase synchronous rotating coordinate system is:

[0027]

[0028] Where Γ represents the abc To V ABC The transformation matrix of .

[0029] Optionally, the working process of the current reference acquisition module specifically includes:

[0030]

[0031] Among them, E ref,A 、E ref,B and E ref,C They represent the voltage reference value input of the A, B, and C axes in the three-phase synchronous rotating coordinate system respectively, E represents the voltage reference value of the reactive power-voltage control output, and δ is the synchronous power angle value of the active power-power angle control output.

[0032] Optionally, the calculation formula of the rotation coordinate transformation module is:

[0033] V abc =Γ -1 V ABC .

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) Simplified system analysis: The three-phase synchronous rotating coordinate system adopted by the present invention allows the waveform collected in the three-phase stationary coordinate system to be directly projected into the synchronous rotating coordinate system. In this coordinate system, all waveform elements are converted into DC quantities, where the fundamental component is presented as a DC bias and the harmonic component is presented as a ripple. This transformation greatly simplifies the analysis process of the system, making the distinction and analysis of the fundamental and harmonic waves intuitive and simple.

[0036] 2) Efficient control strategy design: Using the synchronous rotating coordinate system, the present invention proposes a voltage and current dual closed-loop control strategy, which provides a new reference for power system control design. This control strategy can effectively utilize the DC deviation and ripple characteristics after coordinate transformation, facilitate the design of virtual filters, and more effectively manage the negative and zero sequence components in the system.

[0037] 3) Improving the intuitiveness of the phase angle synchronization analysis of the network: In the coordinate system of the present invention, the synchronization properties of the phase angle, voltage and current are more intuitive, which helps to more accurately analyze and predict the dynamic response of the system, especially under asymmetric or nonlinear working conditions.

[0038] 4) Flexible control output adaptability: The designed control strategy is not only applicable to the synchronous rotating coordinate system, but can also be flexibly transformed into other coordinate systems (such as orthogonal rotating coordinate system, orthogonal stationary coordinate system, three-phase stationary coordinate system) for implementation. This makes the present invention compatible with a variety of existing control systems and provides a wider range of application possibilities.

[0039] Through the above advantages, the present invention not only improves the operating efficiency and stability of the power system under three-phase asymmetric conditions, but also provides a more efficient and intuitive tool for system designers to cope with complex challenges in modern power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0041] Figure 1 A method step diagram of a synchronous rotating coordinate transformation method for a three-phase asymmetric system according to an embodiment of the present invention;

[0042] Figure 2 This is a structural diagram of a grid-connected system according to an embodiment of the present invention;

[0043] Figure 3 The ABC axis projection of the three-phase sinusoidal voltage acquisition waveform offset by 0° in the embodiment of the present invention;

[0044] Figure 4 The ABC axis projection of the three-phase sinusoidal voltage acquisition waveform offset by 15° in the embodiment of the present invention;

[0045] Figure 5 This is a block diagram of the voltage and current double closed-loop structure under the ABC axis of an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] First, the prior art used in the present invention is introduced:

[0048] The grid-type inverter is a working mode of the energy storage converter. It can independently establish the reference voltage and frequency without anchoring to the voltage and frequency of the grid. This means that the grid-type inverter can operate without being connected to the main grid, such as in an island state. Compared with the traditional grid-following inverter, the grid-type inverter acts as a voltage source in the grid, while the grid-following inverter acts as a current source.

[0049] Key features: Independent operation capability: can operate without grid connection. Voltage source characteristics: provides stable voltage in the grid. Technical advantages: enhances system flexibility and reliability.

[0050] Application scenarios: Off-grid system: As an independent power system in remote areas or post-disaster reconstruction. Microgrid: As a bridge to connect or disconnect with the main grid in the microgrid. Energy storage system: Provide stable output in the energy storage system to enhance the energy management efficiency of the system.

[0051] The main circuit used in the present invention is a three-phase two-level bridge full-control circuit. Taking the network-type control method as an example, the system structure diagram is as follows: Figure 2 shown.

[0052] Q 1 ~Q 6 Represents the switch tube number; L and C represent the inductance and capacitance of the low-pass filter respectively; Z l a , Z lb , Z lc are the line impedances of phases abc respectively; U, I, P, Q represent the voltage, current, active power and reactive power values ​​respectively; E represents the voltage reference value of the reactive power-voltage control output; δ represents the synchronous power angle value of the active power-power angle control output; the superscript * represents the controller output carrier, and the subscripts abc and ABC represent the values ​​in the three-phase stationary coordinate system and the three-phase synchronous rotating coordinate system respectively.

[0053] Embodiment 1

[0054] A synchronous rotating coordinate transformation method for three-phase asymmetric systems, such as Figure 1 As shown, the method includes:

[0055] Step S1, collecting the instantaneous voltage value of the common grid connection point, and defining the a-axis in the three-phase rotating coordinate system as the reference A-axis.

[0056] Assume that the three-phase voltage source is expressed in the time domain of the three-phase stationary coordinate system as:

[0057]

[0058] Where U am , Ubm , U cm are the amplitudes of the three-phase voltage sources respectively; ω represents the electrical angular velocity of the three-phase voltage source; Represents the phase difference relative to the phase reference point. The present invention is based on a three-phase stationary coordinate system, which makes the three-phase coordinate system rotate synchronously at an angular velocity of ω.

[0059] Step S2: Based on the reference A-axis, transform the output voltage and output current of the grid-type inverter from a three-phase stationary coordinate system to a three-phase synchronous rotating coordinate system.

[0060] At the beginning, the three-phase synchronous rotating coordinate system coincides with the three-phase stationary coordinate system. a and the motion of the rotating coordinate system, the phase difference between the A axis and the a axis is ωt, and the phase quantity U a The angle difference from the A axis is always This is the motion process of the three-phase synchronous rotating coordinate system. Assume that any point V in the three-phase stationary coordinate system abc =[V a ,V b ,V c ] T The projection to the three-phase synchronous rotating coordinate system is V ABC =[V A ,V B ,V C ] T . V abc and V ABC The transformation relationship is expressed as:

[0061]

[0062] Where Γ represents the abc To V ABC The transformation matrix of .

[0063] Figure 3 It is the ABC axis projection of the three-phase sinusoidal acquisition waveform with a line voltage of 380V and a phase shift of 0°. Figure 4 It is the ABC axis projection of the three-phase sinusoidal acquisition waveform with a line voltage of 380V and a phase shift of 15°.

[0064] If the three-phase is asymmetrical, the sum of the three coordinates under the ABC axis is not zero, and the degree of three-phase imbalance can be determined based on the offset.

[0065] Step S3, obtaining a voltage reference value based on the voltage reference values ​​of the A, B, and C axes in the three-phase synchronous rotating coordinate system, and obtaining a current reference value based on the voltage reference value through a voltage PI link.

[0066] The voltage reference value of the reactive power-voltage output of the network control is input into the dual-loop control branch as the voltage reference value through the following calculation:

[0067]

[0068] Where E ref,A 、E ref,B and E ref,C Respectively represent the voltage reference value input of the A, B, and C axes in the three-phase synchronous rotating coordinate system. Then, the voltage reference value of each axis is subtracted from the A, B, and C axis components of the voltage collected in step S2. The current reference values ​​of the A, B, and C axes are obtained through the voltage PI link.

[0069] Step S4, calculating the difference between the current reference value and the A, B, and C axis components of the collected current in the three-phase synchronous rotating coordinate system, and obtaining the voltage carrier under the A, B, and C axes in the three-phase synchronous rotating coordinate system.

[0070] The current reference value in step S3 is subtracted from the A, B, and C axis components of the current collected in step S2, and the voltage carrier under the A, B, and C axes is obtained through the current PI link.

[0071] Step S5: Based on the voltage carrier, the three-phase synchronous rotating coordinate system is inversely transformed into a three-phase stationary coordinate system to obtain a three-phase sinusoidal carrier, thereby completing a synchronous rotating coordinate transformation method for a three-phase asymmetric system.

[0072] The control output carrier generated by the inner loop control based on the three-phase synchronous rotating coordinate system needs to be inversely transformed into the coordinates under the abc axis. Its linear transformation is expressed as:

[0073] V abc =Γ -1 V ABC

[0074] The carrier time domain expression under the abc axis will correspond to the PWM signal, which is input to the switching device, completing the control process. In the grid-connected control system of the grid-forming type, the power angle value is determined by the differential flow of active power; in the grid-following type grid-connected control system, the power angle follows the grid phase, so the transformation matrix Γ is a time-varying variable about δ under any grid-connected condition.

[0075] This embodiment will describe the specific application process of the present invention through an inner loop control case.

[0076] Inner loop design example: Design of voltage or current control in asymmetric conditions based on a three-phase synchronous rotating coordinate system. Figure 5 The structural block diagram of the voltage and current double closed loop under the ABC axis is shown.

[0077] H in the figure u (s) and Hi (s) are the proportional integral link transfer functions of the voltage outer loop and the voltage inner loop, respectively. The proportional integral link transfer function is specifically:

[0078]

[0079] Among them, k pu and k iu They represent the proportional constant and integral constant of the voltage outer loop proportional integral link respectively; k pi and k ii They represent the proportional constant and integral constant of the proportional-integral link of the inner current loop respectively.

[0080] Embodiment 2

[0081] A synchronous rotating coordinate transformation system for a three-phase asymmetric system, the system comprising:

[0082] The data acquisition module is used to collect the instantaneous voltage value of the public grid-connected point and define the a-axis in the three-phase rotating coordinate system as the reference A-axis.

[0083] Assume that the three-phase voltage source is expressed in the time domain of the three-phase stationary coordinate system as:

[0084]

[0085] Where U am , U bm , U cm are the amplitudes of the three-phase voltage sources respectively; ω represents the electrical angular velocity of the three-phase voltage source; Represents the phase difference relative to the phase reference point. The present invention is based on a three-phase stationary coordinate system, which makes the three-phase coordinate system rotate synchronously at an angular velocity of ω.

[0086] The coordinate conversion module is used to transform the output voltage and output current of the grid-type inverter from a three-phase stationary coordinate system to a three-phase synchronous rotating coordinate system based on the reference A axis.

[0087] At the beginning, the three-phase synchronous rotating coordinate system coincides with the three-phase stationary coordinate system. a and the motion of the rotating coordinate system, the phase difference between the A axis and the a axis is ωt, and the phase quantity U a The angle difference from the A axis is always This is the motion process of the three-phase synchronous rotating coordinate system. Assume that any point V in the three-phase stationary coordinate system abc =[V a ,V b ,V c ] T The projection to the three-phase synchronous rotating coordinate system is V ABC =[V A ,VB ,V C ] T . V abc and V ABC The transformation relationship is expressed as:

[0088]

[0089] Where Γ represents the abc To V ABC The transformation matrix of . Figure 3 It is the ABC axis projection of the three-phase sinusoidal acquisition waveform with a line voltage of 380V and a phase shift of 0°. Figure 4 It is the ABC axis projection of the three-phase sinusoidal acquisition waveform with a line voltage of 380V and a phase shift of 15°.

[0090] If the three-phase is asymmetrical, the sum of the three coordinates under the ABC axis is not zero, and the degree of three-phase imbalance can be determined based on the offset.

[0091] The current reference acquisition module is used to obtain a voltage reference value based on the voltage reference value input of the A, B, and C coordinate axes in the three-phase synchronous rotating coordinate system, and obtain a current reference value based on the voltage reference value through a voltage PI link.

[0092] The voltage reference value of the reactive power-voltage output of the network control is input into the dual-loop control branch as the voltage reference value through the following calculation:

[0093]

[0094] Where E ref,A 、E ref,B and E ref,C They represent the voltage reference value input of the A, B, and C axes in the three-phase synchronous rotating coordinate system. Then, the voltage reference value of each axis is subtracted from the A, B, and C axis components of the voltage collected in the coordinate conversion module. The current reference values ​​of the A, B, and C axes are obtained through the voltage PI link.

[0095] The voltage carrier calculation module is used to calculate the difference between the current reference value and the A, B, and C axis components in the three-phase synchronous rotating coordinate system to obtain the voltage carrier under the A, B, and C coordinate axes in the three-phase synchronous rotating coordinate system.

[0096] The current reference value of the current reference acquisition module is subtracted from the A, B, and C axis components of the current collected in the coordinate conversion module, and the voltage carrier under the A, B, and C axes is obtained through the current PI link.

[0097] The rotating coordinate transformation module is used to transform the voltage carrier through the three-phase synchronous rotating coordinate system to the three-phase stationary coordinate system to obtain the three-phase sinusoidal carrier, thereby completing the synchronous rotating coordinate transformation method for the three-phase asymmetric system.

[0098] The control output carrier generated by the inner loop control based on the three-phase synchronous rotating coordinate system needs to be inversely transformed into the coordinates under the abc axis. Its linear transformation is expressed as:

[0099] V abc =Γ -1 V ABC

[0100] The carrier time domain expression under the abc axis will correspond to the PWM signal, which is input to the switching device, completing the control process. In the grid-connected control system of the grid-forming type, the power angle value is determined by the differential flow of active power; in the grid-following type grid-connected control system, the power angle follows the grid phase, so the transformation matrix Γ is a time-varying variable about δ under any grid-connected condition.

[0101] This embodiment will describe the specific application process of the present invention through an inner loop control case.

[0102] Inner loop design example: Design of voltage or current control in asymmetric conditions based on a three-phase synchronous rotating coordinate system. Figure 5 The structural block diagram of the voltage and current double closed loop under the ABC axis is shown.

[0103] H in the figure u (s) and H i (s) are the proportional integral link transfer functions of the voltage outer loop and the voltage inner loop, respectively. The specific functions are:

[0104]

[0105] In the formula, k pu and k iu They represent the proportional constant and integral constant of the voltage outer loop proportional integral link respectively; k pi and k ii They represent the proportional constant and integral constant of the proportional-integral link of the inner current loop respectively.

[0106] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A synchronous rotating coordinate transformation method for a three-phase asymmetric system, characterized in that the method include: Step S1, collecting the instantaneous voltage value of the common grid connection point, and defining the a-axis in the three-phase rotating coordinate system as the reference A-axis; Step S2: based on the reference A axis, transform the output voltage and output current of the grid-type inverter from the three-phase stationary coordinate system to the three-phase synchronous rotating coordinate system; Step S3, obtaining a voltage reference value based on the voltage reference values ​​of the A, B, and C axes in the three-phase synchronous rotating coordinate system, and obtaining a current reference value by passing the voltage reference value through a voltage PI link; Step S4, calculating the difference between the current reference value and the A, B, and C coordinate axis components in the three-phase synchronous rotating coordinate system, and obtaining the voltage carrier under the A, B, and C coordinate axes in the three-phase synchronous rotating coordinate system; Step S5: Based on the voltage carrier, the three-phase synchronous rotating coordinate system is inversely transformed into the three-phase stationary coordinate system to obtain a three-phase sinusoidal carrier, thereby completing the synchronous rotating coordinate transformation method for the three-phase asymmetric system.

2. The synchronous rotating coordinate transformation method for a three-phase asymmetric system according to claim 1, characterized in that: In step S2, based on the reference A axis, the process of transforming the output voltage and output current of the grid-type inverter from the three-phase stationary coordinate system to the three-phase synchronous rotating coordinate system specifically includes: Assume that the phase difference between axis A and axis a is ωt, and the phase quantity U a The angle difference from the A axis is always Any point V in the three-phase stationary coordinate system abc =[Va , V b ,V c ] T The projection to the three-phase synchronous rotating coordinate system is V ABC =[V A ,V B ,V C ] T ,The formula for transforming the three-phase stationary coordinate system to the three-phase synchronous rotating coordinate system is: Where Γ represents the abc To V ABC The transformation matrix of .

3. The synchronous rotating coordinate transformation method for a three-phase asymmetric system according to claim 1, characterized in that: In the step S3, the voltage reference value is obtained based on the voltage reference values ​​of the A, B, and C axes in the three-phase synchronous rotating coordinate system, and the current reference value is obtained through the voltage PI link based on the voltage reference value, which specifically includes: Among them, E ref,A 、E ref,B and E ref,C They represent the voltage reference value input of the A, B, and C axes in the three-phase synchronous rotating coordinate system respectively, E represents the voltage reference value of the reactive power-voltage control output, and δ is the synchronous power angle value of the active power-power angle control output.

4. The synchronous rotating coordinate transformation method for a three-phase asymmetric system according to claim 3, characterized in that: In step S5, based on the voltage carrier, the three-phase synchronous rotating coordinate system is inversely transformed into a three-phase stationary coordinate system to obtain the content of the three-phase sinusoidal carrier, which specifically includes: V abc =Γ -1 V ABC 。 5. A synchronous rotating coordinate transformation system for a three-phase asymmetric system, the system being used to implement the synchronous rotating coordinate transformation method according to any one of claims 1 to 4, characterized in that the system include: A data acquisition module is used to collect the instantaneous voltage value of the common grid connection point and define the a-axis in the three-phase rotating coordinate system as the reference A-axis; A coordinate conversion module, used for converting the output voltage and output current of the grid-type inverter from a three-phase stationary coordinate system to a three-phase synchronous rotating coordinate system based on a reference A axis; A current reference acquisition module is used to obtain a voltage reference value based on the voltage reference values ​​of the A, B, and C coordinate axes in the three-phase synchronous rotating coordinate system, and obtain a current reference value by passing the voltage reference value through a voltage PI link; A voltage carrier calculation module is used to calculate the difference between the current reference value and the A, B, and C coordinate axis components in the three-phase synchronous rotating coordinate system to obtain the voltage carrier under the A, B, and C coordinate axes in the three-phase synchronous rotating coordinate system; The rotating coordinate transformation module is used to transform the voltage carrier through the three-phase synchronous rotating coordinate system to the three-phase stationary coordinate system to obtain the three-phase sinusoidal carrier, thus completing the synchronous rotating coordinate transformation method for the three-phase asymmetric system.

6. The synchronous rotating coordinate transformation system for three-phase asymmetric system according to claim 5, characterized in that: The workflow of the coordinate conversion module specifically includes: Assume that the phase difference between axis A and axis a is ωt, and the phase quantity U a The angle difference from the A axis is always Any point V in the three-phase stationary coordinate system abc =[V a ,V b ,V c ] T The projection to the three-phase synchronous rotating coordinate system is V ABC =[V A , V B , V C ] T ,The formula for transforming the three-phase stationary coordinate system to the three-phase synchronous rotating coordinate system is: Where Γ represents the abc To V ABC The transformation matrix of .

7. The synchronous rotating coordinate transformation system for three-phase asymmetric system according to claim 5, characterized in that: The working process of the current reference acquisition module specifically includes: Among them, E ref,A 、E ref,B and E ref,C They represent the voltage reference value input of the A, B, and C axes in the three-phase synchronous rotating coordinate system respectively, E represents the voltage reference value of the reactive power-voltage control output, and δ is the synchronous power angle value of the active power-power angle control output.

8. The synchronous rotating coordinate transformation system for a three-phase asymmetric system according to claim 6, characterized in that: The calculation formula of the rotation coordinate transformation module is: V abc =Γ -1 V ABC 。

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