A positive and negative sequence decoupled grid voltage feedforward control method

Abstract

The application relates to a grid voltage feedforward control method for positive and negative sequence decoupling, which comprises the following steps: a feedforward signal calculation module can adjust the amplitude of a high-frequency component of a feedforward value, can realize lead or lag compensation by adjusting a phase angle compensation parameter, can compensate the phase of the high-frequency component, and reasonable adjustment of the two degrees of freedom can stabilize grid connection of a grid-connected inverter under a weak grid; the feedforward signal calculation module finally outputs four variables,,, and ; the four variables,,, obtained through the feedforward signal calculation module are respectively subjected to inverse Park transformation according to positive and negative sequence coordinate systems to obtain, and in the positive sequence coordinate system and, and in the negative sequence coordinate system; and and are obtained synchronously. The application can have good performance when the grid voltage is unbalanced, can realize independent control of positive and negative sequence currents, and can improve the stability of grid-connected operation of the inverter under a weak grid.

Description

Technical Field

[0001] This invention belongs to the field of power electronic control technology, specifically relating to a positive and negative sequence decoupling grid voltage feedforward control method for photovoltaic grid-connected inverters that can adapt to unbalanced grids. Background Technology

[0002] To improve the quality of grid-connected current and reduce the impact of grid-connected voltage fluctuations on the current, mainstream grid-connected inverters typically incorporate grid voltage feedforward control. Currently, common voltage feedforward control methods often employ the following approach: acquiring three-phase grid voltage signals and converting the three-phase AC signals into DC signals in the dq coordinate system using the Park transform. However, since the grid-connected voltage generally contains many harmonic components and unavoidably introduces high-frequency interference during sampling, these interferences can negatively impact the operational stability of the grid-connected inverter. Therefore, low-pass filtering is generally applied to the variables in the dq coordinate system, and the filtered value is used as the grid voltage feedforward value.

[0003] As mentioned above, existing feedforward control methods generally do not compensate for higher harmonics, and cannot mitigate the impact of high-frequency components of the grid connection voltage and sampling interference. This method can achieve good control results when the grid voltage balance is good. However, when the grid voltage is unbalanced, it is difficult to meet the control requirements. The specific reasons are as follows: When the grid voltage is unbalanced, negative sequence components will be generated. As mentioned above, when performing Park transformation on the grid voltage, the transformation is based on the positive sequence component. At this time, the negative sequence component cannot be fully represented, resulting in poor grid connection current control. In some cases, the generation of uncontrolled negative sequence current components may even cause the machine to disconnect from the grid or be damaged. Summary of the Invention

[0004] This invention designs a positive and negative sequence decoupled grid voltage feedforward control method. The technical problem it solves is that when the existing grid voltage is unbalanced, a negative sequence component will be generated. When performing Park transformation on the grid voltage, the transformation is based on the positive sequence component. At this time, the negative sequence component cannot be fully represented, resulting in poor grid current control effect. In some cases, the generation of uncontrolled negative sequence current components may even cause the machine to disconnect from the grid or be damaged.

[0005] To solve the aforementioned technical problems, the present invention adopts the following solution:

[0006] A grid voltage feedforward control method with positive and negative sequence decoupling includes the following steps:

[0007] Step 1: Collect the grid voltage at the grid connection point, decouple it according to positive and negative sequence, and obtain 4 variables. , , , ;

[0008] Step 2: Use positive sequence components Software phase-locking is performed to enable the system to stably follow the phase angle θ of the positive sequence component of the grid voltage;

[0009] Step 3: Separate the positive and negative components , , , Input feedforward signal calculation module;

[0010] Step 4: The feedforward signal calculation module can adjust the amplitude of the high-frequency component of the feedforward value. By adjusting the phase angle compensation parameter, it can achieve lead or lag compensation and compensate for the phase of the high-frequency component. Reasonable adjustment of these two degrees of freedom can enable the grid-connected inverter to stably connect to the grid under weak grid conditions. The feedforward signal calculation module finally outputs four variables. , , , ;

[0011] Step 5: Calculate the four variables obtained from the feedforward signal calculation module. , , , Perform inverse Park transformations according to the positive and negative coordinate systems respectively to obtain the positive-order coordinate system. , and negative order coordinate system , Positive and negative order are obtained synchronously. and ;

[0012] Step 6: Perform an inverse Clack transformation to obtain the three-phase stationary coordinate system. Using this value as the final feedforward value for PWM modulation, positive and negative sequence decoupled grid voltage feedforward control can be achieved.

[0013] Preferably, in step 1 , , , All of them contain higher harmonics, which provides a basis for subsequent separate processing of the fundamental wave and harmonics.

[0014] Preferably, in step 1 , , , The four variables are calculated from the three-phase grid voltage using the positive and negative sequence decoupling formula. When the three-phase grid voltage values ​​change simultaneously or when the voltage value of one phase changes, different values ​​of the four variables will be obtained; the values ​​of the four variables change in real time.

[0015] Preferably, the feedforward signal calculation module includes a low-pass filter LPF and an adjustment parameter K. , , , The components are processed sequentially by low-pass filters LPF and K, and the phase of the high-frequency components is compensated by the components themselves.

[0016] Preferably, before performing the inverse Park transformation in step 5, the output values ​​of the positive-sequence current d, positive-sequence current q, negative-sequence current d, and negative-sequence current q of the current loop are respectively superimposed onto... , , , superior.

[0017] Preferably, in step 5, the inverse Park transformation stably follows the phase angle θ of the positive sequence component of the grid voltage.

[0018] A photovoltaic grid-connected inverter is characterized by using the above-mentioned grid voltage feedforward control method.

[0019] The positive and negative sequence decoupled grid voltage feedforward control method has the following beneficial effects:

[0020] (1) The present invention can perform well when the grid voltage is unbalanced, realize independent control of positive and negative sequence current, and improve the stability of the inverter in grid-connected operation under weak grid conditions.

[0021] (2) The present invention provides decoupled control of positive and negative sequences, which can set different parameters for positive and negative sequences respectively to meet various grid connection environments.

[0022] (3) The feedforward control method of the present invention has a faster response speed than conventional methods when the parameters can be adapted to weak power grids, and can provide better dynamic response during voltage ride-through. Attached Figure Description

[0023] Figure 1 : Block diagram of the feedforward signal calculation module in this invention. Detailed Implementation

[0024] The following is combined with Figure 1 The present invention will be further described as follows:

[0025] like Figure 1 As shown, a grid voltage feedforward control method with positive and negative sequence decoupling includes the following steps: collecting the grid voltage at the grid connection point, performing positive and negative sequence decoupling on it, and obtaining four variables. , , , Using positive sequence components Software phase-locked loop (PLL) is implemented to enable the system to stably follow the phase angle θ of the positive-sequence component of the grid voltage. The positive and negative sequence components are then... , , , The input feedforward signal calculation module adjusts the amplitude of the high-frequency component of the feedforward value. By adjusting the phase angle compensation parameters, it achieves lead or lag compensation and compensates for the phase of the high-frequency component. Reasonable adjustment of these two degrees of freedom enables the grid-connected inverter to stably connect to the grid under weak grid conditions. The feedforward signal calculation module ultimately outputs four variables. , , , The four variables obtained after passing through the feedforward signal calculation module , , , Perform inverse Park transformations according to the positive and negative coordinate systems respectively to obtain the positive-order coordinate system. , and negative order coordinate system , Positive and negative order are obtained synchronously. and Performing an inverse Clack transformation yields the three-phase stationary coordinate system. Using this value as the final feedforward value for PWM modulation, positive and negative sequence decoupled grid voltage feedforward control can be achieved.

[0026] In step 1 , , , All of them contain higher harmonics, which provides a basis for subsequent separate processing of the fundamental wave and harmonics.

[0027] In step 1 , , , The four variables are calculated from the three-phase grid voltage using the positive and negative sequence decoupling formula. When the three-phase grid voltage values ​​change simultaneously or when the voltage value of one phase changes, different values ​​of the four variables will be obtained; the values ​​of the four variables change in real time.

[0028] The feedforward signal calculation module includes a low-pass filter LPF and an adjustment parameter K. , , , The components are processed sequentially by low-pass filters LPF and K, and the phase of the high-frequency components is compensated by the components themselves.

[0029] Before performing the inverse Park transform in step 5, the output values ​​of the positive-sequence current d, positive-sequence current q, negative-sequence current d, and negative-sequence current q of the current loop are superimposed onto... , , , superior.

[0030] In step 5, the inverse Park transform stabilizes the phase angle θ of the positive sequence component of the grid voltage.

[0031] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the implementation of the present invention is not limited to the above-described manner. Any improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A grid voltage feedforward control method with positive and negative sequence decoupling, characterized in that, Includes the following steps: Step 1: Collect the grid voltage at the grid connection point, decouple it according to positive and negative sequence, and obtain 4 variables. , , , ;in, , , , All contain higher harmonics; Step 2: Use positive sequence components Software phase-locking is performed to enable the system to stably follow the phase angle θ of the positive sequence component of the grid voltage; Step 3: Separate the positive and negative components , , , Input feedforward signal calculation module; Step 4: The feedforward signal calculation module can adjust the amplitude of the high-frequency component of the feedforward value. By adjusting the phase angle compensation parameter, it can achieve lead or lag compensation and compensate for the phase of the high-frequency component. Reasonable adjustment of these two degrees of freedom can enable the grid-connected inverter to stably connect to the grid under weak grid conditions. The feedforward signal calculation module finally outputs four variables. , , , The feedforward signal calculation module includes a low-pass filter (LPF) and an adjustment parameter K. , , , It is processed sequentially by low-pass filters LPF and K, and compensates for the phase of high-frequency components by itself. Step 5: Calculate the four variables obtained from the feedforward signal calculation module. , , , Perform inverse Park transformations according to the positive and negative coordinate systems respectively to obtain the positive-order coordinate system. , and negative order coordinate system , Positive and negative order are obtained synchronously. and Among them, the inverse Park transform stably follows the phase angle θ of the positive sequence component of the grid voltage; Step 6: Perform an inverse Clack transformation to obtain the three-phase stationary coordinate system. Using this value as the final feedforward value for PWM modulation, positive and negative sequence decoupled grid voltage feedforward control can be achieved.

2. The grid voltage feedforward control method with positive and negative sequence decoupling according to claim 1, characterized in that: In step 1 , , , The four variables are calculated from the three-phase grid voltage using the positive and negative sequence decoupling formula. When the three-phase grid voltage values ​​change simultaneously or when the voltage value of one phase changes, different values ​​of the four variables will be obtained; the values ​​of the four variables change in real time.

3. The grid voltage feedforward control method with positive and negative sequence decoupling according to claim 1, characterized in that: Before performing the inverse Park transform in step 5, the output values ​​of the positive-sequence current d, positive-sequence current q, negative-sequence current d, and negative-sequence current q of the current loop are superimposed onto... , , , superior.

4. A photovoltaic grid-connected inverter, characterized in that: It applies the positive and negative sequence decoupling grid voltage feedforward control method described in any one of claims 1-3.

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