弱电网下基于电压扰动补偿的并网变换器改进控制方法

在弱电网条件下，并网变换器的控制系统与电网阻抗相互耦合，导致并网系统的稳定性降低，其中并网点电压扰动对锁相环和直流电压环的影响是导致并网变换器稳定性下降的关键因素。变换器阻抗模型是系统稳定性分析的基础，因此，首先在dq坐标系下，建立了包含电流环、锁相环和直流电压环等环节的三相并网变换器小信号阻抗模型。由阻抗模型中各变量的传递关系，能够找出并网点电压对锁相环和直流电压环输出的扰动通道，推导出扰动分量对控制器输出影响的表达式。在此基础上，将锁相环和直流电压环输出扰动补偿项添加到d轴和q轴电流环控制器，进而提出了基于并网电压扰动补偿的控制方法。理论分析结果表明，该方法可以在弱电网条件下有效降低电网阻抗与控制器耦合的影响，提高并网系统的稳定性。实验结果验证了理论分析的正确性和所提方法的有效性。

Improved Control Method of Grid-connected Converter Based on Voltage Disturbance Compensation in Weak Grid

The control system of grid-connected converter and the grid impedance are coupled to each other in the weak grid, which affects the system stability. The impact of the voltage disturbance at the point of common coupling(PCC)on the phase-locked loop(PLL)and the DC voltage loop are the key factors resulting in decreased stability of the grid-connected converter. The converter impedance model is the basis of system stability analysis. Firstly, this paper develops a small-signal impedance model of the three-phase grid-connected converter including the current loop, PLL and DC voltage loop in the dq frame. Combined with the transfer relationship of each variable in the impedance model, the disturbance channel of the PCC voltage to the output of PLL and DC voltage loop can be obtained, and the expression of the impact of disturbance component on the controller output is derived. On this basis, the output disturbance compensation terms of PLL and DC voltage loop are added to the d-axis and q-axis current loop controllers. Then the control method based on PCC voltage disturbance compensation is proposed. The theoretical analysis results show that the method can effectively reduce the impact of grid impedance and controller coupling in the weak grid and improve the stability of grid-connected system. The experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed method.