弱电网下基于电压扰动补偿的并网变换器改进控制方法

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.