电网电压前馈控制VSG的阻抗建模与并网稳定性分析

针对电网电压谐波背景下虚拟同步发电机（VSG）并网电流畸变及并网稳定性下降问题，文中提出了一种基于电流环的电网电压前馈控制策略。从入网电流传递函数出发，设计电压前馈控制模块以消除背景谐波的影响，并基于谐波线性化方法分别建立加入前馈控制前后的VSG序阻抗模型，对其在各频段阻抗特性及并网稳定性上的影响进行对比分析。结果表明，引入该前馈控制等同于在VSG输出端并联虚拟阻抗，输出阻抗的高频段幅频曲线上移，可以改善非理想电网条件下的并网电流质量。同时，中高频段相频特性由容性矫正为感性，可以消除并网条件下的谐波振荡风险，提高交互系统稳定性。最后，基于实时仿真实验平台（RT-LAB）硬件在环实验验证了文中控制策略及理论分析的正确性。

The impedance modelling and stability analysis of VSG with grid voltage feedforward control

To solve the problems of current quality decreasing and poor grid stability of virtual synchronous generator (VSG) under the condition containing background harmonic,a power grid voltage feedforward control strategy based on current loop for VSG is proposed. In order to eliminate the influence of grid voltage background harmonics on grid connected current,the voltage feedforward control function is derived according to the input current transfer function. The impedance model of VSG with and without feedforward control are established based on the harmonic linearization method. The influence on both the impedance characteristics at different frequency range and stability of grid connection are compared and analyzed. The results show that the introduction of the feedforward control is equivalent to parallel virtual impedance at the output of VSG,so the amplitude frequency curve of output impedance in high frequency band moves up,which can improve the grid connected current quality under non ideal grid conditions. At the same time,the phase frequency characteristics of medium and high frequency band are corrected from capacitive to inductive,which can eliminate the risk of harmonic oscillation under grid connected conditions,and improve the stability of interactive system. Finally,a hardware in the loop experimental platform is built to verify the correctness of the control strategy model and related analysis.