弱电网并网运行时会产生谐波干扰以及电网电压频率波动等问题,导致逆变器输出电流谐波失真。弱电网并网环境对锁相环(phase locked loop,PLL)的性能提出了更高的要求。针对弱电网下并网逆变器的控制要求,在分析并网电压源型逆变器(voltage source converter,VSC)控制模型基础上,提出一种弱电网下PLL的优化方案。该方案采用超前补偿器补偿平均滑动滤波器(moving average filtering,MAF)的相位延迟以提高系统的动态响应；引入前馈频率估计环,提高系统在电网电压频率偏差较大时的锁相精度,仿真验证改进的PLL的有效性。建立并网VSC系统实验平台对本文所述改进方法进行验证。实验结果表明,经PLL改进后的VSC系统在弱电网条件下具有良好的鲁棒性,逆变器入网电能质量得到了保证。
英文摘要:
When the weak grid is connected to the grid, it will generate a lot of harmonic interference, grid voltage frequency fluctuations and other problems, which will cause harmonic distortion of the inverter output current. The weak grid connection environment places higher requirements on the performance of the phase locked loop (PLL).Aiming at the control requirements of grid-connected inverters in weak grids, based on the analysis of the control model of grid-connected voltage source inverters (VSC), a phase-locked loop (PLL) optimization strategy for weak grids was proposed.This strategy uses a lead compensator to compensate the phase delay of the moving average filtering (MAF) to improve the dynamic response of the system; the feed-forward frequency estimation loop is introduced to improve the phase-locking accuracy of the system when the grid voltage frequency deviation is large,and the simulation verifies the effectiveness of the improved PLL.Establish a grid-connected VSC system experimental platform to verify the improved method. The experimental results show that the VSC system improved by the PLL has good robustness under weak grid conditions, and the power quality of the converter connected to the grid is guaranteed.