VSG低电压穿越的特性分析及控制方法研究

A Study on Characteristic Analysis and Control Methods of Low Voltage Ride Through for the VSG

虚拟同步发电机(VSG)为风电、光伏等可再生能源提供了一种友好的并网方式。然而,常规VSG在电网电压跌落后易出现过流问题而退出运行。该文基于VSG的典型模型对其在电网电压对称故障后的动静态特性进行了分析,并提出一种改进的低电压穿越控制方法。所提方法在并网情况下切出VSG的无功-电压控制环节,通过有功和无功功率的协同控制避免VSG在电网电压跌落后的稳态过流,并引入基于最大故障相电流的时变虚拟阻抗以抑制VSG在电网电压跌落和恢复时刻的瞬态故障电流。基于Matlab/Simulink构建了VSG并网仿真模型,验证了VSG在电网故障后特性分析和低电压穿越控制方法的有效性。

Virtual synchronous generator(VSG)provides a friendly grid-connected method for renewable energy. However,the conventional VSG is prone to be overcurrent and out of use when grid voltage sag happens. In this paper,the static and transient characteristic of the VSG during symmetrical grid fault is analyzed based on its basic model and a modified low voltage ride-through(LVRT)control method is proposed. The proposed method cuts off the reactive power-voltage control loop of the VSG in grid-connected mode,and protects the VSG from overcurrent in steady state by the coordination control of active and reactive power,at the same time,provides reactive power support to the grid. Besides,an adaptive virtual impedance according to the maximum phase current is introduced to suppress the amplitude of transient fault current. Simulation results based on Matlab/Simulink have proved that the characteristic analysis and the proposed LVRT control method are effective.