针对电网阻抗的大型光伏并网系统稳定性分析与提高策略

大型光伏并网系统中,一般采用多逆变器并联结构来提高总的光伏并网系统的容量。由于光伏电站的结构特点,随着并网容量的增加,电网阻抗值相对于某一个光伏发电单元而言将会被等效放大,从而导致逆变器控制策略失效且并网失败。文中在光伏并网系统开关平均模型的基础上,详细分析了电网阻抗对于逆变器输出电压和电流的影响,并针对电网阻抗导致的光伏并网系统的不稳定现象,采用虚拟阻抗思想,通过输出电流反馈,实现指令电流与输出电流的协调配合,等效消除电网阻抗对并网电压稳定性和并网电能质量的影响,从而保证系统的稳定运行。最后,通过仿真分析和试验验证了理论分析的正确性。

Analysis and Improvement Strategy for Stability of Large-scale Grid-connected Photovoltaic System Considering Grid Impedance

In the large-scale grid-connected photovoltaic(PV)system, the multi-inverter paralleled structure is used to improve the capacity of the system. According to this structure, as PV capacity is increased, the value of grid impedance can be equivalently enlarged with respect to a single PV power generation unit, which will directly result in failure of the control strategy for inverters, and finally a failure of connecting the PV system to grid. Based on the switch averaged model of the grid-connected PV system, this paper analyzes the influence of grid impedance on inverter output current and voltage. Then, by the output current feedback method, the automatic coordination between reference current and actual output current is realized to equivalently eliminate the influence of grid impedance on the stability of grid-connected voltage and the power quality, so as to guarantee the normal operation of system. Finally, the correctness of the theory is verified by the simulation analysis and experiment.