配电网对称跌落下光伏系统不稳定机理及对策研究

Research on Instability Mechanism and Countermeasures of Photovoltaic System under Symmetrical Sag of Distribution Network

针对中压配电网对称跌落下并网运行的光伏系统不稳定的现象,分析了该现象的发生机理,并提出了基于配电网对称跌落下无功电流边界条件的光伏逆变器低电压穿越控制方法,以保证含光伏系统的中压配电网继电保护的正常运行。基于光伏并网逆变器技术规范要求及电路原理,分析了含分布式光伏系统的中压配电网在对称跌落下不稳定现象的发生机理,获得无功电流边界条件;在此基础上,提出了改进的光伏逆变器低电压穿越控制方法;通过MATLAB/Simulink仿真试验证明,改进的光伏逆变器低电压穿越控制方法,可有效解决中压配电网对称跌落下出现的并网运行的光伏系统不稳定、输出电流相位不规律问题。

Aiming at the phenomenon of instability operation of grid-connected photovoltaic(PV)system under symmetrical sag of medium voltage distribution network,mechanism of this phenomenon is analyzed,and a low voltage ride through(LVRT)control method of PV inverter based on the boundary condition of reactive current under symmetrical sag of distribution network is proposed to guarantee normal operation of relay protection of medium voltage distribution network with PV system.Based on the technical specifications of grid-connected PV inverter and circuit principles,the mechanism of instability of typical medium voltage distribution network with distributed PV system under symmetrical fault is analyzed,and the boundary conditions of reactive current are obtained.Simulations in Matlab/Simulink are done in the cases of symmetrical sag in medium voltage distribution network when PV inverter with or without improved LVRT control method,which verify the validity of the improved control method.The simulation results show that the improved LVRT control method can effectively solve the problem of instability and irregular output current phase of PV system in grid connected operation under symmetrical sag of medium voltage distribution network.