光伏并网系统低电压穿越控制策略研究

Study on low voltage ride-through control strategy in grid-connected photovoltaic system

在分析二极管箝位式(NPC)逆变器的基础上,建立其dq坐标下的数学模型,设计了具有电压前馈环节的电压平方外环电流内环的双闭环的控制策略,实现正常电网情况下的光伏并网控制。针对电网电压跌落的情况,采用了双二阶广义积分的锁相环进行电压跌落检测,该方法保证了对电网跌落深度的有效检测,基于跌落的深度设计了无功支撑的控制策略对跌落电压进行控制而达到不脱网运行的目的。仿真结果表明,当电网发生对称和不对称电压跌落时,能够对跌落电压进行检测并控制,使系统具有低电压穿越能力,提高了系统的适应性和稳定性。

Based on the analysis of diode neutral point clamped(NPC)inverter,the mathematical model in dq coordinate is established,and the double closed-loop control strategy of outer voltage square loop and inner current loop with voltage feed-forward link is designed to realize the grid-connected photovoltaic control under normal grid conditions.Aiming at the presence of power grid voltage sag,double second-order generalized integral phase-locked loop is adopted to detect the voltage sag,the method ensures the effective detection of sag depth in power grids.According to the sag depth,the control strategy of reactive power support is designed to control the voltage sag,so as to achieve the purpose of grid-connected operation.Simulation results show that when symmetrical and asymmetrical voltage sag occurs in power grid,the sag voltage can be detected and controlled,which makes the system have the ability of low voltage ride through and improve the adaptability and stability of the system.