不对称电网故障下级联型光伏并网逆变器的低电压穿越控制

Low voltage ride-through controlling of cascaded inverter for grid-connected photovoltaic systems under asymmetric grid fault

级联型并网逆变器在大容量光伏并网中具有较好的应用前景,有利于解决光伏阵列间的光照不均匀造成的发电效率低的问题。研究了在不对称电网故障条件下级联型光伏并网逆变器的低电压穿越控制策略。首先分析了在不对称电网故障条件下网侧电压的数学模型,总结出不同故障条件下三相网侧电压幅值与相位之间的规律。基于上述规律分析了不同故障条件下级联型光伏并网逆变器的控制方法,并提出了基于旁路原理的低电压穿越控制策略。最后建立了级联型光伏并网逆变器低电压穿越控制策略的仿真模型。通过算例仿真,验证了控制策略设计的正确性和有效性。

Cascaded grid-connected inverter has good application prospects in large-capacity grid-connected photovoltaic systems,which helps to solve the problem of lower generation efficiency caused by unequal irradiance between PV arrays.The Low Voltage Ride Through(LVRT)control strategy of cascaded inverter for grid-connected photovoltaic systems under asymmetric grid fault conditions is studied.First,the mathematical model of voltages in grid side is researched under asymmetric grid fault conditions.The law of amplitude and phase of three phase voltages in grid side is summarized under different fault conditions.The control method of cascaded inverter for grid-connected PV systems is analyzed based on the above law,and the low voltage through control strategy based on bypass principle is proposed.Finally,the simulation model of the low voltage through control strategy of cascaded inverter for grid-connected PV systems is established.The correctness and effectiveness of control strategy design are verified by simulation under fault conditions.