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

Cascaded grid-connected inverter has good application prospects in large-capacity grid-connected photovoltaic systems. It helps to solve the problem of lower generation efficiency caused by unequal irradiance between PV arrays. This paper studies Low Voltage Ride Through (LVRT) control strategy of cascaded inverter for grid-connected photovoltaic systems under asymmetric grid fault conditions. 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.