Research Of PV Inverter Control Strategy Under Unbalanced Grid Voltage

Because of environmental pollution and energy crisis, clean and renewable energies are favored by the world, especially photovoltaic. Ingird actual operation, the unbalanced grid voltage will bring some problemsto grid-connected photovoltaic systems.Based on a large number of measured data,this paper carried out an analysis about unbalanced voltage in actual grid operation. Then, the inverter output current control structure under positive and negative sequence synchronous rotating reference frame is obtained by the analysis of PV inverter mathematical model during balanced and unbalanced voltage. Further, a simpler PV inverter current control structure under stationary reference frame is obtained by using PR regulator.The PV inverter output current referencecalculation is a key technology inPV inverter control under unbalannced grid voltage. Based on instantaneous active-reactive control (IARC) and average active reactive control (AARC), this paper proposed flexible active reactive control to reduce output power fluctuation and output current harmonics simultaneously. By the analysis of instantaneous power theory, this paper proposed another PV inverter output current reference calculation method with variables. The proposed method won’t bring harmonic current problems, and can also eliminate fluctuations in active power or reactive power fluctuations. Theoretical analysis and simulation results verify the validity of the proposed calculation methods of current reference. Finally, the comparison between two proposed output current reference calculation methods was carried out.Focusing on the study of PV inverter output peak current under unbalanced voltage, this paper presented a new peak current calculating method, and then proposed a peak current limiting method which can ensure the output current of PV inverter not exceed the permit value during unbalanced voltage sags. The simulation results verify the validity of the proposed method. The PV inverter control strategy under unbalanced voltage studied in this paper can provide some reference for the improvement of photovoltaic system adaptability and low voltage ride through capability.