Control strategy of PV inverter under unbalanced grid voltage sag

The presence of unbalanced voltage sag in grid actual operation gives rise to the output power fluctuation of PV inverter, the increasing of output current harmonics and unbalanced current. The calculation of the output current reference is a key technology in the control of PV inverter and has important influence on the output of the PV inverter under unbalanced grid voltage. Base on the instantaneous power theory, this paper proposed a calculation method of PV inverter current reference under unbalanced voltage sag. The proposed method will not bring harmonic current problems, with the benefits of selectively elimination of active power fluctuations, reactive power fluctuations or negative sequence component. In addition, the inverter output active and reactive power fluctuation can be flexibly adjusted by changing the value of the variable given in the proposed calculation method. Theoretical analysis and simulation results verify the validity of the proposed calculation method of current reference.