Improved power control of photovoltaic generation system under unbalanced grid voltage conditions

In order to ride through the unbalanced grid fault, the output power of photovoltaic inverter will fluctuate and its output current will rise and distort under unbalanced grid voltage. This paper proposes an improved formula of reference current and its optimal coefficients method for the photovoltaic inverter under unbalanced grid voltage sag, taking into account the requirements of active and reactive power control. Then the analytic formula of its current harmonic distortion, three-phase current peak, active and reactive power fluctuation, DC voltage fluctuation and the control factor of its output current reference were derived. Considering the constraints of inverter phase current and the dc voltage fluctuation of capacitance in dc side, the optimal model of inverter current reference was established with minimum integrated amplitude of the active and reactive power function as a goal. The correctness of the proposed method has been verified by PSCAD/EMTDC simulation software.