Hybrid instantaneous active power control for PWM rectifier under grid voltage dips considering the limitation of phase current

When the grid voltage dips, the power handled by the PWM rectifier must be reduced. This paper analyses the mathematical model of a grid-connected inverter under unbalanced grid voltages based on the instantaneous power theory. The two control objectives of the PWM rectifier are introduced, one for symmetrical three-phase grid currents and the other for suppressing the fluctuation on the active power. Considering the limitation of phase current, an improved control strategy which is a hybrid of these two control objectives, is proposed to increase the average active power and decrease the fluctuation on the active power. The analysis in this paper is carried out in the P.u. system, so some simplified conclusions can be drawn. Corroboration of the expected features of the proposed control strategy is carried out by means of experiments.