Dual sequence current controller without current sequence decomposition implemented on DSRF for unbalanced grid voltage conditions

Dual sequence current control is the key technique for grid-connected voltage source converter to ensure the performance or fulfill grid requirement under unbalanced grid voltage conditions. In this paper, after reviewing and analyzing the existing dual sequence current controller (DSCC), a simple DSCC is proposed based on double synchronous reference frame (DSRF) without the need of current sequence decomposition. The positive-sequence current is controlled in the positive SRF with a PI controller, while the negative-sequence current is controlled in the negative SRF only with an integrator controller. To avoid the ineffectiveness of the inductor current feed-forward (ICFF) decoupling technique in DSRF, only the decoupling components in the positive SRF is performed. This ensures the same performance with the conventional current controller under normal grid voltage conditions. Further, a new decoupling technique with reference current feed-forward can be optionally employed to provide decouple effect for both positive-sequence and negative-sequence current control. Simulation results will demonstrate the validity of the proposed DSCC.