Control scheme in hybrid synchronous stationary frame for PWM ac/dc converter under generalized unbalanced operating conditions

This paper proposes a new control scheme of improved transient response for the pulsewidth-modulation ac/dc converter under generalized unbalanced operating conditions. The overall-bandwidth diminishing filter/functional block for extracting positive and negative sequence components has been avoided by employing dual current regulators in positive- and negative-rotating synchronous frames. The steady-state error due to 120-Hz ac signals has been reduced by employing a resonant-gain path in the current regulator. This paper also proposes simplified current-reference calculation scheme in the regulation of instantaneous active/reactive power. Compared to the previous works, the proposed control method has better transient response in compensation for generalized unbalanced operating conditions (unbalanced input supply and unbalanced input impedances) of wide range while still satisfying unity input power-factor correction and ripple-free dc-output-voltage regulation without adding any external hardware. The proposed control system has been analyzed and tuned based on the ac small signal perturbed model under unbalance. Simulation and experimental results confirm the proposed control method under severe unbalanced operating conditions.