Improved predictive current control of grid-connected DC-AC converters under unbalanced grid voltage conditions

This paper proposes an improved predictive current control scheme for grid-connected DC-AC voltage source converters (GC-VSCs) when the grid voltage is unbalanced. The control scheme is based on space vector modulation (SVM) technique and implemented in the stationary reference frame without involving any current-sequential decomposition process. Due to the requirement for controlling the ac terms of both positive and negative sequence components, detailed compensation methods due to the control delay and the finite sampling frequency are analyzed and designed for the proposed predictive current control scheme to improve the control accuracy and to increase the control bandwidth. Experimental results are provided and compared with those of conventional vector control with dual PI current control schemes to demonstrate the effectiveness of the proposed control strategy during steady-state and transient conditions under unbalanced grid voltage conditions.