Flexible grid connection technique of voltage source inverter under unbalanced grid conditions based on direct power control

This paper proposes a flexible grid connection technique of voltage source inverter (VSI) based on direct power control strategy under unbalanced grid conditions. Based on the mathematical model in αβ stationary reference frame of VSI, the generalized power reference compensations expressions for adjustable current unbalance and power fluctuations are deduced based on the active and reactive power expressions. Three different algorithms for control parameters are designed to regulate the current negative sequence, the active power ripples or the reactive power ripples at the same time. Furthermore, MCCF (Multiple Complex Coefficient Filter) is applied to separate positive and negative fundamental components of grid voltage and current, and PIR (Proportional Integral Resonant) controller is used to track the instantaneous power references. The experimental results verify that the proposed control strategy is adaptive to the flexible control targets.