Generalized Power and Current Control for Three-Phase Four-Wire Converter under Unbalanced Grid Conditions

Three-phase grid-connected converter usually adopts different power and current control strategies under unbalanced conditions according to the practical application, but the power relationship is mainly discussed in three-phase three-wire system, and zero sequence power is not considered. Though theoretical analysis of the vector relationship between instantaneous power and current, a general expression of reference current for three-phase four-wire converter under unbalanced faults is proposed in this paper, which can realize switching between five fixed objective controls. On this basis, three coordinated objective control strategies are presented, which can be applied to three-phase four-wire converter with different neutral phase overcurrent capability. The proposed control can be easily implemented in alpha beta 0 stationary frame by using only two parameters without phase-locked loop, and can satisfy the case of single-phase and two-phase grounding faults. Simulation results are provided to verify the proposed method.