Three-Dimensional Coordinate Transformation Theoryfor Three-Phase Four-Wire Unbalanced Power Electronic System

Abstract

This paper proposes a three-dimensional coordinate transformation theory, which can convert three-phase unbalanced ac quantities into balanced two-phase orthogonal ac quantities and one constant dc quantity, and these three quantities can be further converted into three constant dc quantities by using three-dimensional Park coordinate transformation. By applying the proposed three-dimensional coordinate transformation along with three-dimensional Park coordinate transformation to three-phase four-wire or four-leg unbalanced ac power electronic systems, these ac power electronic systems can be directly converted into dc power electronic systems, so the proportional-integral controllers can be employed to realize the error-free control of the three-phase unbalanced currents for these ac power electronic systems.