Tan-Sun Coordinate Transformation System Theory and Applications for Three-Phase Unbalanced Power Systems

Abstract

This paper proposes a new-type Tan-Sun coordinate transformation system, which is an extended version of Clarke coordinate transformation system. The main purpose of the proposed coordinate transformation system is to convert three-phase unbalanced alternating-current quantities into two orthogonal alternating-current quantities with equal amplitudes, and further into two direct-current quantities without second harmonic components through Park transformation method. By applying Tan-Sun coordinate transformation system to three-phase unbalanced converters, we can realize the direct-current decoupling of the three-phase unbalanced currents in the direct-quadrature synchronous rotating coordinate system, so the control methods developed for three-phase converters under balanced voltage conditions can be migrated into those under unbalanced voltage conditions directly. Three-phase unbalanced phase-locked loop technique and active and reactive power definition and calculation for three-phase unbalanced power systems based on Tan-Sun coordinate transformation system are also proposed in this paper. The comparison between Tan-Sun coordinate transformation system and the traditional coordinate transformation system under unbalanced voltage conditions both from the aspects of theory analysis and simulation and experimental verification is provided, and these results indicate the superiority of Tan-Sun coordinate transformation system.