New Stationary Frame Transformation for Control of a Three-Phase Power Converter Under Unbalanced Grid Voltage Sags

Abstract

The paper deals with a new nonlinear transformation providing representation of unbalanced threephase signals (voltage and currents) as vectors which have constant components in a new rotating frame. Using the proposed transformations the control system of a power electronic converter operating with an unbalanced grid can be equipped with proportional-integral PI controllers, without the use of resonant terms, for which anti-wind-up structures are more complicated and non-intuitive. The paper presents derivation of new direct and inverse transformations, features, a power converter model in a new frame, simulation results showing the waveforms of signals transformed to the new non-Cartesian frame, and simulation and experimental results of voltage oriented control for a grid connected power converter.