Controller design of a grid-tie inverter bypassing DQ transformation

This paper proposes a novel approach for the controller design of a three-phase grid-tie inverter. First, the paper analyzes the input-output map of the system consisting of the cascade connection of a diagonal transfer function pre- and post-multiplied by DQ (direct-quadrature) and inverse DQ transformations which are prevalently used as a controller for systems with a rotating axis. It shows that the input-output map is time invariant when the angular velocity of DQ transformation is constant and derives the transfer function. It extends the result when the angular velocity is not constant, and derives an LPV state-space representation of the input-output map. Second, the paper analyzes the input-output map in terms of the positive and negative phase sequence components. Finally, the paper applies the analysis to the controller design for a grid-tie inverter bypassing DQ transformation. The efficacy of the proposed method is verified by a simulation and an experiment.