Control of a Three-Phase Power Converter Connected to Unbalanced Power Grid in a Non-Cartesian Oblique Frame

The paper presents a new approach to positive and negative sequence current vector control of a grid connected three-phase three-wire power electronic converter operating under grid voltage imbalance conditions. The concept utilizes representation of unbalanced converter current in the new coordinate’s frame in which the current vector components are constant. 

The nonlinear trigonometric transformation of twodimensional current vector components from the stationary frame to the new frame is found on-line depending on the reference current asymmetry. The presented concept of new coordinate’s utilization allows implementation of proportionalintegral terms as current regulators without the use of resonant terms and without the use of the measured current symmetrical sequences decomposition. The paper presents the theoretical approach, simulation results, as well as laboratory tests results.

Index Terms — AC–DC power conversion, current control, Clarke’s transformation, Park’s transformation