Control of Δ-Y transformer based grid forming inverter for unbalanced stand-alone hybrid systems

This paper proposes a new vector (dq) control strategy for a three-leg grid forming inverter with Δ-Y transformer for operation with three-phase four-wire hybrid stand-alone power system. The main challenge for the grid forming inverter is to provide balanced output voltages to highly unbalanced loads, i.e., due to the presence of single phase load/PV sources, with a fast speed of response. A new per-phase dq control strategy considering the phase shift of the Δ-Y transformer is presented in this paper which allows one to avoid the conventional slow symmetrical components calculator (SCC), while achieving zero error, i.e. voltage balancing, in steady-state and fast dynamic response. Effectiveness of the proposed control strategy is evaluated based on time-domain simulation studies.