Per-phase vector (dq) controlled three-phase grid-forming inverter for stand-alone systems

Hybrid mini-grids usually employ diesel generator sets (gensets) as grid forming units in three-phase four-wire systems. The impact of unbalances in power demand (load) and renewable power injection on the power quality is relatively small due to the also small output impedance of the rotating generators. However, when a battery inverter is required to form the grid, the power quality can deteriorate significantly in the presence of unbalanced power injection/demand in the system, due to the larger impedance of the low-pass output filter. The conventional approach of using three-phase dq control and symmetrical components decomposition (SCD) usually results in slow dynamic response. This paper proposes a per-phase dq technique that does away with the need for SCD and presents superior dynamic performance as demonstrated by simulation.