Control of Isolated Four-Quadrant Single-Stage Three-/Single-Phase X-Rectifier for EV On-Board Chargers

Overview & Synopsis

The single-stage isolated eXtended-functionality rectifier (X-Rectifier) electric vehicle (EV) on-board charger (OBC) employs 650V GaN monolithic bidirectional power transistors (M-BDS) in the input stage, provides sinusoidal input currents and four-quadrant operation in three-phase and split/single phase grids without power derating, operates from asymmetrical three-phase mains, provides reactive power if needed, and supports extremely asymmetric phase loading in standalone vehicle-to-load (V2L) mode. This paper presents a new improved phase-modular control method for the X-Rectifier that enables tracking of arbitrary and independent phase current references regardless of the instantaneous grid voltage (i.e., enables four-quadrant operation). The method supports grid-tied (i.e., grid-to-vehicle, G2V, or vehicle-to grid, V2G) and grid-forming (i.e., V2L) operation. Further, aiming towards a practical realization of the X-Rectifier, the paper addresses implementation aspects of the M-BDS half-bridges, like commutation logic around the grid-voltage zero crossing, fault handling, and soft-switching behaviour. Finally, a realized 5.5 kVA hardware demonstrator of the X-Rectifier is used to validate the proposed control method experimentally for all operating modes, including grid-tied three- and single-phase four-quadrant operation (G2V, V2G, and full reactive power modes). Further, robust V2L operation is verified with real-world loads, i.e., in three-phase mode with asymmetrical loading of the phases including a woodworking power tool, and in single-phase mode with a high-power vacuum cleaner with high inrush current and hence momentary overload of the X-Rectifier demonstrator.