Optimized Modulation of Isolated Bidirectional Single-Stage Three-/Single-Phase X-Rectifier for EV On-Board Chargers

Inhalt:
The three-/single-phase ac input single-stage isolated eXtended-functionality rectifier (X-Rectifier) EV on-board charger (OBC) employs 650V GaN monolithic bidirectional power transistors (M-BDS) in the input stage, provides sinusoidal input currents and bidirectional operation in three-phase and split/singlephase grids without power derating, operates from asymmetrical three-phase mains, provides reactive power if needed, and supports extremely asymmetric phase loading in islanding/standalone mode. This paper first presents an improved X-Rectifier standard modulation method (M#1) with significantly lower current stresses compared to a previously published proof-of-concept method while being applicable for all operating modes discussed above. Next, the optimization of M#1 regarding semiconductor losses is discussed and the implementation of near-optimum secondary-side duty-cycle calculation (named M#2) without requiring high-dimensional look-up-tables is introduced. Considering a 6.6kW X-Rectifier and a typical charging process, simulation results indicate an improvement of the average semiconductor efficiency from 98.6% for M#1 to 98.9% for M#2, i.e., a semiconductor loss reduction of about 20%.