Bidirectional Non-Isolated Three-Phase Onboard Charger with a Low-Voltage Lower-Phase Operation Mode

Abstract:
Compared to isolated design, non-isolated onboard chargers are more susceptible to common-mode issues but promise a higher power density by omitting bulky inductive elements. A single-stage, non-isolated design for an onboard charger is presented, which can be operated in three-phase or a lowerphase mode and offers measures against common-mode problems. The system voltage of the charger has been optimized for 800V traction battery packs and allows charging of the battery even below 650V, despite a non-isolated, three-level design. Possible common-mode current problems which could trip residual current devices (RCDs) are investigated and drastically mitigated through a selection of suitable modulation schemes. Furthermore, a hardware prototype is presented, as well as measurement results of the single-phase operation, common-mode currents and efficiency.