UC Berkeley

On-board battery chargers are a key component of electric vehicles of all types. Conventionally, they may be used to recharge a vehicle's battery pack, but as they are connected to the grid, they can also be used to provide ancillary grid services, such as reactive power support and longer-term battery-to-grid backup. On-board chargers also represent a potentially significant portion of a vehicle's weight and can take up considerable volume. This paper discusses the design and implementation of a high power density Level II charger converting between 400 VDC and 240 VAC, utilizing two interleaved flying-capacitor multilevel converter stages combined with a full H-bridge unfolder or active rectifier. The focus of this work is the ac-dc/dc-ac power stage, with the goal of high efficiency and power density. Thus, power factor correction (PFC) control and twice-line-frequency buffering are not discussed or implemented in this work. Experimental results show a peak system efficiency of greater than 98.9%, a power output of 7 kW, and an effective switching frequency at the inductor switch nodes of 720 kHz.