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High-Frequency CRM AC/DC Converter for WBG-Based 6.6kW On-Board Charger

Fig. 1. Prototype of 6.6kW on-board charger.
Plug-in electric vehicles (PEVs), which include plug-in hybrid electric vehicles (PHEVs) and bat-tery electric vehicles (BEVs), are becoming more and more popular due to more efficient energy utilization and less combustion emission. One crucial challenge of PEV's commercialization is the demand for a lightweight, compact, and efficient on-board charger (OBC) system. The state-of-the-art level-2 OBC products are majorly Si-based design, which has a switching frequency of less than 100kHz, a 3~12W/in3 power density, and at most a 92~94% efficiency. In addition, the feature of bidirectional power flow of the OBC system is strongly desired by consumers accord-ing to market research conducted by automobile companies. However, Si-based OBC products cannot provide this function without significant sacrifice to power density and/or efficiency.

The emerging wide-bad-gap (WBG) power semiconductor devices provide the enabling tech-nology to dramatically increase the efficiency and power density of switch-mode power supplies with potential lower cost and better manufacturability. Therefore, by using WBG devices to de-sign the 6.6kW OBC system, the target is to increase the switching frequency to higher than 300kHz with doubled or tripled power density, at least 95% efficiency, and bi-directional power flow capability.

In this research, four different system architectures are, first evaluated and compared. The best candidate is the proposed novel variable DC-link voltage system architecture. Then, the fo-cus of this paper will turn to the design of the AC/DC stage so that detailed design considera-tions are elaborated, including the evaluation of 1.2kV SiC MOSFETs for device selection; a programmed extra off-time function to realize a whole line cycle zero-voltage-switching (ZVS) and eliminate dominant turn-on loss; and a proposed universal control strategy for both rectifier mode and inverter mode operation. Finally, a prototype is demonstrated with 98.5% efficiency and 47W/in3 power density of the AC/DC stage and 96% efficiency and 24W/in3 power density of the total system.


Fig. 2. Tested efficiency.
Fig. 3. Proposed inverter control.
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