A High-Efficiency High-Power-Density On-Board Low-Voltage DC–DC Converter for Electric Vehicles Application

The on-board low-voltage dc-dc converter (LDC) in electric vehicles (EVs) is used to connect the high-voltage battery with the low-voltage auxiliary system. With the advancement of auxiliary equipment in EVs, the output current of the LDC can be hundreds of amperes, which will cause high-conduction loss and severe thermal concern. In this article, a high-efficiency high-power-density on-board LDC is presented. To reduce current stress and improve efficiency, three-phase interleaved LLC dc-dc converters are paralleled to provide 270 A load current. Synchronous rectifier is used to reduce secondary conduction loss. zero-voltage-switching (ZVS) turn-on of primary switches and ZCS turn-off of secondary switches are achieved, thus switching loss can be reduced significantly. Moreover, phase-shedding technology is used to improve light load efficiency. Switch-controlled capacitor (SCC) technology is used to achieve accurate load current sharing among the three phases, which protects the devices against high-current stress, reduces the conduction loss, and improves the reliability of the system. As SCC switches achieve ZVS turn-on and turn-off by its nature, the loss of the SCC circuit is of less concern with regard to the rated output power. In addition, GaN HEMTs are used in the primary side to improve the power density and eventually help achieving light weight. A 3.8-kW (14 V/270 A) LDC prototype is developed and tested. Experimental results show good current balancing among the three phases. A peak efficiency of 96.7% at 140 A load and a full load efficiency of 95.8% are achieved with 3 kW/L power density and 1.5 kg weight.