GaN-based Non-isolated On-board Charger with Active Filtering

Abstract

Air pollution is one of the world’s leading risk factors for death. And transportation is one of the largest pollution sources. Therefore, electrification becomes a necessary step in reducing air pollution and save lives. As a result, electric vehicles are becoming the future trend in automotive industries. However, there are still some of the concerns which stop consumers from purchasing electric vehicles. Charging faster and longer driving range are two factors that consumers care most. So how to solve these concerns? A high-efficiency charger could be one solution. Level 2 charger takes less time in charging than level 1. But with the lack of charging facilities right now, charging should be available in all situations. This thesis investigates a high-efficiency on-board charger (OBC) that could be used both at residences and at charging stations. The OBC is able to operate at a wide output battery range as well. High efficiency means low losses. Therefore, the proposed topology uses the least number of components to minimize the losses as much as possible. The efficiency is further optimized by using wide bandgap device Gallium Nitride. Since Gallium Nitride shows superior performance in high power applications. The proposed OBC combines a GaN-based bridgeless totem-pole PFC with a synchronous buck converter with innovative active filtering to allow a much smaller dc-link capacitance. The carefully designed passive components occupy less space and help improve power density. Film capacitors are used to replace the conventional electrolytic capacitors since the latter do not have good reliability for automotive applications. The proposed OBC is designed with small current ripple percentage and small output voltage ripple percentage. The simulation results show a high peak efficiency over 98% at both level 1 and level 2 charging mode. The power factor (PF) is over 0.998 and the total harmonic distortion percentage (THD %) is less than 5% at full load condition (3.3 kW). In one sentence, the charger is simple, high efficiency, works with a universal charging system, with a wide output range, and compact.