Zero-voltage soft-switching DC-DC converterbased charger for LV battery in hybrid electric vehicles

Abstract

This study presents the implementation of a DC-DC power converter for battery charging from 200 V lithium-ion or nickel metal hydride (NiMH) battery to lead-acid battery (typically 12 V) utilised in hybrid vehicles such as Toyota Prius. For hybrid car, a low-voltage (LV) battery is utilised to power air conditioner, main lights, and different actuators in engine controlling unit etc. The LV battery is usually recharged by car alternator. For the sake of improving fuel efficiency, it is important to regulate charging by using the charging control scheme, where the battery charging is implemented in deceleration interval avoiding the acceleration interval of the car. The hybrid car is equipped with a high-voltage (HV) NiMH battery. The lead-acid LV battery is charged from the HV storage battery. The advantage of this charging method is recognised not only to replace the alternator from the car, but also to make efficient braking touching for the car driver, because the regenerative breaking recovered energy can be totally absorbed in the main HV battery. Moreover, the overall efficiency could be easily improved because the total efficiency of charging DC-DC circuit is greater than that of the car alternator.