A New Circuit Topology for Battery Charger from 200V DC Source to 12V for Hybrid Automotive Applications

The research target is the development of the DC/DC converter for charging from 200V NiMH or Li-Ion battery to 12V Lead-acid storage battery in hybrid cars such as Toyota Prius. In car, a 12V Lead-acid storage battery is used to operate air conditioner, main lights and various actuators in engine control unit etc. Before the lead-acid battery ends up all the discharge, it should be charged using the alternator. In order to improve fuel efficiency, it is necessary to implement a so-called charge control, where the battery charge is executed in deceleration period avoiding the acceleration period of the car. In Hybrid cars, as a high voltage NiMH battery is equipped, it is possible to charge 12V Lead-acid storage battery from the high voltage battery. By using this scheme, it is realized not only to take off the alternator but also to improve braking touch for the car driver, because all regenerative energy can be absorbed in the high voltage battery. Furthermore the fuel efficiency can be improved easily for the reason why the efficiency of DC/DC converter is much higher than that of alternator.