Control strategy for multiple input DC-DC power converters devoted to hybrid vehicle propulsion systems

Customer demands for greater acceleration, performance, and vehicle range in pure EVs plus mandated requirements to further reduce emissions in HEVs increase the appeal for combined on-board energy storage systems and generators. This paper deals with the control system of an original HEV propulsion system that includes fuel cell generator and storage energy system combining ultracapacitor tank and battery. The three on-board power sources supply the vehicle traction drive through a multi-input DC-to-DC power converter which provides the desired management of the power flows. In particular, in the proposed arrangement the ultracapacitor tank is used for leveling the battery load current during transients resulting from either acceleration or braking operation of the vehicle. The paper outlines the features of the control unit of the DC-to-DC power converter being used in the proposed propulsion system and describes the main characteristics of a 35 kW prototype developed to conduct laboratory experiments and validate the control strategy.