Power Control Strategy for Fuel Cell Hybrid Electric Vehicles

Fuel cell is one of alternative power sources, which can replace the conventional internal combustion engine. But, it has some drawbacks such as low efficiency at high power output and inability of energy regeneration. So, hybridization of the fuel cell has been proposed to overcome these drawbacks. And the fuel cell hybrid system is preferred in a viewpoint of cost and performance.

HMC's fuel cell hybrid system consists of a fuel cell, a battery, and a bi-directional dc/dc converter. Bi-directional dc/dc converter plays a key role that controls power distribution between fuel cell and battery. Conceptually, the fuel cell is main power source and the battery is auxiliary power source. In this paper, the power control strategy for fuel cell hybrid system is proposed to satisfy two control targets. One is to get high system efficiency and the other is to maintain battery's SOC(state of charge) in high efficiency region of the battery. So, the control strategy can be also divided into two parts, which are system efficiency care part and SOC control part. The system efficiency can be improved by controlling power distribution between fuel cell and battery. And a bi-directional dc/dc converter controls the SOC of battery. Sometimes there exists contradictory situation that two control targets cannot be satisfied simultaneously. In that case, the SOC control has priority to the system efficiency. The proposed control strategy is evaluated by experiments.