Ultracapacitor Boosted Fuel Cell Hybrid Vehicle

摘要

With the escalating number of vehicles on the road, great concerns are drawn tothe large amount of fossil fuels they use and the detrimental environmental impacts fromtheir emissions. A lot of research and development have been conducted to explore thealternative energy sources. The fuel cell has been widely considered as one of the mostpromising solutions in automobile applications due to its high energy density, zeroemissions and sustainable fuels it employs. However, the cost and low power density ofthe fuel cell are the major obstacles for its commercialization.This thesis designs a novel converter topology and proposes the control methodapplied in the Fuel Cell Hybrid Vehicles (FCHVs) to minimize the fuel cell's cost andoptimize the system's efficiency. Unlike the previous work, the converters presented inthe thesis greatly reduce the costs of hardware and energy losses during switching. Theyneed only three Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) tosmoothly accomplish the energy management in the cold start, acceleration, steady stateand braking modes. In the converter design, a boost converter connects the fuel cell to the DC busbecause the fuel cell's voltage is usually lower than the rating voltage of the motor. Inthis way, the fuel cell's size can be reduced. So is the cost. With the same reason, thebidirectional converter connected to the ultracapacitor works at the buck pattern whenthe power is delivered from the DC bus to the ultracapacitor, and the boost converter isselected when the ultracapacitor provides the peaking power to the load. Therefore, thetwo switches of the bi-directional converter don't work complementarily but in differentmodes according to the power flow's direction.Due to the converters' simple structure, the switches' duty cycles aremathematically analyzed and the forward control method is described. The fuel cell isdesigned to work in its most efficient range producing the average power, while theultracapacitor provides the peaking power and recaptures the braking power. Thesimulation results are presented to verify the feasibility of the converter design andcontrol algorithm.