Power Split of Fuel Cell/Ultracapacitor Hybrid Power System by Backstepping Sliding Mode Control

A fuel cell/ultracapacitor hybrid power system supplying an electric vehicle must efficiently split power among distinct power sources while adapting to variations in power demands. This paper shows that a backstepping-sliding-mode controlled two-input, bidirectional dc-dc converter can achieve the end. The two-input design of the converter system enables sharing power demands between the fuel cell and ultracapacitors. The bidirectional design of the converter system allows electrical currents to rush into or out of the ultracapacitors such that either fuel-cell generated current or regenerated current can charge the ultracapacitors. The backstepping sliding-mode control strategy enables the converter system to maintain a stable output voltage while tracking power split commands under nonlinear dynamics and time-varying load. Simulation and experimental results show that the proposed design is efficacious.