Energy-regenerative fuzzy sliding mode controller design for ultracapacitor-battery hybrid power of electric vehicle

In order to deal with two major problems of electric vehicle (EV): the short driving range and the short life of batteries, a hybrid power system was designed and applied to the EV. It was composed of an ultracapacitor with high-specific power and long life, four lead-acid batteries with high-specific energy, and a bi-directional DC/DC converter. To improve the stability and reliability of the system, based on researching energy-regenerative process and fuzzy sliding mode controller (Fuzzy-SMC), the energy-regenerative mathematical model of the system was established, and the energy-regenerative Fuzzy-SMC for the system was designed. The experimental results show that the Fuzzy-SMC is superior to PID controller at response speed, steady-state tracking error and resisting perturbation. Additionally, comparing with the EV which uses batteries as its single power source, the ultracapacitor-battery hybrid power system can recover more energy, lengthen the life of batteries, and increase the driving range by 36.8% with PID controller, and by 42.1% with Fuzzy-SMC.