Electric Vehicle Regenerative Braking Energy Efficient Recycling Control Strategy

The sustainable development of automobile industry is facing two major challenges: energy reliability and environmental protection. Many countries are working on how to development electric vehicle (EV), which has zero discharge and zero pollution. However, the range of electric vehicle is much smaller than conventional fuel vehicle. This insufficient has seriously affected industrialization and the rapid promotion of the electric vehicle. Regenerative braking to recycle the braking energy is an effective approach to extend the operating rang of an electric vehicle. At present, how to efficiently recycle regeneration energy of electric vehicle has already become the main question in low intensity brake process.In this paper, the electric vehicle regenerative braking's structure and the principle of work are summarized at first, so are the restrictions which affect the regenerative braking of EV. After that, the electric vehicle model is analyzed, which provides foundation for analysis system performance and control strategy.Electric vehicle induction motors are usually characterized by their low magnetizing inductance, which causes significant amount of iron loss. Classical vector control has poor efficiency under light load since it still adopts the constant magnetic flux control under low brake torque request. Through the analysis of typical driving cycle, we discuss the operation characteristics of electric motor in brake process. The mathematic model of the induction motor in a synchronously rotating frame considering iron losses is established, operation characteristics and energy conversion of rotor flux oriented controlled induction motor in brake process are discussed, then followed by giving the expression of induction motor losses, a high efficiency regenerative braking control strategy based on loss model is proposed. The control strategy redistributes the magnetizing current and torque current according to speed and brake torque request, which can improve the efficiency by finding the balance between induction motor's copper losses and iron losses. The simulation result shows that there is obvious improvement in recycling efficiency of regenerative braking energy, which confirms the validity of the control strategy. The energy saving result is remarkable, especially for the vehicle that mainly runs in urban areas.At the end, the paper discusses the braking force distribution strategy of electric vehicle simulation software ADVISOR. Taking the front wheel driving electric vehicle as an example, a fuzzy distribution strategy is proposed. On the one hand, the strategy assigns the braking force to the driving wheel as much as possible with the wheel not being locked, on the other hand, under the guarantee the vehicle has enough braking intensity and safety, the regenerative braking is preferred. The simulation result shows that there is obvious improvement in recycling efficiency of regenerative braking energy, which confirms the validity of the fuzzy control strategy. The strategy provides a way to enhance the electric vehicle propulsion system efficiency, which can use the limited energy to lengthen the electric vehicles' travel distance effectively.