Research Of Regenerative Braking Energy Recovery For Electric Vehicles

Electric vehicles have become to the popular clean forms of transportation to solve environment pollutions and resources shortage because of its characteristics for none emission and braking energy recovery. It could not run a long distance, which is limited by the finite capacity of batteries. In order to enhance the driving range there is a hot-spot in recent years to design effective control strategies of regenerative braking which could coordinate the relationships between mechanical braking force and regenerative braking force. To solve these problems, there were two control strategies designed for a specific front wheel drive electric vehicles in this paper after the research status being analyzed. There are six chapters. The main research contents and results as follows:1. By analyzing two typical regenerative braking systems, the braking force distribution of parallel and series braking energy recovery, and the principles of regenerative braking were elaborated. Equations to restrict the braking force distribution were set up according to the ECE regulations. By analyzing constraints for the capacity of motor regenerative braking, the disturbing functions for energy recovery were proposed to correct the actual regenerative braking force.2. To improve the energy recovery efficiency in traditional parallel control strategy of regenerative braking and ensure the ratio of mechanical braking force between vehicle wheels constant, an improved parallel strategy was designed based on ECE regulations. There are also shortages of series strategies. The driven wheels under optimal braking performance strategy would consume large part of braking energy when the braking intensity is small. The strategy of optimal braking energy recovery is very complex. In order to solve these problems, a series control strategy of regenerative braking based on ECE regulations was designed. The braking force was distributed with two different methods in accordance with ECE regulations and vehicle characteristics.3. Lead-acid batteries and an AC asynchronous motor were separately chosen to be the power and energy source. The mathematical model of regenerative braking system was established based on the specific characteristics of front wheel driving electric vehicles. Curves of braking force distribution were drawn with the equations. Then, the mathematical models of control strategies for regenerative braking were also established.4. The simulation models of regenerative system and control strategies were established in the software Advisor by hybrid modeling approach. The models were simulated under two typical urban driving cycles and compared with the original strategy of the software and optimal braking performance.5. The simulation results show that under urban driving cycles which have low braking intensity and high braking frequency, both of the control strategies designed in this paper has similar braking energy recovery effect better than the frame of reference. The two designed strategies could either make up for the deficiencies of traditional strategies or enhance the braking energy utilization, and provide theoretical basis for the design of regenerative braking systems.