Regenerative Braking Control Strategy For The Front-wheel-drive CVT Hybrid Electric Vehicle

Along with the increasingly serious environment and energy crisis, hybrid electric vehicle (HEV) is becoming a main developmental direction of automobile industry, and regenerative braking technology is one of the key measures to achieve the goal of HEV energy conservation and environmental protection. On the one hand, using regenerative braking technology can improve vehicle energy utilization, reduce fuel consumption and exhaust emission, extend travel distance. On the other hand, regenerative braking technology also can reduce the mechanical brake friction loss, prolong its service life, thus reduce vehicle maintenance cost.This paper uses a front-wheel-drive CVT hybrid electric vehicle as research object. First of all, based on design requirements, the structure of composite braking system scheme is designed, then the working process of the control system and three kinds of brake operating mode are analyzed. Combined with the braking energy loss in the transmission process, the main factors which influence the braking energy recovery are described. Then, We set up the simulation model of composite braking system components by using the method with the combination of theoretical modeling and numerical modeling, and research deeply the control strategy of permanent magnet synchronous motor (PMSM) drive system. Through the analysis of the basic theory of traditional PMSM direct torque control and the effect of stator voltage vector, we put forward a kind of PMSM fuzzy direct torque control strategy based on vehicle brake power. We design two fuzzy controllers which respectively use different voltage vector selection schemes as the fuzzy control rules. Finally, based on the braking dynamics analysis, we determine the vehicle braking stability range. According to performance indexes of max braking energy recovery and best braking effect, we respectively design two braking force distribution control strategy. ADVISOR was used as a simulation platform in order to study the performance of the synergic electric system in different driving conditions. Simulation results show that using conventional non-zero voltage vector selection scheme can make the motor drive system a fast and accurate torque response ability when braking power is high, and torque ripple is small. However, using zero-contained vector of voltage vector selection scheme can make the motor drive system a high steady state efficiency when braking power is low, and the conversion efficiency of regenerative braking energy is high. In addition, the braking force distribution control strategy which based on the maximum braking energy recovery is suitable for driving occasions with low speed and high braking frequent. The braking force distribution control strategy based on the best braking effect is suitable for driving occasions with high speed and low braking frequency.