Simulation Of Doubly-Fed Cascade Driving Electric Vehicle Regenerative Braking Control System

Regenerative braking is the main approach of energy saving of electrical vehicle. Its performance is mostly affected by motor drive system, power conversion system and battery charging/discharging characteristics.With the funding of Liaoning natural science fund project (20092052) of"The Optimizing Control Strategy Research of Doubly-Fed Motor with Double Inverter Device of Hybrid Electric Vehicle"and Shenyang science project (1071112-2-00) of"The Key Technology of Doubly-Fed Motor Direct Torque Control (DTC) of Hybrid Electric Vehicle", this thesis adopts doubly-fed induction motor as its motor, and employs dual wheel doubly-fed cascade driving structure, control method of the core components is researched, such as dual wheels driving traction system and conversion unit.Firstly, the process and principles of EV brake are described. The main factors that impact EV regenerative braking energy recovery are analyzed. The performance of dual wheel doubly-fed system and energy transfer process are analyzed in regenerative braking state.Secondly, energy transfer process of doubly-fed induction motors under different conditions is analyzed. Because the power transformation unit of doubly-fed motor is too complicated, a dual wheel doubly-fed cascade system is employed. This power conversion unit has a simple structure. The advantages of doubly-fed machine's multi-channel energy transfer can be remained. According to the requirements of EV regenerative braking, doubly-fed motor direct torque control scheme is designed, and system operation process is deeply analyzed. By analyzing the simulation results of dual wheel doubly-fed motor cascade in driving straight and braking, it is proved that driving performance can be satisfied. It is also proved that braking energy of the slowing down motor can be transferred between two motors. Finally, several topological structures of bi-directional DC/DC converter are given. According to different requirements of vehicle, Buck-boost bi-directional DC/DC converter is chosen as vehicle converter. And the theory when it works and the process of energy flow are deeply researched. Because of its characteristics of nonlinearity and variable structure in electric driving and braking, fuzzy PI control method is proposed. And with a dual drive EV as its load. According to the characteristics and actual performance requirements of EV, a fuzzy PI controller is designed. Simulation results show that bi-directional DC/DC converter and variable structure control strategy can well meet the requirement of power transformation.