Study On Control Strategy Of Electric Driving And Regenerative Braking For Pure Electric Vehicle

With the advantages of high efficiency, low noise and little pollution emission, pure electric vehicles (PEV) are leading a revolution in automobile industry under the pressure of the natural environment protection and the growing oil shortage nowadays. So far, inadequate driving range is still the major fencing to hinder the development of PEV, new efforts are necessary to improve the usage efficiency and regenerative braking recycling for limited energy available. Supported by a provincial scientific project, this dissertation mainly focuses on the PEV issues like electric drive system, regenerative braking, dual-energy storage system (DESS), and optimization & control strategies of PEV. Specifically, the main work and contributions of the dissertation are summarized as follows:1. On the basis of analyzing the dynamic model of PEV and DC motor, the dynamics-simulating model for vehicles driven by permanent DC motor is established, which can better reflect the influence of wind resistance. Because of the universality and applicability of general DC motor model, a new dynamic graph for motor-dragging vehicles is constructed mainly by the parameters & links in the general DC motor, assisted by some nonlinear links. Meanwhile, the formula for inertia and time constant is summed up, in which the physical meaning of parameters is clearer, and the combination of vehicle and motor is more reasonable.2. The control strategy for driving and regenerative braking is investigated systematically. For PEV with sole-energy storage system, the vehicle speed is taken as the control objectives, and various control schemes are studied in the driving state, including the system constitution, steady structure and dynamic response, as well as the features and application scope. Moreover, in order to make the regenerative braking more effective, the principle of regenerative braking for PEV is analyzed, the control strategy for energy recycling is studied and simulated in Matlab.3. Based on the design scheme to reassemble a city transit bus to a test PEV, the structure of PEV is briefly introduced, and the electric circuit of control system is implemented. The overall design scheme for the control system is proposed, the device selection, circuit design and software development are accomplished, a circuit board, a triggering protection circuit and two quadrant PWM power converter are manufactured. Furthermore, for the convenience of debugging and parameters illustration, the intelligent meter panel is designed and tested in laboratory.4. Regarding to the dual-requirements for high-energy density and high-power density, the DESS is designed to be a composition of battery and ultra-capacitor plus bi-direction DC/DC converter in parallel. The main-loop circuit of DESS is constructed, and the working states are analyzed. After analyzing the power and energy requirements, the structure and parameters of DESS are presented in term of mathematical computation. Finally, aforementioned results are verified by extending ADVISOR simulator with dual-energy storage auto-sizing.5. According to the different running states of PEV, the fuzzy self-tuning control strategy for bi-directional DC/DC converter is designed. In forward running state, the converter is employed to achieve voltage stability for balancing the voltage output between the battery and ultra-capacitor. In regenerative braking state, the converter is used to provide constant charging current for the battery and ultra-capacitor. The simulation model of DC/DC converter is estalished in MATLAB, and the simulation results prove that the controlling method is correct and effective.6. In order to improve the performance of braking force distribution and energy management, two fuzzy optimal control strategies are proposed for PEV with DESS. A simulation w.r.t. economical efficiency, power parameter, power efficiency and braking energy recycling is performed. The results show that the proposed fuzzy strategies can more effectively distribute the output power of DESS, improve the property in DESS, and attain a better acceleration and economic performance.7. A software platform with friendly interface specialized for the simulation of the pure electric vehicle (PEV) with DESS is established by the redevelopment of ADVISOR. The new platform overcomes the shortcoming that ADVISOR can not simulate DESS's performance. Combined with typical cycle conditions, the performance simulation is performed for PEV with DESS and control strategies. The simulation results show that both the dynamic property and the economical efficiency of the PEV with DESS are improved.