Design And Optimization For Electric Vehicle Powertrain With CVT

The boom of researches on Electric vehicle (EV) is under the background that environmental problems and energy issues have become increasingly prominent and emergent. Researches on key technologies for electric vehicles including: vehicle control and management system, powertrain, battery and its management system.Vehicle powertrain efficiency greatly influences its performance, so research which aim to improve the control strategy for electric vehicle powertrain is necessary.The speed ratio of continuously variable transmission (CVT) can be changed continuously, which could decrease road loads' affect on electric vehicle motor's operating, in this case, the operation range of the electric motor is determined by the transmission speed ratio's range (maximum & minimum transmission speed ratio), motor minimum & maximum speed and maximum output torque of the motor, so in theory, by changing the CVT speed ratio can regulate motor's speed to the best economy speed which could improve the efficiency of electric vehicle powertrain as well as vehicle economy.In this thesis, I built the vehicle model under MATLAB /Simulink platform, connecting the motor and CVT in series arrangement, by adjusting the transmission speed ratio in meeting the requirements of road loads for adjusting motor to target speed for economic, which could leading to the improvement of the vehicle economy.By improving the classic PID control strategy and applied the improved one in the vehicle model, the simulation results show that the improved PID control algorithm is better in control effect when compare with the classic PID algorithm.The first part of the thesis described the development of EV, CVT and related technologies, reviewed the latest researches in this field and proposed the aim of the thesis.The second part of the thesis, mainly introduced different EV components' arrangement and different types of electric motor which could be applied in EV powertrain. And select the EV powertrain arrangement and the type of motor for the research. The third part of thesis introduced the basic principles of CVT, PID control algorithm and each parameter's effect on the control effect.The fourth part of the thesis demonstrated the necessary parameters for modeling, details of modeling for vehicle's sub-models and discussed the methods to determine the motor optimal operate curve.Finally, by comparing simulation results to demonstrated the classic PID parameters' impact on the control effect and the limitations of the PID algorithm. By applied the improved PID algorithm within the vehicle model, simulation results show that the improved PID algorithm could overcome the shortcoming of the classic PID algorithm.