Control Strategy Of Four-wheel Independent Drive Electric Vehicle Based On Improved Vehicle Velocity Estimation Algorithm

With the advantages at vehicle motor control and active safety control, four-wheel independent drive electric vehicle becomes an important research direction of electric vehicle. Four-wheel independent drive electric vehicle has some advantages such as independently control of torque, easily measurement of torque, multiple drive modes which mainly include four-wheel drive mode and two-wheel drive mode. However, there is a problem with the switched drive mode, which would have an adverse effect on the precision of vehicle velocity estimation, the vehicle stability as well as the comfort. In order to solve the problem, a control strategy based on vehicle velocity estimation is proposed, aimed to reach a high vehicle velocity control accuracy, improve the vehicle stability as well as the comfort. The main work is as follows:1. The model of four-wheel independent drive electric vehicle and drive mode are studied. Three degree of freedom vehicle model, dynamic model of wheel and the HSRI tire model are studied. Moreover, drive mode switch methods, including a genetic algorithm based drive mode active switch strategy and a drive mode passive switch strategy are studied.2. An improved vehicle velocity estimation algorithm is designed and applied for multiple drive modes. A vehicle velocity estimation algorithm based on Unscented Kalman Filter is designed in four-wheel drive mode condition, while a vehicle velocity estimation algorithm based on wheel rotational speed is designed in two-wheel drive mode condition.3. A control strategy based on improved vehicle velocity estimation algorithm is presented. A controller based on improved vehicle velocity estimation algorithm is proposed, and vehicle velocity is designed as the control target. Besides, a vehicle velocity smoothing algorithm is proposed to smooth the vehicle velocity saltus step. A simulation is built on CarSim and Matlab/Simulink to evaluate performance of the proposed control stategy. Simulation results show that the control strategy not only reach a high vehicle velocity control accuracy, but also improve the vehicle stability as well as the comfort.For the control strategy proposed in this paper, not only the vehicle stability but also comfort are considered by using four independent drive wheels. This study would be useful to the development of four-wheel independent drive electric vehicle.