Nonlinear model predictive slip control based on vertical suspension system for an in-wheel-motored electric vehicle

In order to improve the safety and dynamic performance of electric vehicles, prevent the wheel from getting locked or slipped when braking or accelerating, and maximize the longitudinal force on low-friction coefficient roads, it is necessary to control slip ratio of each wheel in the stable region. Combining the theory of the nonlinear model predictive control (NMPC), this paper presented a slip controller based on vertical suspension system for the electric vehicle equipped with four in-wheel motors. The model of vertical suspension system, which is established by adding the vertical force analysis on basis of the longitudinal motion model, is a four degrees of freedom model. By making the slip ratio of each tire individually converge to the optimal longitudinal slip ratio within a very short response time, the proposed controller can keep the traction or braking torque of each wheel in a reasonable level, by considering constraints of the In-wheel motor and the slip ratio. The effectiveness of the proposed controller is verified in the environment of Simulink, and the longitudinal slip ratio of each tire can catch the optimal longitudinal slip ratio in short time.