Model predictive slip control for electric vehicle with four in-wheel motors

In order to solve the problem that the electric vehicle wheels may lock up when braking or spin out when accelerating on low-friction coefficient [low-μ] roads, this paper presented a nonlinear model predictive controller for slip control of electric vehicle equipped with four in-wheel motors. The advantage of the proposed nonlinear model predictive control based (NMPC) slip controller is that it can act not only as an anti-lock braking system (ABS) by preventing the tires from locking up when braking, but also as a traction control system (TCS) by preventing the tires from spinning out when accelerating. Besides, the proposed slip controller is also capable of assisting the hydraulic brake system of the vehicle by automatically distributing the braking torque between the wheels using the available braking torque of the in-wheel motors. In this regard, the proposed NMPC slip controller guarantees the optimal traction or braking torque on each wheel on low-μ road condition by individually controlling the slip ratio of each tire within the stable zone with a much faster response time, while considering actuator limitations and wheel slip constraints and performance metrics. The performance of the proposed controller is confirmed by running the electric vehicle model with four individually driven in-wheel motors built in AMESim, through several test maneuvers in the co-simulation environment of AMESim and Simulink.