Sliding Mode Wheel Slip Control for Regenerative Braking of an All-Wheel-Drive Electric Vehicle1

Abstract

Regenerative braking is one of the main advantages of electric propulsion systems. In such systems, the vehicle brake controller has to prioritize safety while maximizing the recovered energy at all times. This paper proposes a two-step hierarchical brake controller for a dual-motor all-wheel-drive electric vehicle. In the first step, a novel sliding mode controller (SMC) generates the total braking torque on each axle to independently control the slip on the front and rear wheels. In the second step, the torque split controller assigns motor and friction brake torques to maximize the recovered energy. By incorporating the effects of changing vehicle speed, the proposed SMC controller accounts for the nonlinearities in vehicle dynamics and tire model and considers the weight transfer due to vehicle deceleration while being robust to disturbances. Using simulations, we show that while the traditional SMC formulation is not effective during emergency braking scenarios, the proposed formulation successfully generates control commands to bring the vehicle to a stop position at a minimum distance. Furthermore, our controller can maintain both wheels in the stable slip region, even when starting from a locked position. The performance of the proposed controller is evaluated for an emergency braking scenario and on an aggressive segment of the US06 cycle.