Two-time-scale braking controller design with sliding mode for electric vehicles over CAN

Abstract

This paper proposed a braking torque controller via two-time-scale design with a sliding mode for electric vehicles with four in-wheel motors. According to the different changing rates between the vehicle and wheel motion during the braking process, the design of the braking controller is carried out in two steps. In the first step, a nominal braking controller is developed over the slow-time scale without considering the tire-road friction. Then, a tire-road friction observer is adopted in the fast-time scale to recover the performance of the nominal braking controller. Owning to the high nonlinearity and complexity of the braking system, a sliding mode surface is further added in the nominal braking controller to ensure the stability and robustness of the proposed braking controller. A braking supervisor is adopted to enable the proposed braking controller, which is based on the wheel slip as well as vehicle speed condition. And a torque allocation scheme is presented for the coordination between the regenerative braking system and the friction braking system in each wheel. Co-simulation is conducted using MATLAB/Simulink and CarSim. The effectiveness of proposed controller under different braking conditions is fully validated. A delicate controller area network (CAN) bus model is developed via SimEvent, by which the robust performance of proposed braking controller against CAN-induced time-varying delays is also investigated.