Abstract: In order to improve the driving stability of distributed drive electric vehicles under various steering conditions and coordinate the rotational speed difference control between wheels, a differential steering control strategy integrating both a composite rotational speed control method and a slip rate control method is proposed. Firstly, the relationship between the optimal slip rate and the road adhesion coefficient is investigated, and their correlation is fitted to ensure the system operates near the optimal slip rate. Then, a fuzzy controller is employed to process the inputs-including the deviation between the actual yaw rate and the desired yaw rate, the deviation between the actual side slip angle and the desired side slip angle, and the vehicle speed, and output a coordination coefficient for the two control methods. Under stable conditions, the rotational speed control method is utilized to achieve desired wheel speed tracking via sliding mode variable structure control. Under unstable conditions, the slip rate control method calculates the additional yaw moment by sliding mode variable structure control, while a single/dual-wheel switching controller allocates the torque. Finally, simulation results shown that, under high-speed and low-adhesion conditions, the proposed control strategy reduces the maximum yaw rate and side slip angle by 37.96 % and 52.82 % respectively, compared to a single control method, significantly improving vehicle handling stability.

Key words: electric vehicle, stability, differential steering control, coordination coefficient