Slip ratio estimation for electric vehicle with in-wheel motors based on EKF without detection of vehicle velocity

It is necessary to detect vehicle speed to calculate the slip ratio in slip control systems. However, it is hardly to measure the vehicle speed directly for electric vehicle (EV) with in-wheel motors. So, this paper proposed a new slip ratio estimation method for EV with in-wheel motors based on Extended Kalman Filter (EKF) without detecting the vehicle speed. This method takes advantage of the features of driving motors to directly estimate the slip ratio of four wheels at the same time without detecting vehicle speed. First, according to the measurable torque and rotate speed of four wheels, deduce the estimating equations without the vehicle speed. Then, apply the EKF algorithm to design the slip ratio estimator, the EKF can effectively deal with the non-linear control problem and can easily synchronous processing with high performance. Finally, the good performance of the proposed estimator is confirmed by running the electric vehicle model with four in-wheel motors through several test maneuvers.