Sliding model control based on estimation of optimal slip ratio for railway wheel slide protection using extremum seeking

It is very important for railway vehicles to have a good braking performance to avoid the phenomenon of idling and skidding, which can be implemented by looking for and keeping an optimal slip ratio. The optimal slip ratio is a value existing in the creep zone of functions between friction coefficient and slip ratio corresponding to the maximum adhesion. Controller based on the sliding mode control needs to be entered an reference slip ratio which can be used to find out the optimal control by the designer and can be tracked by actual slip ratio by the controller. Moreover, as an indispensable factor for calculating slip ratio, vehicle velocity is estimated by the proposed algorithm based on locomotive dynamic model. Then the optimal control ensures the actual slip ratio is equal to or close to the best reference slip ratio generated by extremum seeking algorithm dynamically. According to those functions, the optimal slip ratio changes dynamically once the pavement behavior changes. The simulation result demonstrates that compared with constant reference slip ratios, the proposed dynamical seeking algorithm for optimal reference slip ratio achieves the effect of real-time adjustment for braking torque, which prevents the brake torque from being too large or small and guarantees the braking performance.