Disturbance observer for dynamic estimation of friction force in railway traction systems

Nowadays locomotives for high speed trains are characterized by high specific power. Particularly in this case, when the adhesion force coefficient between rail and driving wheel suddenly decreases, slip phenomena occur. This is because the adhesion coefficient between the wheels and rails has a peak at certain slip velocity. As the adhesive force changes in specific rail condition, the driving wheels of the locomotive suddenly slip. In order to realize a stable and robust anti-slip control system, in case of large variation of the adhesion force coefficient, this paper proposes a new first disturbance observer for a dynamic estimation of the friction force. The observer is carried out by means of the mathematical model of the mechanical structure of the transmission unit, taking into account the elastic couplings between the wheel-set and the electrical motor. In the final part of the paper numerical simulation results are presented to confirm the stability and robustness of the proposed observer.