Adhesion estimation based novel approach to control wheel slip in electric locomotives

Conventional wheel slip control method uses slip velocity as control variable to reduce output motor torque for arresting wheel slip. It suffers from some of the major setbacks which are substantiated in this paper by case studies from Indian Railway locomotives. Further this paper proposes novel approach using estimated adhesion torque to control wheel slip level in electric locomotives. From single rail wheel longitudinal plant dynamics, it can be derived that the adhesion torque is seen as load torque on the motor and therefore can be estimated using a state observer. Proposed control is based on the hypothesis that if the difference between the input motor torque and the estimated adhesion load torque on motor exceeds the pre-defined threshold value, excessive torque is generated. This excessive torque contributes to wheel acceleration and needs to be suppressed quickly by reducing the output motor torque. Thus, using estimated adhesion torque (motor load torque) directly to detect and control slip this paper contributes in eliminating the need to acquire train velocity information for slip control.