Wheel slip determination capability of locomotive driven by model predictive control

Most of the railway traction vehicles are moved thanks to the transfer of traction, braking force by small contact area between wheels and rail (steal to steal contact). The ability of force transfer by contact area or also the sum of the contact area physical properties is called adhesion. In order to utilize maximum transferable force, a slip controller has to be added into traction drive control structure. Slip control method based on the adhesion slope characteristic detection requires addition of sweep signal into reference torque command. The sweep signal should have particular frequency and amplitude to ensure proper signal detection and thus slip controller function. This is simple for low power drives with relatively high modulation frequency of the traction inverter, but becomes complicated for high power drive with low switching frequency of the semiconductor devices. The paper studies possibility of the Model Predictive Control (MPC) strategy application to support the slip controller function. The considered slip controller is based on the speed and current response of the torque reference signal injection. Therefore, the controller requires high torque control accuracy. Results of MPC are compared with the Direct Torque Control (DTC) strategy that is often used for control of high power drives with induction motor (IM).