Comparison of Estimation Techniques for Railway Traction Vehicle Wheel Slip Control

Power semiconductor converters of railway traction vehicles are controlled by sophisticated regulators. They must respond immediately and with high dynamics to changes in adhesion conditions on the track to utilize the available adhesion. This is the task of the wheel slip controller. Wheel slip controllers for railway traction vehicles are developed for many tenths of years, and many methods based on different principles have been developed. The principle of the slip controller that can fulfil the asked requirement estimates an adhesion characteristic slope in an operating point. These types of slip controllers can run at any part of the adhesion characteristic and ensure that the operating point is in the stable area of the adhesion characteristic for most of the operating time. The slip controllers can effectively avoid the maximum point overstepping. Therefore, undesirable phenomena like increased wheel and rail wear, high slip velocity, the increased stress of mechanical parts or stick-slip oscillations can be minimized. The methods require knowing the actual value of an adhesion coefficient for their correct operation. However, the adhesion coefficient is not measured during regular train operation because it requires additional equipment that is not standardly mounted on the vehicle. Therefore, the adhesion coefficient is typically estimated by an estimator.