Re-adhesion control strategy based on the optimal slip velocity seeking method

In the railway industry, re-adhesion control plays an important role in attenuating the slip occurrence due to the low adhesion condition in the wheel-rail inter- action. Braking and traction forces depend on the normal force and adhesion coefficient at the wheel-rail contact area. Due to the restrictions on controlling normal force, the only way to increase the tractive or braking effect is to maximize the adhesion coefficient. Through efficient uti- lization of adhesion, it is also possible to avoid wheel-rail wear and minimize the energy consumption. The adhesion between wheel and rail is a highly nonlinear function of many parameters like environmental conditions, railway vehicle speed and slip velocity. To estimate these unknown parameters accurately is a very hard and competitive challenge. The robust adaptive control strategy presented in this paper is not only able to suppress the wheel slip in time, but also maximize the adhesion utilization perfor- mance after re-adhesion process even if the wheel-rail contact mechanism exhibits significant adhesion uncer- tainties and/or nonlinearities. Using an optimal slip velocity seeking algorithm, the proposed strategy provides a satisfactory slip velocity tracking ability, which was demonstrated able to realize the desired slip velocity without experiencing any instability problem. The control torque of the traction motor was regulated continuously to drive the railway vehicle in the neighborhood of the opti- mal adhesion point and guarantee the best traction capacity after re-adhesion process by making the railway vehicle operate away from the unstable region. The results obtained from the adaptive approach based on the second- order sliding mode observer have been confirmed through theoretical analysis and numerical simulation conducted in MATLAB and Simulink with a full traction model under various wheel-rail conditions.

Determination of the dynamic characteristics of locomotive drive systems under re-adhesion conditions using wheel slip controller

To investigate the re-adhesion and dynamic characteristics of the locomotive drive system with wheel slip controller,a co-simulation model of the train system was established by SIMPACK and MATLAB/SIMULINK.The uniform running and starting conditions were considered,and the influence of structural stiffness of the drive system and the wheel slip controller on the re-adhesion and acceleration performance of the locomotive was investigated.The simulation results demonstrated that the stick-slip vibration is more likely to occur in locomotives with smaller structural stiffnesses during adhesion reduction and recovery processes.There are many frequency components in the vibration acceleration spectrum of the drive system,because the longitudinal and rotational vibrations of the wheelset are coupled by the wheel‒rail tangential force when stick-slip vibration occurs.In general,increasing the structural stiffness of the drive system and reducing the input energy in time are effective measures to suppress stick-slip vibration.It should also be noted that inappropriate matching of the wheel slip controller and drive system parameters may lead to electro-mechanical coupling vibration of the drive system,resulting in traction force fluctuation and poor acceleration performance.