Automatic Slip Controller for Railway Vehicles Using Fuzzy Logic

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Addis Ababa University


The moment applied on the wheel by the traction motor has to be transferred in to tangential force in order to guarantee the longitudinal motion of train vehicle. The force that is transmitted between wheels and rail is called the adhesion force which is the product of normal force and adhesion coefficient. The adhesion coefficient depends on the slip velocity, conditions of rail surface, a train velocity and temperature in the contact area. From parameters that can influence the adhesion coefficient slip velocity the vital one. Therefore slip controlling is important in order to prevent wear of the wheels and the rail and to use the present adhesion effectively. On this thesis the relation between the wheel road adhesion force coefficient and slip ratio is developed based on Burckhardt Static Modell (BSM) which treats the wheel as a circular beam supported by springs. First the longitudinal slip ratio is to be calculated as the speed difference of the driven and non-driven wheels. Where, the non-driven wheel presents speed of the train vehicle and the driven wheel velocity is considered as the wheel-rail contact specimen. Then adhesion torque observer is designed in order to estimate the existing adhesion in real time. This torque is then applied as a load torque for Proportional Integral (PI) controller based speed loop. After developing proper speed loop to control wheel speed, Fuzzy Logic Controller (FLC) based slip controller is installed inside to compensate traction torque fluctuation caused by adhesion load. The FLC has two inputs namely the slip ratio error and the rate of slip ratio error. Using linguistic rules to increase and decrease compensating torque, the FLC generates adhesion coefficient which will be multiplied by the normal force and wheel radius to be added or subtracted from the traction torque. Then the advantage of the controller is evaluated by considering the speed response with and without the slip controller. For the slip ratio varying drastically from 0.7 to 0.01 and vice versa, the wheel speed response shows up to 50% overshoot and undershoot in the early stage of the accelerating speed. However, the FLC slip controller compensates this up and down to 6% which is a remarkable result to smooth the motion of the system.



Slip, Adhesion coefficient, Fuzzy logic controller (FLC), Proportional Integral (PI)