Electrical drives for railway traction: observer for friction force estimation

High speed trains are characterized by high specific power of railway convoys. These trains are designed to run always transmitting the maximum traction effort to the wheel: this condition introduces problems of adhesion and implies a careful analysis of adhesion and skidding phenomena. It is possible to guarantee the maximum traction effort transmission if the friction force can be identified and if adequate control systems of the drive are utilized. To set up anti-skidding control algorithms it is necessary to know at the macroscopic level, and to define, an analytical characterization of the adhesion phenomenon and the skidding which occurs. In the paper a method for the identification of friction force is proposed. The identification is realized by means of an observer carried out from the mathematical model of the physical system and of the driving motor. The observer is described and the results of some simulation tests are discussed.