A control approach for robust trajectory tracking of an induction motor (IM) servodrive based on the variable structure system (VSS) theory is described. Direct application of discontinuous control intended for continuous time systems will result in chattering since the switching frequency cannot exceed the sampling one. By combining VSS and Lyapunov designs a new discrete time algorithm is developed which possesses all the good properties of the sliding mode systems while avoiding the unnecessary discontinuity of the control input and thus eliminating chattering. The discrete-time sliding mode control is applied to develop currents, flux and motion control of an induction motor. The validity of the algorithm was verified by simulation and experiment. The experimental system consists of a transputer and a microcontroller, thus allowing parallel processing.
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