Disturbance rejection analysis and fpga based implementation of a second order sliding mode controller fed induction motor drive

This paper presents a unified approach to deal with sliding mode controllers used for induction motor drives. The study digs deep to identify matched and unmatched disturbances and derive conditions to satisfactorily reject the same. The investigation reveals fundamental limitations of hysteresis (first order sliding mode) controllers those can be overcome by higher order controllers. Second order sliding mode controllers are investigated to achieve disturbance rejection and chattering free performance. It is shown that the drive with second order sliding mode controllers maintains constant switching frequency and decoupling between torque and flux simultaneously in the face of sudden speed, load, or parameter variations. Also, it is shown that the dynamic performance can be drastically improved at higher sampling frequencies keeping the switching frequency constant. Extensive simulations are carried out in Matlab/Simulink. Imple- mentation of such a drive becomes feasible with low cost FPGAs due to their inherent parallel processing capability. A vector controlled induction motor drive is developed and the controller is implemented using FPGA to corroborate the simulation results through experimentations