Robust chattering free sliding mode control of servo drives

A new discrete-time control algorithm has been developed by combining Variable Structure Systems (VSS) and Lyapunov design. It possesses all the good properties of sliding mode control and avoids the unnecessary discontinuity of the control input, thus eliminating chattering, which has been considered as a serious obstacle for applications of VSS. A unified control approach for the stator currents and torque control, based on the discrete-time sliding mode, for application in indirect vector control of an IM drive, is developed. The sliding mode approach can be applied to the control of an IM servo drive due to the replacement of the hysteresis controller with the widely used PWM technique. All the theoretical issues are verified by experiments. The experimental system consists of a transputer T805 and a microcontroller, which enables parallel processing.