Experimental investigation of variable structural PID control for switched reluctance motor drives

In this paper, the authors present the performance of a variable structure PID control scheme as applied to a switched reluctance motor (SRM) for speed control. The usefulness of the SRM as a servomotor has been limited due to its strong nonlinear electromechanical characteristics which result in significant torque and hence speed ripples. It has been shown that conventional fixed gain PI controllers are not able to meet the stringent requirements of servomotor systems. This paper describes the design method of a variable structure PID (VSPID) control system. In this controller, the PD mode is used in the case of large errors to speed up the response, whereas the PI mode is applied for small error conditions to eliminate the steady-state offset. Flexible changes of the controller structure from PD to PID to PI mode and resilient controller parameters of VSPID during transients could thereby solve the typical conflict in nature between steady-state error and dynamic performance. Hardware implementation of the VSPID controller has been achieved using Texas Instrument's TMS320C50 digital signal processor. Experimental results obtained for the speed control of an SRM show improvements over conventional fixed gain PI controllers