Direct Torque Tracking PI-Controller Design for Switched Reluctance Motor Drive Using Singular Perturbation Method

The problem of torque tracking PI-controller design for switched reluctance motor (SRM) drive is discussed, where SRM magnetization characteristics are highly nonlinear, and torque is a complex and coupled function of phase current and rotor position. A distinctive feature of the control system designed is that two-time-scale motions are artificially forced in the closed-loop system by the selection of control law parameters. Hence, singular perturbation method is used to analyze the closed-loop system properties. Stability conditions imposed on the fast and slow modes, and a sufficiently large mode separation rate, can ensure that after fast ending of the fast-motion transients, the torque tracking error dynamics are as desired by the control system design specifications and they are insensitive to SRM nonlinearities. An accurate polynomial model of a prototype SRM magnetization characteristics is used for simulation studies of the proposed controller. However, only a simple trapezoidal profile for SRM inductance is used for calculation of the control voltage. Simulation results for constant motor torque at different speeds show that motor peak-to-peak torque ripples are minimized to about 5% of the average torque, especially for low speed operation.