Flux and torque control of switched reluctance machines

The theory and implementation of a flux-linkage controller applied to a switched reluctance motor drive are described. Analysis of the simplified discrete time load model shows that a simple flux-linkage controller can produce a `dead-beat´ system response. Comparison of the response from a discrete time PID current controller, hysteresis current controller and the new flux-linkage controller, show that the flux controller has a much improved response. The experimental controller is used to control an IGBT converter, driving a commercial 7.5 kW switched reluctance motor. A method of constant torque operation is introduced. This takes account of limitations imposed by the finite DC-link voltage and rotor speed when calculating the reference values. The method is based on `flux ramps´, where the ramps are chosen to give constant shaft torque, and remain within the capabilities of the power converter. Correct selection of the flux ramps allows constant torque operation to be achieved over a wide speed and torque range. Measured results for the experimental drive demonstrate the low torque ripple achieved for motoring and generating operation over a range of speed and torque values