A Simple Nonlinear Logical Torque Sharing Function for Low-Torque Ripple SR Drive

A novel and simple nonlinear logical torque-sharing function (TSF) for a switched reluctance motor (SRM) drive is proposed. This novel scheme using nonlinear TSF manipulates currents in two adjacent phases during commutation, so that efficiency and torque ripple in an SRM drive can be considerably improved. For constant torque generation, the switching of one-phase windings is regulated, and torque reference for the other phase stays at the previous state under the condition of a certain current limit given by the overall drive power rating. Every torque state monitored by the nonlinear logical condition determines a regulated or nonregulated torque control among two phases overlapped in commutation region, where one phase is incoming to produce the majority of torque and the outgoing current in the other phase is decreasingly controlled by the logical condition. Due to the same switching state in a nonregulated phase and the reduction of commutation period by the proposed control method, the switching number can be significantly reduced, and hence, the switching loss can be reduced. In case that one-phase regulation cannot satisfy a proper torque reference required for minimum torque ripple operation, a two-phase regulation mode is employed in the novel nonlinear TSF. In order to include magnetic nonlinearity in torque control and decrease a current tail at the end of commutation, the current of the incoming phase needs to be controlled in an increasing manner, and at the same time, the outgoing phase current tracks on an opposite direction so that torque sharing between two phases can be smoothly achieved with a minimum current crossover. The proposed control scheme is verified by some computer simulations and experimental results.