Optimal-efficiency excitation of variable-reluctance motor drives

The authors examine the optimal-efficiency excitation of a variable-reluctance motor (VRM) drive operating at constant speed. The drive comprises a motor, an inverter, an excitation and a control strategy. The excitation refers to a prescribed relationship between the phase currents and rotor position that results in the desired drive behaviour. The excitation is considered from an integrated viewpoint such that overall drive efficiency is maximised for a given torque and speed. An algorithm for the determination of optimal excitation is presented. The algorithm is based on the determination of excitation that nominally meets the drive torque-speed requirement, followed by optimisation of this excitation to improve efficiency. Other performance criteria, such as torque ripple or acoustic noise, could be considered in a similar manner, with appropriate models. The authors apply the algorithm to a high-power (60 kW) VRM drive