A simple motion estimator for variable-reluctance motors

A simple motion estimator is presented for inverter-driven variable-reluctance motors. The estimator probes unexcited phases with short voltage pulses from the inverter, and evaluates the resulting currents to measure the phase inductances. From these inductances, instantaneous motor position is estimated. Individual position estimates are optionally combined by a state observer to produce smoothed position and velocity estimates. Next, the secondary phenomena of eddy currents in the motor laminations, inverter switching noise, magnetic coupling between motor phases, and quantization introduced by digital implementation are all examined for their effects on estimator performance. Each phenomenon is addressed by a modification of the estimator. Finally, the estimator is evaluated experimentally using an inverter-driven three-phase motor having six stator poles and four rotor poles. The estimator is implemented digitally with an Intel 8031 microcomputer and little extra hardware.<>