Rotor-Position Estimation of Switched Reluctance Motors Based on Damped Voltage Resonance

This paper proposes a method to obtain the rotor position of switched reluctance motors (SRMs) by means of voltage measurements. It is shown that the combination of a motor and a power-electronic converter defines a resonant circuit, comprising the motor phase inductances and the parasitic capacitance of converter switches, power cables, and motor phase windings. For salient machines, in general, the associated resonance frequency of the circuit depends on the rotor position. In the position-estimation method, an initial voltage distribution is imposed over the impedances of the resonant circuit after which the circuit is let to oscillate freely. During this phase of free oscillation, the induced voltage over a phase winding exhibits a damped oscillatory behavior, from which position information can be retrieved. An overview is given of the different possibilities to trigger the voltage resonance. It is shown that the proposed position-estimation method has favorable characteristics such as measurement of large-amplitude voltages, robustness against temperature deviations of motor and power semiconductors, very high update rates for the estimated position, and absence of sound and disturbance torque. Experimental results are given for a sensorless commutation scheme of an SRM under small load.