Influence of eddy currents on resonance-based position estimation of switched reluctance drives

A known way to estimate the position of a switched reluctance motor without the use of a shaft position sensor is by excitation of a resonant circuit comprised by an idle motor phase winding and an external capacitor. This paper discusses the influence of the frequency of the sinusoidal excitation signal on the phase inductance. It is shown that the inductance decreases with increasing excitation frequency. This effect is most pronounced when the rotor is in the aligned position. It is furthermore shown that the frequency for the injected signal should be chosen based on a trade-off between position estimation resolution and bandwidth. The frequency-dependence of the inductance and losses of the magnetic core can be predicted by means of a wide frequency complex permeability model, which takes into account the effect of eddy current losses in the machine core laminations. Results obtained by finite element simulations show a good correspondence between calculated and measured values of the phase inductance and power loss.