Initial rotor position estimation of an interior permanent magnet synchronous machine using carrier-frequency injection methods

This paper presents a method using carrier frequency injection to estimate the initial rotor position and magnet polarity for an interior permanent magnet synchronous machine. A non-saturating inductance model of the machine provides no information about the polarity of the rotor magnet because the position observer based on this model is locally stable at both poles. To distinguish the polarity of the rotor magnet, the magnetic saturation effect can be used. A 2^nd order Taylor series can be used to describe the nonlinear magnetic saturation relationship between the current and the flux linkage in the d-axis rotor reference frame. The 2^nd order term produces the 2^nd harmonic component of the carrier frequency, and the sign of its coefficient identifies the polarity of the rotor magnet being tracked. Both simulation and experimental results show good response of the position observer at rotor electrical positions of ±0.5π rad using either a rotating vector in the stationary reference frame or a pulsating vector in the estimated rotor reference frame.