Anisotropy comparison of reluctance and PM synchronous machines for low speed position sensorless applications

Position sensorless control of reluctance- and PM synchronous machines at zero and low speed is possible using high frequency voltage injection and proper demodulation. The so-called anisotropy position, which is tracked by the HF sensorless scheme, is different to the actual rotor position: the difference contains both offset and time-varying components, which may be explained by carefully considering the high frequency behaviour of the machine and the effect that fundamental excitation and rotor position has upon it. This paper gives insight into the HF behaviour of machines and serves as a practical guide for implementation of stable and robust position estimation at zero and low speed.