Sensorless control of non-salient PMSM using simultaneous injection of two HF signals

In recent years, sensorless techniques based on HF carrier injection have become very popular as they are capable to estimate rotor position in a wide speed range. They can provide precise control over interior PMSMs without the accompanying need for a position sensor. However, in surface-mounted PMSMs, the estimation of rotor position is only reliable at light loads due to the very small saliency arising from main flux saturation. The anisotropy caused by stator flux saturation is not necessarily in alignment with rotor position especially at heavy loads. In this paper a novel solution is proposed to make use of the sensorless scheme in a surface-mounted PMSM even at heavy loads.