Position Sensorless Control of Synchronous Reluctance Machines Based on Magnetic Saturation Depending on Current Phase Angles

Position sensorless control of synchronous reluctance machines (SynRMs) is not easy due to nonlinear correlations caused by extensive magnetic saturation. This paper first investigates stability of a conventional saliency-based method and reveals it becomes unstable due to cross-coupling effect at high torque with high magnetic saturation even when the effect is low enough not to cause disappearance of the saliency nor to reverse the estimated d- and q- axes. A novel method to overcome this instability is proposed, which utilizes magnetic saturation depending on current phase angles. Verification by simulations and experiment confirmed that the proposed method achieves stable sensorless operation at high torque and increases the maximum feasible torque by 80% compared to the conventional methods.