Robust Initial Position Estimation of Permanent Magnet Machine With Low Saliency Ratio

In permanent magnet (PM) machine drives, the initial position is typically estimated based on the machine inductance variation and the flux saturation. The saliency-based method using the voltage signal injection has demonstrated the reliable position estimation for high salient PM machines at initial state. However considering the saliency-based drive on low salient machines, several implementation issues appear due to the low signal-to-noise ratio of position dependent signals. This paper addresses the implementation issues on saliency-based initial position estimation. It is shown that conventional saliency-based estimation methods might not be able to obtain the correct rotor position on low salient machines due to secondary saliency harmonics. A two-step estimation process is proposed to improve the initial position estimation accuracy on low salient PM machines. Two PM machines with different saliency ratios are tested for the experimental evaluation.