Surface permanent magnet synchronous machine self-sensing position estimation at low speed using eddy current reflected asymmetric resistance

This paper proposes an alternative position self-sensing method of surface permanent magnet (SPM) machines at low speed using high frequency (HF) signal injection. SPM machines traditionally do not have enough spatial saliency signals because their symmetric rotors result in near zero inductance variation. The proposed solution is to track the HF eddy current reflected asymmetric resistance for position estimation. It will be shown that the spatial variation of resistance can be enhanced when a HF signal is superimposed. Finite element analysis is performed to investigate the asymmetric resistance in different SPM machines. By superimposing a d-axis pulsating vector HF signal, SPM machines can achieve the self-sensing position estimation performance with reduced degradation at high load conditions. Implementation methods are developed to estimate the resistance-based spatial saliency signal for speed and position closed-loop control. A SPM machine prototype with a ring magnet rotor is used for the experimental evaluation.