An Improved Analysis Method of Irreversible Demagnetization for a Single-Phase Line-Start Permanent Magnet Motor

This paper presents an effective analysis method of irreversible demagnetization for a line-start permanent magnet (PM) motor considering the magnetic field produced by secondary conductor bars. The magnetic field produced by the secondary conductor bars opposes the variation of the magnetic field caused by the primary part, and these result in the reduced magnetic field acting on the PM. By using finite element analysis in the transient magnetic field, currents in the primary and secondary conductors are estimated and used for demagnetization analysis of the magneto-static field. Therefore, conditions closer to actual situations can be achieved. Both the general demagnetization analysis method, using only primary currents, and presented analysis method are compared and the results are verified by experiments. General demagnetization analysis leads to over-estimation of the magnetic field acting on the PM, and results in excessive PM usage.