Improvement of rotor structure on irreversible demagnetization in double-layered IPMSM with Dy-less magnet

The use of interior permanent magnet synchronous motors (IPMSMs) with rare-earth magnets has recently been on the rise. When IPMSMs are operated to expand the operating speed range by flux-weakening control, irreversible demagnetization might occur in the magnets in the rotor and deteriorate motor characteristics. To prevent this, dysprosium (Dy) is added to rare-earth magnets. However, it is desirable to reduce the amount of Dy because Dy is scarce and expensive. This study investigates the rotor structure of double-layered IPMSMs with Dy-less rare-earth magnets for reducing the irreversible demagnetization. We demonstrate that the proposed rotor structure with Dy-less magnets improves the irreversible demagnetization while having little influence on motor performance.