Design of a Variable-Flux Permanent-Magnet Synchronous Motor for Adjustable-Speed Operation

This paper suggests a possible design of variable flux motor for adjustable speed operation. A method to calculate electrical parameters to meet variable speed conditions is suggested, and the basic motor shape is decided using the relationships between the calculated electrical parameters and motor geometry. The difference between coercivity of two types of magnet is used to control the flux. To prevent irreversible demagnetization of low-coercivity magnet, the approximate shape of magnet is decided by calculating the operating point of the magnet using an equivalent magnetic circuit. The optimum shape of magnet considering the nonlinear characteristics is suggested using a finite-element method. To validate the design, magnetizing/demagnetizing, and load operation tests are conducted.