Two-Speed Line Start Permanent Magnet Synchronous Motor With Dual Magnetic Polarity

This paper presents a design of a line start permanent magnet (PM) synchronous motor capable of operating in two different synchronous speeds without requiring a drive unit. The proposed design is based on variable pole numbers for the stator and the rotor. In general, the two-speed operation is realized by the combination of electromagnetic torque and reluctance torque, which enables the motor to operate as a synchronous PM motor at high speed and a synchronous reluctance motor at low speed. However, the proposed design enables the motor to operate as a PM motor at both low- and high-speed regions. The stator winding consists of two independent windings to switch the operating pole count for low- and high-speed applications. For the motor to operate in two different operating speeds, the rotor must be capable of creating two different magnetic polarities (pole numbers) to adapt itself to the operating stator pole number. For this purpose, PMs are specially arranged such that the magnetic flux density has a distribution similar to the resultant flux of two rotors with different magnetic pole numbers. This forms a rotor with dual magnetic polarity and enables the motor to operate as a synchronous PM motor at two operating speeds. The finite element analysis simulation results confirm the effectiveness of the proposed design in both steady-state and transient regime. To further validate the proposed solution, the performance of the motor has been verified by experimental measurements on the motor prototype.