Improved Design of Synchronous Homopolar Motor With Ferrite Magnets With Increased Resistance to Irreversible Demagnetization for Subway Train

Nowadays rare-earth magnets available in the market are limited, while demand for them is increasing, therefore development of electrical machines without magnets of this type becomes extremely important. Simultaneously, synchronous machines without magnets have poorer torque to weight and torque to volume characteristics compared to machines equipped with magnets. The compromised solution is usage of cheap ferrite magnets as a source of auxiliary machine flux. However, the most serious disadvantage of ferrite magnets is the possibility of unrecoverable demagnetization. In order to solve the abovementioned problem this paper proposes a novel design of ferrite assisted synchronous homopolar motor (FASHM), which is equipped with magnets of special shape, resulting in higher resistivity to demagnetization. This research provides theoretical analysis of working characteristics of the motor of proposed design, developed for subway train, and compares them with the characteristics of the motor without the proposed design features. The FEM modelling demonstrates that the proposed design is superior to the existing solution. It has higher resistivity to unrecoverable demagnetization of the ferrite magnets, consumed current and power loss are decreased, the mass of motor and price of the magnets are reduced.