Improving speed and power density of electrical machines through regional changes in properties of electrical steels

Increasing the power density of a motor by increasing its speed is a feasible and attractive method. When designing high-speed motors, it is always necessary to take into account the mechanical strength of the rotor, as the high centrifugal force of the rotor at high speeds can lead to rotor cracking. Therefore, for rotors, such as interior permanent-magnet synchronous rotors and synchronous reluctance rotors, which have flux bridges to withstand the centrifugal forces of rotors, wider flux bridges are required as the speed increases. However, wider flux bridge may result in higher flux leakage and lower torque. The power density of the motor might not increase. This paper proposes new ways to increase the mechanical strength and reduce the flux leakage of the synchronous rotors. Improvements to the motor are evaluated and techniques for obtaining the required magnetic materials are illustrated.