Halbach Array PM Machine Design for High Speed Dynamo Motor

For high speed motors, smaller rotor diameters are required to make the surface speed less than 250 m/s. At the same time, dynamo motors for propulsion systems often require high torque. In such an environment, permanent magnet (PM) synchronous motors are more suitable than induction motors. In this work, a 270 kW dynamo motor is designed with a Halbach array using samarium-cobalt PMs. It utilizes the rotor back iron and carbon fiber sleeve on the rotor surface. Two design goals are set when the rotor inner and outer radii are fixed preferentially: minimization of PM usage and maximization of air gap field. A magnetic equivalent circuit is utilized to identify the saturation level of the rotor back iron and air gap field density. The Levenberg-Marquardt algorithm is applied to find the optimal coverage of radial magnet in a pole pitch and the optimal PM height. It is also observed that the resulting Halbach array motor is superior to surface-mounted PM motor in torque performance when the same amount of PM is used. A prototype motor was built on a real scale, but with a reduced stack length.