Single Halbach Field Magnet Desined from Dual Halbach Field Magnet for Rotating Machines

A coreless synchronous motor with a dual Halbach field magnet (DHFM) has been developed. A cylindrical DHFM equally converted from paralleled dual Halbach array of Permanent magnets (PMs) with the square cross section. The magnetic flux density distribution generated by the DHFM contains little space harmonics. The DHFM gives superior features such as little torque ripple and non-cogging torque to the high-speed rotating machines. However, it was difficult to cool the armature coil at high torque output. This paper proposes a single Halbach field magnet (SHFM) to solve this problem. The SHFM is constructed by replacing the outer part of the DHFM from the gap center with a ferromagnetic material. The SHFM gives better cooling performance to the coreless synchronous motor. The paper reports the test results of a 10 kW 10,000 rpm motor prototype for load and speed. Results were obtained with a total efficiency of 91% at continuous rated operation and a coil temperature of 60°C. The prototype testing proved that the SHFM can give superior features to high-speed rotating machines.