Switched flux hybrid magnet memory machine

A novel switched flux permanent magnet machine (SFPMM) with both normal NdFeB and low coercive force (LCF) magnets has been developed in this paper. Outside a conventional SFPMM, the LCF magnets are mounted on the back of every U-shaped stator lamination segment with parallel magnetisation direction and alternative polarities. A lamination ring yoke is placed around all the LCF magnets, while extra magnetisation coils are wound on each of them. By injecting different directions of current pulses into the magnetisation coils, the polarities of the LCF magnets can be rewritten in order to enhance or weaken the field generated by normal NdFeB magnets. Therefore the back EMF and torque capability could be adjusted in a wide range. In this paper, the operation principle and machine topology are introduced firstly. Then the stator/rotor pole combinations and design considerations of the machine have been discussed. With the help of two-dimensional finite element software, a 6/5 stator/rotor pole machine has been globally optimised as an example to show the machine performances such as open-circuit field and back EMF, dq-axis inductances, torque capabilities and magnetisation. Finally, a prototype with the same dimensions has been manufactured and tested to validate the analysis results.