Design of Ferrite-Assisted Synchronous Reluctance Machines Robust Toward Demagnetization

The design of ferrite-assisted synchronous reluctance machines is investigated, with particular attention to the pivotal aspect of avoiding irreversible demagnetization. Geometric rules for obtaining a robust design are proposed and described analytically. The safe operating area is quantified in terms of the corresponding maximum electrical loading. Such demagnetization limit is dependent on the operating temperature and the machine size. Furthermore, the comparison between the continuous load and demagnetization conditions shows that small- and medium-sized machines can be stiffer against demagnetization, with respect to larger machines, and have room for transient overload. The analysis is validated by finite elements, and a design example is given, namely, a 12-pole direct-drive machine, rated 910 N · m at 200 r/min.