Analysis and Experimental Study of Permanent Magnet Machines With In-Situ Magnetization

This paper evaluates the performance of surface-mounted permanent-magnet (PM) machines with anisotropic rare-earth magnets magnetized using its own stator windings. The magnets in this process (often called in-situ magnetization) are magnetized after complete assembly. For manufacture of PM machines using this process, part of the magnet may suffer from weaker magnetization due to the magnetizing flux pattern, in particular on the two sides of the anisotropic magnets. The machine performance can thus be affected and needs to be evaluated. The current required to sufficiently magnetize the machine should be carefully studied. In this paper, both finite element analysis and experiments on prototype PM machines manufactured with in-situ magnetization are used. The concentrated and distributed winding machines are both considered. The results show that distributed winding machines can magnetize the rotors more easily than concentrated winding ones. Also, it is found that a magnetizing field of 2.5 times coercivity allows the machine back EMF magnitude to achieve the levels of pre-magnetized cases.