An alternative PM machine configuration suitable for low speed and beyond — Rated speed applications

Permanent magnet synchronous machines (PMSM) are being used in numerous applications. Some of requirements need a single machine to operate, below and above the rated speeds. As there is no direct field control method in a permanent magnet (PM) rotor, injection of negative direct axis current is done to implement a flux weakening, which in turn, helps to achieve speeds beyond the rated speed. An alternative method for flux weakening is of great interest currently and different variable flux permanent magnet (VFPM) configurations have been proposed. A new method of VFPM arrangement is proposed in this paper. Further, the design of components associated with VFPM assembly is also discussed. The performance comparison of conventional PMSM and VFPM is carried out. With the help of variable flux arrangement, operating speed of machine is extended to 2600 rpm from 1100 rpm. Further very good improvement in power factor and efficiency is observed in variable flux arrangement.