Power factor improvement of synchronous reluctance motors (SynRM) using permanent magnets for drive size reduction

The performance of a synchronous reluctance motor (SynRM) depends on the direct-axis inductance (L_d) and the quadrature-axis inductance (L_q) of the machine. Increasing the saliency ratio L_d/L_q and making the difference between these inductances (L_d-L_q) large are well known methods for achieving high torque density and power factor. Placing the right amount of permanent magnets inside the rotor in the proper position will significantly improve the performance of this permanent magnet-assisted SynRM (PMa-SynRM). The PMa-SynRM offers higher power factor, which will reduce the size of the inverter. This study investigates the effect of Ferrite and NdFeBr permanent magnets on a 1.5kW SynRM, which has the capability of holding block shape magnets inside one of the rotor air barriers. Analytical analysis and finite element analysis (FEA) are used to compare the use of Ferrite against NdFeBr. Finally, the effects that using high or low cost magnets have on machine power factor and output performance have been studied.