Improvements in THD and Demagnetization of the Rare-Earth-Free Interior Permanent Magnet Synchronous Reluctance Motor with Novel Magnetization Orientations for EV Application

Synchronous reluctance motor (SyRM) is gaining a great deal of attention from researchers and becoming popular due to its various advantages. Absence of rotor windings and rare-earth permanent magnets (PMs) are some of its salient features. Poor power density, efficiency, and power factor, however, are the drawbacks that seek attention. To overcome these limitations, ferrite PMs are placed across the barriers, topology known as interior permanent magnet synchronous reluctance motor (IPM-SyRM). This solution addresses some of the limitations. The PMs located within the outer barriers are highly prone to demagnetization because they operate at low values of permeance coefficient (PC). In order to operate in the field-weakening region, current angle (α) is rotated towards q-axis. This increases the q-axis magnetomotive force (mmf) and reduces the d-axis mmf. Also, in comparison to the d-axis flux path, the q-axis flux path is not a harmoniously permeable one. As a result, there are multiple crossings of the flux in the airgap; thereby introducing multiple higher order harmonics in the flux linkage. In this region, ferrite PMs placed in the outer barriers distort the air gap flux distribution further. Harmonics in the flux linkage become apparent in the terminal voltage of the motor. As a result, it requires a high dc-link voltage to supply a sinusoidal current in the field-weakening region. In this paper, a novel ferrite IPM-SyRM with Y34 ferrite PM is proposed which addresses the demagnetization of magnets placed in barriers and total harmonic distortion (THD) in the terminal voltage. The comparison between conventional IPM-SyRM (with FB13B ferrite PM) and novel IPM-SyRM (with Y34 ferrite PM) is carried out. The novel IPM-SyRM improves the THD significantly and prevents the demagnetization of magnets placed in the outer barriers. The 2-D finite element analysis (FEA) simulation results are presented which validate the above claims.