Inductance calculation in variable-flux flux-intensifying permanent magnet synchronous machines using improved frozen permeability method

In permanent magnet synchronous machines (PMSMs), the flux is produced by two components-armature current and PMs. The flux produced by armature current can be removed when the current is set to zero, while the flux produced by PMs always exists in conventional PMSMs. In design process, it is necessary to separate them according to excitation in order to accurately calculate the d- and q-axis inductance. Conventional methods to calculate the d- and q-axis inductance, such as phasor diagram method, divides the individual flux relying on simple phasor superposition, which assumes the flux produced by PMs at load condition keep the same as that of no-load condition. However, the permeability of iron core is changed by the armature reaction, resulting in a variation of flux by PMs. This paper proposed a improved frozen permeability method to calculate the dand q-axis inductance in a VFI-PMSM, which utilizes Alnico magnet . Besides the iron core, the permeability of the PMs is frozen according to load condition . Individual flux from each source field calculated using conventional and improved frozen permeability methods are presented and compared . Moreover, the PM operation point, dand q-axis inductance calculated by the two methods is compared respectively and will be verified by future experimental results .