Magnet-Frozen-Permeability Fea And Dc-Biased Measurement For Machine Inductance: Application On A Variable-Flux Pm Machine

This paper proposes a magnet-frozen-permeability finite-element method and an experimental approach for inductance analysis of a variable-flux permanent magnet machine. The machine studied uses Alnico magnets, whose nonlinear magnetic properties deteriorate the inductance calculation accuracy. Besides the machine core permeability is frozen, the magnet-frozen-permeability approach freezes nonlinear B-H curves and nonlinear per-meabilities of the magnets in the finite-element analysis. Because the soft magnets have low coercive force, conventional symmetric inductance measurement currents may demagnetize them. This paper presents a zero-start dc-biased current trajectory tracking approach. This approach uses positive current, which avoids demagnetization during the inductance measurement. Meanwhile, based on flux linkage-current curves, influences of resistance can be eliminated. Cross-magnetization effects are evaluated in the two proposed methods. Inductances of these two methods are compared and show good agreements.