The direct (d)- and quadrature (q)-axis inductance characteristics of the interior permanent-magnet synchronous motor (IPMSM) are presented, with an emphasis on the cross-coupling effects. Nonlinear variation of phase inductance is investigated, according to the rotor position on entire stator current excitations. We also propose a new analytical method, called the fixed permeability method (FPM). We applied this method (FPM) to steel-cored permanent-magnet linear synchronous motors for large powered linear motional applications. Experimental data were found to corroborate the findings obtained by the FPM method. We also used FPM to analyze magnetic saturation characteristics of the prototype IPMSM, and compared the air-gap flux density and d- and q-axis inductance with the conventional finite element analysis results.