Radial Electromagnetic Force Estimation Using Strain Gauges in Switched Reluctance Motors

This study proposes a novel estimation method of the radial electromagnetic force in airgaps using strain gauges attached to the stator teeth in switched reluctance motors (SRMs). The proposed method compensates for the errors owing to magnetostriction and the non-uniform strain distribution on stator teeth. To verify the method, two test SRMs are fabricated with two different core materials; the 6.5% high silicon steel (10JNEX900) and amorphous iron (2605SA1), which have significantly different magnetostriction characteristics. Without the proposed compensations, the estimated radial force is higher than the finite element analysis (FEA) results owing to the extra deformation caused by magnetostriction. After applying the proposed method, the estimated force has good correspondence with the FEA results, and the error is reduced from 24% to 4% in the high silicon steel SRM. Regarding the amorphous iron SRM, the force estimated error was as high as 413% without compensations and is reduced to 64% by the proposed method. Additionally, the force waveforms are deformed because of the subtraction of the dominant magnetostrictive strain and phase delay in the amorphous iron SRM. In conclusion, the proposed method is effective in estimating the radial force on core materials with low magnetostriction.