Analytical and Experimental Investigations of Magnetostriction Influence on Strain Measurement in Switched Reluctance Machines

Switched reluctance motors (SRMs) have several advantages: simplicity, robustness and low manufacturing cost, which is considered as one of the alternatives to permanent magnet motors in electric vehicle application. However, due to the doubly salient structure, its severe vibration and acoustic noise prevent its wide application in industries. Strain gauge is proposed as a possible sensor for the electromagnetic force, which is the dominant vibration source in SRMs. However, besides the stretching due to electromagnetic force, magnetostriction deformation is also detected in strain gauge signal during measurement. In this paper, the influence of magnetostriction on strain gauge output in SRMs is studied. Two iron materials, amorphous iron and high silicon steel, are employed to fabricate two test machines with identical designs. Strain gauges are attached to these machines to detect the strain on the stator teeth. Compared with the magnetostriction-ignored strain acquired from finite element analysis (FEA), the measured strain is found to be 8 times and 1.5 times higher in the amorphous iron and the high silicon steel, respectively. It is also found that the significant difference is caused by the magnetostriction based on the measured magnetostriction data of each material.