Abstract
The electromagnetic transduction coefficient has a strong influence on efficiency as well as the sensorless control of linear oscillation electrical machine (LOEM). This paper presents a reciprocal LOEM method for measurement of the electromagnetic transduction coefficient, to investigate the effect of the magnet length on the characteristics of the transduction coefficient. The result shows that the transduction coefficient has two regimes, a constant regime and a nonlinear regime. As the harmonic distortion begins to appear in the induced electromotive force, the electromagnetic transduction coefficient passes from the constant regime to the nonlinear regime, and the corresponding stroke is defined as critical stroke. The range of constant regime equals the observed critical stroke, and the critical stroke is 8.81 mm and 10.78 mm when the length of the permanent magnet is 11 mm and 13 mm respectively. The relationship among the geometrical dimension of yoke and permanent magnet, the critical stroke and the stroke of the LOEM are carefully investigated. Then optimal lengths for both the yoke and the permanent magnet are suggested for the LOEM design with the rated stroke, to achieve the highest efficiency and least material cost simultaneously.
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