Analytic Model of Switched Reluctance Machine Using Combined Fourier-Polynomial Approximation Technique

This paper presents an approach to construct an analytic model of Switched Reluctance Machine (SRM). This approach combines two techniques of Fourier and polynomial approximation for describing the nonlinear characteristics of SRMs, flux-linkage characteristic and torque characteristic. The Fourier approximation is applied for the periodical relationship of rotor position, whereas the polynomial approximation is applied for the nonperiodical relationship of current or flux-linkage. The combined Fourier-polynomial approximation technique leads to a simple formulation of the torque calculation derived from the proposed flux-linkage analytic model. This paper also introduces a method to minimize the number of Fourier coefficients by considering the odd-even property of the SRM characteristics. By this method, the spared number of model coefficients can be better utilized for increasing the harmonics and polynomial order of the model in order to enhance the accuracy. The validity and accuracy of the proposed model are evaluated by comparing the proposed model with the measured SRM characteristics. The evaluation results show that the proposed model is accurate and can be used for analysis and study of behaviours of SRMs.