Effect of mutual coupling on torque production in switched reluctance motors

In many cases, the normal operation of switched reluctance machines requires excitation of two or more phases simultaneously. When multiple phases are conducting simultaneously, the flux paths from each phase will overlap, which may lead to localized saturation. In such cases, the flux linkage must be considered a function not just of the current in the test winding but of all excited windings. The degree of mutual coupling between phases influences the per-phase magnetization curves and torque characteristics. In machines with even phase numbers, the degree of mutual coupling between phases varies due to discontinuities in the phase polarity arrangement. From nonlinear finite element simulations, it is possible to compare the i-ψ loop diagrams under single-phase and multiphase excitations, and hence the torque produced. The mutual flux linkage from each phase can be calculated separately for each rotor position using the frozen permeability method, to further analyze the mutual coupling effects. For a given excitation current profile, the torque can be maximized by careful arrangement of the phase polarities