Linear scalar-potential models for permanent-magnet circuits

Abstract

A scalar-potential equivalent network is developed to represent permanent magnets with linear operating characteristics and their surrounding air regions. The method of allowing for the effect of current in the scalar-potential formulation is explained and demonstrated. The use of the technique is illustrated by means of examples. In the first, the calculation of the leakage factor in a permanent-magnet circuit with an airgap is examined. The influence of magnet permeability on leakage factor and the limitations of a more traditional technique are explained. In the second example, the method for calculating demagnetisation limits is demonstrated for electrical machines with permanent-magnet excitation adjacent to the airgap. The method is applied to the calculation of field flux-density distributions set up by two permanent-magnet rotors, and the results compared with distributions obtained experimentally. Finally, the general ‘dynamic’ problem is considered. When reduced to its most basic form, the network is shown to model static and dynamic magnet behaviour in a manner similar to other techniques which assume point operation within the permanent magnet.