Cogging force reduction using special magnet design for tubular permanent magnet linear generators

Various methods are explained to reduce the cogging force in tubular permanent magnet linear generators. The proposed methods depend on the variation of the permanent magnet construction. These methods include two approaches in the form of sloped magnets, and conical magnets in addition to the conventional method of varying the magnet length. Thus the magnetomotive force which is proportional to the permanent magnet length is not constant in the radial direction. The undesired cogging force ripples are calculated by a two dimensional finite element method. Moreover, the generated electromotive force in the stator coils is calculated for each configuration of the permanent magnet. The experimental results agree well with those obtained from the FEM simulations. Reduction in the cogging force is obtained in the range of 40% while the root mean square of the output voltage is maintained.