No-Load Electromagnetic Performance Analysis of a Mechanically Modulated Permanent Magnet Homopolar Inductor Machine

Conventionally, the nonadjustable air-gap flux density generated by the permanent magnet (PM) of PM machine would cause large core loss during the standby operation state of flywheel energy storage system (FESS), which would reduce the energy conversion ratio of system. To suppress the no-load core loss, a mechanically modulated PM homopolar inductor machine (MM-PMHIM) is proposed. However, the MM-PMHIM has intrinsic three-dimensional (3-D) flux density distribution, which would be time-consuming to analyze the no-load electromagnetic performance by the finite element method, especially in the initial design stage. Addressing this issue, an analytical method based on magnetic equivalent circuit (MEC) considering the different flux weakening states of the MM-PMHIM is proposed in this article. First, the special topology and operation principle of the MM-PMHIM are analyzed. Second, the MECs of this machine under different flux weakening states are established, and the detailed building processes are presented. Third, several main electromagnetic performance indexes, including flux density distribution, flux linkage, back-electromotive force (back-EMF), etc., are fully analyzed. Finally, the no-load electromagnetic performance of the proposed MM-PMHIM under different flux weakening states is evaluated and the effectiveness of the MEC models are proved by finite-element method (FEM) and prototype test. The result shows that the proposed analytical method can quickly and accurately analyze the no-load performance of the MM-PMHIM.