| Energy storage is a key technology and an important way to achieve efficient use of energy. How to achieve high efficiency, high power density and high reliability energy storage has always been research focus of scholars at home and abroad. With favorable feature of simple principle and easy control, the flywheel energy storage technology has drawn a lot of attention. In the flywheel energy storage systems (FESS), the conversion between electrical and mechanical energy is based on motor and its control, therefore the performance of motor has a great influence on performance of the FESS. With simple structure, high-speed operation ability, and low no-load loss, inductor machines will play a great part in FESS, so it is of great importance to do researches on inductor machines, for the purpose of achieving high efficient energy storage.Based on the review of motors used in FESS, the inductor machine is selected to be the study subject. The structure and working principle of the inductor machine are studied, and then the mathematical model is established and armature reaction is analyzed. Due to its special structure, the air-gap magnetic field is homopolar, and the magnetic field of its d-axis armature reaction contains a dc component.The magnetic field of the inductor machine is computed using 3-D finite element method (FEM). The field winding of the inductor machine is designed based on the results above. Then, the no-load and load characteristics are obtained from experiment.The simplified 2-D finite element model of the inductor machine is proposed through analysis of the magnetic field. Then the flux distribution, air-gap flux density and flux linkage of the inductor machine are computed. By comparing the results with those obtained from 3-D FEM, the simplified 2-D finite element model is proved to be valid. The effects of rotor parameters of the inductor machine on the performance are analyzed. The results show that the maximum air gap flux density is mainly determined by rotor teeth angle, while the minimum is determined by rotor slot depth.Due to the DC-biased magnetization, the iron loss of the inductor machine is different from that in conventional machines. The influence of DC-biased magnetization on magnetic properties of core is analyzed. Then the hysteresis loops, magnetization curves and iron loss curves are measured while different DC-biased magnetization is applied. Experimental results show that the DC-biased magnetization leads to distortion of hysteresis loops of cores, and it is the reason for what the iron loss is affected.
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