Development of variable magnetic flux motor suitable for electric vehicle

Permanent magnet motors are widely used in electric vehicles (EVs) due to their high efficiency and small volume. However, the electric current that is applied to weaken the magnetic field has to be increased because the induced electromotive force is increased in proportion to the revolution speed. Therefore, the motor efficiency decrease at high revolution speeds. In this study, we developed a variable magnetic flux motor (VFM). That has a control method for mechanically weakening the magnetic field in order to improve the motor efficiency at high revolution speeds. Compared to a conventional motor, the VFM has a wider driving region. Additionally, its high efficiency region expands to the high revolution speed region. At a high revolution speed of 4500 min^-1, the prototype VFM can improve motor efficiency by 13%.