A super high speed PM motor drive system by a quasi-current source inverter

This paper describes a surface mounted PM motor with the ratings of 5 kW and 150000 RPM for super high speed drive applications such as a machine tool. A much larger air gap, compared with that of the existing PM motors, is utilized to reduce the slot ripples and hence the resultant eddy current loss in the metallic sleeve that retains the permanent magnets, otherwise this loss would be objectionable at such high speeds. The motor is supplied from a quasi-current source inverter with the DC current controlled by a chopper and operated at a near unity power factor by the use of a simple position sensor-less control, to improve the motor efficiency. The analytic results are presented to show the slot ripple reducing effect of increasing the air gap length. To investigate the losses of the sleeve, several motors with different sleeves were manufactured and tested. Typical experimental results on these prototypes are given, which show that motor efficiency of higher than 90% can be realized at the rated torque over a wide speed range