100 kRPM Brushless Motor Design 4

[sdk_imported]

Hello,

I would like to see some discussion about high-speed brushless motor & controller design(60-120kRPM, 1-5kW). Our biggest challenge is preventing rotor heating and maintaining stable speed control. We currently are using two-pole segmented magnets, segmented magnet sleeves, high resistivity materials, high speed switching, and external inductors ... but, we are still having issues. Will any of the following help me?

Slotless configuration
Non-PWM based speed control
Laminated rotor yoke
Something else I'm not thinking of..

If anyone has successfully designed and tested a motor in this speed and power class I would very interested in hearing from you. Finally, do you know any companies that make motors like this in large quantities?

Thanks.
Scott

 

[Clyde38]

First, I must say that I find this forum most interesting. I am spending far too much time reading the interesting discussions.

I have one suggestion. Search for IEEE papers on copper sleeving (rotor)for this application. I don't recall the exact figures, but the rotor heat (from eddy current) was drastically reduced by employing this techinque.

 

[UKpete]

Clyde, I believe you are correct. If the electrical conductivity of the sleeve is high (i.e. copper or aluminium) then the rotor losses go down. The magnet is effectively screened by the sleeve. One problem though is the hoop strength of the sleeve - there are high strength copper alloys but they have a creep (or stress relaxation problem) at temperatures above about 150°C. Maybe aluminium alloy is best. There was a GE patent on a copper screen some years ago.

 

[jbartos]

Suggestion: Visit

http://www.emoteq.com/images/bdhnew.pdf

for:
The new range of BDH brushless/brushed servo drives has been designed to drive high velocity Servo-Motors at speeds
in excess of 100,000 rpm. These motors have virtually no inductance making them difficult to drive with normal PWM servo amplifiers. The BDH uses a high frequency proprietary PWM technique together with a high-speed MOSFET output stage and other proprietary circuitry to achieve precise control of the motor. The second and probably the most important problem is that of controlling
and monitoring the significant energy stored in a high speed rotating mass. The BDH is designed and built to do both with additional monitoring for loss of hall sensors and an Over-speed limit.

 

[drFreeze]

hello SDK

as I see it a 120kRPM 2 pole motor needs a 2kHz sine wave - it is quite easy to achieve this up to a few kW with small filters. I have done something similar. ask if you want more help.
BR
Ian