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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Well, proper design means optimising the overall design of the system. Reducing the current ripple means increasing the PWM switching frequency, hence suffering more switching losses in the inverter. If the increased switching losses outweigh the reduced losses in the motor, then it's not an optimal system.
Skin effect losses from actual torque-producing harmonics in a motor with a non-sinusoidal back EMF are another story, possibly a lot more interesting.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Well with usual DC motors the "negligible ripple frequency" is below 20 kHz, and for modern MOSFETs and Schottky diodes, 100 kHz is no problem. Of course there can be some kinds of motors which need higher switching frequency, or use a H-bridge with unipolar drive which doubles the frequency on the motor.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Steve Conner wrote ...
Well, proper design means optimising the overall design of the system. Reducing the current ripple means increasing the PWM switching frequency, hence suffering more switching losses in the inverter. If the increased switching losses outweigh the reduced losses in the motor, then it's not an optimal system.
yes, and the more i learn, and experience, the cheap 9 to 12 USD chinese ESC's are clearly less well designed than the 70-80 US$ Castle ESC's, which actively watch the analog waveform across the phases.
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Skin effect and khz driven electric motors.
