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Unread 03-09-2010, 10:30
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Ether Ether is offline
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Re: Speed Controller Design

Quote:
Originally Posted by Al Skierkiewicz View Post
Ether,
When the locked anti-phase duty cycle is 50% current is flowing 100% of the time. 50% in one direction, 50% in the other, correct?
When the locked anti-phase duty cycle is 50%, voltage drop across the motor is positive 50% of the time and negative 50% of the time. Under these conditions, the motor inductance prevents any significant motor current from developing.

Quote:
An averaging meter will read this as zero while a true reading RMS will not.
Both average and true RMS will be near-zero. At 15000Hz switching frequency and 50% duty cycle, the voltage drop will stay at each polarity only 33 microseconds. This is short compared to the rise time for the current (due to the motor inductance). Thus even the peak current never amounts to much. So the RMS is also near-zero.

Quote:
During a previous discussion (2009) someone measured a CIM motor at .12 mH and 90 mOhm. At 150Hz this is very low but at 15kHz it is significant.
The significant inductance of the CIM at 15KHz (Jaguar) is what suppresses the current at 50% motor duty cycle in locked antiphase.



Last edited by Ether : 03-09-2010 at 11:57.