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Rotor time constant


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#1 Carl

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Posted 09 October 2005 - 09:10 AM

hello Forum

Q/ What is the realtionship between the rotor time constant and the pwm switching frequency. Is there a point where an increase in the carrier frequency has no point. For some reason the figure of 8 switching points comes to mind??
I realise there is a limit to the power device frequency as every switched edge causes heat.
I also appreciate that there is an audio content at lower switching frequencies
The assumption is the higher the carrier frequency the better the AC "form" of the current wave............but is this correct when it comes to motors??

#2 msdaif

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Posted 09 October 2005 - 10:37 AM

Hello Carl

I do not think there is a relationship between the rotor time constant and the switching frequency. The switching frequency is made more than double the hearing frequency of humans. Electric drives are noisy and so having a high switching frequency reduces the noise.

#3 Carl

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Posted 09 October 2005 - 07:08 PM

Hello msdaif

There is one more the higher the carrier wave the more deadtime distortion..hence more ripple in the current wave.
Just something in the back of my head that is bothering me about this carrier wave. Most likely a one liner in some document that I read.




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