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Pump speed hunting


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#1 chaterpilar

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Posted 09 July 2006 - 09:39 AM

Hi !!

We use a VSD to control water pump output pressure, by controlling speed.

During commissioning of this drive we found speed hunting and not stable .
What parameters at drive ( gain, Acc, etc) need to be adjusted to keep the speed steady.
The water consumption is steady.

thanks,


Cheterpilar

#2 jraef

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Posted 09 July 2006 - 06:55 PM

Are you using a PID loop ar at least PI control, either inside the VFD or in an external controller? Without it the speed will hunt forever.
"He's not dead, he's just pinin' for the fjords!"

#3 marke

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Posted 09 July 2006 - 07:42 PM

Hello chaterpillar

Assuming that you are using a PID controller, you can reduce the hunting by playing with the PID settings.

First, I would set the D term to zero, set the I term to a relatively long time. This should make the system slow to respond and eliminate any hunting. With these settings, if you are still getting hunting, you could try reducing the proportional gain. Once you have stopped the hunting, begin to reduce the integral time which will speed up the response. The actual time settings are very dependant on the hydraulics of the pump system.
One thing to watch out for is that if you have slow ramp settings on the drive, you have effectively increased the lag in the control system and it will be more prone to overshoot. You must ensure that the PID sets the response rate rather than the drive ramp settings.

Hydraulic fluctuations can often be reduced by adding in some D component. i.e. increasing the D settings. Get the system stable without any D and then slowly increas the D setting and you will find that there will be an improved transient response up to a particular stetting, and then the transient response will degrade beyond that point.

Best regards,

#4 chaterpilar

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Posted 11 July 2006 - 06:19 AM

Thanks Marke for your prompt and valuable response...

The drive is smoother, I adjusted the Gain and ramp....

Chaterpilar




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