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Values for P, I and D for PID Controlling of VFD

01/31/2018 7:12 AM

Deal All,

I am working in a project that supply and installation of a water treatment plant. As a part of I have to program three VFDs that control three water distribution pumps.

Reference pressure is given by potentiometer (between 0-6 bar) and pump output line pressure (feedback) is measure through 4 - 20mA Sensor. VFD is Schneider ATV 212 18.5 kW. When I have gone through programming manual, values of most parameters for PID control can be understanded. But I am still struggling to understand proper values for proportional gain, integral gain and derivative gain.

Can anyone help me to select proper values for these three parameters?

Thanks & Regards,

Kaushika

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#1

Re: Values for P,I and D for PID Controlling of VFD

01/31/2018 7:49 AM
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#5
In reply to #1

Re: Values for P,I and D for PID Controlling of VFD

01/31/2018 11:31 AM

I don't like the ZN approach at all. It relies on tuning the system while in closed loop mode. This guarantees a tune close to unstable. This is fine but only if it is impossible for the system to change. In closed loop, operational amplifier terminology the phase margin is unknown but tiny.

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#6
In reply to #5

Re: Values for P,I and D for PID Controlling of VFD

01/31/2018 11:48 AM

Indeed. In some situations, overshoot is undesirable, an example being the temperature in an oil cracking furnace: in an overshoot situation it is possible for the tubes to weaken and for the thing to destroy itself.

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#2

Re: Values for P,I and D for PID Controlling of VFD

01/31/2018 8:51 AM

Nobody can tell you what to set them to, without knowing a LOT more information.

You will probably never use the derivative gain, unless you get into some pretty ugly chemical processes, or temperature control.

Here is a link to a paper by Omega that is pretty straight forward. Because it is a temperature loop, they are using the derivative.

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#3

Re: Values for P, I and D for PID Controlling of VFD

01/31/2018 10:02 AM

This may help.

Closed Loop Control with Variable Frequency Drives | iKnow Variable ...

"Clearly, values of P, I and D for a narrow boat will be different to those for a fast system such as winder tension control for example. So our general purpose control system within the variable frequency drive allows setting of P, I, and D values to stabilise virtually any closed loop system. Figure 2 shows how the error is processed in a typical PID system."

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#8
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Re: Values for P, I and D for PID Controlling of VFD

02/01/2018 4:17 AM

Good link, but surprised it didn't say anything about integral action eliminating offset, which you get with proportional-onlyl control. Unless i missed it.

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#4

Re: Values for P, I and D for PID Controlling of VFD

01/31/2018 10:49 AM

...and it's not the <...VFD...> that is being tuned - it is the control loop in which it is a part.

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#7

Re: Values for P, I and D for PID Controlling of VFD

01/31/2018 12:39 PM

I assume you have not taken any control lessons at university and you have no clue about how to use simulation software.

Let's first talk about the gain. Assuming that all your signals have the same order of magnitude, try the gain of 1. Later, if you want to make your system faster, try a bigger gain, like 10, and if you want to make it slower, a smaller number, like 0.1.

The integral part is tuned with about 10% of the process. If you go from 0 to full distribution in 1 min, put 6s.

Finally, the derivative part should be zero, avoiding further problems.

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#11
In reply to #7

Re: Values for P, I and D for PID Controlling of VFD

05/29/2018 3:59 PM

Like this answer. But isn't the rule of thumb is "Double and Halve"?

Keep monitoring the system response, double the gain and check response. If it overshoots then halve it. Repeat till you get to the optimum number. Like many have suggested, you probably don't need the derivative portion.

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#9

Re: Values for P, I and D for PID Controlling of VFD

02/04/2018 4:18 AM

Hi every one!

Thank you very much for your valuable replies. What is the suitable control method from P, PI,PD or PID for controlling water distribution pump (using VFD) to keep constant discharge pressure (given by reference) with feedback signal (from pressure sensor)?

Thanks & Regards,

Kaushika

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#10
In reply to #9

Re: Values for P, I and D for PID Controlling of VFD

02/04/2018 6:59 PM

PI forget the derivative.

In essence, the proportional will compensate for a change in demand caused by a change in the process, and the integral will slowly bring the process variable back to setpoint.

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