PLBVFU1 with network frequency dependence enabled

asked 2020-05-27 00:20:50 -0500

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Hi there, I am having an issue using PLBVFU1 when network frequency dependence is enabled.

What I am finding is that when I use PLBVFU to cause a frequency disturbance and have frequency dependence switched on, the voltage on the infinite bus varies proportionally to the frequency. For example, if I start Vinf = 1.03 and ramp the frequency from 50 Hz to 47 Hz (6% decrease), the voltage also reduces by 6%, to 0.968. When the frequency returns to nominal, the voltage returns to the original value.

I have verified this on the following two cases and the performance is the same:

jconto's working directory (I can't link to it here but it's under the question "Example using PLBVFU1 playback generator") - if I enable frequency dependence then the voltage in the out file is about 0.3% lower the voltage in the plb file while the frequency is low.
I setup a case which has only one machine connected to a bus and no other network elements. The same behaviour is shown.

I have attempted to compensate for this by increasing the voltage in the PLB file by the same amount that it decreases in the simulation. However the voltage is still distorted when the frequency is ramping.

Has anyone else come across this bug? Is there a way around it, other than what I have shown above?

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3 answers

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answered 2022-02-10 07:31:06 -0500

Rahul Bhatia
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Hi everyone, I found the solution to this by setting R- Source (pu) of infinite bus to 0.0001 and then setting the X-Source (pu) to 0 in the power flow solution. As R-Source doesn't vary with frequency, voltage remains constant.

Cheers

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answered 2020-07-23 08:58:50 -0500

Jorge

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Sorry to barge in but I have also experienced the same effect, only that it is when I use an user defined model similar to the PLBVFU.

I am manipulating the frequency at the POI and I leave the voltage singal unmodified and I see a similar effect, the voltage drops in proportion to the frequency.

If you don't mind me asking, what would be the physical explanation (if any) for this effect? and why does increasing the reactance of the generator at the swing bus appears to help?

Thanks!

Jorge

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answered 2020-05-27 11:09:06 -0500

perolofl

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Hi Patrick,

I tried it myself and found the same problem as you. I first thought that decreasing Xsorce would solve the problem, but it made it even worse!!!

Then, I increased Xsorce, and the voltage variation became lower. Eventually, I tested with Xsorce = 10000 pu and now the voltage is very stable.

I show a plot of the simulation below: image description

The blue curve is the generator voltage, and it is stable at 1.03 pu. The green curve is the rotor speed and the red curve is the bus frequency, the are both plotted against the right y-axis.

So, a simple workaround is to increase Xsorce to a very high value.

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Comments

Hi Perolofl, Thanks for your answer, unfortunately it doesn't seem to work when the IB machine has any current flowing through it. The high source impedance means that the internal voltage is enormous and the simulation ends up with a lot of NaNs very quickly.

patrickrossiter ( 2020-05-28 21:22:49 -0500 )edit

I found that this can be replicated in jconto's working directory by changing the machine impedance on line 164 of "playback.py" from 0.0005 to 100 (or something) and re-running the study.

patrickrossiter ( 2020-05-28 21:23:54 -0500 )edit

In my study I used a machine with P=500 MW, Q=200 Mvar and Mbase=900 MVA, so the machine is quite highly loaded.