frequency variation with increasing load

[bunda222]

Hey guys

I'm trying to perform a simulation in Matlab/Simulink to see the frequency variation with a load increase. I'm putting a AC voltage source behind a RL impedance with a PI model of the line. The first load is a RLC parallel load with P= 6kW Ql=1000 var and Qc=-1000 var. The second load is actived 3 seconds later to see the difference. This second load is the same the first one. I was expecting a sustained sub frequency as it happens in real power systems. But the frequency makes a fast variation and gets back to the previous value of 60 Hz. Is my simulation wrong, or is my concept wrong?

I'm sending the file that has been made using Matlab version 2013a.

 

[Skogsgurra]

If you have two systems that tend to oscillate (systems with L and C do that), then the transient when switching in the second system excites the natural frequency of the two coupled systems. That transient dies after some time and the whole system oscillates with 60 Hz. Try running for ten seconds to see the steady state.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[bunda222]

But that is the problem.. I don't want it to oscillate with 60 Hz, if there is a load increase the system should oscillate to a value below 60 Hz.

 

[davidbeach]

What is governor response of your 60Hz voltage source? My guess is that you have an ideal (not a real) source and the additional load has no impact on the source's ability to supply 60Hz.

 

[Skogsgurra]

If you are simulating. And using a voltage source And you want that voltage source to follow load - then you have to select a voltage source that does that. Like a generator model with frequency droop. Does your voltage source have frequency droop?

Yes, David said so, too.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[bunda222]

You guys are right, my voltage source is ideal and I cannot see the change in frequency with the additional load. I am using a single phase system. I guess I may use a Controlled AC Voltage Source to account for this load increase. Using, for example:

f-f0 =-k(P-P0).

And plug into the voltage source the difference in frequency associated with the additional load. What do you think?

 

[PHovnanian]

I'd expect such an analysis to require model parameters for prime mover throttle response, frequency droop (already mentioned) and generator (and load) inertia. That's what will give you behaviors similar to 'real world' performance.