Multiple VSC power flow problem

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Jubeyer

Multiple VSC power flow problem

Hi,

I am trying to integrate a PV system and a battery system along with the grid. I have tested them separately with the grid and both of them working fine but when I have connected both of them together with the grid they start showing very abnormal behaviour like there is backfeeding in PV system, instead of being charged the battery sometimes is getting charged and sometimes discharged etc. I have also noticed that at different points of the system the voltages do not remain fixed. It fluctuates a lot. As you know the VSC block in PSCAD doesn't have any mean to set the grid side voltage.

Can anyone help in this issue? Knowing why this happens is also very important to me.

Regards,
Jubeyer

Status: Open Nov 14, 2017 - 09:27 AM

VSC block random power flow

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Hasan Alrajhi

Nov 14, 2017 - 09:41 PM

Hi There There are several factors that might lead to unstable opreation of your system. 1- The system impedance can effect your sytem stabilty. 2- The controller bandwith might hit the stabilty boundries. To solve your problem. 1- Retune your controller. 2- Connect each sub-system sequentially. I mean that include just the batery model and then test your system. After you satisfied with your system performance then include the PV and so on.

Regards
Hasan

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Jubeyer

on 11/14/2017 9:53:31 PM | Like (0) | Report

Hi Hasan,
I have actually done that step by step. First I have connected my PV system with my two generators system and it was working well. I have also checked my battery while being connected with the two generator system which was also ok. But when I include them together, the system starts behaving abnormally.
Assuming I might have some problem in designing my own system, I have tried two of the PSCAD's system given in the knowledge base (PV system one with constant voltage control and another with constant power control ) and include them with a voltage source in a single model. The result is again the same. And I have done it for several other systems as well. My observation says when you have two vsc's present in your system tied with two DGs the system behaves abnormally. If you can provide me any well functioning model where there are two types of DGs are connected to the grid via vscs that'll be also great. To be frank, I am not very well in designing decentralized control etc.

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Hasan Alrajhi

on 11/14/2017 10:01:54 PM | Like (0) | Report

Keep in your mind that if you are working based on grid connected mode that means your control must be based on PQ control. Also if you are working based on Islaneded mode then you controller must be based on Droop control

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Jubeyer

on 11/14/2017 10:06:10 PM | Like (0) | Report

I am using synchronous machines instead of voltage source (so it is islanded from that point of view). Can you give some link/idea how the controller be based on droop control. In PQ control we take the dq tranformed signal but what about droop controller?

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Jubeyer

on 11/14/2017 10:10:42 PM | Like (0) | Report

Sorry, I think I have understood what you're trying to say. You're talking about the V-f control, right?

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Hasan Alrajhi

on 11/14/2017 10:29:37 PM | Like (0) | Report

Yes, I am talking about whether P-f and Q-V control or PQ

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Hi Hasan,
I have actually done that step by step. First I have connected my PV system with my two generators system and it was working well. I have also checked my battery while being connected with the two generator system which was also ok. But when I include them together, the system starts behaving abnormally.
Assuming I might have some problem in designing my own system, I have tried two of the PSCAD's system given in the knowledge base (PV system one with constant voltage control and another with constant power control ) and include them with a voltage source in a single model. The result is again the same. And I have done it for several other systems as well. My observation says when you have two vsc's present in your system tied with two DGs the system behaves abnormally. If you can provide me any well functioning model where there are two types of DGs are connected to the grid via vscs that'll be also great. To be frank, I am not very well in designing decentralized control etc.
Keep in your mind that if you are working based on grid connected mode that means your control must be based on PQ control. Also if you are working based on Islaneded mode then you controller must be based on Droop control
I am using synchronous machines instead of voltage source (so it is islanded from that point of view). Can you give some link/idea how the controller be based on droop control. In PQ control we take the dq tranformed signal but what about droop controller?
Sorry, I think I have understood what you're trying to say. You're talking about the V-f control, right?

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