Hi everyone,
I am analyzing the effect of PV penetration in small signal stability. My test system is the two area system from Kundur book shown in file 1. The PV controller is as shown in the file 2. It only has an ac voltage regulating loop which consists of a PI controller.
I then tested the system. For a fixed PV generation (700MW in this case), when I change the integral gain (Ki), I found out that the inter area damping decreases! The initial gain of Ki is 50 where the corresponding inter area damping was 2% but when I reduce it to around 15, it reduces to around 0.8% as can be seen from file 3.
I am a little bit confused. Does this result mean that he PV integral controller can affect the interarea electro-mechanical mode of oscillation?
Cheers
Where is the PV generator located in image 1?
In practice, the PV system in stand-alone operation does not produce any oscillatory mode, however researchers have found that with the penetration of PV into the existing conventional system, there is every possibility that the interaction of PV (with controller) and conventional generation yield positive/negative damping torques. You may look into the attached reference:
1. To answer your query, did you try to find the participation factor of your PV system. This can easily be performed by linearizing your system along an operating point. Naturally what you will find is that there will be interaction of the SGs in your system with your PV system. This means that what ever controller you use for your PV system will have its affects on other system parameters. (This is considering the fact that what ever simulations that you have performed are without any other assumptions or errors).
2. I can explain the same effect in an another way. Your SGs will have their own AVRs for one area and SGs+PV system in another area. The AVRs will have their own controllers while you are introducing another controller for your PV system. Naturally the controllers do interact with each other. If you design the controller for one area and then you design the controller for the other area, this does not mean that the overall system will be stable. It might result in lower damping ratio for the overall system and may cause the system to become unstable.
if you want to see the affect of your controller in your system, the best way is to linearize your system, plot root locus of your system with various values of Kp and Ki and see what optimum value of Kp and Ki that you can use with maximum damping ratio. Once you do this exercise, you will understand the interaction of different controllers.
Thank you Syed, I actually already did the participation analysis. The participation factor of state variables of PV controllers were quite less but still present in the critical mode.
I just had to verify whether this result was logical or not as i want to submit my work for publication.
Good then that means point 2 that I made in my answer is valid for your case.
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