Dear Researchers,
I have a simple (but rather confusing for me) question to ask. What are the rules to decide the output reference of a PI controller. For example if i am regulating frequency error using PI controller what should be the output of PI. In some papers i read the output is phase angle while some authors took it as deltaPower. My question is how to exactly decide this. I know there is a relation between deltaPower and phase angle but you have to change the controller according to your PI output. I hope i have explained well enough for you to start a healthy discussion on it.
For different applications we have to design a reference. PI tuning is the best way to find useful references.
what is your application? If you using your PI controller for droop characteristics then yes deltaP will have a relation with frequency. If you are using it for controlling phase angle then again frequency will have a relation.
I am asking this question generally. Like a DC Link voltage in two stage grid connected PV inverter is regulated and the output of PI is used to regulate grid current.
Is it practical to say that if i regulate power the output of PI can also be deltaP ? Syed A. Raza
Shah Fahad for grid connected PV inverters, the outer loop will be of real power regulation. So the output of the outer PI controller will give the current reference for the inner loop.
I wrote this just for the sake of an example. Anyways thank you for the help.
A PI controller forms a relation of the output to the input.
The input and the outputs of the system are your's to choose.
Example: For a Drone the input may be the Voltage to the propellers and the Output would be the Propeller speed. Now how much voltage change would bring the desired output is set by the gains of your PI controller.
Similarly for your application if the input to the PI is the change in frequency then the output of the PI controller should be the value that you want to be affected with this change in frequency.
Normally chnage is frequncy is related to the change in Active power and for a Inverter we know that the Active power can be controlled by the Id current. So the output should be the Change in current Id.
As we also know the Active power can also be controled by the phase angle of the voltage and current. so that can be an output as well. Depends on your control.
Ehsan Khan Thank you for your detailed explanation. I really appreciate your time. One last thing, considering your statement, the input and output can be chosen by you. If i want to regulate power and i want to generate power reference of another kind from the output of PI. Is this something meaningless ? because i have done that and it gives me the same result as i want.
Shah Fahad I had the same Quesiton some time ago. My previous answer reflects my understanding. I state this as i don't consider my self an expert in the field, feel free to correct or add to the answer.
That said, what i understand is that, the PI/PID controller tells us how an Output changes with respect to a change in Input.
Example: to regulate a change of 0.5 Hz frequency at the Grid might require 500W of active power to be increased. As can be seen a small change in frequency requires a large change to regulate.
What i'm basically trying to say is that the output is just a value that represents the amount of change needed. It has no units (W, Amp, V). So in principle what you said is possible and would give you the desired results as you stated.
for your system PI controller would basically tell us how the change in your measured power(the power you want to regulate) would give a change in your output (Ref power in your case).
Ehsan Khan I understand your point. A good discussion indeed. Thank you so much.
Shah Fahad You're welcome :)
Looked at some of your research. Very interesting work i must say
Ehsan Khan Thank you for reading. Looking forward towards more quality research. :)
As Sayed said that the dc-link voltage regulation control loop generates the d-component reference current for the inner current control loop. To see the model of the outer dc-link voltage control you can read this paper:
M. Karimi-Ghartemani, S. A. Khajehoddin, P. Jain and A. Bakhshai, "A Systematic Approach to DC-Bus Control Design in Single-Phase Grid-Connected Renewable Converters," in IEEE Transactions on Power Electronics, vol. 28, no. 7, pp. 3158-3166, July 2013.
- Badges
- Science topic
- Similar topics
- Mathematical Sciences
- Control Theory
- Control Systems