Good morning, I am currently studying the fundamentals of hierarchical control in microgrids. I know the role of current and voltage loops in the overal structure but I am experiencing some difficulties to understand how they are related themselves and also to Primary Control. Moreover I would like to study how the PI controllers in these loops are designed, namely: which input/outputs are to be considered, how transfer functions G(s) are obtained, why limiting values is required in the regulating process is required etc...
Could you pls kindly suggest some technical literature where I could review those topics with a certain detail? Thanks in advance!
To design the PID/PI controller we first obtain the transfer function (control to output transfer function) and then according to required compensation the values of controller parameters can be obtained. For example if we want to design a PID controller for a DC-DC buck converter then first we need to derive it's small signal control to output transfer function and then after combining all the components, the loop transfer function is obtained and then the controller is designed using frequency response or other methods. This paper may be useful for you:
Conference Paper Design of digital PID controller for voltage mode control of...
Probably the most easiest way to go about this problem is do the following. This is applicable to every software that you are using:
1. Make a fixed DC source as input to the inverter. Say 400 V.
2. Have a grid connection to the inverter. This way you will be regulating P and Q.
3. With an LC filter stage, make an overall plant control loop with the PI controllers
4. Design the PI controllers based on either: Routh-Hurwitz method, bode plots or through step response. Either way, you should be able to get the desired parameters depending upon your design.
5. Once you have designed your inverter for grid connected mode, now remove the grid and make an outer voltage control loop for your inverter.
6. Repeat steps 3-4 and see the response.
For more information on designing a PI controller you can look at:
Data Control Schemes for DC-DC Converter Stages for PV/Battery ba...
To maintain a particular quantity, which quantity should be controlled, that's the output of the PI controller. e.g. For maintaining voltage across capacitor constant, PI should calculate the charging current. So, it depends on logic and knowledge of system.
For tunning the PI controller, you can use one from many available methods for closed loop system. You may use the famous Ziegler Nichols method which will give you initial guess for Kp, Ki and then you can go for trial and error to get desired results.
I recommend a book dealing with control fundamentals to clear the concept of transfer functions. Once you understand that, you will be able to identify your inputs and outputs. The scenario you have sited implies inner current loop and outer voltage loop. I recommend you search and read a book which describes theory in a way which you can grasp. Sorry I cannot give you a short cur.
Hi Juan,
Adding to Mohan's reply, you may find the following book to be a good starting point:
- P. T. Krein, Elements of Power Electronics. Oxford University Press, 1998 or subsequent editions.
Cheers !
-Sanjay
Dear Juan,
This paper introduces the theory of the grid connected inverter with a voltage and current control loops in addition to a full modeling, simulation, and experimental implementation in an easy to understand language:Article Simulation and Implementation of Grid-connected Inverters,
Best wishes
I will recommend "
Grid Converters for Photovoltaic and Wind Power Systems". This is a wonderful book that can answer your questions. You can downlad from here " http://gen.lib.rus.ec/search.php?req=Grid+Converters+for+Photovoltaic+and+Wind+Power+Systems&open=0&res=25&view=simple&phrase=1&column=def ".
A small but critical add-on to the reply by Syed Raza.
It may seem attractive on a simulation, but I would suggest some caution in case of implementation on real systems. The control that he suggests may not do all to well in presence of renewable sources on the DC side that are susceptible to temporal variations !
Regrettably, two of the most popular renewable sources: wind and PV, are likely to pose challenges. (Recall that by the suggestion, we are beginning with a fixed source on the DC side !)
My apologies if that sounds a bit discouraging.
-Sanjay
Find the attached paper which contains the design of PI controllers for hierarchical control of AC microgrids. This paper will help you so much in this area.
- Badges
- Science topic
- Similar topics
- Biological Science
- Bioecology
- Systems Ecology
- Landscape Ecology
- Connectivity