Hello Parisa,

This is not my paper, so I am only trying to help you with my interpretations:

Hope that helped.

-Sanjay

Hello Mr sanjoy. thanks alot for your useful explanations. but some problems are unclear for me. wn is nominal value example "60 Hz" that should be maintained along islanding system, is it true? when there is an increase in the load, the frequency decreases. it means the frequency "60Hz" decreases or no, the output frequency of power controller decreases? Power controller mimics to governor. I want to found it's relationship with behavior governor. How to do power sharing? reference values at no-load are changed? how? by modifying the droop controller or changing reference value at no-load? I read a paper about power sharing that do it by improving the droop. but i become confused. please help me more. thanks

Parisa,

Since the inverter in the islanded system will be working with other conventional units, it has to have compatibility with those units. This is where the frequency drop in linear proportion to active load enters the picture. Please note that this is not a requirement of an inverter based source - when operating entirely on its own (no synchronous generators connected), it is probably not required at all !

To understand how frequency drop in linear proportion to active load works in a multi-generator system, I suggest you consult any good book on power system control, an example of which could be:

G. L. Kusic, Computer AIded Power System Analysis, Prentice Hall.

Incidentally, the voltage drop in linear proportion to reactive load is something that is exclusive to inverter control. An equivalent of this does not exist in the case of synchronous generators, which are conventionally served by AVR-excitation systems.

With best wishes.

-Sanjay

sanjay. thank you for your guidance. It was useful

regards

Hi Somesh,

Just a minor add-on !

wn and Vn are nominal no doubt, but they may not necessarily be 1.0pu ! That would depend on the extent of islanding, and the way nominal voltage and frequency play out as decided by the islanding.

Cheers !

-Sanjay

Hi,

Dear friends ' sanjay and somesh', thanks for your answers. according to your explanations, W* and V* change according to load changes. our aim in the control is " maintaining Vn and Wn along islanding". W* and V* change as active and reactive loadings change in real time but vn and Wn are constant. So voltage and frequency of microgrid is constant and stable. Are my explanations true?

somesh,I understood but when the frequency will be 43.33 Hz, how does it return to 50 Hz for system stability ?

thanks for your help.

it means the v/f droop controller provides a primary voltage and frequency regulation in the islanded microgrid?

for eliminating the deviation, we need secondary control?

somsh, your explanations were a big help. I thank you most warmly

Hello Mr. Somesh, the discussion is very good,i got many of my doubts cleared.My project is nearly related to this.What my doubt is how to give a particular VA rating for an inverter.I got to design an 80KVA inverter, i designed the bridge,filter and all the control and pwm.Now how can i say this has this much rating,voltage is constant but current varies with load, or else does it depends on the transformer which we connect after inverter in order to supply a load. And what happens if load it exceeds the rating.Please i want some detailed explanation.

Thanks in advance.

Dear Sai Kiran, for giving a particular VA rating you can use saturation block( current limitter) after voltage controller. you should limit current according to VA rating.

i think if load exceeds the rating, the sys will become unstable because load wont be supplied and there isn't any balance between generation and demand.

Thank you very much for answering Parisa,

yes,i understood now,by giving this current limit value it will become the voltage and max.current,so the VA rating,it is the case when the control in three phase system.From my project, I have an idea that Id which controls the real power and Iq(usually negative) which controls the reactive power,so when i measure the rated current from KVA how should i use the limiter,i mean both Id and Iq,shall i control individually or any way to control it.

What if i convert the Id and Iq to abc frame and use the limiter and again to dq frame.Is this the correct way.Please do answer.

Thanks in advance.

current command (Idq) is limited by Imax, Imax represents the maximum allowable magnitude of the inverter currents. so when you measured the max current, put it in saturation block. please check the attached paper

Yes it worked, Thank you very much parisa.

I used the logic from the above paper, i am able to control the current.There are still oscillations in the power supplied by the DER even thought fault is removed.I need to stabilise it somehow.It will be helpful to me if you can send any material regarding this synchronization of microgrid with utility grid.In my paper network synchronization is given,but it is getting distorted.Anyways,thanking you for your help.

regards,

Hi, I think you have the idea regarding this microgrid and control from your previous replies.Actually my project is to make an enhanced control instead of basic control which imporves the performance of microgrid during fault.From your previous suggestions,it was very helpful.In my simulation,i made an inverter using droop,voltage and current controller using feed forward technique.When i made a dg and when i connect it to grid using a transformer it is ok,i mean the power supplied by dg is equal to Pref. set.But when i create a transient fault for few seconds,power supplied by dg disturbed and eventhough the fault is removed there are so much oscillations such that the power from dg becomes negative.Actually from the paper it has to settle at some lower level.It is Fig. no 10 in the paper.LG fault perioud is 0.5 to 0.5913.Yellow line is the power.I tried changing the current limiter,but it didnt worked.During grid connected mode,when the fault is removed,power supplied by inverter or dg has to be settled at some lower point.but it is showing very heavy three oscillations and it is getting settled after nearly 2 seconds.Because of this type of response my work halted.If you have idea please help in some way.I am attaching my reference paper.

Please do reply.

Thanks in advance.

Dear researcher,

i worked on voltage and frequency control of microgrid in islanded mode, and i do not have enough information about synchronization in the simulation. but when the microgrid disconnected from the grid, in islanded mode it should supply the loads. my idea is,  at first check your sys in islanded mode if it works, frequency and voltage control are ok and probably your mistake is on synchronization sys. to realize the grid-connected Operation between microgrid and distribution network, it is required both have the same frequency and voltage magnitude and phase. check synchronization control. measure the frequency and voltage, they should be near the nominal values to reconnection.

Thank you for your answer.

I will check with synchronization again.During islanded mode,the frequency and voltage are working good,based on the set values the voltage and frequency are varying with load.It is good.Do you have an idea about the faults  and the power response during this islanded mode.I mean what happens when fault is created while working in parallel.This really showing me worst response during fault.

If your work involves this,suggest me some ways

when fault is created and the microgrid gets islanded. when the active power provided by the VSCs is larger than the load, the Vscs will increase the active power output to make the sys stable. when Pout by Vscs is smaller than the load, the Vscs will reduce the Pout. enhanced control employs feed-forward techniques, it makes better sys stable. two references are attached.

hope these help you

Thank you very much Parisa,

Thanks for helping and these papers are helpful.I will get to you again after using the data.

thank you once again.

Hello Parisa ...

I am working on the droop controller in microgrid.Can you please provide explaination how to make simulink model for droop controller.

it will be greatful if u will provide your simulink model.

Hello Gulezar, for Simulink model of droop controller (conventional droop control) at first u need to calculate active and reactive powers (look at the given references in my page), droop control has 3 parts, 1. power controller that active and reactive powers are calculated by output current and voltage of inverter, then are  passed through low-pass, filters, then by droop characteristics lines, references  frequency and voltage are gotten

now u should produce sin wave by references voltage and frequency. second and third parts are voltage and current controller that are designed to reject high frequency disturbances. i hope, these help u

Thank you so much parisa,

Thanks for your explaination.with this expaination i will try to simulate.

Dear Parisa Karamoddin , Sanjoy Roy

can you please explain me how Wn=1 p.u instead of 50/60 Hertz. also Pn is written in p.u

can you please explain how to calculate in p.u system?what should be the base value,actual value.

thank you

Hi Mitul (Mitul Shah),

I suggest you read the basic text on power systems by Grainger and Stevenson, which is commonplace and easily available.

With best wishes.

-Sanjay

The V/f droop control is as follows, there are two relationships, the first between voltage and reactive power, while the second between the frequency and active power. The first relationship is independent on the second. Vn is the nominal or reference value of voltage which is usually 230 V or 220 V while fn is the reference value of frequency which is usually 50 Hz or 60 Hz.