Advantge Of DFIG

It does seem a bit careless to force readers to go to www.acronymfinder.com before a posting is fully understood. It is far better to define an abbreviation before using it.

www.acronymfinder.com gives DFIG as "doubly fed induction generator".

Reading this will maybe help.

or this!

One possibility is that without using them, a DFIG cannot be matched to the local grid and cannot therefore export its harvested power. Quite an advantage!

So technically its a necessity while being a commercial advantage!

Quite.

Instead of asking such questions, kindly explain your understanding off DFIG. How does DFIG work- and the I will tell you why DFIG is not such a beautiful solution as you think it to be. I too work with students - who throw jargons, without understanding. So give me your understanding of the problem and solution first. Then I will tell you loopholes in your arguments.

I've sometimes longed for loopholes in my arguments

( below the belt...my bad )

ok sir
i m doing a small project research type that why we spendind money on converters used in the doubly fed induction generator. we have other variable speed wind turbine generators there also. i was confused in the paragraph i read somewhere that it controls the speed of the rotor and frequency of the output voltage. suppose a fault occured on the transmission line and we have to stop the converters from demaging from overcurrent during fault occurance, we will use some protection there meanwhile some reactive power compensation will also be requiring.. so despite of all these why shouldn't we use any other variable speed wind turbine generator which donot have this extra circuitary?

Did no-one read post #3?

On the contrary.

... read somewhere it controls the speed of the rotors . . .

Maybe re-read this. Maybe post a link of the source.

How I read it in the links I posted it adjusts the 3 phase power generation to the grid frequency by using a slip ring assembly to account for different rotor speeds.

You probably can use other methods. But there is a working solution.

Good luck with your project. Sounds interesting as it will get you deep into wind power generation and technology!

I did come to know about DFIG from another PhD student just a month back.As I am an electronic engineer, I was not convinced of plenty of matrix, mathematical equations shown to me regarding DFIG. Obviously even that student is struggling to understand. I only said as the wind speed changes, turbine speed changes. V= (dΦ/dt)*N changes. So by avoiding power electronic blocks (details can be discussed after the concept is understood) & accepted), how DFIG can be interfaced to the grid puzzles me.

Take for example a 400KV line carrying 500 amps current carrying 400*0.5= 200 Megawatts of power. Why should anyone think of feeding another 100 KW of solar or wind power (taking into account that these inverters cannot generate less than 2 % voltage THD). WHY? Then we have another group of Ph D's working on how to improve THD on line caused by wind or solar renewable being connected to the grid. Then we have another set of PhD working on impact of renewable on relay co-ordination and faulty tripping etc etc.

In Computers- every computer has an ID and cyber police keep a watch on what is uploaded on the net- but not so on utility grid!!!!!! Anyone can upload junk and get away!!!

All the best for you.

As others pointed out, the converter is used to keep the frequency, voltage, and phase produced by the generator to the "optimal" value.

The converter acts as the excitation system for the machine. The frequency produced by the machine is the algebraic sum of the converter signal and rotor frequency. Of course, the number of electrical poles is important.

Acting as a governor, one can force the "slip" frequency in the induction machine and control the torque on the rotor, hence its speed in the wind.

We usually use a MPPT (Max power point tracking) algorithm to drive the whole thing. Then we use various vector controller to calculate the proper waveform to inject in the rotor using the converter.

This way, you can produce the optimum power at a wide range of power factor if you need to.

The converter used on the wound rotor is typically 1/3 the size of the AC/DC/AC converter that would do a similar job directly on the line when using a synchronous machine or an standard induction machine.

The converter is usually self powered by the machine's rotor but can also be used to inject more power in the network if connected to a supplementary DC source such as a solar panel. This is a good advantage. Two birds with one stone. (in theory...)

Have fun with your project!

"This is a good advantage. Two birds with one stone. (in theory...)"

I too felt these PhDs were aiming for something like this by pure simulation techniques using some Real Time Simulators.
I felt the rotor speed is governed by the wind speed turbine (whether you use or don't use gears does not matter). Excitation power is derived from the grid- this can only give grid synchronous frequency. May be even if power amplifiers are used to change the amplitude of excitation, the output of the machine will be a combination of wind speed (rotor speed frequency) and excitation frequency. It will be a modulated waveform. But will it ever be pure sine with both voltage amplitude and frequency within close limits with teh grid supply? I ahve serious doubts.

It is better to use power electronic blocks and isolate the machine as rotor speed varies widely.