Grid tie Inverter as Current Source

Thread Starter

Chacabucogod

Joined Nov 16, 2013
26
I was reading about grid tie inverters and how they work, but something I didn't understand is how they feed the greed with current. So I began reading several forums about it , and while some say that the output voltage of your inverter has to be a bit higher than the greed voltage, others say that the inverter acts as a current source. I didn't quite understand how that would work, but now that I think about it, it seems right. While using mosfets as switches you're turning them from cut-off to saturation, and as far as I understand, mosfets in saturation mode act as current sources. Am i right thinking that this is how it works? Or is there another mechanism out there that makes sure a grid tie inverter feeds current to the source?

Thank you.
 

crutschow

Joined Mar 14, 2008
34,827
MOSFETs in a inverter aren't used in the saturation region, the are used the full-on ohmic (linear) region, thus they act as a voltage source. (The confusion comes from the saturation region being defined as the full-on conditions for a BJT but it's not for a MOSFET.)

But current based negative feedback in the inverter can make the output appear as a current-source.
 

Thread Starter

Chacabucogod

Joined Nov 16, 2013
26
Ohh Alright. Can you explain me more about the current based negative feedback? You are telling me that I will have a shunt resistor at the output and according to the current I need I will modulate the voltage?

Thankyou by the way!
 

uwed

Joined Mar 16, 2015
64
There is a outer control loop which makes the inverter voltage closely follow the AC voltage of the grid. Then there is an inner (faster) current control loop which allows independent control of the current waveform. By controlling the AC input current of the inverter to be in phase or 180 deg phases-shifted to the inverter voltage, both energy flow directions are possible any time (application-dependent).
 

alfacliff

Joined Dec 13, 2013
2,458
another thing about grid tie inverters, how much do you think your inverter will affect the grid? how much current is available from thegrid? how much from your inverter? same with grid tie wind power, how much will your wind turbine affect the nuke down the road? you can put power into the grid, but unless you have something much larger than anything on the market today, you will have to measure your output with the electric meter.
 

nsaspook

Joined Aug 27, 2009
13,543
In a perfect world the grid-tie inverter (current source) voltage output would be exactly the same as the grid voltage at any instant as the grid is usually modeled as a infinitely stiff voltage source with perfect conductors but that's usually not the case so they cheat (just slightly higher than the utility voltage with a line isolation inductor for the voltage) a little to prevent power feedback.
 
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