Electronics > Power/Renewable Energy/EV's

how do grid-tie inverters inject power back into the grid?

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I can see how generators do this, but if an inveter exactly exactly matches phase, frequency and voltage then no power will be transferred... Do they have to run a tiny bit ahead of the grid in phase, or at a higher voltage (whatever that means in AC)? Either of which makes power flow into it...

A grid tie is a current source, so it injects current in phase with the grid in a sine waveshape of the same frequency and phase. The amplitude of the current waveform determines the power.
Internally the voltage source from where the current is derived is higher than the grid in order to overcome internal losses.


--- Quote from: hamster_nz on November 11, 2017, 06:50:13 am ---Do they have to run a tiny bit ahead of the grid in phase, or at a higher voltage

--- End quote ---

Put simply, yes.

If it was 100% matched in voltage and phase no current would flow.

This is why it's so critical the electronics/code in grid-tie inverters works correctly.
One little error and it's a no holds barred fight to the death between the inverter and the national grid. (National grid wins)

Fuse or circuit breaker though is the referee, though in most cases the clear winner will be the network, with the inverter being the smoking ruin left afterwards.

Whatever the ac voltage waveform is at any particular instant the inverter needs to pull up against that. It doesn’t have to succeed in pulling it higher, only try. As mentioned, if it is pushing a current into the mains that is proportional to the instantaneous voltage then all is good.


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