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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
What would happen if one had an inverter connected to the mains that was out of phase by a few degrees? Would it just transfer power inefficiently? If it is way out of phase would it then short out?
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Any phase difference will result in current flowing back into the inverter. As you thought, if they were 180 out of phase, you would effectively be trying to short out the line through the inverter, which would likely blow it up. You can probably stand be be a few degrees off, and suffer some reactive current flowing through the inverter. You would have to have some feedback mechanism to ensure the phase lock, though. What the power company says is 60hz, is really just an average 60hz per day, but the actual frequency can wander around a bit. So if your inverter doesnt have this phase locking ability, then it would be just about impossible to get it to work otherwise.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Any good books that describe basic design and theory for building inverters? Something that describes tracking the main's phase for injection into the grid?
BTW, when specs describe THD for "true-sinewave" inverters how is the distortion calculated?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Can't think of any apart from my thesis which I'll pimp again: This chapter describes how I designed and built my own grid-intertied inverter, and explains in some detail how I got it to phase lock to the grid.
The distortion is calculated as: (the RMS sum of all harmonics of the line current except the fundamental) divided by (the RMS sum of all harmonics of the line current including the fundamental).
When building my inverter I used a Tektronix digital scope with the Wavestar software which has a function built in to calculate THD. I think I got down to about 5% IIRC.
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Inverters connected to the grid
