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Small grid-tie inverters? - Page 13

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Posted by daestrom on June 23, 2008, 10:52 pm
 
Bruce Harvey wrote:

I can't tell if you're being sarcastic or not (no smiley??)

Hooking a 250 watt inverter to *the grid* in phase, out-of-phase or any
which phase will do nothing to the grid.  Most it would do is trip the
circuit breaker in the basement.

daestrom


Posted by BobG on June 23, 2008, 11:06 pm
 

==========================
==========================
===
written by Bob G

==========================
===============
  written by BH

==========================
==========================
=
I see you using the word 'unsynchronized' in your reply to my message.
I have taken the liberty of separating my words from yours. God forbid
someone would think I issued those comments. Of course, none of my
messages contain that word, so I think you are confused.

Posted by Bruce Harvey on June 23, 2008, 11:25 pm
 

=====================================================
written by Bob G

========================================
  written by BH

===================================================
I see you using the word 'unsynchronized' in your reply to my message.
I have taken the liberty of separating my words from yours. God forbid
someone would think I issued those comments. Of course, none of my
messages contain that word, so I think you are confused.


Possibly my bad. I maybe misunderstood. I was under the impression from what
I was reading here that the inverter would be connected to a GPO (regular
power outlet) without synchronizing it with the grid. If this is not the
case then I apologize. As mentioned in other posts in this thread the use of
a grid tied inverter is regulated by the law and the utility companies. The
reasons for this are many but mainly for the safety of utility workers and
for the reliability and quality of the grid output. Connecting anything to
the grid here in Australia is regulated by law and all equipment must be
approved for safety reasons. I gather it is a similar setup in the US and
most other countries as well.
The Darwin Award comment was meant to reinforce the danger of doing such a
thing as connecting unsynchronized power to the grid.


Posted by Duane C. Johnson on June 24, 2008, 2:54 am
 Hi Bruce and Bob;

The basic methodology is not to hard to do.
There are several strategies that may be used but I
think one of the best is like this.

1. Use a PLL oscillator with the frequency set to
    60.5 to 61 Hz.
2. Have the oscillator reset back to synchronization
    each time the line voltage passes through zero
    120 times per second.
3. When the "island" is disconnected from the grid
    the inverter will immediately try to go to a
    frequency higher than 60Hz.
4. A. Trip the breakers when the measured frequency
       is out of specification.
    B. Trip the breakers when the measured voltage
       is out of specification, either high or low.
    C. Trip the breakers when the measured current
       is out of specification.
I don't remember the timing specifications of
UL 1741, and others, but I recall that it must trip
after about 2 seconds when the inverter is out of
tolerance.

OK, now the cool totally improper method.
Kids don't do this without adult supervision.
You don't need to be synchronous with the grid in
any way to send power back to the grid.

I did some experiments to learn about grid tie
techniques. I used a high end Yokogawa AC power
meter and a high power current source. I also
had a conventional mechanical KWHr meter. ( disk
type.)

This was connected to the grid and supplied with
an AC power source. The source was a 100kW
Pacific Power electronic amplifier designed to
power our computer for compliance tests.

This amplifier is essentially a huge power
amplifier capable of out AC, DC, and any other
wave shape including square waves at up to about
280 volts.

I injected current into the grid through the
power meter. I could vary the frequency and
wave shape up to about 800Hz and directed the
power meter and KWHr to measure the power and
direction of flow.

I injected the current and showed that power
always flowed to the grid. No mater what the
phase, frequency, voltage or wave shape was.

Further, the mechanical power meter performed
correctly and successfully measured the power and
directly. At least up until higher frequencies
above 500Hz

Duane

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Posted by nicksanspam on July 3, 2008, 12:13 pm
 

Sounds great :-) What's the least-expensive way to do this?

Nick


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