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From: Daku on 19 Jun 2010 12:25
I have a photovoltaic inverter related
question. Recently I have been looking
into the possibility of building a grid-tie photovoltaic inverter. A
number of semiconductor vendors e.g., Freescale,
TI etc., sell controller kitss that have
built-in pulse width modulation units etc.,
to process the DC input from the solar
panel, using Maximum Power Point
Tracking and all.
What seems to be missing, is how to synchronize with the phase of the
grid.
One would imagine that the power grid
would tapped and the isolated input
fed into a phase locked loop to synchronize
with the grid supply phase. One cannot
inject power into the grid without phase
match.
Am I missing some subtle point ? Any
hints, suggestions would be of immense
help.
From: Markus Hamilton on 19 Jun 2010 14:22
On 6/19/2010 12:25, Daku wrote:
> I have a photovoltaic inverter related
> question. Recently I have been looking
> into the possibility of building a grid-tie photovoltaic inverter. A
> number of semiconductor vendors e.g., Freescale,
> TI etc., sell controller kitss that have
> built-in pulse width modulation units etc.,
> to process the DC input from the solar
> panel, using Maximum Power Point
> Tracking and all.
> What seems to be missing, is how to synchronize with the phase of the
> grid.
> One would imagine that the power grid
> would tapped and the isolated input
> fed into a phase locked loop to synchronize
> with the grid supply phase. One cannot
> inject power into the grid without phase
> match.
> Am I missing some subtle point ? Any
> hints, suggestions would be of immense
> help.

What you need to use are inverters which sync to the grid. You might
want to take a look here: http://www.enphaseenergy.com/
These inverters sync the generated AC to the grid AC, so that you can
feed back to the grid. However, when the grid fails, these inverters
usually shut down for 2 simple reasons:
(1) there is no reference anymore to sync the phase
(2) the inverters would immediately be overloaded

You might also want to check this site: http://www.builditsolar.com/

Markus
From: John Larkin on 19 Jun 2010 14:41
On Sat, 19 Jun 2010 09:25:38 -0700 (PDT), Daku <dakupoto(a)gmail.com>
wrote:

>I have a photovoltaic inverter related
>question. Recently I have been looking
>into the possibility of building a grid-tie photovoltaic inverter. A
>number of semiconductor vendors e.g., Freescale,
>TI etc., sell controller kitss that have
>built-in pulse width modulation units etc.,
>to process the DC input from the solar
>panel, using Maximum Power Point
>Tracking and all.
>What seems to be missing, is how to synchronize with the phase of the
>grid.
>One would imagine that the power grid
>would tapped and the isolated input
>fed into a phase locked loop to synchronize
>with the grid supply phase. One cannot
>inject power into the grid without phase
>match.
>Am I missing some subtle point ? Any
>hints, suggestions would be of immense
>help.

Yes, you'd have to sense the line voltage to sync to it, and probably
the inverter-line current.

You could do what the PFC power supply chips do, namely sense the AC
line voltage waveform in real time and make a boost converter's output
current track that. A slow control loop wraps around all that to get
the average, in this case optimum, power transfer. Maybe you could use
one of the PFC controller chips; they're cheap.

The problem is basically to present a negative resistance to the AC
power line.

Get anything wrong and it goes boom. Expect a shoe box full of
exploded fets if you do this from scratch. Wear eye protection.

ftp://jjlarkin.lmi.net/ExFets.jpg

John


From: Cydrome Leader on 20 Jun 2010 02:26
John Larkin <jjlarkin(a)highnotlandthistechnologypart.com> wrote:
> On Sat, 19 Jun 2010 09:25:38 -0700 (PDT), Daku <dakupoto(a)gmail.com>
> wrote:
>
>>I have a photovoltaic inverter related
>>question. Recently I have been looking
>>into the possibility of building a grid-tie photovoltaic inverter. A
>>number of semiconductor vendors e.g., Freescale,
>>TI etc., sell controller kitss that have
>>built-in pulse width modulation units etc.,
>>to process the DC input from the solar
>>panel, using Maximum Power Point
>>Tracking and all.
>>What seems to be missing, is how to synchronize with the phase of the
>>grid.
>>One would imagine that the power grid
>>would tapped and the isolated input
>>fed into a phase locked loop to synchronize
>>with the grid supply phase. One cannot
>>inject power into the grid without phase
>>match.
>>Am I missing some subtle point ? Any
>>hints, suggestions would be of immense
>>help.
>
> Yes, you'd have to sense the line voltage to sync to it, and probably
> the inverter-line current.
>
> You could do what the PFC power supply chips do, namely sense the AC
> line voltage waveform in real time and make a boost converter's output
> current track that. A slow control loop wraps around all that to get
> the average, in this case optimum, power transfer. Maybe you could use
> one of the PFC controller chips; they're cheap.
>
> The problem is basically to present a negative resistance to the AC
> power line.
>
> Get anything wrong and it goes boom. Expect a shoe box full of
> exploded fets if you do this from scratch. Wear eye protection.
>
> ftp://jjlarkin.lmi.net/ExFets.jpg

What was the case style of the very bottom left "exfet"?

I had a hard time recently locating a specific power transistor in a
TO-218 case, with the metal tab and not the lump of plastic with a metal
back like everything seems to be now.

I suspect people using TO-3s felt the same way when the TO-218s came out.

From: Phil Allison on 20 Jun 2010 02:41

"Cydrome Leader"

>
> I had a hard time recently locating a specific power transistor in a
> TO-218 case, with the metal tab and not the lump of plastic with a metal
> back like everything seems to be now.


** Why bother ??

TO-218 is virtually the same pak and construction as TO-3P except you no
longer need to use an insulating bush with the latter.

TO-3 is a whole nuther animal with many advantages over plastic paks.


..... Phil



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