OK Brian,
So I think you are confirming that monitoring AC side voltage is an
acceptable way of deciding when to disconnect the GT inverters.
With my parts list, I have a delay time that would hold the GT inverters
off-line for some period of time (I would probably set to 1 hour) before
coming back on line after tipping off.
Mark
On 11/3/2019 9:53 AM, Brian Mehalic wrote:
With frequency-on/off, frequency power control, or other “inverter integrated”
control based on battery voltage/state of charge there is also control in
regards to when the ac coupled inverters come back on. And yes, this is
definitely needed to prevent overcharge (or get three-stage charging from the
AC coupled system). Of course if it doesn’t work, yes the bus voltage will rise
and trip the BB offline.
AC bus voltage will go down as soon as the ac couple inverters are kicked off,
so if that’s your measured value unless your control system has a delay or
other component to control reconnection and charging i think it could
essentially chatter off and on and off and...
Brian
On Nov 3, 2019, at 9:38 AM, Mark Frye <ma...@berkeleysolar.com> wrote:
Hi William,
Thanks, you bring up issues that are important to me here.
In particular, my situation is that the GT inverter is inter-tied a couple sub
panels upstream of where I want to put the BB inverter. The distance is long,
so I am looking for a solution where I don't have to run a cable between the
two.
In general, I do wonder about using AC line voltage rise to take the Gt
inverters off line. The main goal is to prevent excess voltage at the battery,
so monitoring battery voltage is most direct, and there are simple solutions
for that.
Is AC line voltage a suitable metric for achieving the same goal?
Here is where I could use Wrench knowledge to confirm my thinking, that being:
- With excess energy in the system, the charger moves it into the battery,
raising it's voltage until it reaches it high charging voltage set point
- Once the battery reaches it's high voltage set point, the charger stops
putting energy into the battery
- With no other place to put the excess energy, the AC voltage rises
Am I getting this right, the reason to disconnect AC coupled inverters when the
battery if full is not to prevent the batteries from being overcharged, but
rather to prevent the AC line from becoming unstable?
I am hoping this is correct and that with $200 of industrial grade devices from
Digikey I can implement a robust control that will disconnect the GT inverters
before the AC line goes so high that the BB inverter faults.
Mark
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