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 > > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
