Well yes of course but it has little to do with MPPT. The GTI is basically a programmable DC to AC convertor that have internal control loops based on sensed current and voltage (on both ends). In a standard GTI mode, it cannot regulate output voltage, as it would end up fighting the grid, so it has to float above the grid voltage. The AC power that the GTI pushed out is (with the operating efficiency) the same as the power coming in on the DC lines from the PV. For constant PV power, if line voltage goes up , then current must go down. This is closed loop control but only internal to the GTI; it does not control total power or output voltage. So it can only affect the AC amps for a given PV power in.
And as you note, some new software could be used to control based on new objectives. In the simplest view it is possible to sense the AC line voltage and control the PV power holding the AC voltage within spec and assuming constant loads the current will find it's own level. This is basically what a UPS with double conversion would do. None of this is impossible, just impractical, because the primary design features of the GTI inverter is that it changes from GTI mode to OFF mode off when the line voltage does away. I have little doubt that to get whatever approvals are required, that the GTI manufacturers had to demonstrate this type of fail safe to meet ENC! So there is only GTI and OFF, nothing else. It is purposely designed to have not only nothing else, but failsafe to NOTHING else. So to come in the fact and say, OK we are now going to design a fail safe GTI that has a software controlled UPS mode? You are now going to get into safety interlocks for mutually exclusive operation and the GTI can not accomplish that backfeeding a breaker at the bottom of a panel.
So while the GTI could perform the function with added UPS functionality, there is no way to implement it easily and keep the GTI failsafe "OFF mode". So for the most part until something radically changes in the nature of what a GTI is, any islanding of GTI will probably be by controls outside of GTI itself. Those two modes of control would both achieve line voltage regulation of the island. Load control (e.g. water heater load dump) of source control (e.g. shorting panels) or a combination of both are much more feasible without trying to change the GTI with it's fail safe. Load control would likely not have much impact on the GTI, while I could envision interoperability issues depending upon how much or fast you want to chop the PV power. I guess you could also do load control at the GTI input, but that that might be more difficult than panel control.
You would basically add the output voltage controller to this diagram along with a whole house transfer switch.
And as you note, some new software could be used to control based on new objectives. In the simplest view it is possible to sense the AC line voltage and control the PV power holding the AC voltage within spec and assuming constant loads the current will find it's own level. This is basically what a UPS with double conversion would do. None of this is impossible, just impractical, because the primary design features of the GTI inverter is that it changes from GTI mode to OFF mode off when the line voltage does away. I have little doubt that to get whatever approvals are required, that the GTI manufacturers had to demonstrate this type of fail safe to meet ENC! So there is only GTI and OFF, nothing else. It is purposely designed to have not only nothing else, but failsafe to NOTHING else. So to come in the fact and say, OK we are now going to design a fail safe GTI that has a software controlled UPS mode? You are now going to get into safety interlocks for mutually exclusive operation and the GTI can not accomplish that backfeeding a breaker at the bottom of a panel.
So while the GTI could perform the function with added UPS functionality, there is no way to implement it easily and keep the GTI failsafe "OFF mode". So for the most part until something radically changes in the nature of what a GTI is, any islanding of GTI will probably be by controls outside of GTI itself. Those two modes of control would both achieve line voltage regulation of the island. Load control (e.g. water heater load dump) of source control (e.g. shorting panels) or a combination of both are much more feasible without trying to change the GTI with it's fail safe. Load control would likely not have much impact on the GTI, while I could envision interoperability issues depending upon how much or fast you want to chop the PV power. I guess you could also do load control at the GTI input, but that that might be more difficult than panel control.
You would basically add the output voltage controller to this diagram along with a whole house transfer switch.
Comment