I have been following this Victron Community platform for over 2 years now, read most of the documentation, studied the presentations on Victron Professional, etc. Learned a lot, but there are still some aspects to frequency shifting that aren´t totally clear to me.
Let´s assume following configuration :
- off-grid MP II 5000/48
- AC-coupled PV inverter 5000 VA (compliant to factor 1.0 rule)
- LiFePO4 battery, dimensioned as per minimum Victron specs (or bigger)
there may be MPPT(s) also, but that seems less relevant for the following.
If the battery is nearly full the MP II will frequency shift to signal to the PV inverter to lower its output.
It seems unlikely that this is based on SOC, as is often mentioned on this community platform, but rather based on voltage. SOC is a calculated value and less accurate. Also,I remember having read somewhere in the Victron docs (ESS manual - grid failure ?) that the battery charging rate is decreased from 100% @ 54V to 10% at 57.6V
However this can not be the only criterium.
Let´s suppose (theoretical) :
- battery isn´t nearly full at all, say SOC 60% (voltage roughly 52.3V)
- sunny day, PV inverter is producing at full blast (5000 VA)
- only small loads active (500 VA or less)
The MP II 5000, according to spec, has a maximum charging rate of 70 A, or in rounded figures roughly 3500 VA. So the MP II can only process 3500 VA, but has 5000 - 500 = 4500 VA coming in at AC-OUT.
So where does the remaining 1000 VA go to ? (after all, it will take quite a while to raise the SOC from 60% to 100%, so what happens in the mean time ?)
It therefore seems to me that frequency shifting must also be triggered on incoming load (not to be confused with consumers) at AC-OUT, even if the battery isn´t (nearly) full ?
Furthermore, I assume that since the MP II´s output capacity de-rates with temperature, it´s charging capacity also de-rates with temperature ?
This would mean that there are at least 3 criteria :
- battery voltage
- incoming load at AC-OUT
- temperature
for triggering frequency shifting.
Is there any info available on the frequency shift triggering algorithm ? Are there any other criteria I overlooked ?