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Multiple MPPTs with odd numbers of strings


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I am simulating string inverters (SMA STP) which have 2 MPPTS. It turns out that many times these have odd numbers of strings (5 or 7) so the MPPTs have different numbers of strings attached. I noticed that I was getting significant (>2%) "Inverter Loss over nominal inv. power" even though the Pnom ratio is 1.2 or less. There is no loss when the multiple MPPT box is not selected.

It appears that PVsyst is treating the inverter as two separate halves, for example a 15kW inverter with 5 strings is being treated as two 7.5kW inverters, one with 2 strings (Pnom <1) and one with 3 strings (Pnom>1.3). This is not how the inverter works. Each MPPT input can take enough current to comfortably handle 3 strings, and then all the current goes to a single inverter core which can comfortably handle 5 strings without clipping. Perhaps other inverters do work this way?

I am therefore not using the multi-MPPT feature to avoid getting hit with what I believe is an invalid additional loss.

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