Fronius Quick Guide: Working with the Fronius Symo (UL) and PVSyst (ond pan) Quick Guide [EN]

WORKING WITH THE FRONIUS SYMO AND PVSYST

This document is a guide to working with Fronius Symo .OND files, unbalanced MPPTs, and the unique
requirements of PVSyst when dealing with such files.

Balanced Strings

When using a configuration with all strings having the same number of modules, the easiest way to set the
system up is with one MPPT per inverter. This is done by clicking on the ‘Adjust’ button next to the inverter. This
feature is available on version 6.35 and later.

The ‘Nb of MPPT inputs’ is equal to the number of inverters in the sub-array.

Unbalanced Strings

When using a different string length on each of the Fronius Symo’s two MPPTs, separate sub-arrays must be
created. There will be two sub-arrays for each set of inverters, and ‘Nb of MPPT inputs’ should be the same for
both sub-arrays. PVsyst treats these as separate inverters, but will check to make sure there is the same
number of main and secondary inputs. Care should be taken to put less DC power on the secondary input as it
has a lower input current rating, as noted by the ‘Global Inverter’s power.’

Sub-array #1

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Sub-array #2

Undersized Inverter Power

PVsyst assigns a maximum AC power to each MPPT and treats is as a separate inverter for sizing and

simulation. This is a consequence of the program’s design history
and cannot, at the moment, be changed. With DC-AC ratios much
greater than 100%, it is possible to get an “Inverter is undersized”
error, and the program will not allow the simulation to be run. To

overcome this, it’s possible to adjust the ‘limit overload loss’ in the

‘Albedo –settings’ parameters for the project.

The default setting of 5.0% can be
increased to allow the configuration and
allow the simulation to be run. However,
the simulation will assume the AC power
limit on a per-MPPT basis. Caution is
needed as this unrealistic view of the
inverter operation can cause simulation
losses that would not occur in actuality.
The input current is limited on a per­MPPT basis, but AC power is only limited
on the whole inverter.

It is also possible to not exceed the overload loss limitation and still get an error based on inverter power.

‘Global Inverter’s power’ is determined based on the ratio of DC

current between the main MPPT and secondary MPPT. The physical
limitation on total DC power for the Fronius Symo is 150% and
PVsyst applies this limit to each individual MPPT AC power
allocation. The designer should ensure that 150% of the inverter

power is not exceeded with all input power amongst the two MPPTs.
If this error occurs, the only way to allow the simulation to run is to modify the OND file by clicking ‘Open’ next to
the inverter name.

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