SMA SI 4548-US - Manual (Page 146)

16 Multicluster Operation SMA America, LLC
146 SI4548-6048-US-BE-en-20 Operating Manual
Significance of the SOC thresholds:
When the state of charge of a battery reaches the lower SOC threshold, the load contactor is opened.
The state of charge of the battery of the main cluster and the states of charge of the batteries of the
extension clusters are evaluated. The load contactor disconnects the loads from the stand-alone grid.
When the state of charge of all batteries reaches the upper SOC threshold during recharging, the
load contactor closes. The load-shedding contactor connects the loads to the stand-alone grid.
The load shedding of the Multicluster Box only reacts to the SOC value of the main cluster.
1. Select the parameter "242.01 Lod1SocTm1Str" and set it to the lower SOC threshold.
2. Select the parameter "242.02 Lod1SocTm1Stp" and set it to the upper SOC threshold. The
upper SOC threshold must be at least 10 percentage points above the lower SOC threshold.
3. Set the parameter "242.05 Lod1Tm1Str" and the parameter "242.06 Lod1Tm2Str" each to the
same value, e.g. to 000000. This will switch the time-dependent load shedding off.
16.4 Generator Operation
The generator request of the main master comprises its own request (based on SOC, time, etc.) and
possible requests from one or more extension clusters. The generator remains in a requested state as
long as a request is present.
16.5 Behavior with Different States of Charge
In Multicluster systems, each cluster has its own battery-storage system. To prevent the states of charge
of the various battery storage systems from diverging over time, a function for equalization of the
states of charge is integrated into the Sunny Island inverters. This distributes the power to all clusters,
however, it is not always distributed identically. Instead, the cluster with the highest state of charge
discharges the most power or charges the battery with the lowest power.
The differences in power depend on the difference in the state of charge and total 1% of the nominal
power for each 1% of difference in the state of charge. Thus, when initial charge states differ,
equalization of the states of charge over the course of time is ensured. If all batteries in the various
clusters have the same capacity, the charge states should always be within a few percent of each
other. Only if a fault occurs, or upon deliberate deactivation of individual clusters, can a greater
imbalance arise, but even so, such an imbalance should also be equalized after one day at the latest.
Generator request
The determined generator request at the extension clusters is transferred to the main master via
a communication connection.
Nominal capacity of the battery storage systems
Ideally, the various battery banks should all have the same nominal capacity.
If the nominal capacity varies by up to 30%, a similar average state of charge is ensured via
the equalization function. However, the smallest battery is then cycled more intensively. The
nominal power and overload capacity are no longer the value of an individual device multiplied
by the number of devices. Instead, it is 10% to 20% lower for the cluster with the smaller battery.