(ch) Multicluster systems set up as off-grid systems can form self-sufficient utility grids fed with energy from multiple AC sources in the stand-alone grid (e.g. PV inverter), from a grid-forming PV array and/or with DC charge controllers (e.g. Sunny Island Charger). As a voltage source, the Sunny Island inverter forms the stand-alone grid. The Sunny Island inverter regulates the balance between the energy that is fed in and the energy that is used and features a battery, PV array and load management system.
Battery management
Battery management of the Sunny Island inverter is based on the precise determination of the state of charge. By combining the three most common methods for recording the state of charge, the Sunny Island can achieve a measuring accuracy of more than 95%. This way, battery overcharge and deep discharge are avoided.
Another feature of battery management is the extremely gentle charging control. It automatically selects the optimum charging strategy for the battery type and the situation in which it is used. This means that overcharging can be reliably prevented and the battery can be fully charged on a regular basis. The available charge energy is used optimally at all times (see technical information “Battery Management” at www.SMA-Solar.com).
Generator management
If necessary, the Sunny Island can synchronize with a PV array and connect directly. When the stand-alone grid is connected to the PV array, the voltage and frequency in the stand-alone grid are regulated by the PV array.
The Sunny Island inverter generator management system allows for uninterruptible connection of the stand-alone grid to the generator and uninterruptible isolation from the PV array. The generator management system controls the PV array via a start and stop signal. A PV array current control ensures that the PV array always operates within the parameters set on the Sunny Island. The generator management system allows the use of PV arrays that have a low output power in proportion to its nominal load (see technical document “Sunny Island – Generator Whitepaper” at www.SMA-Solar.com)
Load control
Load control enables control of the AC sources in stand-alone grids, control of a PV array and the targeted disconnection of loads.
The AC sources in the off-grid system are limited in their power output by the stand-alone grid frequency. In case of excess energy, the load control system increases the power frequency. This limits the output power of the PV inverters, for example.
If not enough energy is available for all loads or the battery is to be preserved, the load control system can request energy from a PV array via the generator management system. The generator management system starts the PV array, and the off-grid system is supplied with sufficient energy.
If no PV array is present in the off-grid system or the energy is not sufficient despite the presence of a PV array, the load control system turns the loads off through load shedding. One-level load shedding is integrated in the Multicluster Box.
The load-shedding contactor is controlled directly by the master of the main cluster via communication with the Multicluster Box. If you install an additional load-shedding contactor in a multicluster system, it is controlled with a multifunction relay in the master of extension cluster 1.