SMA SI 3324 - Manual (Page 43)

SMA Technologie AG Automatic Frequency Adjustment
User Manual SI3324/4248-14:FE2406 Page 43
8 Automatic Frequency Adjustment
Clocks that depend on the stability of the grid frequency for their accuracy, become
increasingly inaccurate when subjected to constant frequency deviations. Frequency
fluctuations, i.e. deviations from the nominal frequency (50 Hz) often occur in (e.g.)
stand-alone grids that work with a generator.
The "Automatic FRequency Adjustment (AFRA)" function of the Sunny Island 3324/
4248 allows the use of grid-coupled clocks in these types of stand-alone systems.
By counting all positive zero-crossing points (full waves) at the inverter output of the
Sunny Island 3324/4248, in both battery charging operation and inverter
operation, the inverter constantly measures the actual frequency. These values are
compared with the desired frequency values every twelve hours. If a time difference
of five seconds or more exists then a frequency increase or -decrease is activated.
This frequency adjustment remains active if the time difference is more than one
second.