This reports the AC input frequency measured at the group level, in units of 0.1Hz, the same measurement concept as tsiModuleACinFreq but aggregated to represent this whole AC group's shared feed rather than one module. It is a quick top-level check of whether this group's shared AC source, as opposed to a per-module reading, is holding to its expected frequency, useful when the group shares a common generator or UPS source distinct from other groups on the same site. An admin operating multiple AC groups fed by different backup generators during an extended outage would monitor each group's frequency independently via this object to catch a specific generator's governor drifting before it affects that group's modules.