Frequency regulation in an AC power supply system

A system for frequency regulation in a AC power supply system is disclosed, wherein the system comprises an uninterruptible power supply being electrically connected to the AC power supply system and comprising a phase-locked loop and/or a frequency-locked loop for monitoring the frequency of an AC input voltage received from the AC power supply system, wherein the phase-locked loop and/or the frequency-locked loop is/are designed to be operated with an operation frequency being higher than a nominal grid frequency and being selected to detect a deviation of the monitored frequency from the nominal grid frequency within a predefined time span after a frequency drop-off of the monitored frequency occurred, wherein a control signal () is generated based on the detected deviation of the monitored frequency from the nominal grid frequency, and wherein the generated control signal is used to regulate the power flow between the uninterruptible power supply.