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 ( 19 ) 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.
1 . A system for frequency regulation in an AC power supply system, the system comprising:
an uninterruptible power supply comprising an AC supply input for connection via a grid with the AC power supply system and an AC supply output for connecting with a load,
wherein the AC supply input is connected through a rectifier to a DC-link of the uninterruptible power supply and the DC-link is connected through an inverter to form an AC output voltage for the load to the AC supply output,
wherein the uninterruptible power supply further comprises a phase-locked loop 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 or the frequency-locked loop is 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 the system is configured to generate a control signal based on the detected deviation of the monitored frequency from the nominal grid frequency, and
wherein the system is configured to use the generated control signal to regulate a power flow between the uninterruptible power supply and the grid until the monitored frequency is within a predefined range around the nominal grid frequency.
2 . The system of claim 1 , wherein the phase-locked loop or the frequency-locked loop is designed to be operated with an operation frequency in the kHz range.
3 . The system of claim 2 , wherein the phase-locked loop or the frequency-locked loop is designed to be operated with an operation frequency of 2250 Hz.
4 . The system of claim 1 , wherein the system is configured to generate the control signal when the detected deviation of the monitored frequency from the nominal grid frequency is larger than a specified tolerance.
5 . The system of claim 4 , wherein the system is configured to generate the control signal to regulate an input power of the uninterruptible power supply at its defined maximum power when the detected deviation of the monitored frequency from the nominal grid frequency reaches a configured maximum deviation of the monitored frequency from the nominal grid frequency.
6 . The system of claim 1 , wherein the system is further configured to generate the control signal also based on a rate of change of the detected deviation of the monitored frequency.
7 . The system of claim 6 , wherein a frequency droop curve for regulating an input power drawn by the uninterruptible power supply is modified depending on the rate of change of the detected deviation.
8 . The system of claim 1 , wherein the AC power supply system is a low-inertia power supply system.
9 . The system of claim 8 , wherein the AC power supply system is an islanded/isolated power supply system fed by a generator system.
10 . The system of claim 9 , wherein generator system is a synchronous generator system.
11 . The system of claim 1 , wherein the uninterruptible power supply is a three-phase uninterruptible power supply configured to enable a fast frequency regulation to the AC power supply system and to support the AC power supply system in transient situations.
12 . The system of claim 1 , wherein the uninterruptible power supply is an uninterruptible power supply system that comprises multiple uninterruptible power supply units or modules.