Summary
A study in Nature Energy finds a persistent one-minute frequency pattern in power grids across five continents and traces a source of it to clocked routines in battery-based uninterruptible power supplies. The researchers show that periodic UPS power demand can travel through distribution equipment to a high-voltage grid connection.
Researchers reporting in Nature Energy have identified a persistent one-minute pattern in grid-frequency measurements from power systems across five continents and traced a source of the pattern to clocked control routines in battery-based uninterruptible power supplies (UPSs). Measurements at a research-campus UPS showed recurring battery-current peaks that produced power variations traceable through transformers to a connection with the public 110-kV grid.
The finding points to a subtle way software timing can affect electricity systems: many devices running similar periodic routines can change their power demand at the same time. The authors say these synchronized variations contribute to the observed grid pattern; the study does not attribute every instance of the pattern to UPSs alone.
A regular rhythm in grid frequency
The researchers analysed frequency records from 12 power systems across five continents, ranging from island grids to large interconnected systems. Their Fourier analysis—a method for identifying recurring cycles in a signal—found a narrow peak at a period of exactly one minute. The pattern was visible in measurements taken at both transmission and distribution levels and remained phase-coherent over long periods.
Grid frequency reflects the balance between electricity generation and demand. If demand briefly exceeds generation, frequency falls; if generation exceeds demand, it rises. In the observed one-minute waveform, frequency typically starts higher and then declines during the first part of the minute, consistent with a recurring increase in demand relative to generation.
The size of the frequency response depends partly on system inertia: the stabilizing effect of the rotating mass of synchronous machines connected to the grid. With less effective inertia, a given power imbalance can produce a larger frequency change. For the Continental European grid, the researchers estimate that a 3-mHz pattern amplitude corresponds to a coherent power variation of about 80 MW.
Tracing the pattern to UPS control routines
To look for a source, the team examined high-resolution power measurements from buildings on the Forschungszentrum Jülich campus. Four buildings showed a pronounced one-minute component in their power measurements, and all four had battery-based UPS installations. The researchers then investigated one UPS in detail, measuring battery current and power flows at multiple points in the building’s electrical system.
They observed narrow current peaks at the battery terminals recurring every minute. The UPS manufacturer confirmed that these peaks came from periodic self-tests run by the battery energy-management system. After accounting for the building’s downstream demand, the team detected a corresponding component in power demand and traced it through two transformers and a bus bar to the connection with the public 110-kV grid.
Measurements also linked the timing of the routines to clock synchronization. With the UPS’s Network Time Protocol (NTP) synchronization enabled, the self-test signature shifted in its timing relative to Coordinated Universal Time; with NTP disabled, it drifted more slowly. The researchers interpret this as evidence that periodic routines are reinitialized by external clock synchronization. When many devices run routines on aligned schedules, their individual power changes can add up to a coherent disturbance.
The study finds that hydropower turbine-governor systems can amplify oscillations, but the analyses do not support hydropower dynamics alone as the explanation for the long-term, cross-grid coherence. The researchers also report that the one-minute pattern’s amplitude increased substantially in several grids. In Scandinavia, revised frequency-containment requirements introduced in 2023 were followed by the absence of amplitudes above 10 mHz in 2025.
Mitigating synchronized demand changes
Grid-level frequency-control requirements can reduce the frequency response to a disturbance. To reduce the disturbance at its source, the authors suggest changing device controls so that power adjustments do not occur simultaneously—for example, by randomizing schedules, using adaptive timing offsets or triggering actions in response to events rather than strictly timed cycles.
The study reports a practical example: after discussions with the researchers, a software update to the investigated UPS removed the strict periodicity of current peaks in one battery block. Self-tests still occurred at discrete times, so the change addressed the pattern only partially. The authors argue that as batteries, data-centre UPS systems and connected devices become more common, avoiding synchronized routines will be an increasingly relevant part of power-system control design.