Safe Reconnection Time for Large-Scale Data Center Loads: An Analytical Framework for Transient Stability Assessment

TL;DR

This paper presents an analytical framework to determine safe reconnection times for large data center loads post-disturbance, preventing oscillations and ensuring stable power system operation.

Contribution

It introduces a physics-informed criterion for bounding reconnection windows, enhancing stability analysis for large-scale data center power loads.

Findings

Critical safe reconnection time guarantees stability and convergence.

The framework effectively prevents flapping during reconnection.

Simulations validate the analytical approach's accuracy.

Abstract

The rapid growth of large, power-electronics-rich data center (DC) loads is creating new operational challenges for bulk power systems. A key risk arises when a DC uninterruptible power supply (UPS) disconnects the facility during voltage/frequency disturbances and then reconnects it while the bulk grid is still dynamically settling to a new equilibrium point. Poorly timed reconnection can amplify electromechanical oscillations, deepen frequency deviations, and lead to repeated connect-disconnect \emph{flapping}. In this paper, we develop an analytical framework to characterize the \emph{safe reconnection time} for large DC loads after a disturbance-induced disconnection that avoids flapping. Using a model in the spirit of the classical single-machine infinite-bus system, we capture (i) swing dynamics during the disconnection interval and (ii) voltage-angle coupling at the load bus, which determines the electrical power step at reconnection under constant-power load assumptions. Using energy function method, we characterize the critical safe reconnection time such that for any reconnection time after the critical safe reconnection time, the post-reconnection trajectory is guaranteed to remain within operational limits (frequency/angle/voltage) and converge to the post-reconnection equilibrium, thereby preventing flapping. Time-domain simulations validate the effectiveness of the proposed analytical approach. The results provide a simple, physics-informed criterion that can be used to bound reconnection windows for large DC facilities and inform UPS reconnection logic.