From Liability to Asset: A Three-Mode Grid-Forming Control Framework for Centralized Data Center UPS Systems

TL;DR

This paper introduces a three-mode centralized grid-forming control framework for data center UPS systems, enhancing fault response, grid stability, and load management with simulation-backed results.

Contribution

It proposes a novel three-mode control architecture for MV UPS systems, improving fault handling, grid support, and load regulation in data centers.

Findings

Zero unserved IT energy during faults

Reduced inverter peak current to 0.57 p.u.

Improved PCC voltage minimum to 0.79 p.u.

Abstract

AI workloads are turning large data centers into highly dynamic power-electronic loads; fault-time behavior and workload pulsing can stress weak-grid points of interconnection. This paper proposes a centralized medium-voltage (MV) uninterruptible power supply (UPS) control architecture implemented as three operating modes: Mode 1 regulates a DC stiff bus and shapes normal-operation grid draw, Mode 2 enforces current-limited fault-mode P--Q priority with UPS battery energy storage system (UPS-BESS) buffering and a rate-limited post-fault "soft return," and Mode 3 optionally provides droop-based fast frequency response via grid-draw modulation. Fundamental-frequency averaged dq simulations (50 MW block, short-circuit ratio (SCR) = 1.5, 0.5 p.u. three-phase dip for 150~ms) show zero unserved information-technology (IT) energy (0.00000 MWh vs.0.00208 MWh for a momentary-cessation benchmark), a 0.57 p.u. peak inverter current (vs. 1.02 p.u. for a synchronous-reference-frame phase-locked loop (SRF-PLL) low-voltage ride-through (LVRT) baseline), a nonzero mean fault-window grid draw of 0.20~p.u. (vs.approx 0 for momentary cessation), and an improved settled point-of-common-coupling (PCC) voltage minimum of 0.79 p.u. after one cycle (vs. 0.66 p.u.). A forced-oscillation case study applies a 1 Hz pulsed load (+/- 0.25 p.u.) and shows that the normal-operation shaping filters the oscillation seen by the grid while the UPS-BESS buffers the pulsing component.