Large loads like data center (and similar like but furnace in metal production, hydrogen electrolyser) are quickly being introduced into existing power systems. These cause challenges for power system stability: fluctuations of load profile and behavior during and after grid faults. The load profiles may excite torsional interactions and voltage flicker. The loss of active power during and after grid faults causes high risk for transient stability and frequency stability.

This contribution presents and discusses two distinct storage solutions for improving grid stability in these large load applications: online UPS and line-interactive BESS. One implementation of the online UPS is a modular BESS coupled on medium voltage with two back-to-back power converters - one to the MV grid connection and one to the MV supply side of the large load. This fully decouples the large load from the grid through the DC block interfaced to the DC-link between the two power converters. The line-interactive BESS flattens the load profile through adding an AC BESS to the connection point with rapid active power control.

The contribution will discuss advantages and challenges of both options, from cost, technical and regulatory perspective. Aspects covered include Load smoothing, Backup power, Fault ride through and the grid-side active power balance and frequency support. Simulation results will be discussed for load smoothing and fault-ride through.