Solid-State Transformer

Overview

A Solid-State Transformer (SST) is a power electronics device that converts medium-voltage AC (typically 13.8-34.5 kV from the utility grid) directly to low-voltage DC (400V, 800V, or 1500V) suitable for data center rack distribution. Unlike traditional iron-core transformers followed by separate UPS and rectifier stages, an SST combines the voltage transformation, rectification, and uninterruptible power supply functions into a single integrated unit. This consolidation eliminates multiple conversion stages, reduces physical footprint, and achieves target efficiencies of 98.5% at utilization — comparable to or better than the cumulative efficiency of the multi-stage conventional chain.

The significance of SSTs for data center facilities lies in their potential to fundamentally simplify the power delivery path from utility to server. In a conventional data center, power flows through a substation (medium-to-low voltage AC transformer), a UPS (AC-to-DC-to-AC), a PDU, and finally a rack PSU (AC-to-DC) — each stage adding loss, cost, space, and failure modes. An SST replaces the first several stages with a single device that outputs DC directly, feeding LVDC distribution to racks. Google proved the concept at 1 MW in its own data center test lab in 2025, converting 13.8 kV to +/-400V, and proposed a forward-looking architecture converting 34.5 kV to +/-750V DC as a 20-year standard that accommodates both current 800V rack designs and future 1500V DC targets. Microsoft presented the system-level business case, arguing that the emerging supply chain from EV charging stations, train applications, and DC microgrid deployments will drive cost reduction for data center SSTs. The OCP Power sub-project includes SST as one of its three primary workstreams alongside BESS and HVDC.