Direct current with 400 to 800 volts for servers and industry: HVDC

In Europe, servers and industrial machines are predominantly supplied with single-phase 230 volts alternating current or three-phase 400 volts three-phase current. Switching to direct current with a nominal voltage of 400 to 800 volts promises advantages, especially if batteries are integrated as energy storage devices, if photovoltaics (PV) play a role or if energy can be recuperated.

Because the electrical power is the product of current and voltage (P = U x I), a proportionally lower current flows for the same power at a higher voltage. This reduces ohmic losses in cables and other conductors, or they can be thinner and therefore cheaper.

Several initiatives and projects are developing technology and specifications for High Voltage Direct Current (HVDC) in data centers and factories. Some solutions are based on the charging technology developed for electric cars with voltages of 400 or 800 volts. The cables, switches, converters and protective devices developed for this purpose are already achieving higher production volumes, which reduces prices.

The Open DC Alliance (ODCA) in the ZVEI in turn specifies industrial networks in the voltage range between 400 and 800 volts, for example with nominal voltages of 540 or 650 volts.

HVDC in data centers

The electrical power consumption of AI servers continues to increase with each chip generation. The first server cabinets (racks) with more than 100 kilowatts (kW) are currently in operation, and in the next five years this could rise to 1 megawatt (MW) per rack.

The enormous power per rack in data centers requires both power distribution systems and uninterruptible power supplies (UPS) with very high capacity. Instead of housing UPSs and servers separately, some (hyperscale) data centers have racks with AI servers right next to racks with battery and power converter modules.

If the connection between the battery buffers and the servers is made with DC voltage, the intermediate conversion to alternating current (AC) and the associated losses can be avoided.

This idea is anything but new and has been used in so-called “telco” servers for telecommunications networks for decades, as these traditionally work with -48 volts (from lead-acid batteries).

However, there are already UPS systems for 400 volts DC (400 VDC); the major server brands Dell, HPE and Lenovo also sell optional compatible power supply units for many servers with a rated voltage of 380 VDC, which are specified for 240 to 420 volts.

As part of the Open Compute Project (OCP), there are efforts to supply servers with even higher DC voltages of up to 800 volts. At the OCP Summit in October 2024, Google proposed a concept with three conductors that transmit +400 and -400 volts in relation to the ground line (+/– 400 VDC).

Nvidia is also planning an 800 VDC supply for future AI racks and is cooperating with both Infineon and TI.

HVDC for the industry

Because solar modules are dirt cheap, but grid electricity is expensive, photovoltaics are becoming increasingly profitable for commercial users. Local storage batteries increase the level of self-supply and buffer peaks in demand. For some industrial machines such as robots or forklifts for high-bay warehouses, the recuperation of braking energy also promises significant savings potential.

However, this requires direct current distribution grids to be installed on factory floors. The Open DC Alliance (ODCA) has developed proposals for standardization bodies, such as the “DC Industry System Description” (VDE SPEC 90037 V1.0).

Some manufacturers are already selling components for HVDC installations. The Swiss company Schurter, for example, offers connectors for 400 VDC, while Schaltbau offers contactors for loads in the megawatt range.

There are some fundamental problems to be solved with HVDC technology, such as avoiding arcing when disconnecting electrical connections under load.

(ciw)