Power Tip Sidecars: The New Power Supply Concepts for AI Data Centers

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Taiwan Machine Tool & Accessory Builders' Association (TMBA)

Artificial intelligence is not only changing the way we handle information and data. The power supply concepts in AI data centers also require a fundamental rethink. We explain how the new sidecars work.

Modern AI data centers have to provide enormous computing power, which results in correspondingly high electrical power consumption. According to forecasts, the 1 MW limit is likely to be exceeded by 2028. The power supply concepts of earlier data centers based on a busbar voltage of 50 V can no longer keep pace with this high demand, as currents in the range of 20 kA can no longer be sensibly controlled.

New IT server racks for AI applications therefore rely on a higher busbar voltage of 800 V or ±400 V DC in order to reduce the current by a whole order of magnitude. Figure 1 shows this architecture, which is based on a sidecar—a cabinet that houses the power supply separately from the server rack.

The Sidecar converts the mains voltage of 480 V AC into the bus voltage of 800 V DC and also contains the backup battery, which takes over the power supply in the event of a mains failure until the emergency power generators start up.

More important than power distribution, however, is actually increasing the computing density of the IT server rack. IT racks for AI applications contain hundreds of processors in order to process the necessary calculations quickly. These processors have to communicate with each other in a very small space.

Power Conversion Outsourced from the IT Rack

Outsourcing the majority of the power conversion from the IT rack enables more processors to be used in less space. Each IT tray in the rack is now supplied with the bus voltage of 800 V or ±400 V DC and an intermediate converter in the tray converts this voltage into voltages of 48 V, 12 V or 6 V according to the respective architecture.

This architecture improves the efficiency of power distribution and significantly increases the computing density in the IT rack, but in return requires more space in the IT area of the data center. The next development step is therefore to relocate the AC/DC conversion from the IT area to a separate technical room. Figure 2 outlines this concept.

In Figure 2, the sidecar houses the backup battery, while the AC/DC conversion is outsourced to a solid-state transformer (SST). The solid-state transformer replaces both the medium-voltage transformers and the conversion to 800 V or ±400 V DC. It also performs power factor correction, voltage reduction and rectification in a single power conversion stage.

The emergency power generators must therefore now be connected to the medium-voltage node or via an AC/DC converter at the output of the SST. The bottom line is that this results in a more efficient power distribution network, which creates more space in the IT area to increase computing power.

The Power Converter Functions

Sophisticated power converter functions are just as necessary in the new power supply solutions as in previous generations. These range from power factor correction to DC/DC conversion to 800 V or ±400 V DC, diode OR linking, current distribution, hot-swap functionality and protection functions as well as control and power measurement.

Sophisticated semiconductors are the key to maximizing the performance and efficiency of each of these functions. Among other things, these components are required: Real-time microcontrollers for power factor correction and DC bus voltage generation, high-efficiency wide-bandgap semiconductor switches for LLC topologies and power factor correction.

In addition, precise current and voltage measurement modules for power measurement as well as control and protection functions and compact, highly efficient bias power supplies and gate drivers for various isolated switches in the system. (kr)

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