Column: Electric Vehicles
Changing your power delivery network can unlock new levels of performance
By Phil Davies, Corporate Vice President of Global Sales and Marketing, Vicor P
ower delivery networks (PDNs) are the backbone of any power system. As system power demands rise, traditional PDNs are under tremendous pressure to deliver the performance needed. T ere are two main ways to improve a PDN’s impact
on power system performance with regards to power losses and thermal management: T e fi rst is to reduce the PDN resistance with larger cables and connectors and thicker motherboard power planes. T e second is to increase the voltage of the PDN to reduce its current for a given power delivery, which will in turn reduce the size, weight and cost of the cables, connectors and motherboard copper planes. Traditionally, engineers have used option one, mainly to
capitalise on the large ecosystem existing around single-phase AC and 12V DC-DC converters and regulators. Other reasons include the lack of DC-DC converter topologies that directly convert higher voltages to the point-of-load (PoL) effi ciently and cheaply. However, modern-day power designs are now moving from
option one to option two, increasing the PDN voltage, driven by a signifi cant demand for system load power and new features. For example, data centres, artifi cial intelligence (AI) and machine and deep learning have all caused rack power to soar by over 200%, into the 20kW range, while supercomputer server racks are now approaching 100kW or more. T ese power increases have led engineers to re-evaluate the complete PDNs – from the distribution of power to the racks, the power distribution within the rack and even the PDNs on the server blades due to higher-current CPUs and AI processors; see Figure 1. When rack power was at a 5kW level, single-phase AC to the rack was the norm. T e AC was then converted to 12V for distribution to the server blades. At the 5kW level, the PDN current was 416A (5kW/12V), accomplishing power distribution with heavy-gauge cables.
New power demands As processor power began its dramatic increase, rack power moved up to the 12kW level, so, for a 12V PDN, 1000A had to be managed within the rack. T e OCP (Open Compute Project) consortium, consisting of cloud, server and CPU companies, evolved its 12V
14 April 2023
www.electronicsworld.com Figure 1: Computing peak current trends
Although keeping 12V legacy systems is simpler, with processor peak currents
approaching 2000A, 12V-based PDNs are near impossible for these applications
rack design by moving from cables to bus bars and distributed multiple single-phase AC-to-12V converters within the rack, to minimise the PDN distance and hence resistance to the server blades. T e major change from prior rack power delivery was that, due to the higher power, the single-phase AC was derived from the individual phases of a 3-phase feed to the rack. Companies that build their own racks and data centre solutions
followed suit, moving to 48V delivery. T is cut the high-current PDN problem down to 250A for a 12kW rack, but brought new challenges to the blade power conversion. So, as rack power moved into the
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