POWER DEVICES
DC-to-DC Power Conversion: Building Block Strategies Break Through the Complexity
Blending the art and science of design, Julian Thomas, engineering director at TT Electronics explores how power distribution strategies are critical to the performance and fault tolerance necessary for smart, safe urban air mobility
L
ike most homes, the power distribution within aircraft has traditionally been AC. However, technology developments have
enabled power systems designs to turn towards higher voltage DC distribution systems that can provide greater overall efficiency while simultaneously being more compatible with energy storage (batteries) and load requirements. Yet reliance on AC-DC conversion and distribution is a design approach that inherently multiplies the number of power electronics required – at odds with the principles of Size, Weight, Power, and Cost (SWAP-C) that are so critical to success. The SWAP-C challenge is compounded by exponential growth in
the amount of electrical power required onboard aircraft. More systems are increasingly electric, from more sophisticated cockpit avionics and more electrically actuated systems to creature comforts such as coffee, food service, and entertainment. It’s an upward trend, not only in the amount of power but also in the complexity of overall systems. This generational trend applies to both military and civil aircraft, but
the rise of all-electric aircraft promises even greater disruption on the power landscape. Many of the urban air mobility systems in development are fundamentally DC platforms – powered by batteries storing DC power – eliminating the need for AC-DC power conversion at point of load. Designers of traditional aircraft, with gas
turbines driving auxiliary power units that are naturally AC, must embrace the shift and recognise the critical value of DC power distribution strategies.
Real-world design strategies are complex and diverse When power is both generated and distributed in DC form, voltage conversions are required, dependent on how and where the power will be used onboard the aircraft. Is power delivered and then stepped up or down at the device? Or is it converted and then distributed? There is no ‘right’ answer to this not-so-simple question. Strategies vary widely and consider the systems involved, the type of aircraft and how it is used, system weight, reliability, scalability, longevity, and more. Power needed for a well-defined area of the aircraft, for instance
the 28 Volts typical to cockpit avionics, could be achieved with only power conditioning from a local battery source. Alternatively, the required 28Vdc could be converted centrally and distributed as needed. This approach applies best to smaller, less complex architectures, as wider distribution options can result in heavier cabling wherein power is passed to a variety of devices. A smarter design might increase the voltage as a trade-off to reduce cabling requirements, for example creating a primary
20 DECEMBER/JANUARY 2022 | ELECTRONICS TODAY
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