Aerospace Manufacturing and Design

 

Aerospace Manufacturing and Design has published ‘Unlocking Power Conversion Potential’ The article recently appeared in the March issue. Click the link below to view the full article.

 

Unlocking power conversion potential

(Reproduced from Aerospace Manufacturing and Design)


 

How compliance and collaboration will electrify aircraft.


By: Julian Thomas, Engineering Director, TT Electronics

Power conversion is a uniquely challenging feat when designing converters for critical applications such as engine or flight control systems. Since manufacturers don’t routinely redesign these complex systems, most of today’s commercial aircraft will have a power supply within the engine control system that was designed 25 years ago – proven and performing like clockwork.

But the if it ain’t broke, don’t fix it line of thinking is poised to change if aerospace original equipment manufacturers (OEMs) plan to capitalize on newer technology to drive higher efficiency. Where an old converter design might be 70%-to-75% efficient, a newly engineered version should deliver more than 90% performance efficiency while ensuring safety compliance. To develop smarter technologies for today, as well as breakthroughs on electrified aircraft of tomorrow, progress and performance must break free of resistance to change.

A fresh look at power converters

With production dominated by a few large industry players, existing power converters – for example, auto-transformer rectifier units (ATRUs) – are based on decades-old technology and are commonly non-compliant to the latest airframe harmonic requirements. Used to connect electronic equipment to airframe power, the non-compliant ATRU typically must be granted a performance waiver from the OEM; these waivers essentially acknowledge small outages in performance. ATRUs are safe, but failure to meet standards results in greater heating effects onboard the aircraft and greater limitations on the systems and features that can be engineered into the airframe. As aircraft change and advance technologically, these limitations won’t remain acceptable. For optimal performance, as well as competitive value, there’s a new push for ATRU technology that is fully compliant to the harmonic requirements of advanced aircraft.

Meanwhile, since ATRUs are so integral to electronic aircraft systems they have become key drivers of revenue for manufacturers – even if the manufacturer lacks deep understanding of how their own devices are engineered. Because these firms do not typically have onsite expertise to enable power conversion design at their facilities, a new market is emerging for products that are fully compliant and implement safety-critical features from the earliest design phase.

 

In more electric aircraft (MEA), many mechanical, hydraulic, or pneumatic systems are replaced with electrical equipment to reduce cost and improve performance.

In more electric aircraft (MEA), many mechanical, hydraulic, or pneumatic systems are replaced with electrical equipment to reduce cost and improve performance.

 

Design Priorities

Systems must be safe under all circumstances, yet just because a system works doesn’t mean it’s fully compliant to safety standards. Innovators are tackling this challenge by developing families of robust, safety-critical converters to power the brains of aircraft systems such as engine controls or fly-by-wire control systems. To ensure optimum power generation, energy from the generator must be drawn sinusoidally, reducing harmonics and the negative effect of heat on wiring. However, this design is complicated, so expertise must focus on the safety-critical aspects of performance. Consider a simple input filter for a power converter. There are quirks and oddities around this rudimentary circuit that may not be solved even if the paired voltage converters seem to perform. Complex systems have potential for peculiarities – such as unusual voltage on a single rail – that require specific design talent to avoid system failure.

Compliance and safety lay the foundation of smart design and enable performance excellence, including improvements necessary to drive engineering breakthroughs in modern aircraft design. For example, meeting the input-current harmonic specification ensures safety and protects the interests of aircraft manufacturers, but also positions the industry to unlock the potential of more-electric aircraft (MEA). This is a critical on-ramp to the future of aircraft design, because as planes become more electrified, more electrical systems will be added. All-electric aircraft will require even tighter, lower harmonics on systems’ input current, and manufacturers will face an evolving goal of drawing increasing levels of power from the generators in use.

Driving Innovation

Driving innovation

In this landscape, firms with a global footprint and deep expertise also play a role in pushing forward overall industry innovation and technology breakthroughs – not to mention helping aerospace leaders sustain relevance to the engineered systems of tomorrow. By recruiting talent from system manufacturing and design engineering, innovators are creating teams experienced in developing power electronics systems. This creates a significant industry shift, filling a gap in companies that can provide broad spectrum solutions, allowing industry players to redirect design resources to the next level of aircraft integration.

The ins and outs of ATRUs

Auto-transformer rectifier units (ATRUs) convert the AC power produced by generators into DC power. There might be hundreds of ATRUs onboard a single aircraft, handling a spectrum of power needs, spanning from 1kW to 250kW. These simple and reliable devices deliver quality power using a multi-phase transformer, power diodes, and electromagnetic interference (EMI) filters.

However, legacy ATRUs introduce unwanted harmonics into a system instead of delivering the desired smooth sinewave current pulled from a sinewave voltage. This fails the acceptable level of harmonics defined by the comprehensive DO-160X industry specification, requiring aircraft manufacturers to grant waivers for any ATRU design that falls out of spec. While a waiver doesn’t mean an unsafe device, it acknowledges a less efficient device is being used that produces more heat, limiting the number and type of electrified systems that can be added to the aircraft.

Compliance changes this landscape: Qualified to DO-160 provides a way for manufacturers to fully capitalize on the power potential of their designs in the same or even smaller ATRU footprint. It’s a big win in advanced aircraft systems relying on a fixed amount of power being generated and transmitted – allowing a competitive difference.

Compliance waivers are on their way out, creating a virtuous cycle of innovation that’s critical to improve safety compliance and develop breakthroughs to fuel the growth of electrified aircraft. The industry should recognize this sea change and develop greater awareness of the challenges, possibilities, options, and leadership opportunities driven by excellence in power conversion.

 

 

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