Powering the (More) Electric Aircraft of the (Near) Future

The futuristic concept of the Electric Aircraft is becoming a little less far-out these days. At the recent Paris Air Show in June, a variety of suppliers exhibited electric-power technologies that “are nearly ready for primetime.” The real heavy lifting, though, has already come from the two major commercial aircraft manufacturers, Airbus and Boeing.

In Paris, for example, Honeywell and Safran demonstrated their Electric Green Taxiing System (EGTS) prototype, which uses an APU generator to power motors on an aircraft’s main wheels, enabling the jet to push back and taxi without starting its main engines. “The key attractions at the Air Paris Show were the electric prototypes from big industry players,” said Frost & Sullivan Aerospace and Defense Analyst Alix Leboulanger. “If developments go according to plan, then all-electric commercial aviation could take off by 2035 to 2040.”

Really, the bigger story, though, has already happened, in the switchover to variable-frequency power electronics by Airbus and Boeing. Traditionally, commercial aircraft have used bleed-air from their engines to run a motor that supplied fixed-frequency power (3-phase 115 VAC at 400 Hz) to run their electrical systems. Maintaining a constant 400 Hz requires equipment (such as a constant speed drive) that converts the varying engine speeds to the constant speed, adding weight to the plane. Plus, fixed frequency limited the capabilities of the onboard electrical components to handle advanced applications. In recent years, the two avionics industry heavyweights have begun to adopt the more-sophisticated variable-frequency power architecture as part of a wider effort to build what has come to be known as the More Electric Aircraft (MEA) concept.

Airbus moved first with the A380, which uses four 150- to 380-kVA variable-frequency (380 Hz to 800 Hz) electrical generators. Its power system is fully computerized and many connections have been replaced by solid-state devices for better performance. Airbus has also imposed more stringent electromagnetic interference requirements. And the aircraft is touted as being the first commercial widebody to deploy power-by-wire flight control actuators.

Boeing has followed with the 787 Dreamliner, which completes a transition for the company from bleed-air power to a more-electric architecture.  Engine start, APU start, wing ice protection, cabin pressurization and hydraulic pumps are all powered by variable-frequency (360-800 Hz) generators. Boeing claims that this offers a 300 percent improvement in its electrical systems.

In power electronics, wide variable-frequency often goes by the name “wild” frequency (or AC Wild). We wrote about wild frequency in an article for Avionics Magazine back in 2007 entitled Frequency Change. In it, Ron Storm, president of Behlman Electronics, noted that the adoption of wild frequency will offer “significantly reduced complexity compared to the constant speed hydro-mechanical devices run by previous fixed-frequency power systems.”

“Logically,” Mr. Storm wrote, “if wild frequency is to become widely accepted as the prevalent AC power in avionics, ground support and test equipment capable of providing wild frequency power ranges will be essential.”

To help in this transition, Behlman created a Wild Frequency Information Center to provide background material on the topic for those interested in learning more. We will also try to keep you updated going forward with additional blog posts on the new era of power electronics in aviation. Welcome to the near future.

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