270 VDC power in aircraft

[wingtip]

Hi,
This is on a similar subject to my other post today. Some aircraft under development ,e.g. The JSF, are developing a 270V DC power system rather than 115V 400Hz used on previous aircraft. Does anyone have an explanation for this change in power system design...what are the advantages? Could the change be driven mainly by the emergence of powerful DC motors which can replace hydraulic actuators?

 

[jbartos]

Suggestion: Because of weight constraints, the lightest power distribution systems are getting attention. The AC voltage conversions via heavy transformers are no longer attractive. DC systems with lighter DC-DC converters are preferable. Also, many loads are converting AC to DC anyhow, e.g. electronic devices, etc. Large amount of energy is needed for heating. This may be DC. DC-AC inverters can conveniently change voltage on as needed bases.

 

[IRstuff]

Part of the answer is that 270V is the typical intermediate output from full-wave rectification of the 3-phase 115VAC 400Hz AC input. This means that every subsystem on the plane has a full-wave rectifier front-end and there may be some overall savings if that was done in a central location and the 270VDC was distributed.

Current ratings are only slightly higher than the existing runs, but only 2 wires are needed instead of 3 or 4.

Additionally, by minimizing the AC runs in the aircraft, the overall EM emission level should be less.

TTFN

 

[Skogsgurra]

The same thing is being tried on the ground. Some offices have 325 V DC in test installations for the same reasons that IR and jb mentioned. The main concern here is EMI and mains harmonics, which of course are also important in the "flying city" that an airplane has turned into today.

BTW, 115 V rectified (even in a three phase system and with smoothing capacitors) do not produce more than abt 170 V DC. So I think that the system voltage is more like 115*sqrt(3) or around 200 V. It will give you close to 270 V.

 

[jbartos]

Small encore: The EMI, EMC, galvanic path/connection of dc is something that has to be properly addressed and dealt with to avoid problems of larger magnitudes.