Power Supply Operation on a 400Hz Source

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This text is meant to offer a normal overview on utilizing industrial power provides with an plane 400Hz electrical source.

Most massive plane are fitted with an Auxiliary Power Unit (APU) supplying a part to impartial 115VAC 400Hz source.  The APU is used primarily to start out the plane engines, however can be used to run equipment on the airplane whereas passengers are on board and for preflight checks by the crew when the plane has left the gate.
The explanation 400Hz was chosen over the standard 50/60Hz is due to weight.  A 400Hz generator is far lighter, thus saving gas, and the necessity to help a heavier unit making the airframe lighter.
MIL-STD-704F is the specification that covers Plane Electrical Power Traits for US navy plane, and covers intimately all facets of the necessities.
If an plane is being serviced on the bottom, it's extra handy and safer to not have both the principle engines or the APU operating.  On this case an external 400Hz generator or Floor Power Unit is often out there.  Usually diagnostic tools shouldn't be required to satisfy the complete flight specifications and for value functions a common industrial power provide might be chosen.
TDK-Lambda is commonly requested if one in every of our AC-DC industrial power provides will work off 400Hz enter, often the reply is “sure”; the next explains why:
For low wattage power provides (50W or much less), the enter circuit is a easy full wave bridge rectifier.
Easy full wave bridge rectifier circuit

The AC voltage is filtered after which full wave rectified into high voltage DC.  With a 60Hz enter, the ripple voltage on the majority cap is 120Hz. With a 400Hz enter, the ripple voltage is 800Hz (therefore smaller), having no influence on the power provide efficiency.

For power provides better than 50W, most AC-DC power provides have lively Power Issue Correction circuitry.  Merely put, a enhance converter is used to scale back the enter harmonic currents by altering their form to look extra sinusoidal - as if the load had been resistive.

Enhance Converter
 
The Enhance FET within the above circuit is pushed by a management IC.  The IC regulates the converter receiving suggestions from three sources: the 100-120Hz rectified enter voltage (Level “A”), the inductor present and the DC voltage throughout the majority capacitor.
Though most PFC circuits will function from a 400Hz enter, the wave form of the present harmonics is barely degraded resulting from distortion at Level “A” (now an 800Hz waveform).  This, nonetheless, is often acceptable for floor based mostly tools.
Simplified Diagram Displaying “Y” cap places
To scale back high frequency radiated and performed noise, power provide enter filters use particular “Y” decoupling capacitors related from the Line & Impartial to Chassis (Earth) floor.  Along with high frequency present, these Y capacitors additionally present a path for 50/60Hz present.  The utmost worth of this “earth leakage” present is dictated by the security businesses like UL, notably for tools that's plugged into a common wall socket present in an workplace (for instance).  For giant items of kit that's onerous wired to an AC source, the boundaries are a lot larger.
With a 400Hz enter, the earth leakage present is considerably elevated by way of the “Y” (enter to floor) capacitors as that present is immediately proportional to the enter frequency, I = V x 2πfC.
Nevertheless, floor based mostly tools operating off 400Hz mills falls into the onerous wired class, so this isn't usually a drawback.

One final note; though industrial power provides are security licensed to the Data Expertise Tools normal IEC 60950-1, testing for the report is often performed with a 50-60Hz enter.  Most floor based mostly plane programs don't fall underneath IEC 60950-1 however utilizing a power provide licensed to that normal means the product has been rigorously examined.

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