Info!! Ability Provide Performance On A 400Hz Source

This article is intended to provide a full general overview on using industrial ability supplies amongst an aircraft 400Hz electrical source.

Most large aircraft are fitted amongst an Auxiliary Power Unit (APU) supplying a stage to neutral 115VAC 400Hz source.  The APU is used primarily to commencement the aircraft engines, simply is equally good used to run accessories on the bird spell passengers are on board together with for preflight checks past times the crew when the aircraft has left the gate.

The argue 400Hz was chosen over the traditional 50/60Hz is because of weight.  A 400Hz generator is much lighter, thus saving fuel, together with the demand to back upwards a heavier unit of measurement making the airframe lighter.

MIL-STD-704F is the specification that covers Aircraft Electrical Power Characteristics for the States armed forces aircraft, together with covers inward especial all aspects of the requirements.

If an aircraft is beingness serviced on the ground, it is to a greater extent than convenient together with safer non to possess got either the primary engines or the APU running.  In this instance an external 400Hz generator or Ground Power Unit is usually available.  Often diagnostic equipment is non required to encounter the sum flying specifications together with for toll purposes a regular industrial ability render tin post away last chosen.

TDK-Lambda is oft asked if i of our AC-DC industrial ability supplies volition function off 400Hz input, usually the response is “yes”; the next explains why:

For depression wattage ability supplies (50W or less), the input circuit is a uncomplicated sum moving ridge couplet rectifier.

Simple sum moving ridge couplet rectifier circuit

The air-conditioning voltage is filtered together with so sum moving ridge rectified into high voltage DC.  With a 60Hz input, the ripple voltage on the mass cap is 120Hz. With a 400Hz input, the ripple voltage is 800Hz (hence smaller), having no affect on the ability render performance.

For ability supplies greater than 50W, well-nigh AC-DC ability supplies possess got active Power Factor Correction circuitry.  Simply put, a boost converter is used to cut the input harmonic currents past times changing their shape to look to a greater extent than sinusoidal - equally if the charge were resistive.

Boost Converter

 

The Boost FET inward the higher upwards circuit is driven past times a command IC.  The IC regulates the converter receiving feedback from iii sources: the 100-120Hz rectified input voltage (Point “A”), the inductor electrical current together with the DC voltage across the mass capacitor.

Although well-nigh PFC circuits volition operate from a 400Hz input, the moving ridge shape of the electrical current harmonics is slightly degraded due to distortion at Point “A” (now an 800Hz waveform).  This, however, is usually acceptable for basis based equipment.

Simplified Diagram Showing “Y” cap locations

To cut high frequency radiated together with conducted noise, ability render input filters usage special “Y” decoupling capacitors connected from the Line & Neutral to Chassis (Earth) ground.  In improver to high frequency current, these Y capacitors equally good provide a path for 50/60Hz current.  The maximum value of this “earth leakage” electrical current is dictated past times the security agencies similar UL, specially for equipment that is plugged into a regular wall socket industrial plant life inward an component (for example).  For large pieces of equipment that is difficult wired to an air-conditioning source, the limits are much higher.

With a 400Hz input, the basis leakage electrical current is significantly increased through the “Y” (input to ground) capacitors equally that electrical current is straight proportional to the input frequency, I = V x 2πfC.

However, basis based equipment running off 400Hz generators falls into the difficult wired category, so this is non usually a problem.

One concluding note; although commercial ability supplies are security certified to the Information Technology Equipment criterion IEC 60950-1, testing for the study is usually conducted amongst a 50-60Hz input.  Most basis based aircraft systems produce non autumn nether IEC 60950-1 simply using a ability render certified to that criterion agency the production has been rigorously tested.

Power Guy