Need advice on THD

Hello,

I have designed a power supply using Vicor parts

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I am trying to meet a part of MIL-STD-1399(NAVY)

300A (military power standard) that states:

"no individual harmonic line current from the second harmonic through

20kHz exceeds a magnitude of 100/n percent of the unit's rated full load fundamental current."

Our system only brings in 2.5A and runs 120V 60Hz. The EMI filter we have out in front of the AC/DC vicor module is the JMK filter HH-1355-6.3 that really starts filtering from 10kHz-20Meg which helps get rid of the conducted emissions. I am having problems in the

4kHz-8kHz range of my current THD however and am wondering how I should go about fixing it. A simple filter out in front of the EMI filter would cause a slip in the power factor of the unit which is also regulated by MIL-STD-1399(NAVY) 300A. Are there EMI filters that can kill the lower frequencies (4-8kHz) as well as the high (20MHz)? Have you ever used one that was designed for Power Factor Correction AC/DCs such as the VI-HAM from vicor?

Thank you in advance for any advice, Matt

Reply to
Matt
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"Matt"

** So you have about 1% current around 1/00 th harmonic of 60 Hz ??

Most folk just add a series inductor in the AC line to improve that situation.

A few mH ought to do it.

Just make sure it can handle 4 amps peak without saturation.

...... Phil

Reply to
Phil Allison

Phill, thanks for the reply. If I include this 4mH inductor, wouldnt that cause my power factor to shift? I will give it a try and let yall know if it does ;)

Reply to
Matt

Also, just thought of this, would a common mode be more useful than a single inline inductor?

Reply to
Matt

"Matt" Also, just thought of this, would a common mode be more useful than a

** Got any idea what a "common mode " inductor is ?

Got a fire extinguisher on your hip ?

In case of unexpected anal conflagragrations ?

........ Phil

Reply to
Phil Allison

Isn't power factor a measure of how the load draws real power? Just a ratio of real and complex. I thought any reactive load would change the power factor.

Reply to
Matt

"Matt"

** Is your arse on fire ??

Had a look lately ?

Think I smell smoke.

....... Phil

Reply to
Phil Allison

On Jun 7, 6:30 am, Matt wrote: [.....]

Common mode inductors block common mode current. They do very little for the power factor.

A LC EMI filter in front of the bridge will suppress high frequency currents but not do anything much to the low numbered harmonics. It does increase the impedance in the path back to the power line a little but thats aout it.

An inductor on the output of the bridge will spread the current pulse out. Any frequency that is high enough to have the current pulse be a significant fraction of its cycle will be reduced. When the current int he inductor doesn't quite go to zero, the 3rd harmonic will be down about 7dB.

The inductor also shifts the phase of the input current later.

Reply to
MooseFET

Is the Vicor a PFC converter?

Can you post the failing spectrum analyzer picture over on alt.binaries.schematics.electronic so we can see how bad it is?

Reply to
The Phantom

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