Need advice on THD

[Matt]

Hello,

I have designed a power supply using Vicor parts
(www.vicorpower.com). 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

 

[Eeyore]

Hello,

I have designed a power supply using Vicor parts
(www.vicorpower.com). 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?

Al though you mention no numbers, it seems like you need active power factor
correction.

Graham

 

[Phil Allison]

"Matt"

I have designed a power supply using Vicor parts
(www.vicorpower.com). 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,

** 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

 

[Matt]

"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- Hide quoted text -

- Show quoted text -

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

 

[Matt]

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 - Hide quoted text -

- Show quoted text -

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

 

[Eeyore]

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

It's *LINE CURRENT* this is about ! The actual load !

A common mode filter won't do anything to affect power factor / THD. It's there
for RF !

Graham

 

[Phil Allison]

"Matt" <[email protected]>

** Groper Alert !!

Phill, thanks for the reply. If I include this 4mH inductor, wouldnt
that cause my power factor to shift?

** Got a fucking clue what power factor even is ?

Surprise me - post the definition relevant to your case.

Bet anything you cannot.



....... Phil

 

[Phil Allison]

"Matt" <[email protected]


** Groper Alert !!!

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

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

Got a fire extinguisher on your hip ?

In case of unexpected anal conflagragrations ?




......... Phil

 

[Matt]

"Matt" <[email protected]

** Groper Alert !!!


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

Got a fire extinguisher on your hip ?

In case of unexpected anal conflagragrations ?

........ Phil

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.

 

[Phil Allison]

"Matt"

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.

** Is your arse on fire ??

Had a look lately ?

Think I smell smoke.



........ Phil

 

[MooseFET]

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

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.

 

[Eeyore]

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.

How does a common mode voltage affect the power drawn then ?

And futhermore, THD isn't itself the classic 'power factor' either. It's the
harmonics they're worried about, not the phase angle of the load.

Graham

 

[Eeyore]

An inductor on the output of the bridge will spread the current pulse
out.

Indeed it will.

Another 'trick' worth investigating with line frequency supplies, is using a
smaller size reservoir / filter cap than you might otherwise have done, should
circumstances allow. This also lengthens the conduction period.

Graham

 

[The Phantom]

Hello,

I have designed a power supply using Vicor parts
(www.vicorpower.com). 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

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?