Forums

Large Noise from Bridge Rectifier; Conducted Emission Measurement

Started by Klaus Kragelund July 2, 2014
Hi

I am working on a high power frequency inverter (>1kW) and have a "funny" looking emission graph


The converter is the typical inverter type, EMC filter->3 Phase Rectifier->DC Inductor->DC Link capacitor->6 switch Inverter->Motor

Like this:

www.electronicsdesign.dk/tmp/Inverter.jpeg

We stripped down the circuits and isolated the noise to the EMC filter and bridge rectifier.

The problem is the very high conducted emission noise at 150kHz:

www.electronicsdesign.dk/tmp/NoisefromRectifier.pdf

(Conducted emission plot narrowed in from 150kHz to 2MHz, conducted with a 2-stage EMC filter and a bridge rectifier with a capacitor on the output and a resistive load)

www.electronicsdesign.dk/tmp/PowerModel_V0.pdf

The bridge rectifier is a part of an intregrated power module, but that noise also comes from a standard single phase rectifier

First thought would be that the noise is coming from the reverse recovery of the diodes, but the noise increases a less load (< 200W), and I would think the reverse recovery current glitch would be worse at higher currents running in the bridge rectifier

I have tried with snubbers and that did not help. 

Any insights into the cause and the remedy?

Thanks

Klaus
On 02/07/14 18.22, Klaus Kragelund wrote:
> Hi
...
> > We stripped down the circuits and isolated the noise to the EMC filter and bridge rectifier. > > The problem is the very high conducted emission noise at 150kHz: > > www.electronicsdesign.dk/tmp/NoisefromRectifier.pdf > > (Conducted emission plot narrowed in from 150kHz to 2MHz, conducted with a 2-stage EMC filter and a bridge rectifier with a capacitor on the output and a resistive load)
...
> I have tried with snubbers and that did not help. > > Any insights into the cause and the remedy? > > Thanks > > Klaus
Hi Klaus That is a common problem: How to Eliminate Diode Noise: http://www.ehow.com/how_7970048_eliminate-diode-noise.html Bypass capacitors across rectifier diodes: http://www.audiokarma.org/forums/archive/index.php/t-469495.html Noise from solid state rectifier in tube amp: http://electronics.stackexchange.com/questions/78813/noise-from-solid-state-rectifier-in-tube-amp Quote: "... Diodes can be noisy when used as rectifiers due to reverse recovery induced spikes. Certain types of diodes perform better (schottky and so-called 'soft-recovery' diodes) or are essentially immune (silicon carbide) to this effect. A well-designed circuit can address reverse recovery via the use of appropriate diodes (i.e schottkys and/or silicon carbide where appropriate) and by snubber networks, which absorb and dissipate the spike energy. ..." http://www.valvewizard.co.uk/bridge.html http://www.diyaudio.com/forums/solid-state/134243-what-does-01-cap-bridge-rectifiers-do.html Quote: "... They are there to shunt switching noise. If the capacitors are of the wrong type, they can create more noise than they attempt to remove. The size of the cap vs the expected 'load' is key to their effectiveness. ..." http://www.electro-tech-online.com/threads/capacitor-bypass-of-diodes-in-bridge-rectifiers.40733/ Glenn
On 07/02/2014 12:22 PM, Klaus Kragelund wrote:
> Hi > > I am working on a high power frequency inverter (>1kW) and have a > "funny" looking emission graph > > > The converter is the typical inverter type, EMC filter->3 Phase > Rectifier->DC Inductor->DC Link capacitor->6 switch Inverter->Motor > > Like this: > > www.electronicsdesign.dk/tmp/Inverter.jpeg > > We stripped down the circuits and isolated the noise to the EMC > filter and bridge rectifier. > > The problem is the very high conducted emission noise at 150kHz: > > www.electronicsdesign.dk/tmp/NoisefromRectifier.pdf > > (Conducted emission plot narrowed in from 150kHz to 2MHz, conducted > with a 2-stage EMC filter and a bridge rectifier with a capacitor on > the output and a resistive load) > > www.electronicsdesign.dk/tmp/PowerModel_V0.pdf > > The bridge rectifier is a part of an intregrated power module, but > that noise also comes from a standard single phase rectifier > > First thought would be that the noise is coming from the reverse > recovery of the diodes, but the noise increases a less load (< 200W), > and I would think the reverse recovery current glitch would be worse > at higher currents running in the bridge rectifier > > I have tried with snubbers and that did not help. > > Any insights into the cause and the remedy? > > Thanks > > Klaus >
Might be the turn-on overshoot. Can you measure the voltage across one of the rectifiers? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Wednesday, July 2, 2014 12:22:20 PM UTC-4, Klaus Kragelund wrote:
> Hi > > > > I am working on a high power frequency inverter (>1kW) and have a "funny" looking emission graph > > > > > > The converter is the typical inverter type, EMC filter->3 Phase Rectifier->DC Inductor->DC Link capacitor->6 switch Inverter->Motor > > > > Like this: > > > > www.electronicsdesign.dk/tmp/Inverter.jpeg > > > > We stripped down the circuits and isolated the noise to the EMC filter and bridge rectifier. > > > > The problem is the very high conducted emission noise at 150kHz: > > > > www.electronicsdesign.dk/tmp/NoisefromRectifier.pdf > > > > (Conducted emission plot narrowed in from 150kHz to 2MHz, conducted with a 2-stage EMC filter and a bridge rectifier with a capacitor on the output and a resistive load) > > > > www.electronicsdesign.dk/tmp/PowerModel_V0.pdf > > > > The bridge rectifier is a part of an intregrated power module, but that noise also comes from a standard single phase rectifier > > > > First thought would be that the noise is coming from the reverse recovery of the diodes, but the noise increases a less load (< 200W), and I would think the reverse recovery current glitch would be worse at higher currents running in the bridge rectifier > > > > I have tried with snubbers and that did not help. > > > > Any insights into the cause and the remedy?
Resonance due to under-loaded/damped EMC filter, high current lossy ferrite bead/beed/bede needed.
> > > > Thanks > > > > Klaus
On Wednesday, July 2, 2014 6:39:11 PM UTC+2, Glenn wrote:
> On 02/07/14 18.22, Klaus Kragelund wrote: > > > Hi > > ... > > > > > > We stripped down the circuits and isolated the noise to the EMC filter and bridge rectifier. > > > > > > The problem is the very high conducted emission noise at 150kHz: > > > > > > www.electronicsdesign.dk/tmp/NoisefromRectifier.pdf > > > > > > (Conducted emission plot narrowed in from 150kHz to 2MHz, conducted with a 2-stage EMC filter and a bridge rectifier with a capacitor on the output and a resistive load) > > ... > > > I have tried with snubbers and that did not help. > > > > > > Any insights into the cause and the remedy? > > > > > > Thanks > > > > > > Klaus > > > > Hi Klaus > > > > That is a common problem: > > > > How to Eliminate Diode Noise: > > http://www.ehow.com/how_7970048_eliminate-diode-noise.html > > > > Bypass capacitors across rectifier diodes: > > http://www.audiokarma.org/forums/archive/index.php/t-469495.html > > > > Noise from solid state rectifier in tube amp: > > http://electronics.stackexchange.com/questions/78813/noise-from-solid-state-rectifier-in-tube-amp > > Quote: "... > > Diodes can be noisy when used as rectifiers due to reverse recovery > > induced spikes. Certain types of diodes perform better (schottky and > > so-called 'soft-recovery' diodes) or are essentially immune (silicon > > carbide) to this effect. > > > > A well-designed circuit can address reverse recovery via the use of > > appropriate diodes (i.e schottkys and/or silicon carbide where > > appropriate) and by snubber networks, which absorb and dissipate the > > spike energy. > > ..." > > > > http://www.valvewizard.co.uk/bridge.html > > > > http://www.diyaudio.com/forums/solid-state/134243-what-does-01-cap-bridge-rectifiers-do.html > > Quote: "... > > They are there to shunt switching noise. If the capacitors are of the > > wrong type, they can create more noise than they attempt to remove. The > > size of the cap vs the expected 'load' is key to their effectiveness. > > ..." > > > > http://www.electro-tech-online.com/threads/capacitor-bypass-of-diodes-in-bridge-rectifiers.40733/ > > >
HI Glenn Thanks for the links, but as I wrote that was the first thing I tried. Both purely capacitive snubbers and RC snubbers. There was no change in emissions One suspicion I have is interaction of the diode bridge with the EMC filter, causing undamped ringing. But it's hard to measure, when we are talking 550V DC, to catch a small signal which the differential probe cannot resolve. One idea I had was to drive the bridge rectifier with the same current, at low voltage, so it's possible to measure Cheers Klaus
On Wednesday, July 2, 2014 7:08:39 PM UTC+2, Phil Hobbs wrote:
> On 07/02/2014 12:22 PM, Klaus Kragelund wrote: >=20 > > Hi >=20 > > >=20 > > I am working on a high power frequency inverter (>1kW) and have a >=20 > > "funny" looking emission graph >=20 > > >=20 > > >=20 > > The converter is the typical inverter type, EMC filter->3 Phase >=20 > > Rectifier->DC Inductor->DC Link capacitor->6 switch Inverter->Motor >=20 > > >=20 > > Like this: >=20 > > >=20 > > www.electronicsdesign.dk/tmp/Inverter.jpeg >=20 > > >=20 > > We stripped down the circuits and isolated the noise to the EMC >=20 > > filter and bridge rectifier. >=20 > > >=20 > > The problem is the very high conducted emission noise at 150kHz: >=20 > > >=20 > > www.electronicsdesign.dk/tmp/NoisefromRectifier.pdf >=20 > > >=20 > > (Conducted emission plot narrowed in from 150kHz to 2MHz, conducted >=20 > > with a 2-stage EMC filter and a bridge rectifier with a capacitor on >=20 > > the output and a resistive load) >=20 > > >=20 > > www.electronicsdesign.dk/tmp/PowerModel_V0.pdf >=20 > > >=20 > > The bridge rectifier is a part of an intregrated power module, but >=20 > > that noise also comes from a standard single phase rectifier >=20 > > >=20 > > First thought would be that the noise is coming from the reverse >=20 > > recovery of the diodes, but the noise increases a less load (< 200W), >=20 > > and I would think the reverse recovery current glitch would be worse >=20 > > at higher currents running in the bridge rectifier >=20 > > >=20 > > I have tried with snubbers and that did not help. >=20 > > >=20 > > Any insights into the cause and the remedy? >=20 > > >=20 > > Thanks >=20 > > >=20 > > Klaus >=20 > > >=20 >=20 >=20 > Might be the turn-on overshoot. Can you measure the voltage across one=
=20
>=20 > of the rectifiers? >=20 >=20
Yes, I can measure the voltage. SO you think the diodes are slow to turn on= and that the glitch is what we see? I have measured the diode voltage, and it looks fine, except for a small un= dershoot during turn-off (reverse recovery, but I could not see any change = when adding snubbers) Bytheway, the distance between the quasi peak and average is normally a fix= ed ratio, say 10dB. But in the event of periodic larger noise, the quasi peak get higher. Like = we see in the plot. Sometimes that is from saturation of the common mode in= ductor, but we have confirmed this is not the case, since we are running ve= ry low currents and we have no CM noise (no CM saturation of the CM inducto= r) Cheers Klaus
On Wednesday, July 2, 2014 7:22:34 PM UTC+2, bloggs.fred...@gmail.com wrote=
:
> On Wednesday, July 2, 2014 12:22:20 PM UTC-4, Klaus Kragelund wrote: >=20 > > Hi >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > I am working on a high power frequency inverter (>1kW) and have a "funn=
y" looking emission graph
>=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > The converter is the typical inverter type, EMC filter->3 Phase Rectifi=
er->DC Inductor->DC Link capacitor->6 switch Inverter->Motor
>=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > Like this: >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > www.electronicsdesign.dk/tmp/Inverter.jpeg >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > We stripped down the circuits and isolated the noise to the EMC filter =
and bridge rectifier.
>=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > The problem is the very high conducted emission noise at 150kHz: >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > www.electronicsdesign.dk/tmp/NoisefromRectifier.pdf >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > (Conducted emission plot narrowed in from 150kHz to 2MHz, conducted wit=
h a 2-stage EMC filter and a bridge rectifier with a capacitor on the outpu= t and a resistive load)
>=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > www.electronicsdesign.dk/tmp/PowerModel_V0.pdf >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > The bridge rectifier is a part of an intregrated power module, but that=
noise also comes from a standard single phase rectifier
>=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > First thought would be that the noise is coming from the reverse recove=
ry of the diodes, but the noise increases a less load (< 200W), and I would= think the reverse recovery current glitch would be worse at higher current= s running in the bridge rectifier
>=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > I have tried with snubbers and that did not help.=20 >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > > Any insights into the cause and the remedy? >=20 >=20 >=20 > Resonance due to under-loaded/damped EMC filter, high current lossy ferri=
te bead/beed/bede needed.=20
>=20
Yes, we have thought about that. We then tried with a single stage EMC filt= er, and the problem was almost exactly the same. I could try to add resista= nce in the X and Y capacitors, just to rule it out. Thanks for the reminder= :-) Cheers Klaus
On Wednesday, July 2, 2014 7:24:35 PM UTC+2, Klaus Kragelund wrote:
> On Wednesday, July 2, 2014 6:39:11 PM UTC+2, Glenn wrote: > > > On 02/07/14 18.22, Klaus Kragelund wrote: > > > > > > > Hi > > > > > > ... > > > > > > > > > > > > > > We stripped down the circuits and isolated the noise to the EMC filter and bridge rectifier. > > > > > > > > > > > > > > The problem is the very high conducted emission noise at 150kHz: > > > > > > > > > > > > > > www.electronicsdesign.dk/tmp/NoisefromRectifier.pdf > > > > > > > > > > > > > > (Conducted emission plot narrowed in from 150kHz to 2MHz, conducted with a 2-stage EMC filter and a bridge rectifier with a capacitor on the output and a resistive load) > > > > > > ... > > > > > > > I have tried with snubbers and that did not help. > > > > > > > > > > > > > > Any insights into the cause and the remedy? > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > Klaus > > > > > > > > > > > > Hi Klaus > > > > > > > > > > > > That is a common problem: > > > > > > > > > > > > How to Eliminate Diode Noise: > > > > > > http://www.ehow.com/how_7970048_eliminate-diode-noise.html > > > > > > > > > > > > Bypass capacitors across rectifier diodes: > > > > > > http://www.audiokarma.org/forums/archive/index.php/t-469495.html > > > > > > > > > > > > Noise from solid state rectifier in tube amp: > > > > > > http://electronics.stackexchange.com/questions/78813/noise-from-solid-state-rectifier-in-tube-amp > > > > > > Quote: "... > > > > > > Diodes can be noisy when used as rectifiers due to reverse recovery > > > > > > induced spikes. Certain types of diodes perform better (schottky and > > > > > > so-called 'soft-recovery' diodes) or are essentially immune (silicon > > > > > > carbide) to this effect. > > > > > > > > > > > > A well-designed circuit can address reverse recovery via the use of > > > > > > appropriate diodes (i.e schottkys and/or silicon carbide where > > > > > > appropriate) and by snubber networks, which absorb and dissipate the > > > > > > spike energy. > > > > > > ..." > > > > > > > > > > > > http://www.valvewizard.co.uk/bridge.html > > > > > > > > > > > > http://www.diyaudio.com/forums/solid-state/134243-what-does-01-cap-bridge-rectifiers-do.html > > > > > > Quote: "... > > > > > > They are there to shunt switching noise. If the capacitors are of the > > > > > > wrong type, they can create more noise than they attempt to remove. The > > > > > > size of the cap vs the expected 'load' is key to their effectiveness. > > > > > > ..." > > > > > > > > > > > > http://www.electro-tech-online.com/threads/capacitor-bypass-of-diodes-in-bridge-rectifiers.40733/ > > > > > > > > > > > > > HI Glenn > > > > Thanks for the links, but as I wrote that was the first thing I tried. Both purely capacitive snubbers and RC snubbers. There was no change in emissions > >
I tried with 1nF and 500ohm for a 1kW drive. Any hints to the calculation of the size, just from critical damping of the reverse recovery pulse, or should the X capacitors in front of the 6 phase rectifier be included in the calculation? Cheers Klaus
Klaus Kragelund wrote:


> First thought would be that the noise is coming from the reverse recovery > of the diodes, but the noise increases a less load (< 200W), and I would > think the reverse recovery current glitch would be worse at higher > currents running in the bridge rectifier
The conduction angle shrinks as the load is reduced, so the peak current will occur over a smaller time at lower load. I've never seen where the peak current is actually higher at light load than heavy, but there might be conditions where this could actually happen, when the conduction angle shrinks to near zero width. Jon
Klaus Kragelund wrote:


> One suspicion I have is interaction of the diode bridge with the EMC > filter, causing undamped ringing. But it's hard to measure, when we are > talking 550V DC, to catch a small signal which the differential probe > cannot resolve.
Make a pickup coil and hang it near the area, and also display current from a current probe, and sync to that. Even syncing to a voltage probe would probably be good enough. Then, correlate the pickup coil's signal to the waveform to understand what part of the rectifier's cycle is producing the output. it will almost certainly be pulsed at mains frequency. Jon