CCM boost inductor design

[John Larkin]

On 2 Aug 2019 08:05:04 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Klaus Kragelund wrote...

PFC stage efficiency around 99% is standard:

https://www.infineon.com/dgdl/Infineon-Introduction_to_CoolSiC_Schottky_Diodes_650V_G6-AN-v01_00-EN.pdf?fileId=5546d4625e763904015eb8faeffd5373

Maybe you should rather say it's a standard
goal for a manufacturer showing off exceptional
performance, such as the one in the link.

But I wonder what real-world "standard" values
are for power supplies we generally encounter,
for example in a 500-watt PC power supply. This
brings up the issue that it's not easy to make
accurate measurements of AC-in DC-out losses,
especially down at the 1% level. DC-in DC-out,
yes, but PFC boost converters, no, SFAICT. The
Institute's electronics-engineering lab is well
equipped, but I currently cannot be sure of any
high crest-factor AC-power measurements, to
better than 1% to 2%.

A PFC-corrected supply should ideally look mainly resistive on the AC
side. If it has a high crest factor, send it back.

For that matter, can we trust Infineon's data,
229.6 volts AC, 4.431 amps AC = 1014.9 watts,
e.g., to the 0.01% level, for a 98.198% result
(PFC boost converter design guide, page 20),
without any indication of how it was measured?
The very fact they give the result to 0.001% is
an indication of careless error-bar evaluation.

OK, one note mentions Yokogawa's WT330 meter,
spec: 0.1% of reading + 0.1% of range (300V),
which is 229 +/- 0.529 volts = 0.23% accuracy.
Hmm, it'd be nice to have one of those, but
we're still talking 0.25% not 0.1% certainty.
That's a 25% error at the 1% loss level.

One could measure how much heat the boost converter generates. That
might be a better way to measure small losses, rather than computing
the difference between two big numbers measured with different
instruments.

Or apply DC to the PFC converter input, at a few different voltages,
and extrapolate the behavior for AC input. DC is a lot easier to
measure than AC.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Winfield Hill]

John Larkin wrote...

One could measure how much heat the boost converter
generates. That might be a better way to measure
small losses, rather than computing the difference
between two big numbers measured with different
instruments.

Yes, a good idea, but requiring an unusual piece of
insulation equipment, with tough calibration issues.
Probably the only way, for less than 1% or 0.5% loss.

Or apply DC to the PFC converter input, at a few
different voltages, and extrapolate the behavior
for AC input. DC is a lot easier to measure than AC.

Yes, I thought of that, and it'd probably have to
be my workaround, but leaving one uncertain of the
efficacy of the results. But it's the ideal way to
measure 380V dc converters. After thinking about it,
and considering the basic instrumentation weakness,
I decided to purchase a new-in-box WT310E on eBay.
It's actually a rather impressive instrument. This
was a personal, rather than Institute, purchase.
Now that I'm finishing THE BOOK, time for some fun.


--
Thanks,
- Win

 

[John Larkin]

On 2 Aug 2019 10:11:04 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

John Larkin wrote...

One could measure how much heat the boost converter
generates. That might be a better way to measure
small losses, rather than computing the difference
between two big numbers measured with different
instruments.

Yes, a good idea, but requiring an unusual piece of
insulation equipment, with tough calibration issues.
Probably the only way, for less than 1% or 0.5% loss.

One could put the circuit in a die-cast aluminum box, along with a
power resistor. Thermocouples to the box and ambient. It wouldn't be
hard to measure the box theta using the resistor, then figure out how
much power the booster is dissipating.

Tedious, but probably pretty accurate.

This is actually pretty good:

https://www.amazon.com/gp/product/B018QHQSB8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Winfield Hill]

Klaus Kragelund wrote...

Klaus Kragelund wrote...

PFC stage efficiency around 99% is standard:

It was just an example, which corresponds nicely
to the numbers we have for our PFC converters

How are you going to measure your 99% performance?


--
Thanks,
- Win

 

[Klaus Kragelund]

On Friday, August 2, 2019 at 5:05:21 PM UTC+2, Winfield Hill wrote:

Klaus Kragelund wrote...

PFC stage efficiency around 99% is standard:

https://www.infineon.com/dgdl/Infineon-Introduction_to_CoolSiC_Schottky_Diodes_650V_G6-AN-v01_00-EN.pdf?fileId=5546d4625e763904015eb8faeffd5373

Maybe you should rather say it's a standard
goal for a manufacturer showing off exceptional
performance, such as the one in the link.

But I wonder what real-world "standard" values
are for power supplies we generally encounter,
for example in a 500-watt PC power supply. This
brings up the issue that it's not easy to make
accurate measurements of AC-in DC-out losses,
especially down at the 1% level. DC-in DC-out,
yes, but PFC boost converters, no, SFAICT. The
Institute's electronics-engineering lab is well
equipped, but I currently cannot be sure of any
high crest-factor AC-power measurements, to
better than 1% to 2%.

It was just an example, which corresponds nicely to the numbers we have for our PFC converters

I cannot share more details which would be a breach of my NDA

Cheers

Klaus

 

[Klaus Kragelund]

For 99%, that is difficult

We normally have a very accurate simulation model for the entire converter

We then do individual check on key components to check the model

On the measurement side, we have a special instrument bought at very high cost just for that measurement (I can check the model number next week)

Often the difficult parts are after the rectifier which can be fed with DC to do an extra check (DC measurement is a lot easier)

We also do thermal measurement of each component verified afterwards with a complete dummy load dissipation test where we match all temperature measure ring points

Cheers

Klaus

 

[piglet]

On 29/07/2019 11:50 pm, Klaus Kragelund wrote:

PFC stage efficiency around 99% is standard:

https://www.infineon.com/dgdl/Infineon-Introduction_to_CoolSiC_Schottky_Diodes_650V_G6-AN-v01_00-EN.pdf?fileId=5546d4625e763904015eb8faeffd5373

Sorry for the brief post, busy days

Cheers

Klaus

99%? Doesn't the input bridge rectifier diode loss contribute a percent
or two even before you add in the boost convertor loss?

piglet

 

[Piotr Wyderski]

piglet wrote:

99%? Doesn't the input bridge rectifier diode loss contribute a percent
or two even before you add in the boost convertor loss?

Exactly. The best PFC efficiency I know of is 99.3% according to the
author (claimed to be obtained using a calorimetric meaurement). Totally
bridgeless, with some insanely low switching frequencies, just barely
above the audio range.

You just can't get 99% with the old-school boost approach.

Best regards, Piotr

 

[Winfield Hill]

Piotr Wyderski wrote...

piglet wrote:

99%? Doesn't the input bridge rectifier diode loss contribute
a percent or two even before you add in the boost convertor loss?

Exactly. The best PFC efficiency I know of is 99.3% according to
the author (claimed to be obtained using a calorimetric meaurement).
Totally bridgeless, with some insanely low switching frequencies,
just barely above the audio range.

You just can't get 99% with the old-school boost approach.

Nobody does active rectification? Common at lower voltages.
I think the HV transmission-line guys can get well over 99%.


--
Thanks,
- Win

 

[Steve Wilson]

Winfield Hill <winfieldhill@yahoo.com> wrote:

Nobody does active rectification? Common at lower voltages.
I think the HV transmission-line guys can get well over 99%.

I heard 5% is lost in transmission. That's why some long distance HV
transmissions use DC. But that's not a reason to ignore conversion losses.

If you are shipping 5GW, then 1% is 5e9*0.01 = 50,000,000W. A very good
reason to reduce losses. Where are you going to put the heat?

 

[Klaus Kragelund]

On Sunday, August 4, 2019 at 7:58:13 AM UTC+2, Steve Wilson wrote:

Winfield Hill <winfieldhill@yahoo.com> wrote:

Nobody does active rectification? Common at lower voltages.
I think the HV transmission-line guys can get well over 99%.

I heard 5% is lost in transmission. That's why some long distance HV
transmissions use DC. But that's not a reason to ignore conversion losses.

If you are shipping 5GW, then 1% is 5e9*0.01 = 50,000,000W. A very good
reason to reduce losses. Where are you going to put the heat?

Like Winfield wrote, they operate with higher than 99% efficiency for the converter

Quite impressive

Cheers

Klaus

 

[Klaus Kragelund]

On Saturday, August 3, 2019 at 11:41:30 PM UTC+2, Piotr Wyderski wrote:

piglet wrote:

99%? Doesn't the input bridge rectifier diode loss contribute a percent
or two even before you add in the boost convertor loss?

Exactly. The best PFC efficiency I know of is 99.3% according to the
author (claimed to be obtained using a calorimetric meaurement). Totally
bridgeless, with some insanely low switching frequencies, just barely
above the audio range.

You just can't get 99% with the old-school boost approach.

Correct , that is why I explicit wrote “PFC stage”, also that comparison since the OP was talking about coil losses

Cheers

Klaus

 

[Piotr Wyderski]

Winfield Hill wrote:

> Nobody does active rectification?

It doesn't pay off to stop halfway. In order to have losses low enough
to justify the added complexity you need a sufficiently low R_DS_ON high
voltage MOSFET. That means an expensive superjunction unit or,
preferably, a SiC/GaN device. The SiC ones are particularly price
competitive. But then, having a classic full-bridge arrangement
of the MOSFETs and the sensing circuitry you discover that you can
shave off the downstream boost stage entirely if you just wiggle the
gates in a bit smarter way than a classic SR would do. This is the
totem-pole bridgeless boost configuration. One example (fig. 5 and
everything that follows):

https://www.nxp.com/docs/en/reference-manual/DRM174.pdf

> Common at lower voltages.

Indeed, would be required at the low side of the converter anyway.

Best regards, Piotr

 

[Klaus Kragelund]

Synchronous rectification would be great for the bridge rectifier

We have been toying with that a long time, problem is complexity, price and protection

Protection is difficult since you are right at the ac terminals with no dampening components except for the cm coil, most active components spontaneously turn on when subjected to high dV/dt

Cheers

Klaus

 

[Jan Panteltje]

On a sunny day (Sun, 4 Aug 2019 09:42:38 +0200) it happened Piotr Wyderski
<peter.pan@neverland.mil> wrote in <qi629e$1tsr$1@gioia.aioe.org>:

Winfield Hill wrote:

Nobody does active rectification?

It doesn't pay off to stop halfway. In order to have losses low enough
to justify the added complexity you need a sufficiently low R_DS_ON high
voltage MOSFET. That means an expensive superjunction unit or,
preferably, a SiC/GaN device. The SiC ones are particularly price
competitive. But then, having a classic full-bridge arrangement
of the MOSFETs and the sensing circuitry you discover that you can
shave off the downstream boost stage entirely if you just wiggle the
gates in a bit smarter way than a classic SR would do. This is the
totem-pole bridgeless boost configuration. One example (fig. 5 and
everything that follows):

https://www.nxp.com/docs/en/reference-manual/DRM174.pdf

Common at lower voltages.

Indeed, would be required at the low side of the converter anyway.

Best regards, Piotr

Very nice solution!

 

[Steve Wilson]

Klaus Kragelund <klauskvik@hotmail.com> wrote:

On Sunday, August 4, 2019 at 7:58:13 AM UTC+2, Steve Wilson wrote:
Winfield Hill <winfieldhill@yahoo.com> wrote:

Nobody does active rectification? Common at lower voltages.
I think the HV transmission-line guys can get well over 99%.

I heard 5% is lost in transmission. That's why some long distance HV
transmissions use DC. But that's not a reason to ignore conversion
losses.

If you are shipping 5GW, then 1% is 5e9*0.01 = 50,000,000W. A very good
reason to reduce losses. Where are you going to put the heat?

Like Winfield wrote, they operate with higher than 99% efficiency for
the converter

Yes, I realize that. I was just using 1% for illustration. So for 99.9%
efficiency, the losses are 5e9*0.001 = 5,000,000W, which is still a large
amount of heat to get rid of.

The obvious question is how do they do it?

And can they get higher efficiency?

Quite impressive

Cheers

Klaus

 

[amdx]

On 7/28/2019 9:00 AM, Piotr Wyderski wrote:

Hi,

I would like to make a low-loss boost PFC converter for the following
parameters: 150kHz switching frequency, 180-250VAC input, 600V output
at 500W. It should operate in CCM with 20% deltaIL, so the inductor
will be pretty large: 1.2mH at 4.6A_peak. Basically, I am considering
two options of winding it: a gapped low-loss ferrite core (3C95 or
similar material) or an alloy powder E core EMS-0432115-060. The latter
is currently my preferred choice due to its great wide-swing saturation
characteristics (~1.8uH@0A and still a nice value of 600uH at a 10A
surge). Unfortunately, it will require 108 turns, so for a bobbin
27mm wide and relatively thin 1mm diameter wire means 4 layers of
windings. I am afraid this can introduce some nasty resonances and
make the AC resistance worse due to the proximity effect.

OTOH, this is a 20% CCM inductor, so the AC component is only about
800mA in the worst case. So, should I consider winding it with litz
wire (7x0.4mm is probably the thickest braid I can fit there)

I'm questioning the litzwire size, when I check the charts the
recommended wire for 150kHz is #40 wire, 0.0031 inches or 0.07874 mm.
It think you are saying 0.4 mm which is wasting copper.
If your limit to get the turns needed is 1.2mm, then a litz wire using
the recommended #40 wire with 108 strands is 1.14 mm in diameter.
See chart here,
> https://www.dropbox.com/s/rxhi7fctns4wf39/litz%20chart%20150kHz.jpg?dl=0

Full page gauge/frequency chart.

http://litzwire.com/nepdfs/Round_Litz_Catalog.pdf

Mikek

or

ignore the AC component entirely and go to the lowest DCR achievable,
i.e. a 1.2mm solid wire?

I don't think I can obtain a square 1x1mm magnet wire, the
closest purchasable size is 2x1mm, which for sure will not fit.

The alternative is a planar E58 core wound with 4 layers of 2.5mmx1mm
rectangular wire (54 turns in total). But the inductor would be about
2x the size of the powder core one and have a dangerously sharp
saturation curve.

The boost will be based on a SiC device, but I don't want to go into
the MHz switching range in order to have a physically smaller inductor
-- the parameter I optimize is raw efficiency, not power density.
So I see no point in transforming winding losses into switching and core
losses. Any thoughts, please?

    Best regards, Piotr

 

[Phil Hobbs]

On 8/4/19 1:58 AM, Steve Wilson wrote:

Winfield Hill <winfieldhill@yahoo.com> wrote:

Nobody does active rectification? Common at lower voltages.
I think the HV transmission-line guys can get well over 99%.

I heard 5% is lost in transmission. That's why some long distance HV
transmissions use DC. But that's not a reason to ignore conversion losses.

If you are shipping 5GW, then 1% is 5e9*0.01 = 50,000,000W. A very good
reason to reduce losses. Where are you going to put the heat?

DC transmission is actually mostly to reduce corona losses, which depend
on the peak voltage. You can put twice the power through a given line.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Steve Wilson]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/4/19 1:58 AM, Steve Wilson wrote:
Winfield Hill <winfieldhill@yahoo.com> wrote:

Nobody does active rectification? Common at lower voltages.
I think the HV transmission-line guys can get well over 99%.

I heard 5% is lost in transmission. That's why some long distance HV
transmissions use DC. But that's not a reason to ignore conversion
losses.

If you are shipping 5GW, then 1% is 5e9*0.01 = 50,000,000W. A very good
reason to reduce losses. Where are you going to put the heat?

DC transmission is actually mostly to reduce corona losses, which depend
on the peak voltage. You can put twice the power through a given line.

Cheers

Phil Hobbs

Hydro Quebec uses AC to ship power at 735 KV, and DC to ship at 450 KV. So
there are other reasons beside corona to decide on DC.

The AC losses range from 4.5 to 8%, varying due to temperature and
operating situations. I don't know if temperature affects corona.

https://en.wikipedia.org/wiki/Hydro-Qu%C3%A9bec%
27s_electricity_transmission_system

For DC, you still have to convert it at the transmitting and receiving
ends. With twice the power, it is crucial to reduce the conversion losses.

 

[Steve Wilson]

Steve Wilson <no@spam.com> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

DC transmission is actually mostly to reduce corona losses, which
depend on the peak voltage. You can put twice the power through a
given line.

Cheers

Phil Hobbs

Hydro Quebec uses AC to ship power at 735 KV, and DC to ship at 450 KV.
So there are other reasons beside corona to decide on DC.

Another reason for DC is to connect grids that operate at different
frequencies or phases.

https://en.wikipedia.org/wiki/Quebec_%E2%80%93_New_England_Transmission