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'[slightly OT] power transistors/H-bridges'
1997\09\14@165509 by Pierce Nichols

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       Does anyone know where I can hunt up some power transistors and/or
H-bridges capable of handling approx. 150A @ 26 volts?

       Pierce Nichols

1997\09\14@231803 by Andy Kunz

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At 04:55 PM 9/14/97 -0400, you wrote:
>        Does anyone know where I can hunt up some power transistors and/or
>H-bridges capable of handling approx. 150A @ 26 volts?

Your best bet is probably 4-5 FETs ganged in parallel for each leg of the
H.  What are you driving?

Andy

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1997\09\15@004610 by tjaart

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Pierce Nichols wrote:
>
>         Does anyone know where I can hunt up some power transistors and/or
> H-bridges capable of handling approx. 150A @ 26 volts?
>
>         Pierce Nichols

Is it for that surface-to-air gun?

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1997\09\15@024553 by Thomas Magin

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At 16:55 14.09.1997 -0400, you wrote:
>        Does anyone know where I can hunt up some power transistors and/or
>H-bridges capable of handling approx. 150A @ 26 volts?
>
>        Pierce Nichols
>
Hi,

what do you think about some FETs in parallel ? Maybe 2 IRFP064N. N-Channel
MOSFET from IRF. Udss=55V, Rds(on)=0.008, Id=98A. That's one of the FETs
with the lowest Rds(on) available today ! Conduction losses would be about
45W for each FET.

So long

Thomas
=8-)

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1997\09\15@100125 by Pierce Nichols
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On Sun, 14 Sep 1997, Andy Kunz wrote:

> At 04:55 PM 9/14/97 -0400, you wrote:
> >        Does anyone know where I can hunt up some power transistors and/or
> >H-bridges capable of handling approx. 150A @ 26 volts?
>
> Your best bet is probably 4-5 FETs ganged in parallel for each leg of the
> H.  What are you driving?

       Well, it should be 36 volts, not 26. I'm driving a motor for a
solar-electric boat -- we're planning on using Don Lancaster's magic
sinewaves concept and a three-phase motor to replace the current DC motor.
It's a boat for Solar Splash, and we need to get up to 450A total current
during the sprint.

       Pierce Nichols

1997\09\15@100129 by Pierce Nichols

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On Mon, 15 Sep 1997, Tjaart van der Walt wrote:
>
> Is it for that surface-to-air gun?

       Nope -- it's for each of three phases of a motor that needs to
draw 450A (total) at 36V (not 26 -- that was a typo).

       Pierce Nichols

1997\09\15@144545 by Steve Smith

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The voltage is rather low for IGBT's so the best answer is to look at FET
bridges. Try Seimens, Semikron, IXYS, Toshiba or IR all offer a range of
large FET's / IGBT's and drivers to interface to logic. With FET's watch the
RDSon as this can be the major power loss at these voltage levels. Is it
possable to increase the DC link voltage and hence decrease the current and
losses ?

Cheers Steve.....

1997\09\15@170936 by Pierce Nichols

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On Mon, 15 Sep 1997, Steve Smith wrote:

> The voltage is rather low for IGBT's so the best answer is to look at FET
> bridges. Try Seimens, Semikron, IXYS, Toshiba or IR all offer a range of
> large FET's / IGBT's and drivers to interface to logic. With FET's watch the
> RDSon as this can be the major power loss at these voltage levels. Is it
> possable to increase the DC link voltage and hence decrease the current and
> losses ?

       Well, it's 36, not 26 volts. And no, it can't go higher because
it's for a speed controller for a Solar Splash boat, and the rules limit
us to 36V battery voltage, and 54V peak RMS. No way around it.

       Pierce Nichols

1997\09\15@185220 by Bob Blick

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Hi Pierce,

The problem gets much simpler now that you've described it completely. You
don't need a high side driver, that makes it much easier. You can either
use a gang of mosfets on the low side with a gang of freewheel diodes on
the high side, or a half bridge, but pinch off the high side so you only
use them as diodes.

Use a switch or contactor if you need reverse. You are racing, you want to
minimize conduction losses in your silicon.

Please explain why you want to make your own speed controller instead of
using something like a Curtis PMC?

If you really want to build your own, use lots of mosfets. Keep your
conduction losses to .75 volts or less.

Don't try to drive a gang of mosfets straight off of a PIC or Basic Stamp,
you need more current to overcome the capacitance and Miller effect in the
mosfets.

-Bob


On Mon, 15 Sep 1997, Pierce Nichols wrote:

{Quote hidden}

1997\09\15@194956 by Pierce Nichols

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On Mon, 15 Sep 1997, Bob Blick wrote:

> The problem gets much simpler now that you've described it completely. You
> don't need a high side driver, that makes it much easier. You can either
> use a gang of mosfets on the low side with a gang of freewheel diodes on
> the high side, or a half bridge, but pinch off the high side so you only
> use them as diodes.

       Ok, thank you. This should help.

> Please explain why you want to make your own speed controller instead of
> using something like a Curtis PMC?

       Because there is a concept, called a magic sinewave, that allows
us to get very low distortion power sinewaves (3-phase, too), but it is
new enough not be in any commercial products. We have a DAC PWM DC speed
control now. We think we can build a very good magic sinewave inverter
with these magic sinewaves and get better efficiency and lower motor
weight.

> Don't try to drive a gang of mosfets straight off of a PIC or Basic Stamp,
> you need more current to overcome the capacitance and Miller effect in the
> mosfets.

       I knew that much :).

       Pierce Nichols

1997\09\15@213540 by sdattalo

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Pierce Nichols wrote:

>         Because there is a concept, called a magic sinewave, that allows
> us to get very low distortion power sinewaves (3-phase, too), but it is
> new enough not be in any commercial products. We have a DAC PWM DC speed
> control now. We think we can build a very good magic sinewave inverter
> with these magic sinewaves and get better efficiency and lower motor
> weight.

First a question, do you need DC speed control or an amplitude
controlled sine wave? I think the former, but just in case...
Count on dedicating one PIC for the magic sinewave synthesizer.
Of all the possible bit streams for a given sequence of bits, the
number of unique amplitude controlling low order harmonic distorting
ones is limited. Your alternatives are to 1) live with limited
amplitude control 2) allow more lower order harmonics 3) Increase
the length of the bit stream 4) maybe someone else has a fourth
reason (how about get a Scenix chip then you can have magic software
running on magic hardware).


I would really like to see how much more efficient the "magic"
sine waves are compared to the less ethereally PWM generated ones.
Has anyone done the arithmetic, or perhaps less demanding, has
anyone else even thought about it (or even less demanding does any
one else give a damn)? The number of transitions over a fixed time
interval is lower for the magic sine waves. However, the intermediate
harmonics are higher. Let me quantify: with magic you can exactly cancel
all of the even, and the third, fifth, seventh, and perhaps ninth
harmonics. However, the 11th, 13th, and etc. are relatively large
(please excuse the vagueness). Now with PWM for the same frequency
sine wave there might be a residual 2nd, 3rd harmonic, etc. but the
amplitude doesn't increase until you approach the carrier frequency.

BTW, here's a fairly decent tutorial on PWM motor control:
http://www.argonet.co.uk/education/4qd/ccts/pwm.html


Scott

1997\09\15@220918 by Bob Blick

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Sinewaves. Oh. AC motors. Forget what I said, then. Three half-bridges.
High-side drivers.

Actually, don't forget what I said about conduction losses. At 36 volts, an
AC system may prove to be less efficient than a plain old DC motor and
Curtis controller. I designed the 1000-amp controller for an entrant in the
1994 SEER competition. At 1000 amps, you go to almost any lengths to reduce
conduction loss, or you burn up and die.

Cheerful regards,

Bob

At 07:41 PM 9/15/97 -0400, you wrote:
{Quote hidden}

http://www.bobblick.com/

1997\09\15@223628 by Rick Dickinson

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Scott Dattalo wrote:
>Pierce Nichols wrote:
>
>>         Because there is a concept, called a magic sinewave, that allows
>> us to get very low distortion power sinewaves (3-phase, too), but it is
>> new enough not be in any commercial products. We have a DAC PWM DC speed
>> control now. We think we can build a very good magic sinewave inverter
>> with these magic sinewaves and get better efficiency and lower motor
>> weight.

<snip>

{Quote hidden}

The nice thing about magic sinewaves is that the distortion comes in mainly at
the higher harmonics.  If you are using them to feed a motor (with it's nice
inductive windings), you are essentially pushing your power right into a very
large low-pass filter.  As such, the high-order harmonics aren't much of a
problem.

Take a look at Don Lancaster's pages at http://www.tinaja.com for a lot more
info on magic sinewaves.

- Rick "PIC'ing up the thread" Dickinson

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1997\09\15@224024 by William Chops Westfield

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Is a three phase motor inherently more efficient than a DC motor?
That would be one reason to go to magic sinewaves.

I think you're only generateing "one" sinewave at a time - the other
two phases just pick off the sequence from a different offset, right?

BillW

1997\09\16@005418 by mikesmith_oz.nosp*m

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On 15 Sep 97 at 19:41, Pierce Nichols wrote:

> > Please explain why you want to make your own speed controller instead of
> > using something like a Curtis PMC?
>
>         Because there is a concept, called a magic sinewave, that
>         allows
> us to get very low distortion power sinewaves (3-phase, too), but it
> is new enough not be in any commercial products. We have a DAC PWM
> DC speed control now. We think we can build a very good magic
> sinewave inverter with these magic sinewaves and get better
> efficiency and lower motor weight.

Was going to ask if you were going 3 phase.  You playing with
frequency a lot too?  There MUST be a reason aircraft systems run at
400Hz - one suspects weight is one of the factors, and that would
certainly help anything solar...
MikeS
<mikesmith_oz@nosp*m.relaymail.net>
(remove the you know what before replying)

1997\09\16@030934 by Mal Goris

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Scott Dattalo writes:

> First a question, do you need DC speed control or an amplitude
> controlled sine wave? I think the former, but just in case...
> Count on dedicating one PIC for the magic sinewave synthesizer.
> Of all the possible bit streams for a given sequence of bits, the
> number of unique amplitude controlling low order harmonic distorting
> ones is limited. Your alternatives are to 1) live with limited
> amplitude control 2) allow more lower order harmonics 3) Increase
> the length of the bit stream 4) maybe someone else has a fourth
> reason (how about get a Scenix chip then you can have magic software
> running on magic hardware).

I don't think that amplitude control is really the point of using
magic sinewaves. I didn't even realise that you had any amplitude
control at all. But you do have accurate phase and frequency control
which is important for speed control of AC motors. To implement magic
sinewaves there are only four drive transistor transitions per cycle,
so even if you want 500 Hz you have only 2 kHz switching. Although the
bit sequences that define the magic sinewaves are long it all comes
down to accurately timing the four transitions. That is, you don't
necessarily have to shift 1000-bit sequences to generate magic
sinewaves.

{Quote hidden}

I'm haven't bothered to check the claims of harmonic distortion and
compare with PWM. But power efficiency is going to be heaps better
with the magic sinewaves. If the PWM frequency is 10 times the
sinewave frequency then there will be 20 transitions per cycle (cf 4
transitions for magic sinewaves). The motor will filter out the higher
harmonics so having no low-order harmonics may be all you require.

Magic sinewaves require a dual polarity supply which is less
convenient when you are operating from a solar panel.

Mal Goris
--
http://www.nfra.nl/~mgoris/

1997\09\16@092942 by Pierce Nichols

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On Mon, 15 Sep 1997, Scott Dattalo wrote:

> First a question, do you need DC speed control or an amplitude
> controlled sine wave? I think the former, but just in case...

       Well, the former is what we have now. We want something better,
which is the latter.

> Count on dedicating one PIC for the magic sinewave synthesizer.
> Of all the possible bit streams for a given sequence of bits, the
> number of unique amplitude controlling low order harmonic distorting
> ones is limited. Your alternatives are to 1) live with limited
> amplitude control 2) allow more lower order harmonics 3) Increase
> the length of the bit stream 4) maybe someone else has a fourth
> reason (how about get a Scenix chip then you can have magic software
> running on magic hardware).

       I know it's limited! As for dedicating a PIC, they're cheaper than
power MOSFETs anyhow, so that's certainly not an obstacle. As for limited
amplitude control, I think 256+ amplitudes are quite enough :). We can
live with a certain level of low-order harmonics w/o having a cow -- they
don't need to be tiny fractions of a percent to still get a major
efficiency boost (a large part of that is switching from DC to
three-phase).

> I would really like to see how much more efficient the "magic"
> sine waves are compared to the less ethereally PWM generated ones.

       Last I checked, yes. This according to Don Lancaster
(http://www.tinaja.com).

{Quote hidden}

       Yes, but you still have a big huge chunk of energy in the carrier
instead of the fundamental. FFTing the magic sinewave indicates that the
harmonics are pushed way up and spread way up, as well as slashing the
total harmonic power.

> BTW, here's a fairly decent tutorial on PWM motor control:
> http://www.argonet.co.uk/education/4qd/ccts/pwm.html

       Ok, thanks.

       Pierce Nichols

1997\09\16@094453 by Pierce Nichols

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On Mon, 15 Sep 1997, Bob Blick wrote:

> Sinewaves. Oh. AC motors. Forget what I said, then. Three half-bridges.
> High-side drivers.

       Yup, I do know that much :). The way Mr. Lancaster suggested doing
it (and I agree with after futzing around with it for few hrs last night)
is having each corner of a delta winding connected to a SPDT switch btwn
power and ground.

> Actually, don't forget what I said about conduction losses. At 36 volts, an
> AC system may prove to be less efficient than a plain old DC motor and
> Curtis controller. I designed the 1000-amp controller for an entrant in the
> 1994 SEER competition. At 1000 amps, you go to almost any lengths to reduce
> conduction loss, or you burn up and die.

       That remains to be determined -- this is mostly for the endurance,
because in the sprint we just connect that wonderful Lynch motor we have
across 36V and off we go. The real efficiency bear is in the endurance,
where we're only drawing 70-80A @ 24V -- that's where the PWM loses big
time.

       Pierce Nichols

1997\09\16@094500 by Pierce Nichols

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On Mon, 15 Sep 1997, William Chops Westfield wrote:

> Is a three phase motor inherently more efficient than a DC motor?
> That would be one reason to go to magic sinewaves.

       Absolutely -- the way a DC motor works is by faking AC with the
commutator. Also, three phase motors are lighter (not a trivial concern --
the Lynch motor weighs over 30 lbs -- more than the bare hull, in fact :).
The speed control makes another 5 lbs.

>
> I think you're only generateing "one" sinewave at a time - the other
> two phases just pick off the sequence from a different offset, right?

       Bingo! And you make yr bit-length a multiple of 8, so all your
counters are at the same bit position in different bytes (makes yr code a
little less hairy).

       Pierce

1997\09\16@094744 by Pierce Nichols

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On Tue, 16 Sep 1997, Mike Smith wrote:

> Was going to ask if you were going 3 phase.  You playing with
> frequency a lot too?  There MUST be a reason aircraft systems run at
> 400Hz - one suspects weight is one of the factors, and that would
> certainly help anything solar...

       Yup, 3-phase is the idea. And I hadn't thought about messing /w
the frequency, but we may do that. It may depend heavily on what we can
scrounge up.

       Pierce

"I have a work order for the immediate demolition of your reality tunnel."

       -Bob, RAW Construction Corp.

1997\09\16@100211 by Pierce Nichols

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On Tue, 16 Sep 1997, Mal Goris wrote:

> I don't think that amplitude control is really the point of using
> magic sinewaves. I didn't even realise that you had any amplitude
> control at all. But you do have accurate phase and frequency control

       You get amplitude control by switching btwn different sequences --
you pack a few hundred into a PIC, and shove them out on command.

> which is important for speed control of AC motors. To implement magic
> sinewaves there are only four drive transistor transitions per cycle,
> so even if you want 500 Hz you have only 2 kHz switching. Although the
> bit sequences that define the magic sinewaves are long it all comes
> down to accurately timing the four transitions. That is, you don't
> necessarily have to shift 1000-bit sequences to generate magic
> sinewaves.

       Not quite -- you have more than 4 transitions, by quite a bit. You
usually have a dozen or so tranistions (which is still a small fraction of
an equivalent PWM scheme) per cycle, and your fundamental soaks up most
of the energy, followed by some very high harmonics (which don't actually
take that much). As you mentioned, phase and frequency control are trivial
with magic sinewaves.

> Magic sinewaves require a dual polarity supply which is less
> convenient when you are operating from a solar panel.

       Turns out that with a delta-wound three-phase motor, you can use
magic sinewaves with a single polarity supply (because you can still get
current to go either way in any winding by simply switching its ends).

       Pierce Nichols

1997\09\16@101220 by Herbert Graf

picon face
----------
> From: Mike Smith <mikesmith_oz.nosp*.....amKILLspamspam.....RELAYMAIL.NET>
> To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Subject: Re: [slightly OT] power transistors/H-bridges
> Date: September 16, 1997 00:46
>

> Was going to ask if you were going 3 phase.  You playing with
> frequency a lot too?  There MUST be a reason aircraft systems run at
> 400Hz - one suspects weight is one of the factors, and that would
> certainly help anything solar...

       Yes, weight is a big reason, the transformers needed for 400hz are much
lighter and smaller for the same rating 60 hz transformer. I believe this
is the biggest reason, wreaks havoc on anything audio on a plane, blocking
60hz isn't that bad, blocking 400 hz, well just takes away some of the more
common notes! TTYL

1997\09\16@104249 by mikesmith_oz.nosp*m

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On 16 Sep 97 at 9:40, Pierce Nichols wrote:

> On Tue, 16 Sep 1997, Mike Smith wrote:
>
> > Was going to ask if you were going 3 phase.  You playing with
> > frequency a lot too?  There MUST be a reason aircraft systems run at
> > 400Hz - one suspects weight is one of the factors, and that would
> > certainly help anything solar...
>
>         Yup, 3-phase is the idea. And I hadn't thought about messing
>         /w
> the frequency, but we may do that. It may depend heavily on what we
> can scrounge up.

Ex air force electric motors would be available at a lot of surplus
stores...
MikeS
<mikesmith_oz@nosp*m.relaymail.net>
(remove the you know what before replying)

1997\09\17@032942 by Mal Goris

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Pierce Nichols writes:
> On Tue, 16 Sep 1997, Mal Goris wrote:
> > which is important for speed control of AC motors. To implement magic
> > sinewaves there are only four drive transistor transitions per cycle,
> > so even if you want 500 Hz you have only 2 kHz switching. Although the
> > bit sequences that define the magic sinewaves are long it all comes
> > down to accurately timing the four transitions. That is, you don't
> > necessarily have to shift 1000-bit sequences to generate magic
> > sinewaves.
>
>         Not quite -- you have more than 4 transitions, by quite a bit. You
> usually have a dozen or so tranistions (which is still a small fraction of
> an equivalent PWM scheme) per cycle, and your fundamental soaks up most
> of the energy, followed by some very high harmonics (which don't actually
> take that much). As you mentioned, phase and frequency control are trivial
> with magic sinewaves.

Well, I take back everything I said. I completely misunderstood magic
sinewaves. Actually, I feel cheated because I thought they were
something different to PWM when in fact they are just very carefully
chosen PWM sequences.

Mal Goris
--
http://www.nfra.nl/~mgoris/

1997\09\17@160831 by Steve Smith

picon face
H-bridges Further:-
>         Well, it's 36, not 26 volts. And no, it can't go higher because
> it's for a speed controller for a Solar Splash boat, and the rules limit
> us to 36V battery voltage, and 54V peak RMS. No way around it.

Consider using a boost converter (read SMPS) to convert the battery voltage
to a sensable voltage like 360v DC simple push pull into a transformer at 50K
this should give around 85-90% effecency and then use a varable frequency
drive into a standard 3 phase motor this should minimise the losses and
decrease the drive current levels to the motor. Doing this would make the
motor drive more effecient. I may have missed the point here but is the motor
limited to 54v or is that the maximum voltage from the solar array.

Cheers Steve.....

1997\09\18@031104 by Tom Handley

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  Pierce, this may be of some help. Yesterday I received a "Power Solutions"
update from Harris Semi. They mention their IGBT products that goes up to
60A/600V. They also have a pointer to an electric-powered racer (Streamliner)
that exceeded 300mph at the Bonneville Salt Flats. Their IGBTs were part of
the design. For more info, check out:

     http://www.semi.harris.com/saltflat/

  - Tom

1997\09\18@114024 by Pierce Nichols

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On Thu, 18 Sep 1997, Tom Handley wrote:

<snip>

       Thanks -- we need lower voltage and higher current, but they make
a power MOSFET in the right range /w an on-resistance of 0.007 Ohms, and
that may be what we go for.

       Pierce Nichols

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