Post by thread:[slightly OT] power transistors/H-bridges

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 ================================================================== Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865 Hardware & Software for Industry & R/C Hobbies "Go fast, turn right, and keep the wet side down!" ==================================================================

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? -- Friendly Regards Tjaart van der Walt spam_OUTtjaartTakeThisOuTwasp.co.za ________________________________________________________ | WASP International http://wasp.co.za | | R&D Engineer : GSM peripheral services development | |Vehicle tracking | Telemetry systems | GSM data transfer| |Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973 | | WGS-84 : 26010.52'S 28006.19'E | |________________________________________________________|

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-) ********************************************************** * Thomas Magin FON: ++49-761-4543-489 * * marquette-Hellige GmbH FAX: -507 * * Emergency Systems email: .....maginKILLspam@spam@hellige.de * * Munzinger Str. 3 * * D-79111 Freiburg / Germany * **********************************************************

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

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

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}> 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 >

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

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

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}> >> 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. http://www.bobblick.com/

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}>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. 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 +---------------------------------+---------------------------+ | Enterprise ArchiTechs Company | | | Lotus Certified Notes | Never underestimate the | | Appl. Design & Administration | bandwidth of a station- | |(818)563-1061 rtdKILLspamnotesguy.com | wagon full of tape reels. | | http://www.eArchiTechs.com | | +---------------------------------+---------------------------+

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)

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 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. 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/

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}> 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. > 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

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

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

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

---------- > From: Mike Smith <mikesmith_oz.nosp*.....amKILLspam.....RELAYMAIL.NET> > To: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.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

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)

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/

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.....