A different idea from A More Efficient Bridge Rectifier?
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From: Paul Keinanen on 15 Feb 2010 14:36 On Mon, 15 Feb 2010 04:21:34 -0500, "Paul E. Schoen" <paul(a)peschoen.com> wrote: > >"Paul Keinanen" <keinanen(a)sci.fi> wrote in message >news:uethn5dtjsb29fq6ua08lb9023ii6egunt(a)4ax.com... >> On Sun, 14 Feb 2010 15:53:33 -0500, Spehro Pefhany >> <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >> >>>But if, say, 300 VDC was available world-wide out of the wall, we >>>could all have notebook computers that didn't require those stupid >>>brick things. That would be good. >> >> The IEC specifies extra-low voltage (ELV) below 120 VDC and low >> voltage (LV) between 120..1500 V, thus it would make sense to use a >> voltage close to the top of either range, for a specific level of >> protection requirements. >> >> For instance +/-42 V might be an interesting ELV alternative, provided >> that the suggested 42 VDC automobile standard (3x14 V battery) is >> actually going to be common. Due to the low voltage, the voltage would >> have to be generated in the house, to avoid high losses. >> >> If three phase AC is available and a traditional transformer is used, >> it is easy to generate 6 or 9 phases and use 12 or 18 pulse >> rectifiers, with minimal need for PFC. >> >> However, if only single phase AC is available or if a high frequency >> switcher is used to generate the ELV, then a PFC is required between >> the mains rectifier and switcher. A building would need only a single >> PFC, instead of building the PFC into every load. >> >> On the other hand a +/-750 VDC distribution would fit within the LV >> directive and could carry more power than the current LV AC >> distribution for longer distances with the same conductors. >> >> Since a traditional 50/60 Hz distribution transformer would be needed >> to convert the HV/MV (say 20 kV) to the LV AC distribution, why not >> add some extra secondary windings to that transformer and generate >> extra phases and use 12 or 18 pulse rectifiers to generate the +/-750 >> VDC LV, without much need for PFC. > >Why have LV AC distribution at all? Just make a DC-DC converter operating >at high frequency. If anyone really needs 60 Hz AC, just supply an >inverter. The automotive types are less than $100/KW. There are some interesting ideas about DC distribution at http://www.lut.fi/fi/technology/lutenergy/electrical_engineering/research/electricitymarkets/research/networkbusiness/Documents/DCdistribution_Kaipia.pdf A traditional iron core 100-315 kVA 20 kV/400V distribution transformer is quite cheap, so it does not make much sense of using DC at MV distribution and using a switcher in order to generate DC LV for local distribution. It makes even less sense to use 20 kV AC distribution and then use DC LV distribution and then generate AC LV power for each customer. When most consumers are using mainly DC with DC/DC converters for normal loads and VFDs for motors, the DC distribution will really make sense. Sooner or later, it might be economically viable to use DC also in the MV distribution and replace current HVAC lines with HVDC lines, but this will take a while.
From: Paul E. Schoen on 15 Feb 2010 17:26 "Paul Keinanen" <keinanen(a)sci.fi> wrote in message news:ol7jn5d0hsvn6tm228p9o2bdoguiu315c8(a)4ax.com... > On Mon, 15 Feb 2010 04:21:34 -0500, "Paul E. Schoen" > <paul(a)peschoen.com> wrote: > >> >>"Paul Keinanen" <keinanen(a)sci.fi> wrote in message >>news:uethn5dtjsb29fq6ua08lb9023ii6egunt(a)4ax.com... >>> On Sun, 14 Feb 2010 15:53:33 -0500, Spehro Pefhany >>> <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >>> >>>>But if, say, 300 VDC was available world-wide out of the wall, we >>>>could all have notebook computers that didn't require those stupid >>>>brick things. That would be good. >>> >>> The IEC specifies extra-low voltage (ELV) below 120 VDC and low >>> voltage (LV) between 120..1500 V, thus it would make sense to use a >>> voltage close to the top of either range, for a specific level of >>> protection requirements. >>> >>> For instance +/-42 V might be an interesting ELV alternative, provided >>> that the suggested 42 VDC automobile standard (3x14 V battery) is >>> actually going to be common. Due to the low voltage, the voltage would >>> have to be generated in the house, to avoid high losses. >>> >>> If three phase AC is available and a traditional transformer is used, >>> it is easy to generate 6 or 9 phases and use 12 or 18 pulse >>> rectifiers, with minimal need for PFC. >>> >>> However, if only single phase AC is available or if a high frequency >>> switcher is used to generate the ELV, then a PFC is required between >>> the mains rectifier and switcher. A building would need only a single >>> PFC, instead of building the PFC into every load. >>> >>> On the other hand a +/-750 VDC distribution would fit within the LV >>> directive and could carry more power than the current LV AC >>> distribution for longer distances with the same conductors. >>> >>> Since a traditional 50/60 Hz distribution transformer would be needed >>> to convert the HV/MV (say 20 kV) to the LV AC distribution, why not >>> add some extra secondary windings to that transformer and generate >>> extra phases and use 12 or 18 pulse rectifiers to generate the +/-750 >>> VDC LV, without much need for PFC. >> >>Why have LV AC distribution at all? Just make a DC-DC converter operating >>at high frequency. If anyone really needs 60 Hz AC, just supply an >>inverter. The automotive types are less than $100/KW. > > There are some interesting ideas about DC distribution at > http://www.lut.fi/fi/technology/lutenergy/electrical_engineering/research/electricitymarkets/research/networkbusiness/Documents/DCdistribution_Kaipia.pdf Yes, that's a keeper. Many good points and ISTM an honest assessment of pros and cons. > A traditional iron core 100-315 kVA 20 kV/400V distribution > transformer is quite cheap, so it does not make much sense of using DC > at MV distribution and using a switcher in order to generate DC LV for > local distribution. It makes even less sense to use 20 kV AC > distribution and then use DC LV distribution and then generate AC LV > power for each customer. > > When most consumers are using mainly DC with DC/DC converters for > normal loads and VFDs for motors, the DC distribution will really make > sense. Sooner or later, it might be economically viable to use DC also > in the MV distribution and replace current HVAC lines with HVDC lines, > but this will take a while. Exactly. But it can be done gradually and "phased-in" as it were. It just needs to be formulated into a realistic proposal and then acted upon. There will be many engineering challenges, but that will be the "fun" part that also will inspire innovation and spur the economy, at least the personal economic welfare of electronic and electrical engineers. Paul
From: Tim Williams on 16 Feb 2010 23:18 "JosephKK" <quiettechblue(a)yahoo.com> wrote in message news:5gnmn5lbbc5b3l9bct9i8tdola0uq6t0hr(a)4ax.com... > Nor do i know much about how solid state systems are made for 12 kV and > up. Do they even? Seems to me there's kind of a hole in the middle... VFDs are easy enough to build (easy being a relative term) from watts up to ~1MW. I know they make SCRs rated for 2kV or so, and even more amps, so you can get a few solid megawatts from just a few of the things. For HVDC, they make monster cascodes of them, able to switch ~1MV and some kA's with moderate efficiency (the voltage drop is large over an entire stack, so effiency tops out in the 90-95% range IIRC -- an awful lot of heat when you're switching gigawatts, but still not terrible overall). I have no idea if anyone makes anything inbetween. Megawatt motors are often supplied by AC in the 10s of kV range, but I don't know if anyone makes a VFD-like supply using the same voltage internally (without passing it through a transformer to make ~1kV instead). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 16 Feb 2010 11:56 "MooseFET" <kensmith(a)rahul.net> wrote in message news:5c88921f-ad4c-411d-a63a-41a49a6d78df(a)g8g2000pri.googlegroups.com... > Can you say "Litz wire the size of may arm" No big deal -- they already use aluminum strap for the 240V windings in pole pigs. The big hunk of ferrite would be smaller than the bigger hunk of iron, and volts/turn higher so copper losses can be lower for a given current density. The current ripple can be small because regulation on the input side is already fairly good, so you don't need much powdered iron to filter it, either. You can use big heavy metal boxes to seal in most of the EMI, and extra filtering (you *will* need more powdered iron for this part) to keep it off the wires. Switching might be one of the bigger problems... switching HVDC is notoriously troublesome. Electronic switches just wouldn't be good enough for fault clearing and line switching. You still need mechanical beasties, and existing AC designs won't handle it (= still more infrastructure expense). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: MooseFET on 16 Feb 2010 09:59
On Feb 15, 11:36 am, Paul Keinanen <keina...(a)sci.fi> wrote: > On Mon, 15 Feb 2010 04:21:34 -0500, "Paul E. Schoen" > > > > <p...(a)peschoen.com> wrote: > > >"Paul Keinanen" <keina...(a)sci.fi> wrote in message > >news:uethn5dtjsb29fq6ua08lb9023ii6egunt(a)4ax.com... > >> On Sun, 14 Feb 2010 15:53:33 -0500, Spehro Pefhany > >> <speffS...(a)interlogDOTyou.knowwhat> wrote: > > >>>But if, say, 300 VDC was available world-wide out of the wall, we > >>>could all have notebook computers that didn't require those stupid > >>>brick things. That would be good. > > >> The IEC specifies extra-low voltage (ELV) below 120 VDC and low > >> voltage (LV) between 120..1500 V, thus it would make sense to use a > >> voltage close to the top of either range, for a specific level of > >> protection requirements. > > >> For instance +/-42 V might be an interesting ELV alternative, provided > >> that the suggested 42 VDC automobile standard (3x14 V battery) is > >> actually going to be common. Due to the low voltage, the voltage would > >> have to be generated in the house, to avoid high losses. > > >> If three phase AC is available and a traditional transformer is used, > >> it is easy to generate 6 or 9 phases and use 12 or 18 pulse > >> rectifiers, with minimal need for PFC. > > >> However, if only single phase AC is available or if a high frequency > >> switcher is used to generate the ELV, then a PFC is required between > >> the mains rectifier and switcher. A building would need only a single > >> PFC, instead of building the PFC into every load. > > >> On the other hand a +/-750 VDC distribution would fit within the LV > >> directive and could carry more power than the current LV AC > >> distribution for longer distances with the same conductors. > > >> Since a traditional 50/60 Hz distribution transformer would be needed > >> to convert the HV/MV (say 20 kV) to the LV AC distribution, why not > >> add some extra secondary windings to that transformer and generate > >> extra phases and use 12 or 18 pulse rectifiers to generate the +/-750 > >> VDC LV, without much need for PFC. > > >Why have LV AC distribution at all? Just make a DC-DC converter operating > >at high frequency. If anyone really needs 60 Hz AC, just supply an > >inverter. The automotive types are less than $100/KW. > > There are some interesting ideas about DC distribution athttp://www.lut.fi/fi/technology/lutenergy/electrical_engineering/rese... > > A traditional iron core 100-315 kVA 20 kV/400V distribution > transformer is quite cheap Big transformers are also very efficient. Getting equal efficiency with something electronic is not very easy. The switcher still most likely has to have inductive elements so it takes some clever design to get there. Can you say "Litz wire the size of may arm" > When most consumers are using mainly DC with DC/DC converters for > normal loads and VFDs for motors, the DC distribution will really make > sense. Sooner or later, it might be economically viable to use DC also > in the MV distribution and replace current HVAC lines with HVDC lines, > but this will take a while. It may happen that industrial loads go DC first. There is more money per installed system to work with. Most buildings use electronic ballasts in the lighting already. It would make sense to do the lighting load as its own system since they mostly already have there own wiring runs. The lighting load could have a DC-DC converter per run. Each would handle a few KW. They would be logically connected so that they start up in turn to reduce the rate that the current rises during turn on. |