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Are DC-DC convertors applicable for high-power industrial applications? Can a mega pack battery output be converted 10kVDC without an AC step ?

tonmoy 3y ago
As far as I have heard modern power electronics is sophisticated enough to do that
cellularmitosis 3y ago
Yes, though at that voltage range you’ll need to stray into somewhat esoteric parts, like silicon carbide mosfets / igbt’s https://www.power-mag.com/pdf/feature_pdf/1461163294_Woifspeed_Feature.pdf https://www.power-mag.com/pdf/feature_pdf/1461163294_Woifspe...
- nunuvit 3y ago
  Haha SiC and IGBTs are hardly esoteric. If anything, GaN is esoteric. You just wouldn't know it because industrial doesn't get the same press as computer power supplies.
  - cellularmitosis 3y ago
    Thanks! Just a hobbyist, glad to hear industry perspective on this!
    - nunuvit 3y ago
      Cool. Be safe, don't play with SiC or IGBTs, the high voltage will kill you. GaN will be more mainstream in a few years, Infineon just bought GaN Systems.
- algo_trader 3y ago
  x10 for this link!
jacquesm 3y ago
Check out the hardware involved in HVDC transmission lines to get an idea of what 'high power DC' looks like.
VLM 3y ago
"can" yes. Industrially, no. You're asking for an automotive ignition without a coil, pretty much not done. Various logic chopping options exist to be technically correct. If you define a pulse as not being "AC" because its not a constant waveform or its not wall outlet 50 hz or 60 hz, then sorta kinda thats an engine ignition coil. If you define a tesla coil as not being AC because its a resonant ckt with a quarter wave antenna colocated, then sorta kinda sure no AC.
kwantam 3y ago
Yes, dc/dc conversion is definitely applicable in high-power applications. As one example, high-voltage DC power transmission [1] is in widespread use globally, and always requires a dc/dc conversion step for connection to local grids. In addition to dc/dc conversion during transmission, converting from DC to AC (known as inversion) uses essentially the same techniques. To answer your question more directly: stepping a battery's output to 10 kV is a good example of an application that would almost always be done with a dc/dc converter in an industrial application. (Aside: "without an AC step" is slightly tricky. If by AC you mean 50 or 60 Hz, definitely can and should be avoided. But AC is generally used to refer to any non-constant voltage or current, and if that's what you mean then the answer is no since a dc/dc converter works by switching, which by definition means there's some sinusoidal voltage somewhere in the circuit.) (Source: I used to design integrated circuits for industrial control.) [1] https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current
- algo_trader 3y ago
  > almost always be done with a dc/dc converter in an industrial application. thanks. lots of good details in this thread. > if by AC you mean 50 or 60 Hz, definitely can and should be avoided. Yes, i meant avoiding the maintenance and losses of an actual transformer
ejiblabahaba 3y ago
This is absolutely something you could do, in the sense that no one in electrical engineering will raise an eyebrow if you call your DC-DC conversion with an "AC" step in the middle a DC-DC converter. There's fundamentally going to be alternating currents in any DC-DC design, but typically at the inputs and outputs it looks like an average DC current with a small amount of AC ripple. The kind of DC-DC converters that work well for megabattery to 10kVDC conversion will look very different from the kind of DC-DC converters that step up your 3.3V rail to 5V for some low-power peripheral, and may actually have individual components that completely reverse current direction for more efficient current transfer. You pretty much need a transformer to handle the high power transfer and voltage ratio mismatch. Depending on the pack voltage you might use multiple stages cascaded, but typical 400V-800V packs can step up to 10kV in a reasonable number of turns (12-25). The battery pack side probably has IGBTs or SiC FETs driving some kind of large bridge switcher (or several parallel bridges); the 10kV side probably has some big chonker diodes in a rectifier bridge, though they conceptually could be replaced with synchronous switches if you could find thyristors with fast enough switching speed and better efficiency (usually it's not worth it). Technically this topology runs the transformer primary current in both directions (hence the rectifier at the output) so I guess this is the "AC" stage in the middle... But it's worth pointing out that the AC portion is incidental to operation, unlike something like a Tesla power wall using an AC inverter to feed power into the AC grid, and a grid-connected charger converting that back to DC.

tonmoy 3y ago

As far as I have heard modern power electronics is sophisticated enough to do that

cellularmitosis 3y ago

Yes, though at that voltage range you’ll need to stray into somewhat esoteric parts, like silicon carbide mosfets / igbt’s https://www.power-mag.com/pdf/feature_pdf/1461163294_Woifspeed_Feature.pdf https://www.power-mag.com/pdf/feature_pdf/1461163294_Woifspe...

nunuvit 3y ago
Haha SiC and IGBTs are hardly esoteric. If anything, GaN is esoteric. You just wouldn't know it because industrial doesn't get the same press as computer power supplies.
- cellularmitosis 3y ago
  Thanks! Just a hobbyist, glad to hear industry perspective on this!
  - nunuvit 3y ago
    Cool. Be safe, don't play with SiC or IGBTs, the high voltage will kill you. GaN will be more mainstream in a few years, Infineon just bought GaN Systems.
algo_trader 3y ago
x10 for this link!

jacquesm 3y ago

Check out the hardware involved in HVDC transmission lines to get an idea of what 'high power DC' looks like.

VLM 3y ago

"can" yes. Industrially, no. You're asking for an automotive ignition without a coil, pretty much not done. Various logic chopping options exist to be technically correct. If you define a pulse as not being "AC" because its not a constant waveform or its not wall outlet 50 hz or 60 hz, then sorta kinda thats an engine ignition coil. If you define a tesla coil as not being AC because its a resonant ckt with a quarter wave antenna colocated, then sorta kinda sure no AC.

kwantam 3y ago

Yes, dc/dc conversion is definitely applicable in high-power applications. As one example, high-voltage DC power transmission [1] is in widespread use globally, and always requires a dc/dc conversion step for connection to local grids. In addition to dc/dc conversion during transmission, converting from DC to AC (known as inversion) uses essentially the same techniques. To answer your question more directly: stepping a battery's output to 10 kV is a good example of an application that would almost always be done with a dc/dc converter in an industrial application. (Aside: "without an AC step" is slightly tricky. If by AC you mean 50 or 60 Hz, definitely can and should be avoided. But AC is generally used to refer to any non-constant voltage or current, and if that's what you mean then the answer is no since a dc/dc converter works by switching, which by definition means there's some sinusoidal voltage somewhere in the circuit.) (Source: I used to design integrated circuits for industrial control.) [1] https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current

algo_trader 3y ago
> almost always be done with a dc/dc converter in an industrial application. thanks. lots of good details in this thread. > if by AC you mean 50 or 60 Hz, definitely can and should be avoided. Yes, i meant avoiding the maintenance and losses of an actual transformer

ejiblabahaba 3y ago

This is absolutely something you could do, in the sense that no one in electrical engineering will raise an eyebrow if you call your DC-DC conversion with an "AC" step in the middle a DC-DC converter. There's fundamentally going to be alternating currents in any DC-DC design, but typically at the inputs and outputs it looks like an average DC current with a small amount of AC ripple. The kind of DC-DC converters that work well for megabattery to 10kVDC conversion will look very different from the kind of DC-DC converters that step up your 3.3V rail to 5V for some low-power peripheral, and may actually have individual components that completely reverse current direction for more efficient current transfer. You pretty much need a transformer to handle the high power transfer and voltage ratio mismatch. Depending on the pack voltage you might use multiple stages cascaded, but typical 400V-800V packs can step up to 10kV in a reasonable number of turns (12-25). The battery pack side probably has IGBTs or SiC FETs driving some kind of large bridge switcher (or several parallel bridges); the 10kV side probably has some big chonker diodes in a rectifier bridge, though they conceptually could be replaced with synchronous switches if you could find thyristors with fast enough switching speed and better efficiency (usually it's not worth it). Technically this topology runs the transformer primary current in both directions (hence the rectifier at the output) so I guess this is the "AC" stage in the middle... But it's worth pointing out that the AC portion is incidental to operation, unlike something like a Tesla power wall using an AC inverter to feed power into the AC grid, and a grid-connected charger converting that back to DC.