Power Electronics Future

IGBTs and switching transistors, EV motor controllers handling megawatts, DC-DC converter economics vs transformers, semiconductor fault current limitations

While the rise of high-power IGBTs and switchmode conversion offers a path toward smaller, more efficient DC grids that bypass the massive copper and steel requirements of traditional transformers, significant technical hurdles persist. Proponents suggest that transitioning to DC could maximize existing line capacity and leverage modern semiconductor breakthroughs, yet critics warn that silicon components currently lack the robust fault-current resilience of oil-bathed transformers. This shift remains contentious because, despite the potential for miniaturization and automation, grid-scale power electronics still face much higher costs, lower reliability, and the extreme difficulty of breaking high-voltage DC arcs. Ultimately, any potential transition must balance the elegance of modern solid-state control against the proven, century-old durability of the current AC infrastructure.

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The early limit was because high voltage DC required producing it at the generator, whereas you could produce high voltage AC by generating at a lower voltage and then stepping it up with a transformer for long distance transmission.

The rules are changing because of switchmode voltage conversion, using transistors to switch the voltage at a high frequency, where the magnetics (transformers, inductors) can be much smaller and more efficient, then converting back to DC. This is how virtually all smaller power supplies have been made for years, the only question (which I don't know) being how far along we are at reaching the voltage levels of long distance transmission in this way.

I'd think that hustling us towards DC with electronic voltage conversion would be a reasonable strategic goal for dealing with the transformer problem, worthy of support by a government.

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Virtually all HVDC transmission currently operating is point to point mostly for control reasons. My understanding is it's very difficult to coordinate multiple converter stations - power flow in DC networks is fully determined by the control systems of the converters unlike AC networks which in general lack active control devices (see the FACTS family of devices for examples that can be used in AC networks to actively control power flow).

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That link talks about 5MW 35kv AC / 800v DC converters.. completely different thing, they try to sell a single-source PV invertor-to-35KV AC solution first, then 35KV to 800V DC second, to have a sorta complete solution of PV-to-datacenter. And it's only 5MW. And only 35KV AC. For moving 100MW even over a few km you would need 110KV at least. I think. An overhead wire can handle about 600A of current, that's the physical limit and the reason for kilovolts there.

Consider also that there is nothing existing in transmission and switching gear certified for HVDC it being rare one-off projects so far, while AC is ubiquitious, more-or-less mass-produced and many people are trained in its maintenance.

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I mean if you wanna leapfrog china just throw more money into switched mode inverters and rectifiers. You don't have to use transformers. As long as you have a black cheque, there are plenty of options.

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I've been wondering for awhile about the economics of the AC vs DC grid thing. Historically, AC made a lot more sense because transformers are simple and relatively straightforward to make. But now we have amazing capabilities to handle enormous amounts of power with modern IGBTs and similar power-switching transistors. (A modern high-end EV motor controller, for instance, might be able to handle a megawatt of power. Not continuously, but still.) Is a DC-DC converter now more economically viable than an equivalent transformer? The former is more techincally complicated, but the latter is bulky and requires large quantities of expensive input materials like copper.

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A big problem with solid state electronics is fault current handling. The grid would become extremely brittle if it was purely a DC conversion setup. Semiconductors don't do too well outside their happy zone. All it takes is some wind and tree to fire up a very large arc welder. If you can't momentarily handle 10x+ the rated system capacity, you are gonna have a really bad time. Ordinary transformers in oil bath can take a hammering for many cycles. A semiconductor wouldn't make it through one.

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Still roughly 2x the cost and about 10x lower MTBF.

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That seems like it's within striking distance of competitive, no? You get some major advantages in size and production automation. Perhaps it's ok for it to die sooner if you can get it built now and then replace it later.

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Or, alternatively, you switch to DC to get more current capacity over existing wires. (At a given voltage, a wire can generally carry more DC current because it doesn't have the same "skin effect" that AC has.) Even if the hardware at the substation is more expensive, it might be cheaper than upgrading the transmission lines.

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well aside from being effectively 20 times more expensive over entire operation...

DC switches (as in, just a power switch) are vastly more expensive because while in AC you have 100 breaks in current a second, DC is constant so it is far harder to break. So even if you had device that could use both (not hard with SMPS, they have rectification as first step), it's still essentially " replace everything".

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The protections side is a big problem - most HVDC has circuit breakers operating on the HVAC sides of the link so going to full DC transmission presumably wouldn't eliminate that equipment.

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"Transformers are necessary to make the AC system work."

This isn't quite wrong but the motivation is backwards: AC is necessary to make transformers work.

1. All grids need to move energy at high voltage and low current to minimize losses.

2. This requires a mechanism to step voltages up and down for transmission.

3. In 1890 the only such mechanism was the transformer.

4. Transformers only work on AC, not DC.

Hence our legacy grid is AC.

Nowadays we have an additional mechanism: Power electronics. Power electronics work on both AC and DC, so transformers with their huge requirements for copper and steel are no longer necessary.

We need to accelerate the transition of our grid to DC because DC grids are simpler and cheaper than AC grids.

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Grid-scale power electronics are also extremely niche and expensive, perhaps moreso than transformers. HVDC is used where it has a significant advantage, but ease of conversion is not one of those.

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> so transformers with their huge requirements for copper and steel are no longer necessary.

smelting some copper and steel and wounding it up is far, far, far, far cheaper than replacing it with power silicon(which might be smaller, but overall needs tons more of energy to produce)

It will be also less reliable. Transformers deal with any overload far better and routinely run for like 50+ years

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