Theoretical AC vs DC question regarding future of electricity and PCs

[SubLimation7]

I read the whole Wikipedia page on HVDC... but they summarize it well.  Seems like HVDC overcame some hurdles quite well since every source I've looked at says it's actually better (TODAY, not the 1880s) than AC over long distances.  But it seems like they still want to switch it back to AC for your house, and FWIW when I read the word expensive I basically convert it to we haven't figured out the best way yet. Eg. Lithium Ion (or storage of energy in general).  Also note that a lot of the tech that makes HVDC more competitive is fairly recent, such as the HVDC "ultra-fast" circuit breakers.

 

Definitely some people playing with DC powered houses though:

https://www.digitaltrends.com/cool-tech/nexthome-dc-powered-home/ (not the only article you trolls out there, feel free to google yourself)

 

"Up top, the solar panels might actually be making too much energy — more than the house can use. Often, homeowners sell that surplus back to the power company, but the DC home can take it and store it in the Bosch "or any other" storage system, with no extra conversion step. That’s one reason NextEnergy wanted to build the NextHome: AC must be converted to store it."

 

I see that being incredible useful in the future, power grids will always be there I'm sure, but even today there are some pretty cost effective solar solutions and if we took out all the converting....  I could definitely see a future where the power grid is the backup.

 

Click below to see Advantages/Disadvantages (from Wikipedia)

Spoiler

Advantages of HVDC over AC transmission

"A long distance point to point HVDC transmission scheme generally has lower overall investment cost and lower losses than an equivalent AC transmission scheme. HVDC conversion equipment at the terminal stations is costly, but the total DC transmission line costs over long distances are lower than AC line of the same distance. HVDC requires less conductor per unit distance than an AC line, as there is no need to support three phases and there is no skin effect.

Depending on voltage level and construction details, HVDC transmission losses are quoted as less than 3% per 1,000 km, which are 30 – 40% less than with AC lines, at the same voltage levels.^[23] This is because direct current transfers only active power and thus causes lower losses than alternating current, which transfers both active and reactive power.

HVDC transmission may also be selected for other technical benefits. HVDC can transfer power between separate AC networks. HVDC powerflow between separate AC systems can be automatically controlled to support either network during transient conditions, but without the risk that a major power system collapse in one network will lead to a collapse in the second. HVDC improves on system controllability, with at least one HVDC link embedded in an AC grid—in the deregulated environment, the controllability feature is particularly useful where control of energy trading is needed.

The combined economic and technical benefits of HVDC transmission can make it a suitable choice for connecting electricity sources that are located far away from the main users.

Specific applications where HVDC transmission technology provides benefits include:

• Undersea cables transmission schemes (e.g., the 580 km NorNed cable between Norway and the Netherlands,^[24] Italy's 420 km SAPEI cable between Sardinia and the mainland,^[25] the 290 km Basslink between the Australian mainland and Tasmania,^[26] and the 250 km Baltic Cable between Sweden and Germany^[27]).
• Endpoint-to-endpoint long-haul bulk power transmission without intermediate 'taps', usually to connect a remote generating plant to the main grid, for example the Nelson River DC Transmission System in Canada.
• Increasing the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
• Power transmission and stabilization between unsynchronised AC networks, with the extreme example being an ability to transfer power between countries that use AC at different frequencies. Since such transfer can occur in either direction, it increases the stability of both networks by allowing them to draw on each other in emergencies and failures.
• Stabilizing a predominantly AC power-grid, without increasing fault levels (prospective short-circuit current).
• Integration of renewable resources such as wind into the main transmission grid. HVDC overhead lines for onshore wind integration projects and HVDC cables for offshore projects have been proposed in North America and Europe for both technical and economic reasons. DC grids with multiple voltage-source converters (VSCs) are one of the technical solutions for pooling offshore wind energy and transmitting it to load centers located far away onshore.^[28]

Cable systems

Long undersea / underground high-voltage cables have a high electrical capacitance compared with overhead transmission lines, since the live conductors within the cable are surrounded by a relatively thin layer of insulation (the dielectric), and a metal sheath. The geometry is that of a long co-axial capacitor. The total capacitance increases with the length of the cable. This capacitance is in a parallel circuit with the load. Where alternating current is used for cable transmission, additional current must flow in the cable to charge this cable capacitance. This extra current flow causes added energy loss via dissipation of heat in the conductors of the cable, raising its temperature. Additional energy losses also occur as a result of dielectriclosses in the cable insulation.

However, if direct current is used, the cable capacitance is charged only when the cable is first energized or if the voltage level changes; there is no additional current required. For a sufficiently long AC cable, the entire current-carrying ability of the conductor would be needed to supply the charging current alone. This cable capacitance issue limits the length and power carrying ability of AC powered cables. ^[29] DC powered cables are limited only by their temperature rise and Ohm's Law. Although some leakage current flows through the dielectric insulator, this is small compared to the cable's rated current.

Overhead line systems

The capacitive effect of long underground or undersea cables in AC transmission applications also applies to AC overhead lines, although to a much lesser extent. Nevertheless, for a long AC overhead transmission line, the current flowing just to charge the line capacitance can be significant, and this reduces the capability of the line to carry useful current to the load at the remote end. Another factor that reduces the useful current carrying ability of AC lines is the skin effect, which causes a non-uniform distribution of current over the cross-sectional area of the conductor. Transmission line conductors operating with direct current do not suffer from either of these constraints. Therefore, for the same conductor losses (or heating effect), a given conductor can carry more current to the load when operating with HVDC than AC.

Finally, depending upon the environmental conditions and the performance of overhead line insulation operating with HVDC, it may be possible for a given transmission line to operate with a constant HVDC voltage that is approximately the same as the peak AC voltage for which it is designed and insulated. The power delivered in an AC system is defined by the root mean square (RMS) of an AC voltage, but RMS is only about 71% of the peak voltage. Therefore, if the HVDC line can operate continuously with an HVDC voltage that is the same as the peak voltage of the AC equivalent line, then for a given current (where HVDC current is the same as the RMS current in the AC line), the power transmission capability when operating with HVDC is approximately 40% higher than the capability when operating with AC.

Asynchronous connections

Because HVDC allows power transmission between unsynchronized AC distribution systems, it can help increase system stability, by preventing cascading failures from propagating from one part of a wider power transmission grid to another. Changes in load that would cause portions of an AC network to become unsynchronized and to separate, would not similarly affect a DC link, and the power flow through the DC link would tend to stabilize the AC network. The magnitude and direction of power flow through a DC link can be directly controlled, and changed as needed to support the AC networks at either end of the DC link. This has caused many power system operators to contemplate wider use of HVDC technology for its stability benefits alone.

 

Disadvantages

The disadvantages of HVDC are in conversion, switching, control, availability and maintenance.

HVDC is less reliable and has lower availability than alternating current (AC) systems, mainly due to the extra conversion equipment. Single-pole systems have availability of about 98.5%, with about a third of the downtime unscheduled due to faults. Fault-tolerant bipole systems provide high availability for 50% of the link capacity, but availability of the full capacity is about 97% to 98%.^[30]

The required converter stations are expensive and have limited overload capacity. At smaller transmission distances, the losses in the converter stations may be bigger than in an AC transmission line for the same distance.^[31] The cost of the converters may not be offset by reductions in line construction cost and lower line loss.

Operating a HVDC scheme requires many spare parts to be kept, often exclusively for one system, as HVDC systems are less standardized than AC systems and technology changes faster.

In contrast to AC systems, realizing multiterminal systems is complex (especially with line commutated converters), as is expanding existing schemes to multiterminal systems. Controlling power flow in a multiterminal DC system requires good communication between all the terminals; power flow must be actively regulated by the converter control system instead of relying on the inherent impedance and phase angle properties of an AC transmission line.^[32] Multi-terminal systems are rare. As of 2012 only two are in service: the Hydro Québec – New England transmission between Radisson, Sandy Pond and Nicolet^[33] and the Sardinia–mainland Italy link which was modified in 1989 to also provide power to the island of Corsica.^[34]

High-voltage DC circuit breaker

HVDC circuit breakers are difficult to build because some mechanism must be included in the circuit breaker to force current to zero, otherwise arcing and contact wear would be too great to allow reliable switching. In November 2012, ABB announced development of the world's first ultra-fast HVDC circuit breaker.^[35][36] Mechanical circuit breakers are too slow for use in HVDC grids, although they have been used for years in other applications.

The ABB breaker contains four switching elements, two mechanical (one high-speed and one low-speed) and two semiconductor (one high-voltage and one low-voltage). Normally, power flows through the low-speed mechanical switch, the high-speed mechanical switch and the low-voltage semiconductor switch. The last two switches run parallel with the high-voltage semiconductor switch.

Initially, all switches are closed (on). Because the high-voltage semiconductor switch has much greater resistance than the mechanical switch plus the low-voltage semiconductor switch, current flow through it is low. To disconnect, first the low-voltage semiconductor switch opens. This diverts the current through the high-voltage semiconductor switch. Because of its relatively high resistance, it begins heating very rapidly. Then the high-speed mechanical switch is opened. Unlike the low-voltage semiconductor switch, which is capable of standing off only the voltage drop of the closed high-voltage semiconductor switch, this one is capable of standing off the full voltage. Because no current is flowing through this switch when it opens, it is not damaged by arcing. Then, the high-voltage semiconductor switch is opened. This actually cuts the power. However, it is not quite 100% off. A final low-speed mechanical switch disconnects the residual current.^[36]"

 

Please keep in mind I am not saying that DC is better across the board AT ALL (especially not in the case of electric motors, as proven by Tesla), there is also plenty I still do not fully understand, I imagine some of the people posting on this thread know much more than I do on the topic.  I just wanted to have a little debate and get my mind going on the topic.  If I get curious again I'll break down and learn about DC and AC on a more fundamental level.

 

I'll take 3 powerwalls, one electric car, this fancy solar roof, and a DC wired digital home please!  I like LEDs more anyway, but most ACs run straight from AC...  and refrigerators... damn thats like 70% of my power already....  Anyone know if converting AC to DC or DC to AC is more efficient currently?

 

Just read an interesting tidbit, when AC is converted to DC it still pulses (I'm sure I was told that in school at some point), so we would have much cleaner power if things were fed DC from the start and require much less filtering in sensitive devices which I imagine would help offset a lot of the conversion costs of DC to AC.  I'm about to post a question on Quora about which way is more efficient, not finding anything definitive online, but after reading the different methods it sounds like all but the bridge rectifier diode configuration are quite inefficient converting AC to DC, you get the full signal but it looks like it would introduce a bit of resistance.  With DC to AC you have to make the electricity pulse at 60hz, by mechanical means, obviously there is some efficiency lost here as well. 

 

Verdicts in... AC to DC is more efficient 

 

Now for another thing that bothers me occasionally... 

Let's talk about heat!  What is heat? Science is still arguing over this.... 

Jk, let's not go there.

 

Someone needs to make me some wurtzite boron nitride drill bits damnit....

[SubLimation7]

3 hours ago, burnttoastnice said:

The motherboard does that to some extent already, but having the motherboard doing all the power conversion would make it much more expensive, having lots of metal blocks and random fans placed all over the place to cool down the power equipment. Plus, PCs wouldn't be as modular, and then the motherboards power delivery would be a limiting factor in how powerful a gpu can be installed etc unless gpus started shipping with dedicated power supplies.

I'm not sure why you would need more heatsinks/fans, except for the initial stepdown maybe, and it seems like you wouldn't need much/any conversion since all of the power coming out of the PSU is DC already?  Seems like it would just be a matter of having the proper resistance on the respective devices assuming manufacturers were smart enough to standardize "port" voltage.  The DC to AC conversion the motherboards already do (or so I'm told by some guy on a forun lol, I personally don't understand what component would use AC, PWM isn't AC) and there is already tons of cabling running anyway to carry the DC from power supply, I wouldn't mind a thicker motherboard if it eliminated PSU.

 

There very well may be some part of it that's going over my head, but that's my general understanding.

[burnttoastnice]

6 minutes ago, SubLimation7 said:

I'm not sure why you would need more heatsinks/fans, and it seems like you wouldn't need much conversion since all of the power coming out of the PSU is DC already?  Seems like it would just be a matter of having the proper resistance on the respective devices.  The DC to AC conversion the motherboards already do, and there is already tons of cabling running anyway to carry the DC from power supply, I wouldn't mind a thicker motherboard if it eliminated PSU.

 

There very well may be some part of it that's going over my head, but that's my general understanding.

 

I was under the impression that you suggested the motherboard did all the power conversion (which would eliminate the need for a PSU, seeing as the power coming from the wall would be DC) which would mean all the power delivery equipment gets relocated onto the motherboard. The rest of the post is basically based on this impression, so if that's not what you meant then ignore

 

 

Power supplies currently have one giant fan cooling things down, but if that power conversion equipment is moved onto the motherboard, there'd probably be a 110V DC to 12V DC supply for the PCIe, another 110v DC to 12v DC for the CPU power delivery (higher overclocks yay!), and another 110v to 5v for the USB (and coming from that some lower power 3.3v for the chipsets, and 1.3v for the RAM, but these don't need cooling). The PCIe and CPU power modules on the motherboard would probably be expected to handle up to 10A, maybe 20-40A for an enthusiast board.

 

That's easily 120W in two different places of the motherboard generating heat, along with heat losses in the CPU VRMs, a fan would be a necessity to keep these cool. Clever heatsink designs could let the user rely on system fans to keep everything on the motherboard running at a decent temperature, but ultimately custom water loop users would have the better looking motherboards and more effective cooling, provided the motherboard is a massive water block.

 

But lower power systems wouldn't need any kind of additional cooling - take the Pico PSU for example, which is capable of a beefy 160w power output without needing any kind of cooling at all. If anything, the motherboard would just need a 12v input brick, with the required power delivery scaled back and located on a small heatsink somewhere (if necessary). The external pico PSU brick would obviously get warm during high load, but if any heat-related fault develops with it, replacement is a simple task. If everything's integrated onto the motherboard and a heat-related fault develops, that could be an expensive problem

[SubLimation7]

3 minutes ago, burnttoastnice said:

 

I was under the impression that you suggested the motherboard did all the power conversion (which would eliminate the need for a PSU, seeing as the power coming from the wall would be DC) which would mean all the power delivery equipment gets relocated onto the motherboard. The rest of the post is basically based on this impression, so if that's not what you meant then ignore

 

 

Power supplies currently have one giant fan cooling things down, but if that power conversion equipment is moved onto the motherboard, there'd probably be a 110V DC to 12V DC supply for the PCIe, another 110v DC to 12v DC for the CPU power delivery (higher overclocks yay!), and another 110v to 5v for the USB (and coming from that some lower power 3.3v for the chipsets, and 1.3v for the RAM, but these don't need cooling). The PCIe and CPU power modules on the motherboard would probably be expected to handle up to 10A, maybe 20-40A for an enthusiast board.

 

That's easily 120W in two different places of the motherboard generating heat, along with heat losses in the CPU VRMs, a fan would be a necessity to keep these cool. Clever heatsink designs could let the user rely on system fans to keep everything on the motherboard running at a decent temperature, but ultimately custom water loop users would have the better looking motherboards and more effective cooling, provided the motherboard is a massive water block.

 

But lower power systems wouldn't need any kind of additional cooling - take the Pico PSU for example, which is capable of a beefy 160w power output without needing any kind of cooling at all. If anything, the motherboard would just need a 12v input brick, with the required power delivery scaled back and located on a small heatsink somewhere (if necessary). The external pico PSU brick would obviously get warm during high load, but if any heat-related fault develops with it, replacement is a simple task. If everything's integrated onto the motherboard and a heat-related fault develops, that could be an expensive problem

Now that makes a bit more sense lol!

 

I was quite confused on the contradiction between the 1st and 2nd half of your post, you sounded very knowledgeable at first and then I was like... um.... lol

[cj09beira]

Even if you could have no psu you would want one, reason being that psu's can fail and you don't want to have to change the whole board if that happened. 

Also you can't have 100v anything on motherboards it would be a nightmare for audio signals and would be very hard on the vrms

[SubLimation7]

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