Assuming one was starting from scratch and didn't care whether the available appliances of the day required AC or DC power, but all the power coming into the home was solar, what would the motors on the appliances look like? Would it still be desirable to use AC motors, and if not, would it be practical (other than for the obvious reasons) for appliances to use a standard DC voltage?
I don't mean to suggest that we abandon ac powered appliances, I'm just curious about what electrical wizards would come up with, if they were doing it all over again.
Motors would almost certainly still be AC. They are way more efficient, cheaper to build and require almost no maintaince. DC motors do not have those same characteristics.
But they'd probably run on a higter voltage and frequency.
"Brushless DC" motors seem to be taking over due to switching electronics dropping in price, no? And while those are technically AC motors, it's not the kind of AC that comes right off the line.
Motors that run on constant 60Hz seem to be a historical shortcut, whose demand is fading as the control benefits of variable frequency drive are available for less and less. And if HVDC transmission is gaining popularity, then how long are utilities going to keep doing the conversion to AC "for free" ?
It seems to me that if we were in a bizarro world where common end-user power had always been DC, every motor would just be paired up with an appropriate driver circuit, even designed around the specific inductance of the motor. With solid state circuitry, all house fans would be infinitely variable, etc.
Of course there's a huge installed base of a few types of items that would need 60Hz backwards compatibility. I get a good chuckle from thinking about legacy clocks requiring an inverter that contains a high-accuracy crystal - maybe that inverter could even run ntpd.
I looked into this a while ago, when I was replacing the pump on my swimming pool. This is a bit of a special case, as there are gains to be made from using a variable speed drive. Whilst a variable speed drive may increase electrical losses, the slower water flow may reduce losses due to turbulance by a greater amount, leading to a net increase in efficiency for volume of water moved.
As far as I can gather, for variable speed motors a brushless permanent magnet DC motor is more efficient for small power applications (< 1-2kW), but as the power goes up, a high efficiency three-phase induction motor with a variable-speed drive become more efficient than the DC motor. A high efficiency induction motor has extra copper in the rotor, to reduce resistive losses.
For fixed speed applications, you'd think the above variable speed performance would reflect the performance for a DC supply, as the DC supply requires switching in both cases. For a three-phase AC supply, you'd think the induction motor would win, due to the absence of switching.
I don't mean to suggest that we abandon ac powered appliances, I'm just curious about what electrical wizards would come up with, if they were doing it all over again.