Synchronous reluctance motors where torque density isn't a strict requirement, and brushless separately excited synchronous motors (synchro motor with electromagnets on the rotor) for high torque/energy density applications?
In all applications where it is possible to use motors without permanent magnets, that is usually done, because the motors without permanent magnets are normally cheaper.
If you had read the article you’d know they have their own mine: “Hardly any firms, even in China, do what MP is attempting: produce finished magnets starting with ore that the company mines itself” Mostly China doesn’t mine materials but has concentrated the refining capacity in China for many commodities. Thankfully, we do have backup capacity so we won’t be totally screwed if China cuts us off, and the refining technology is well understood and in a conflict we or our allies can cut them off from many raw materials so their refining advantage isn’t a checkmate.
Unless I'm working on old information, this is not correct. The overwhelming majority of neodymium mining capacity is currently in China.
> you’d know they have their own mine:
Sure, but to make a difference from a geopolitical perspective, we need more than that. And I don't see those kind of mines being opened on a large scale anywhere in the west. Regulations are challenging and environmental resistance is significant.
For high torque density applications, heat dissipation is often the limiting factor on duty cycle.
Also, the slip rings capable of passing high current to an electromagnet rotor are expensive and less robust than permanent magnets.
Essentially: it’s possible but I haven’t seen an application where it’s practical.
The new designs are all inductively coupled, i.e. they have a rotating transformer coil built into the shaft. No brushes, no slip rings.