Driving 3-phase motor from 2 amplifier phases

[Benta]

Are BLDC motors typically permanent magnet motors or squirrel cage?

BLDC motors always have permanent magnets inside.

Not necessarily. Larger types may have field windings. Those are rare, though.

[Dave]

Not necessarily. Larger types may have field windings. Those are rare, though.

Could you please provide an example of such motor?

To my understanding, you can't have a field winding on the rotor without having some sort of brushes in place to transfer the current onto the spinning rotor, therefore it would not be a brushless motor anymore (BLDC).

[Benta]

The "brushless" part relates to commutation. Slip rings is another story.
It's a question of the classification of the motor.
Some automotive drives used this experimentally to cut cost, neodymium or cobalt-samarium magnets aren't cheap in the needed size.

[Zero999]

Slip rings require brushes, so are not brushless.

There is really no such thing as brushless DC motor.

[jbb]

I’m not sure if you’re using amplifiers to drive the motor for testing or for some kind of low noise operation, but I have an efficiency concern; I expect that the power factor on your two amplifiers could be quite bad under some conditions. This could lead to unexpectedly high dissipation in a Class B amp.