Later, people discovered that the rotor did not need an electromagnet to make a cage for squirrels. Since the magnetic force line of the virtual magnet cuts the cage stick of the cage, it is determined by the great right hand to generate current. A closer look at it shows that the current is also a three-phase, so the rotor produces a virtual magnet that rotates around it, similar to the stator's principle of generating a magnetic field. The virtual magnet of the fixed rotor rotates the same in space. So the mouse cage has a similar effect to the electromagnet, but the current in the mouse cage is generated by its relative motion to the stator virtual magnet, and the mouse cage virtual magnet is not independent. The mouse cage speed is always slower than the stator virtual magnet speed, and the synchronization speed can not be reached(otherwise, there will be no relative motion, the current will not be generated, and the mouse cage magnetic field will not be generated).
In analysis, the synchronous machine has a rotor independent magnetic field, like an active load in the circuit. The step machine, because everything in the rotor is generated by the stator, is equivalent to passive load. In terms of design, of course, synchronous motors are more complex.
