With this magnetic field, we can imagine an invisible magnet turning at the stator. If the rotor is a magnet, then the rotor is driven, that is, the motor. On the contrary, if the rotor drives the invisible magnet, it becomes a generator(first, the rotor drives the virtual magnet. The rotor must be subjected to a resistance moment. The virtual magnet receives a power moment. Note! The force is the intermediary(or sign) of energy conversion. After all, the virtual magnet is virtual and the stator is not moving. Then the stator definitely obtains the electromotive force. If the stator is loaded, there will be a current, or a three-phase, and there will be a magnetic field with a current that will interfere with the magnetic field generated by the rotor. This is called an armature reaction. The electromotive force obtained at the stator after the load is carried is not the same as that obtained when the load is empty).
Under the guidance of the above principle, the rotor is made into an electromagnet, and the exterior is powered by a single power source. Then the motor is called a synchronous machine. The reason why the synchronous machine is called the rotor's magnetism is generated independently. So the rotor can reach the speed of the virtual magnet. The independent generation of rotor magnetism is a good thing, making it easy to adjust the synchronous machine, such as adjusting reactive power.
