Motors can be divided into DC motors and AC motors due to different input currents:
(1) DC motor - a motor that rotates with a DC current is called a DC motor. Due to the different ways of connecting the magnetic field circuit and the armature circuit, they can be divided into series-excited motors, split-excitation motors, and compound-excited motors;
(2) AC motor - an induction motor in an AC motor, its strong induced current (eddy current) is generated in the rotating magnetic field, and the copper rod on the rotor continuously cuts the magnetic field lines. According to Lenz's law, this induced current has a resistance to the magnetic field. The effect of relative motion with the rotor occurs, so the rotor rotates with the magnetic field. However, the rotation speed of the rotor is not as high as that of the magnetic field transformation, otherwise the magnetic field lines will not be able to be cut by the copper rod.
A motor that rotates with alternating current is called an alternating current motor. There are many types, mainly:
a. Rectifier motor - make the series-excited DC generator used as an AC motor, that is, this type of motor, because the alternating current turns in the magnetic field and the armature circuit at the same time, so the direction of the couple moment remains unchanged. Turning non-stop. This kind of motor is also called "universal motor" because it can use both AC and DC. Vacuum cleaners, sewing machines and other household appliances use this type of motor.
b. Induction motor - a device that places the rotor in a rotating magnetic field and rotates the rotor due to the action of eddy currents. The rotating magnetic field is not caused by mechanical methods, but is caused by alternating current in pairs of electromagnets, so that the properties of the magnetic poles are cyclically changed, which can be regarded as a rotating magnetic field. Usually a three-phase induction motor (with three pairs of magnetic poles) is used. The motion of a DC motor is just the opposite of a DC generator, where the induced current is formed by the induced electromotive force, so they are in the same direction. In the motor, the current is the direction of the induced electromotive force supplied by the external power supply and the direction of the armature current I is opposite.
c. Synchronous motor - a motor in which the armature rotates from one pole to the next pole, which is exactly the same cycle as the direction of the incoming current. This kind of motor cannot start by itself, and another motor or special auxiliary winding must be used to make it reach the appropriate frequency before it can be connected to the alternating current. If the load changes and the rotational speed changes, the rotational speed is not in line with the frequency of the alternating current, which is enough to make it out of step, and tends to stop or cause damage. Because of many restrictions, it is not widely used.
