What are the classifications of drive motors? (2)

According to Lenz's law, the effect of induced current always resists the cause of the induced current, which is to try to make the conductor on the rotor no longer cut the magnetic induction line of the stator's rotating magnetic field. This result is that the conductor on the rotor will "catch up" with the rotating electromagnetic field of the stator, causing the rotor to follow the rotating magnetic field of the stator, and ultimately causing the motor to start rotating. Due to the rotor always catching up with the rotational speed of the stator's rotating magnetic field, and in order to generate induced current by cutting the magnetic induction line, the rotor's speed is always slightly slower than the speed of the stator's electromagnetic field (2%~6%), which is asynchronous operation. Therefore, this type of motor that generates induced current is called an asynchronous motor.

3. Permanent magnet synchronous motor

In asynchronous motors, the formation of rotor magnetic field involves two steps: the first step is to generate induced current in the rotor winding by rotating the stator magnetic field; The second step is to induce current to generate a rotor magnetic field. Under the influence of Lenz's law, the rotor follows the rotating magnetic field of the stator, but it can never catch up, hence it is called an asynchronous motor. If the current in the rotor winding is not induced by the rotating magnetic field of the stator, but is generated by itself, then the rotor magnetic field is independent of the rotating magnetic field of the stator, and its magnetic pole direction is fixed. According to the principle of same-sex repulsion and opposite attraction, the rotating magnetic field of the stator will push and pull the rotor to rotate, causing the rotor magnetic field and the rotor itself to rotate synchronously with the rotating magnetic field of the stator. This is the working principle of synchronous motors.

Permanent magnet synchronous motors have a higher power to mass ratio, smaller size, lighter weight, larger output torque, and excellent maximum speed and braking performance. Therefore, permanent magnet synchronous motors have become the most widely used electric motors in electric vehicles today. However, when permanent magnet materials are subjected to vibration, high temperature, and overload current, their magnetic permeability may decrease or demagnetization may occur, which may reduce the performance of permanent magnet motors. In addition, rare earth permanent magnet synchronous motors require the use of rare earth materials, and the manufacturing cost is not very stable.

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