Elevator industry, the traction machine has permanent magnet synchronous motor and permanent magnet asynchronous motor two, what is the difference between them?
In general, there are old-fashioned elevator should be used mostly synchronous motor, because the synchronous machine mechanical characteristics and stability, but, nearly 20 years, asynchronous motor frequency drive has made rapid development, asynchronous motor characteristics of the software problem has been very good The application of the technology, such as direct torque control, makes the manufacturers claim that the characteristics of the asynchronous motor are equal to or higher than the characteristics of the synchronous motor. Therefore, the synchronous motor and the asynchronous motor are only two different periods and different application methods.
AC motor to rotate requires two conditions: first, there is an active rotating magnetic field; second, there is a magnetic field driven by this active magnetic field. In general, the rotating magnetic field from the stator winding, three-phase AC power naturally formed a rotating magnetic field. The difference between a synchronous motor and an asynchronous motor lies in the source of the rotor magnetic field. The synchronous motor requires an excitation power source, or a permanent magnet, so that the rotor always has a magnetic field that can be driven by the rotating magnetic field provided by the stator. As long as the braking torque is reasonable, the final rotor speed can always reach the stator in the rotating magnetic field speed, that is, synchronous speed. This kind of motor is synchronous motor. Asynchronous motor is simply closed end of the whole family is relatively simple. The magnetic field of the rotor is derived from the rotating magnetic field provided by the stator windings to cut the current generated by the conductor in the rotor. In other words, the induced current generated by the rotating magnetic field cutting rotor from the stator produces a second magnetic field based on the rotor, and the rotor rotates due to the interaction of the two magnetic fields. The greater the difference in speed between the rotor and the rotating magnetic field, the greater the rotor current, and the stronger the effect of the two magnetic fields. As the speed increases, the rotor current is getting smaller and smaller, but never. This creates that the rotor speed must have a certain difference from the synchronous speed to maintain the rotating magnetic field to cut the rotor conductor. To maintain the continuous rotation of the rotor. The difference between this speed and the speed of synchronous speed is the slip rate. Asynchronous motor speed never reach the synchronous speed, so called asynchronous motor
