When the three-phase stator windings of the permanent magnet motor (each phase difference of 120° electrical angle) are supplied to the three-phase alternating current of frequency f, a rotating magnetic field that is shifted at the synchronous speed will be generated.
In the steady state, the main pole magnetic field rotates synchronously with the rotating magnetic field, so the rotor rotational speed is also the synchronous rotational speed. The stator rotating magnetic field is kept relatively static with the main pole magnetic field established by the permanent magnet, and they interact and generate electromagnetic torque. The drive motor rotates and performs energy conversion.
The permanent magnet variable frequency air compressor adopts permanent magnet motor + frequency converter (PM motor). The screw main unit and the permanent magnet motor share the same main shaft. The motor has no bearing. The rotor with permanent magnet is directly mounted on the protruding shaft of the male rotor. Transmission efficiency is 100%. This structure eliminates the traditional motor bearing failure point and achieves maintenance-free operation of the motor.
The rare earth permanent magnet material has excellent magnetic properties. After magnetization, it does not need additional energy to establish a strong magnetic field. It is used to replace the electric excitation field of the traditional motor. The permanent magnet variable frequency motor is not only efficient but also simple in structure. It is reliable in operation and can be small in size and light in weight. It can achieve high performance (such as special, special high-speed, ultra-high response speed) that can not be compared with traditional electric excitation motors, and can also be made into special motors that can meet specific operational requirements, such as elevator traction motors and automotive-specific motors.
The combination of rare earth permanent magnet motors with power electronics technology and microcomputer control technology has improved the performance of motors and transmission systems to a new level:
The permanent magnet variable frequency motor always maintains the rate under any load, which is more than 38% energy saving compared with the ordinary motor, and more than 10% energy saving than the induction variable frequency motor.
The superior performance that can be started immediately after the motor is stopped, starts and stops indefinitely without affecting the life of the motor, and the starting current does not exceed 100% of the full load current.
Since the permanent magnet variable frequency motor has the advantages of low speed and high output torque, its variable frequency control mode is generally wider than the ordinary induction variable frequency motor. The permanent magnet variable frequency motor is 30% smaller than the same power motor, and the weight is reduced by 35%, making maintenance easier. Therefore, improving the performance and level of the supporting technical equipment is an important development direction for the motor industry to adjust the industrial structure.
At present, the permanent magnet variable frequency motor is the best choice for the screw air compressor drive motor. It is more energy efficient than the ordinary three-phase asynchronous variable frequency motor!