When the three-phase stator winding of the permanent magnet motor (each phase differs by 120° electrical angle) is connected to a three-phase alternating current with a frequency of f, a rotating magnetic field moving at a synchronous speed will be generated. In steady state, the main pole magnetic field rotates synchronously with the rotating magnetic field, so the rotor speed is also the synchronous speed. The stator rotating magnetic field is always relatively stationary with the main pole magnetic field established by the permanent magnet. They interact with each other and generate electromagnetic torque, driving the motor to rotate and convert energy. The permanent magnet variable frequency air compressor adopts a high-efficiency permanent magnet motor + inverter (PM motor). The screw main engine and the high-efficiency permanent magnet motor share the same main shaft. The motor has no bearings. The rotor with permanent magnets is directly installed on the extended shaft of the male rotor, and the transmission efficiency is 100%. This structure eliminates the failure points of traditional motor bearings and realizes maintenance-free motors. The rare earth permanent magnet material has excellent magnetic properties. After magnetization, it no longer requires external energy to establish a strong permanent magnetic field, which is used to replace the electromagnetic excitation field of traditional motors. The high-efficiency permanent magnet variable frequency motor is not only efficient, but also simple in structure, reliable in operation, small in size and light in weight. It can not only achieve high performance (such as ultra-high efficiency, ultra-high speed, ultra-high response speed) that traditional electromagnetic motors cannot match, but also can be made into special motors that can meet specific operating requirements, such as elevator traction motors, automotive special motors, etc. The combination of rare earth high-efficiency permanent magnet motors with power electronics technology and microcomputer control technology has brought the performance of motors and transmission systems to a new level: High-efficiency permanent magnet variable frequency motors always maintain high efficiency under any load, saving more than 38% energy compared to ordinary motors and more than 10% energy compared to induction variable frequency motors. The superior performance of the motor can be started immediately after shutdown, unlimited start and stop without affecting the life of the motor, and the starting current does not exceed 100% of the full load current. Because permanent magnet variable frequency motors have the advantages of low speed and high output torque, their variable frequency control mode is wider than ordinary induction variable frequency motors. Permanent magnet variable frequency motors are 30% smaller in size and 35% lighter in weight than motors of the same power, and are easier to maintain. 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, high-efficiency permanent magnet variable frequency motor is the best choice for screw air compressor drive motor. It is more efficient and energy-saving than ordinary three-phase asynchronous variable frequency motor!