Variable-frequency motor

Variable-frequency motors allow the speed of the motor to be adjusted, thereby enabling energy savings depending on the load conditions. A regular motor is a device with a fixed speed that cannot be adjusted.

The structural difference between motors of this type and ordinary motors (with constant frequency and voltage) is as follows: 1) Insulation class, which is generally F grade or higher, to enhance the insulation strength against ground as well as between windings; particular attention must be paid to the insulation’s ability to withstand shock voltages. 2) Regarding the vibration and noise issues of the motor, it is necessary to fully consider the rigidity of the motor’s components as well as the overall structure, and strive to increase its natural frequency in order to avoid resonance with various force waves. 3) Cooling method: Forced ventilation cooling is generally used, that is, the cooling fan of the main motor is driven by an independent motor. 4) Measures to prevent shaft current: Bearing insulation should be employed for motors with a capacity exceeding 160 KW. Primarily, it leads to magnetic circuit asymmetry, as well as the generation of shaft current. When the currents generated by other high-frequency components act together, the shaft current increases significantly, which can result in bearing damage; therefore, insulation measures are generally required. 5) For constant-power variable-frequency motors, when the speed exceeds 3000/min, a special high-temperature-resistant lubricant should be used to compensate for the increase in bearing temperature.

1. From the perspective of power frequency, variable-frequency motors are inferior motors; ordinary motors are the good ones； 2. Since the PWM-modulated wave output by the inverter simulates sine wave alternating current and contains a large number of harmonics, it generally needs to be filtered through a reactor before it can be fed into a conventional motor; otherwise, the motor will overheat ； 3. To accommodate the PWM-modulated wave output by inverters, which simulates sine wave alternating current and contains numerous harmonics, special invertor-driven motors have been developed; their function can essentially be understood as that of a reactor combined with a conventional motor ； 4. In other words, for motors of the same power, variable-frequency motors have a larger core cross-section than conventional motors, more turns in their coils, larger wire diameters, higher insulation standards, as well as dedicated cooling fan motors ； 5. To meet the requirements of weak-magnetic speed control, consideration was given to the bearing capacity and the dynamic balance of the high-speed rotor ； 6. This type of variable-frequency motor does not possess improved torque characteristics; it merely overcomes the issue that conventional motors are not suitable for using PWM-modulated waves to simulate sine wave alternating current ；