Ordinary asynchronous motor is designed by constant frequency and constant pressure, can never completely adapt to the requirements of the frequency control of motor speed. In general, is not recommended inverter with ordinary three-phase asynchronous motor's speed control.
    Generally dedicated frequency conversion motor, there will be a special cooling device, namely external cooling fan, and from the aspects of production process, the more strict, make material insulation level is higher, than the general motor heat resistance, and the inverter frequency range widely from 5 HZ to 100 HZ, can even several hundred HZ frequency. Ordinary motor generally there is no specific powder air cooling fan, often with a fan wings, and is able to run the frequency range is relatively narrow, generally is not higher than the fundamental frequency, the lowest frequency at around 30 hz, common near the fundamental frequency inverter.

    The influence of inverter on motor:
    1，the efficiency and the problem of temperature rise of the motor
    Regardless of what kind of frequency converter, in the operation have varying degrees of harmonic voltage and current, operation of the motor under non sinusoidal voltage and current. To data, by the sine wave inverter PWM is widely used as an example, the low order harmonics is essentially zero, the remaining ratio of carrier frequency of about twice the size of a harmonic component is 2u+1 (U modulation). Harmonics will cause motor stator copper loss and rotor copper (aluminum) to increase consumption, iron loss and additional loss, most notably the rotor copper (aluminum) consumption.  Because asynchronous motor is close to the corresponding to the fundamental frequency synchronous speed rotation, therefore, harmonic voltage in a larger slip cutting rotor, the rotor will produce great loss. In addition, we need to consider additional copper because of the skin effect caused by consumption. These losses will make the additional heating motor, reduce efficiency, output power decreases, such as ordinary three-phase asynchronous motor run in inverter output of non sinusoidal power supply conditions, the temperature rise in general to increase 10% - 20%.
    2, motor insulation strength
    Current small inverter, many control methods using PWM. His carrier frequency is about several thousand to tens of kHz, which makes the motor stator windings to withstand very high rate of voltage rise, equivalent to the steepness of the great impact on voltage applied on the motor, the motor turns insulation withstand a more severe test. In addition, the rectangular chopped impulse voltage generated by the PWM inverter is superimposed on the operating voltage of the motor, which is a threat to the electric motor on the ground.