Compared with the motor driven by sine wave, the power factor and efficiency of the motor will be deteriorated and the temperature rise will increase due to the influence of high harmonics in the output waveform of the inverter. When the frequency converter drives, the output current of the frequency converter should be equal to that of the fundamental power supply. The output current of inverter is composed of basic current and higher harmonic current. Therefore, the basic characteristics of motor driven by frequency converter will be different from that of power frequency power supply.

In general, when the motor is in rated operation, the motor current supplied by frequency converter increases by 5% ~ 10% and the temperature rise increases by 20% compared with that supplied by power frequency. Therefore, the inverter fed motor should not operate at rated frequency with full load.

In addition, because the ordinary motor is cooled by the cooling fan installed on the motor shaft, the motor will overheat due to the insufficient cooling capacity of its own cooling fan during continuous low-speed operation. In order to solve this problem, the following countermeasures can be taken:

1. The motor is equipped with cooling fan, and the self cooling mode is changed to other cooling mode to increase the cooling capacity.

2. Choose a motor with larger capacity.

3. Improve the insulation level of the motor to achieve the purpose of increasing the upper limit of motor temperature rise.

4. Use special motor for frequency converter.

5. Control the operating range of the motor to avoid long-term operation at low speed.