Because the voltage of the drive motor of the inverter contains abundant high-frequency components.The voltage waveform of the inverter-driven motor is not a sine-wave voltage, but a pulse-width modulation (PWM) voltage. This waveform contains rich high-frequency components. The main frequency component is the repetition frequency of the PWM pulse and its multiples. Frequency, PWM pulse repetition frequency This is called the carrier frequency of the frequency converter. The carrier frequency of different inverters is different, generally 1 ~ 12kHz. For a PWM voltage with a carrier frequency of 1kHz, the current flowing into the motor is mainly 1kHz, 2kHz, 3kHz, 4kHz, 5kHz, etc. These high-frequency currents increase the motor winding loss and core loss. The theoretical analysis shows that the winding loss is proportional to the square root of the frequency, and the core loss is proportional to the square of the frequency. Therefore, when such high-frequency current flows in the motor, The losses increase sharply, resulting in overheating.
The solution to motor overheating is to reduce high-frequency components in the motor drive voltage. The method to achieve this is to install a SWF sine wave filter at the output of the VSD. The sine wave filter transforms the PWM voltage waveform into a sine wave voltage waveform suitable for the motor, as shown in Figure 2, thereby eliminating the phenomenon of motor overheating.
When purchasing a sine wave filter, you must understand the carrier frequency of the VFD, otherwise there may be adverse consequences.
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