Why do inverter-driven motors overheat? This is because the voltage driven by the inverter contains rich high-frequency components.
The voltage waveform of the inverter-driven motor is not a sine wave voltage, but a pulse width modulation (PWM) voltage, as shown in Figure 1. According to Fu Liye's analysis, this waveform contains rich high-frequency components. The main frequency component is the repetition frequency of the PWM pulse and its integral multiple frequency. The repetition frequency of the PWM pulse is called the carrier frequency of the inverter.
Different inverters have different carrier frequencies, generally 1–12 kHz. For a PWM voltage with a carrier frequency of 1 kHz, the current flowing into the motor consists mainly of currents at 1 kHz, 2 kHz, 3 kHz, 4 kHz, 5 kHz, and so on. These high-frequency currents increase motor winding losses and core losses. Theoretical analysis shows that winding losses are proportional to the square root of frequency, while core losses are proportional to the square of frequency. Consequently, when such high-frequency currents flow through a motor, core losses rise sharply and cause overheating.
The solution to motor overheating is to reduce the high-frequency component in the motor drive voltage. The way to achieve this is to install a SWF sine wave filter at the output end of the frequency converter. The sine wave filter converts the PWM voltage waveform into a sine wave voltage waveform adapted to the motor, as shown in Figure 2, thereby eliminating the phenomenon of motor overheating.
The sine wave filter will emit larger noise and be accompanied by higher temperature. These are normal phenomena. It can be considered that it is the sine wave that takes up the energy that causes the motor to emit noise and increase the temperature, thus protecting the motor.
When purchasing a sine wave filter, you must understand the carrier frequency of the frequency converter, otherwise there may be adverse consequences. For example: The temperature of the hoist is very high and it makes loud noise. I want to make adjustments. This is a very typical problem, just install a SWF filter. Before purchasing the filter, the information provided by the hoist manufacturer is that the frequency converter carrier frequency is 2kHz. But after installation, it was found that the noise was louder and the motor temperature was higher.
After on-site testing, it was found that the actual carrier frequency of the frequency converter is 1kHz. The parameters of the sine wave filter need to be modified again. After modifying the parameters, the whistling sound of the motor basically disappears, and the temperature drops from the original 65℃ to 53℃. Reducing the temperature of the motor is very beneficial to extending the life of the motor. In addition, after installing a sine wave filter, it can also eliminate bearing current and extend the life of the motor.
(Source: Haima Industrial Design)