How does the carrier frequency of a frequency converter affect EMC?

The carrier frequency (PWM switching frequency) of a frequency converter directly impacts EMC performance, requiring a trade-off between efficiency, noise, and EMI. Higher carrier frequencies increase the number of IGBT switching operations, leading to increased switching noise energy per unit time. This causes the fundamental and harmonic frequencies of conducted and radiated interference to shift to higher frequencies, potentially with increased amplitude. This makes the design of input/output filters more challenging, requiring filter components to maintain good performance at higher frequencies. However, higher carrier frequencies can also help reduce motor noise and torque ripple. In EMC design, a compromise carrier frequency should be chosen, as low as possible while still meeting motor performance requirements.

Random PWM or harmonic injection PWM techniques can be used to spread switching noise energy across a wider frequency band, reducing peak values at specific frequencies and making it easier to meet EMC limits. When using a fixed carrier frequency, sensitive frequency bands, such as communication bands, should be avoided. Filter design needs to be optimized for the selected carrier frequency and its main harmonics. EMC pre-testing is conducted to observe the noise spectrum at different carrier frequencies, selecting the frequency point with the best EMI performance. Audiotech's filter products cover a wide frequency band and can adapt to the filtering needs of frequency converters at different carrier frequencies.