How does soft switching improve the EMC of frequency converters?

Soft-switching technology significantly improves the EMC performance of frequency converters. In traditional hard-switching frequency converters, IGBTs switch when the voltage and current are not zero, generating large dv/dt and di/dt, which are major sources of EMI noise. Soft-switching technologies, such as zero-voltage switching or zero-current switching, allow power devices to switch states when the voltage or current crosses zero, thereby significantly reducing the rate of change of voltage and current during the switching process. The improvements are reflected in: smoother switching waveforms, virtually eliminating voltage and current spikes and oscillations, and reducing high-frequency noise energy at the source. Reduced switching losses allow for the use of higher switching frequencies without overheating, and higher switching frequencies can sometimes distribute noise energy to more easily filtered frequency bands.

Due to the reduced dv/dt, the common-mode current coupled through the parasitic capacitance of the motor cable is significantly reduced. Therefore, frequency converters using soft switching typically have much lower conducted and radiated emission levels than hard-switching frequency converters of the same power, and the requirements for input and output filters are correspondingly reduced. However, soft-switching circuits are generally more complex, more expensive, and more difficult to control. Common soft-switching topologies include resonant DC links and active clamping. Eintech provides high-performance capacitors and magnets for advanced topologies, supporting the implementation of soft-switching technology.