How to adapt the LCL filter of the frequency converter to EMC

To adapt an LCL filter to a frequency converter to improve EMC, key considerations include resonance suppression and matching with the converter's output characteristics. An LCL filter consists of an inverter-side inductor, capacitor, and grid-side inductor, effectively attenuating switching frequency harmonics, but it carries the risk of resonance peaks. Design considerations for EMC adaptation include: parameter design ensuring the resonant frequency is significantly higher than the carrier frequency and significantly lower than the controller bandwidth, typically below half the switching frequency. Connecting a damping resistor in series with the capacitor branch is essential for suppressing resonance; the resistor value needs optimization to balance damping effect and losses. The saturation current of the filter inductor must be greater than the maximum peak current of the converter output.

The introduction of an LCL filter alters the output voltage characteristics, requiring compensation in the control algorithm to prevent oscillations. During installation, the filter should be placed as close as possible to the converter output terminals, with short and thick connecting wires. The impact of the filter on the converter output dv/dt and common-mode voltage needs to be evaluated, and a common-mode inductor should be used if necessary. Simulations and experiments should be conducted to verify the filter's insertion loss and system stability. LCL filters can significantly reduce high-frequency noise on motor cables, thereby reducing radiated emissions and motor bearing current. Eintech Electronics can provide design consultation for LCL filters and key components such as high-current inductors and damping resistors.