How to coordinate onboard and external filters in a frequency converter

The combined use of onboard filters and external filters in a frequency converter can construct a multi-layered, high-efficiency EMI suppression system. Onboard filters typically target mid-to-high frequency noise and are installed on the internal PCB of the frequency converter, close to the noise source or port. Examples include parallel connection of a high-frequency ceramic capacitor at the DC bus capacitor and the placement of ferrite beads and capacitors at the control power input. External filters are usually installed externally to the frequency converter, close to the power input or output terminals, to handle low-frequency, high-energy conducted noise and suppress cable radiation. The principle of their combination is: the onboard filter provides "fine-tuning," suppressing specific high-frequency noise and local noise; the external filter provides "rough-tuning," providing a wide-bandwidth basic attenuation.

During design, overlap or dead zones in the frequency response of the two should be avoided; ideally, they should complement each other. During installation, the external filter must be properly grounded, and its metal casing should be connected to the frequency converter chassis with low impedance. Input and output cables should be routed separately when connecting onboard filters and external filters to avoid coupling. During system integration, the EMC performance of using only onboard filters, only external filters, and both should be tested to select the optimal combination. E-Tech Electronics offers both high-performance surface-mount ferrite bead capacitors for onboard applications and complete external EMI filters, providing customers with a one-stop solution.