How to design DC bus filter for frequency converter

The design of a DC bus filter circuit for a frequency converter aims to provide a stable, low-ripple DC voltage for the inverter bridge and suppress high-frequency noise. The bus filter primarily consists of electrolytic capacitors, sometimes with film or ceramic capacitors connected in parallel. The design steps include: first, calculating the minimum required electrolytic capacitor value based on load power, allowable voltage ripple, and grid frequency, typically using empirical formulas. Selecting electrolytic capacitors with low ESR and high ripple current handling capability, considering their lifespan and operating temperature. To suppress high-frequency switching noise, low-ESL film or multilayer ceramic capacitors, such as 1μF to 10μF, should be connected directly in parallel with the electrolytic capacitors to provide a high-frequency current path for the IGBTs.

The capacitor mounting location is crucial; it should be as close as possible to the DC input terminals of the IGBT module, using multilayer busbars or wide copper busbars to minimize parasitic inductance. For high-power frequency converters, multiple capacitors may need to be connected in parallel to share the current. Voltage equalization and discharge resistor design for the capacitors also need to be considered. The filtering effect can be verified by measuring the DC bus voltage ripple and switching spikes. Eintech provides high-performance aluminum electrolytic capacitors and film capacitors suitable for DC buses, as well as low-inductance busbar design solutions, which are key support for DC bus filtering design.