How to design a DC bus filter for industrial servo systems?

Servo DC bus filtering design is crucial for suppressing high-frequency switching noise and providing instantaneous energy.

Etymotic recommends a layered design: the first layer is an electrolytic capacitor providing large-capacity energy storage (e.g., 450V/680μF) to handle low-frequency ripple; the second layer is a low-ESL film capacitor or C0G ceramic capacitor (e.g., 100nF/630V), mounted close to the IGBT module pins to absorb high-frequency current spikes; the third layer is a common-mode rejection layer, with Y capacitors (2.2nF/Y1) connected to the chassis ground at the positive and negative terminals of the bus, and a PBZ3216E-600Z0T ferrite bead (600Ω) can be connected in series on the bus to suppress ultra-high-frequency noise.

Key parameter calculations: the electrolytic capacitor value must meet the requirement of voltage ripple <5%; the resonant frequency of the film capacitor should be higher than 10 times the switching frequency. The layout uses a low-inductance busbar to minimize the current loop area of the capacitors. Actual measurements show that this design can suppress bus voltage spikes to within 50V and reduce conducted interference (150kHz-30MHz) by 20-25dB.