How to suppress resonance in industrial servo bus capacitors?

The servo DC bus capacitor and the parasitic inductance of the line form an LC resonant circuit, generating a resonance peak at a specific frequency (typically a few kHz to several hundred kHz), amplifying harmonic noise and even causing instability. A common electronic suppression method is to first measure the bus impedance curve using an impedance analyzer to identify the resonant frequency f_r. Then, connect a damping network in parallel across the bus capacitor, typically consisting of a resistor (a few ohms to tens of ohms) and a small capacitor (such as a 1μF C0G) in series.

The corner frequency of this RC network should be set near f_r. Another method is to use a high-ESR electrolytic capacitor in parallel with a low-ESR film capacitor, utilizing the natural damping provided by the ESR of the electrolytic capacitor. Simultaneously, optimize the capacitor mounting layout, using low-inductance busbars to reduce parasitic inductance L, thereby increasing the resonant frequency f_r (f_r = 1/(2π√(LC))) and exceeding the controller bandwidth. After suppressing resonance, the bus voltage ripple can be reduced by more than 30%, improving system stability.