How to suppress resonance in the inverter bus capacitor

Suppressing resonance caused by the DC bus capacitor and parasitic parameters in the frequency converter is crucial for system stability and EMC. Resonance is mainly formed by the equivalent series inductance of the bus capacitor, the parasitic inductance of the bus circuit, and the equivalent series resistance of the capacitor itself. Suppression methods include: selecting low ESL bus capacitors, such as multi-pin, short-lead electrolytic capacitors, or directly using film capacitors. Replacing a single large capacitor with multiple small-capacity capacitors in parallel can reduce overall ESL. For capacitor mounting, using multilayer busbars or wide, short copper busbars minimizes parasitic inductance in the circuit.

Connecting a small-value, high-power damping resistor in parallel across the capacitor, or using a capacitor with loss characteristics, can dissipate resonant energy. Directly connecting high-frequency characteristic MLCCs or film capacitors in parallel with the bus capacitor can absorb high-frequency components and change the resonant point. Obtaining the bus impedance-frequency curve through measurement or simulation can pinpoint the resonant point and address it accordingly. Optimizing the PWM control strategy avoids exciting the resonant frequency. Bus resonance can cause voltage spikes, current oscillations, and additional EMI, which must be suppressed through careful selection and layout. Eintech provides low-ESL bus capacitors and damping components to help solve resonance problems.