Optimization of Metalized Film Capacitor Connection to Reduce Stray Inductance

In power electronic applications, due to switching components, the inverter dc-bus generates current pulses at low frequencies and high frequencies (HFs). Usually, a dc-bus capacitor is sized to absorb the current peaks at the switching frequency and to stabilize the dc voltage. For decoupling the HF harmonics, an additional capacitor is required. This decoupling capacitor needs to have a low impedance over a wide range of frequencies. However, their performances for the HF range are highly limited by their stray inductance. In order to minimize the need for an additional decoupling capacitor at HFs, this paper proposes to improve the connections of the dc bus capacitor. Busbar configuration and printed circuit board allow reducing parasitics of the cabling. Several types of interconnections are proposed and characterized in this paper. Both two-terminal and four-terminal capacitors are evaluated and compared regarding operating frequency ranges. The measurement and modeling results show a significant improvement for HF decoupling by using quadrupole coaxial connections.