Characterization of Equivalent Series Inductance for DC Link Capacitors and Bus Structures

The equivalent series inductance (ESL) of the DC link capacitor and associated bus structure connecting to the switch module has important implications for optimization of electric vehicle inverters. In many cases, additional snubber (bypass) capacitors can be eliminated for sufficiently low ESL, thus reducing cost, weight and volume. This paper presents ESL measurements for realistic capacitor/bus structures using a practical method previously documented [1]. Supporting magneto-dynamic finite element analysis results are also presented and shown to agree quite well with the measurements. The measurement and simulation results demonstrate that a 1000 μF 600V Power Ring Film Capacitor has an ESL of approximately 3 nH with a properly designed terminal structure. The bus structure is shown to dominate the total ESL for both horizontal and vertical inverter topologies when using annular form factor film capacitors with an optimal terminal configuration.