Application of a Quasi-Static EM Solver to Optimization of Low Inductance Film Capacitors

A large high voltage film capacitor typically consists of numerous "windings" connected in series and parallel, as necessary to achieve the desired voltage and capacitance rating. The discharge properties of such a capacitor are determined by the equivalent series resistance (ESR) and equivalent series inductance (ESL) of the overall assembly, as determined by the properties of the individual windings combined with the structure into which they are assembled, as well as the frequency dependent impedance of the load. A quasi-static electromagnetic solver has been used to compute the frequency-dependent ESR and ESL of capacitor structures which minimize capacitor inductance. The properties are frequency-dependent as a result of the variation in the relative values of resistive and inductive impedances with frequency, which changes the current distribution in the structure and, therefore, the magnetic field (and resulting inductance) as well as power dissipation (resistance) generated by current flow. The ultimate objective is to optimize film capacitors for ns discharge applications and compute the discharge characteristics into a given load.