Capacitor Technologies: Characterization, Selection, and Packaging for Next-Generation Power Electronics Applications

DC-bus capacitors take up substantial space in an electric vehicle (EV) traction inverter, limiting the traction drive's volumetric power density. Film capacitors are typically used, but other capacitor technologies with higher energy densities can help reduce the overall size. In this article, several commercial capacitor technologies are considered for use as dc-bus capacitors for EV traction inverters. They are characterized, evaluated, and compared for optimized design for volume reduction. This article also proposes a novel capacitor packaging technique that utilizes symmetrically distant parallel capacitor branches from termination, which improves electrical and thermal performance compared to a traditional flat-printed circuit board-based design. The proposed design was prototyped for a 100-kW traction inverter, and then, the thermal and electrical characteristics were evaluated under various operating conditions. Results show that the proposed symmetrical design has 40% lower layout inductance and 80% lower temperature difference than a traditional package among the parallel capacitor branches.