Film Capacitors for High Temperature AC-DC Inverter Applications

Abstract:
High temperature commercial quality capacitors have been built and tested using newly introduced dielectric film that can operate at high temperatures reaching 150 °C. At 900 volts and 150 °C the capacitors passed 2000 hours of life testing and passed 3600 hours at 1000 volts and 130 °C. Insulation resistance (IR), dielectric losses (tan δ) and equivalent series resistance (ESR) were stable over the test duration. A positive capacitance change (DeltaC) was noted early in the test and remained acceptable at the end of the test. Reaching 900V and 1000V performance was enabled by appropriate segmented metallization of the dielectric film and process optimization for building capacitor elements. Achieving 150deg C performance was possible due to stable inherent dielectric characteristics (Dk and Df) of the high heat polymer film. Operating at high temperature and high voltage is advantageous for efficiency improvement in AC-DC inverter modules, in particular those based on SiC technology. Additionally, the demand for active cooling can be reduced or eliminated giving rise to compact module design and bringing the capacitors closer to the SiC switch for lower induction losses. Compact designs may offer opportunity for weight reduction in electric vehicles.