High Temperature Capacitors for Hybrid Electric Vehicles

Active Signal Technologies, in collaboration with Novacap, Alfred University and Lockheed Martin, proposes to further develop its high-temperature capacitor technology and deliver multiple 700-V modules to the Army. The modules will be populated with 1-µF capacitors based on a newly-developed sodium bismuth titanate (NBT) dielectric with outstanding electrical performance to 200°C and beyond. While the original design allowed for flow of 115°C coolant between the layers making up the module stack, Phase-I testing demonstrated that the high-temperature capability and low ESR of the NBT capacitor enables operation at 150°C ambient without forced cooling. The NBT dielectric, Type H, was selected for this application because of its very low combined temperature and voltage coefficient which gives rise to a net capacitance change < 20% across the band from -40°C to +200°C at full voltage stress. In Phase II, minor variations on the formulation will be investigated to increase dielectric constant and reduce component size, and sintering studies including nano-processing techniques are introduced to reduce intrinsic flaw size, raise breakdown strength and lower the sintering temperature to enable the use of cheaper electrodes. DC HALT studies will be conducted and a novel 60-kHz life/screening test developed to ensure reliability.