High Temperature Capacitors for Hybrid Electric Vehicles

Active Signal Technologies, in collaboration with Novacap, Alfred University and Lockheed Martin, proposes in Phase I to build a compact-design 700-V, 50 &#956;F high temperature capacitor module. The module is populated with 1 &#956;F capacitors based on a newly developed sodium bismuth titanate (NBT) dielectric with outstanding electrical performance to 200°C and beyond. Its novel design allows for 115°C coolant flow between the module stack layers, and the geometrical layout of components within the array layers provides for very low ESR and ESL. NBT was selected 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. The capacitor is particularly well suited to handling high ripple current because of its low loss (< 2%) and low frequency dispersion to 60 kHz. The proposal addresses key issues of reliability, failure modes, size and cost. New formulations are investigated to increase dielectric constant and reduce component size. In the Phase I Option and Phase II, nano processing techniques will be introduced to reduce intrinsic flaw size, raise breakdown strength and lower sintering temperature to enable the use of base metal electrodes.