Energy Buffer Capacitors for Use in Dynamic Power Conversion ACUs

This NASA Phase I SBIR proposal addresses the development of energy buffer capacitors to replace multilayer ceramic (MLC) capacitors used in the advance controller unit (ACU), of dynamic power conversion systems. Dynamic power conversion systems designed for long duration deep space missions, require stable and reliable ACUs to precisely control the function of the energy conversion system and provide DC power to the spacecraft. MLCs have poor capacitance stability with temperature, voltage and time on voltage. This development proposes to design, produce and evaluate energy buffer capacitors using Nanolam capacitors, developed for use in inverters of hybrid and electric vehicles. Nanolam capacitors comprise 10,000s of high temperature radiation cured polymers that have superior capacitance and dissipation factor stability in the temperature range of -196oC to +200oC. Nanolam capacitors are self-healing, prismatic in shape and they are radiation tolerant. One unique feature of the Nanolam capacitor technology is the use of submicron polymer dielectric layers. It has been demonstrated that as the thickness of the cross-linked amorphous dielectrics decreases below about 1.0mm, the breakdown strength increases significantly, which results in capacitors with superior energy density. Internal series sections allow Nanolam capacitors with dielectric thicknesses of few hundred nanometers to service applications with voltages as high as 10,000V. The proposed development will produce and evaluate energy buffer Nanolam capacitors with a rating of 1200mF/175VDC for an 120V power bus. A single Nanolam capacitor will be used to replace at least ten individual MLC parts, mounted on a PCB to make up the 1200mF. The major project objective is to demonstrate superior capacitance stability, energy density and specific energy to MLCs as well as deliver parts to the NASA technical personnel for independent evaluation.

Radioisotope dynamic power conversion systems controllers, as well as roll-out photovoltaic array controllers used to power Hall thrusters, are tailored mostly to 120V and there is some ongoing development with 300V systems. Nanolam capacitors can replace multilayer ceramic capacitors in multiple circuits of a single controller. Potential circuit applications include power factor correction in a rectifier circuit, energy buffer in an AC/DC inverter and DC-link in a DC/DC inverter.

Developing lower voltage capacitors will greatly expand the Nanolam market size and application space. Non-NASA applications include inverters for residential and commercial PV systems, battery chargers, inverters for 48V automotive applications, used in soft hybrids as well as internal combustion vehicles with stop and go systems, and capacitors for commercial aviation and commercial satellites.

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