All NASA Power Processing Units (PPUs) including DC to DC and DC to AC converters and inverters require a DC-link capacitor, placed between the DC source (PV solar array or battery) and the switching power semiconductors. NASA technical personnel has identified a failure mode in Multi-Layer Ceramic (MLC) DC-link capacitors currently used in PPUs that can cause them to short. Polymer Multi- Layer (PML) capacitors that Sigma Technologies proposed as a solution, have self-healing properties and do not short. The Phase I development demonstrated that the PML parts have superior capacitance stability with temperature and voltage bias. MLC capacitance drops by as much as -80% at -196oC and -40% at +200oC , while PML capacitance variation is limited to -15% and 0% respectively. Furthermore, PML capacitors have approximately 5X higher energy density and 10X higher specific energy. In the Phase II program plug compatible PML capacitors with multi-pin electrodes will be produced and evaluated with a voltage rating specifically designed for 120V PPUs. Some PML parts will be produced with the same capacitance as that of MLCs and others with higher capacitance but equal or lower volume. Equal capacitance parts will dramatically reduce capacitor size and weight and will improve reliability. Higher DC-link capacitance is always desirable in PPU circuits, because and it can further minimize ripple current, voltage fluctuations and transient suppression. Use of higher capacitance PML parts, will improve the functionality and reliability of the overall PPU circuit, without a penalty in weight and volume. PML capacitors will be supplied to NASA technical personnel during the development period for electrical and environmental evaluation. The potential business opportunity of expanding the PML capacitor market to that of high voltage and high capacitance MLCs, which are prone to micro-cracking, are costly and have inferior dielectric properties, will be explored.
Potential NASA Commercial Applications: (Limit 1500 characters, approximately 150 words) Radioisotope power systems (RPS), Advanced Modular Power Systems (AMPS) and Solar Electric Propulsion (SEP) are programs that will directly benefit from this development. Hall thruster PPUs voltage requirements include a 120V input for a 300V direct drive. Also, roll-out photovoltaic arrays are tailored to 120V and 300V for SEP applications. These are voltage ratings that are ideally suited to PML capacitors. In addition to the higher voltage DC-link capacitors targeted by this program, lower voltage PML capacitor can replace tantalum (Ta) capacitors that are commonly used in many aerospace systems. When compared to Ta capacitors, the prismatic PML parts have a wider voltage range, higher frequency response, superior lower temperature performance and lower Equivalent Series Resistance (ESR), which often forces the use of multiple capacitors in parallel to reduce heat dissipation.
Potential NON-NASA Commercial Applications:
: (Limit 1500 characters, approximately 150 words) Capacitors are used in most all electrical and electronic systems ranging from consumer electronics, to industrial electronics, medical instrumentation, transportation, communications and defense. DC-Link capacitors are needed to absorb ripple currents and transient voltage pulses created by switching devices such as IGBT, IGCT and MOSFETs used to convert lower DC voltage to higher DC and AC voltages. The proposed PML DC-link capacitors, have applications in inverter circuits used in renewable energy power generation systems, including photovoltaics and wind power generation, hybrid and electric vehicles and modular energy storage systems tied to the smart grid. PML capacitors are smaller, they have lower cost and higher performance, which will improve life and reliability of power converters. Hybrid and electric automotive drives will particularly benefit from the higher temperature and lower volume and weight of PML capacitors. Sigma Technology has partnered with several automotive OEMs and Tier-1 automotive suppliers and is in the process of supplying PML capacitor samples for evaluation. Unlike the surface mount PML parts developed for NASA these are larger capacitors, that carry 100s of Amps and will be used to replace metallized polypropylene capacitors which are larger that PML and have temperature limitations.
Technology Taxonomy Mapping: (NASA's technology taxonomy has been developed by the SBIR-STTR program to disseminate awareness of proposed and awarded R/R&D in the agency. It is a listing of over 100 technologies, sorted into broad categories, of interest to NASA.) Conversion Distribution/Management
