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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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44 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Single Event Transients in Voltage Regulators for FPGA Power Supply Applications

As with other bipolar analog devices, voltage regulators are known to be sensitive to single event transients (SET). In typical applications, large output capacitors are used to provide noise immunity. Therefore, since SET amplitude and duration are generally small, they are often of secondary importance due to this capacitance filtering. In low voltage applications, however, even small SET are a concern. Over-voltages may cause destructive conditions. Under-voltages may cause functional interrupts and may also trigger electrical latchup conditions. In addition, internal protection circuits which are affected by load as well as internal thermal effects can also be triggered from heavy ions, causing dropouts or shutdown ranging from milliseconds to seconds. In the case of FPGA power supplies applications, SETS are critical. For example, in the case of Actel FPGA RTAX family, core power supply voltage is 1.5V. Manufacturer specifies an absolute maximum rating of 1.6V and recommended operating conditions between 1.425V and 1.575V. Therefore, according to the manufacturer, any transient of amplitude greater than 75 mV can disrupt normal circuit functions, and overvoltages greater than 100 mV may damage the FPGA. We tested five low dropout voltage regulators for SET sensitivity under a large range of circuit application conditions.

Poivey, Christian↗
NASA NTRS2009

Performance and Safety Testing of Varta Li-Ion Polymer Cells

Varta Cell Characteristics: Voltage : 3.7 V Capacity : 1.21 Ah Dimensions : 5mm X 37mm X 38.5 mm MOSFET switches for Overvoltage and Undervoltage. Initial Screening Results 29 Cells delivered: Statistics on Ph ysical Screening: Thickness (mm): Average- 5.08; Weight(g)- 22.8938; OCV (V)- 3.787; CCV (V)- 3.491.

Patel, Pranav↗
NASA NTRS2010

Hazards Due to Overdischarge in Lithium-ion Cylindrical Cells in Multi-cell Configurations

Lithium-ion cells in the cylindrical Commercial-off-the-shelf 18650 design format were used to study the hazards associated with overdischarge. The cells in series or in parallel configurations were subjected to different conditions of overdischarge. The cells in parallel configurations were all overdischarged to 2.0 V for 75 cycles with one cell removed at 25 cycles to study the health of the cell. The cells in series were designed to be in an unbalanced configuration by discharging one cell in each series configuration before the start of test. The discharge consisted of removing a pre-determined capacity from the cell. This ranged from 50 to 150 mAh removal. The cells were discharged down to a predetermined end-of-discharge voltage cutoff which allowed the cell with lower capacity to go into an overdischarge mode. The cell modules that survived the 75 cycles were subjected to one overvoltage test to 4.4 V/cell.

Jeevarajan, Judith↗
NASA NTRS2012

Safety and Long-Term Performance of Lithium-ion Pouch Cells

Lithium-ion batteries have the highest energy density of the batteries available in the commercial market today. Although most lithium-ion cell designs use a metal can design, this has changed significantly in recent years. Cell designs are offered in the pouch format as they offer better volumetric and gravimetric energy densities and in some cases, higher tolerance to abuse or off-nominal conditions. In the past decade, several state-of-the-art lithium-ion pouch cell designs have been tested. The pouch cell designs have become more robust in the past two years but there are still a few issues that need to be looked into for optimization. The pouch cells seem to have a tendency to swell when left in storage under ambient conditions. The cells also swell under overvoltage and undervoltage conditions. A significant issue that has been observed is the swelling of the cells under a vacuum condition which could lead to deformation of the cell pouch after this exposure. This last factor would be very critical in the use of these cell designs for space applications as vacuum exposure is used to check for cell and battery leaks before it is flown into space. In rare cases, corrosion of the aluminum layer of the pouches has been observed in stored cells. Pouch material analysis has been carried out in an effort to understand the strength of the pouches and determine if this is a factor in the corrosion as well as unsafe condition of the cells as deformation of the inner layers of the pouch could occur when the cells swell under the various conditions described above. Pouch materials are typically aluminized plastic, made up of a layer of Al sandwiched between one or more layers of polymeric material. Deformations or cell manufacturing processes could lead to a compromise of the inner polymeric layer/s of the pouch leading to the corrosion of the Al layer in the aluminized pouch material. The safety of the pouch cell designs has been determined for cells from various manufacturers. The results are varied and in some cases, unexpected. This paper presents a summary of the tests carried out on a few li-ion pouch cell designs from various cell manufacturers. The data will include performance under different conditions specifically cycling under vacuum conditions with and without restraints as well as safety test data. The presentation will also include detailed analysis of the pouch material for the cells studied.

Jeevarajan, Judith↗
NASA NTRS2018

Advanced Stirling Convertor Control Unit Testing at NASA Glenn Research Center in the Radioisotope Power Systems System Integration Laboratory

Future NASA missions could include long-duration flyby, orbital, lander, or rover applications where generating power from sunlight may be limited. Radioisotope power systems (RPSs) provide a dependable power source for missions where inadequate sunlight or operational requirements make other power systems impractical. Over the past 16 years, NASA Glenn Research Center has been supporting the development of RPSs. The advanced Stirling radioisotope generator (ASRG) utilized a pair of advanced Stirling convertors (ASCs). Although flight development of the ASRG has been canceled, much of the technology and hardware continued development and testing to guide future activities. Specifically, a controller for the convertor(s) is an integral part of a Stirling-based RPS. For the ASRG design, the controller maintains stable operation of the convertors, regulates the alternating current produced by the linear alternator of the convertor, provides a specified direct-current output voltage for the spacecraft, and synchronizes the piston motion of the two convertors to minimize vibration as well as manage and maintain operation with a stable piston amplitude and hot-end temperature. It not only provides power to the spacecraft but also must regulate convertor operation to avoid damage to internal components and maintain safe thermal conditions after fueling. Lockheed Martin Coherent Technologies, Inc., has designed, developed, and tested an ASC control unit engineering development unit (ACU EDU) to support this effort. GRC used the ACU EDU as part of its nonnuclear representation of a RPS that also consists of a Dual advanced Stirling convertor simulator (DASCS), and associated support equipment to perform a test in the Radioisotope Power Systems System Integration Laboratory (RSIL). The RSIL was designed and built with flexibility to evaluate hardware utilizing RPS technology. The RSIL provides insight into the electrical interactions between as many as three radioisotope power generators, associated control strategies, and typical electric system loads. The first phase of testing included a DASCS that was developed by Johns Hopkins University Applied Physics Laboratory and simulates the operation and electrical behavior of a pair of ASCs in real time via a combination of hardware and software. Testing included the following spacecraft electrical energy storage configurations: capacitor, battery, and supercapacitor. Testing of the DASCS and ACU in each energy storage configuration included simulation of a typical mission profile and transient voltage and current data during load turnon and turnoff. Testing for these devices also included the initiation of several system faults such as short circuits, electrical bus overvoltage, undervoltage, and a "dead bus" recovery to restore normal power operations. The goal of this testing was to verify operation of the ACU(s) when connected to a spacecraft electrical bus. The results of these tests are presented here.

General↗
NASA NTRSDate not supplied

Extending the Life of NASA’s Tracking and Data Relay Satellite (TDRS)-8: TDRS-8 Power Challenges And Planning for End of Mission

The United States National Aeronautics and Space Administration (NASA) Near Space Network’s Space Relay (SR) System provides communication relay services to a number of scientific and manned space missions with its Tracking and Data Relay Satellite (TDRS) constellation. NASA’s eighth Tracking and Data Relay Satellite (TDRS) has been experiencing a decline in the health of its power subsystem, and recent reliability analyses indicate that the end of its mission serving the Space Relay is imminent. Launched in 2000, TDRS-8 is the oldest TDRS built upon a Boeing 601 platform, and as such it is the first TDRS to experience these age-related failures. The most prevalent elements of the power subsystem to decline are the solar array circuitry and the Bus Voltage Limiters (BVLs), which prevent too much power from the solar arrays being transferred to the bus by shunting excess current. This means that while the loss of solar array circuits introduces concerns that the solar arrays will continue providing the spacecraft with enough current to remain power positive, the loss of BVLs introduces a concern that the bus may not be adequately protected from overvoltage events. Spacecraft engineers at the TDRS primary ground terminal, the White Sands Complex (WSC) in Las Cruces, New Mexico, and at NASA's Goddard Space Flight Center (GSFC) have also been working in collaboration with Boeing to develop innovative techniques to extend the serviceable life of TDRS-8.

tdrs↗
NASA NTRS2019

A Simple Control to Reduce the Voltage Stress of Non-Conducting Switches in Three-Level ANPC Converter

With the development of wide band-gap (WBG) technology, the switching speed of power semiconductor devices is increased, which makes circuits more sensitive to parasitics. For three-level active neutral point clamped (3L-ANPC) converters, the over-voltage of non-conducting switches can be an issue. This paper analyzes the multiple commutation loops in 3L-ANPC converter and summarizes the impact factors of the over-voltage for the non-conducting switch. It is found that the nonlinearity of the output capacitance of the device can significantly influence the over-voltage. A simple control without introducing any additional hardware circuit is proposed to attenuate the impact of the nonlinearity. With the proposed control, the peak over-voltage of the non-conducting switch can be reduced significantly. Multi-pulse test is conducted for a 3L- ANPC converter built with silicon carbide (SiC) MOSFETs. The testing results show that the peak over-voltage decreases from 892 V to 624 V with the proposed control. More detailed analysis and experimental results will be provided in the final paper.

SiC MOSFET↗
NASA NTRS2019

Design of Low Inductance Busbar for 500 kVA Three-Level ANPC Converter

The adoption of SiC devices in high power applications enables higher switching speed, which requires lower circuit parasitic inductance to reduce the voltage overshoot. This paper presents the design of a busbar for a 500 kVA three-level active natural clamped converter. The layout of the busbar is discussed in detail based on the analysis of the multiple commutation loops, magnetic cancelling effect, and DC-link capacitor placement. The loop inductance of the designed busbar is verified with simulation, impedance measurements and converter experiment. The results can match with each other and the inductances of small and large loop are 6.5 nH and 17.5 nH respectively, which is significantly lower than the busbars of NPC type converters in other references.

SiC MOSFET↗