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Lalli, V. R.

Publications and source records attributed to Lalli, V. R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Photovoltaic power system reliability considerations

An example of how modern engineering and safety techniques can be used to assure the reliable and safe operation of photovoltaic power systems is presented. This particular application is for a solar cell power system demonstration project designed to provide electric power requirements for remote villages. The techniques utilized involve a definition of the power system natural and operating environment, use of design criteria and analysis techniques, an awareness of potential problems via the inherent reliability and FMEA methods, and use of fail-safe and planned spare parts engineering philosophy.

Lalli, V. R.↗
NASA NTRS1980

Photovoltaic power system reliability considerations

This paper describes an example of how modern engineering and safety techniques can be used to assure the reliable and safe operation of photovoltaic power systems. This particular application was for a solar cell power system demonstration project in Tangaye, Upper Volta, Africa. The techniques involve a definition of the power system natural and operating environment, use of design criteria and analysis techniques, an awareness of potential problems via the inherent reliability and FMEA methods, and use of a fail-safe and planned spare parts engineering philosophy.

Lalli, V. R.↗
NASA NTRS1978

Measurement of control system response using an analog operational circuit

Ten basic steps are established for an analog method that measures control system response parameters. An example shows how these steps were used on a speed control portion of an auxiliary power unit. The equations and calculations necessary to describe this subsystem are given. The mechanization schematic and simulation diagram for obtaining the measured response parameters of the control system using an analog circuit are explained. Methods for investigating the various effects of the control parameters are described. It is concluded that the optimum system should be underdamped enough to be slightly oscillatory during transients.

Lalli, V. R.↗
NASA NTRS1977

Traveling-wave tube reliability estimates, life tests, and space flight experience

Infant mortality, useful life, and wearout phase of twt life are considered. The performance of existing developmental tubes, flight experience, and sequential hardware testing are evaluated. The reliability history of twt's in space applications is documented by considering: (1) the generic parts of the tube in light of the manner in which their design and operation affect the ultimate reliability of the device, (2) the flight experience of medium power tubes, and (3) the available life test data for existing space-qualified twt's in addition to those of high power devices.

Lalli, V. R.↗
NASA NTRS1975

System reliability analysis through corona testing

A corona vacuum test facility for nondestructive testing of power system components was built in the Reliability and Quality Engineering Test Laboratories at the NASA Lewis Research Center. The facility was developed to simulate operating temperature and vacuum while monitoring corona discharges with residual gases. The facility is being used to test various high-voltage power system components.

Lalli, V. R.↗
NASA NTRS1975

Reliability approach to rotating-component design

A probabilistic methodology for designing rotating mechanical components using reliability to relate stress to strength is explained. The experimental test machines and data obtained for steel to verify this methodology are described. A sample mechanical rotating component design problem is solved by comparing a deterministic design method with the new design-by reliability approach. The new method shows that a smaller size and weight can be obtained for specified rotating shaft life and reliability, and uses the statistical distortion-energy theory with statistical fatigue diagrams for optimum shaft design. Statistical methods are presented for (1) determining strength distributions for steel experimentally, (2) determining a failure theory for stress variations in a rotating shaft subjected to reversed bending and steady torque, and (3) relating strength to stress by reliability.

Kececioglu, D. B.↗
NASA NTRS1975

Corona-vacuum failure mechanism test facilities

A nondestructive corona-vacuum test facility for testing high-voltage power system components has been developed using commercially available hardware. The facility simulates operating temperature and vacuum while monitoring coronal discharges with residual gases. Corona threshold voltages obtained from statorette tests with various gas-solid dielectric systems and comparison with calculated data support the following conclusions: (1) air gives the highest corona threshold voltage and helium the lowest, with argon and helium-xenon mixtures intermediate; (2) corona threshold voltage increases with gas pressure; (3) corona threshold voltage for an armature winding can be accurately calculated by using Paschen curves for a uniform field; and (4) Paschen curves for argon can be used to calculate the corona threshold voltage in He-Xe mixtures, for which Paschen curves are unavailable.-

Lalli, V. R.↗
NASA NTRS1975

System reliability analysis through corona testing

In the Reliability and Quality Engineering Test Laboratory at the NASA Lewis Research Center a nondestructive, corona-vacuum test facility for testing power system components was developed using commercially available hardware. The test facility was developed to simulate operating temperature and vacuum while monitoring corona discharges with residual gases. This facility is being used to test various high voltage power system components.

Lalli, V. R.↗
NASA NTRS1974

Converter design techniques and applications

The design of transistorized voltage converters of the series, shunt, and switching types is developed and explained. The shunt converter has the smallest size, lowest weight, and lowest parts count. Regulation and stability are very good but efficiency is poor. The series converter is somewhat larger in size, heavier, uses more parts, and has an order of magnitude (10 to 1) decrease in regulation performance in comparison with the shunt converter. The switching converter tends to be a compromise with increased size, weight, and circuit complexity to gain in efficiency and regulation over a series converter. A switching converter will usually exhibit ringing in the output filter for some types of loads so it has only fair stability performance.-

Lalli, V. R.↗
NASA NTRS1974

Converter design techniques and applications

Transistorized direct current voltage converters offer a number of advantages over other types because of their small size, low weight, high efficiency, high reliability, precision accuracy and wide range of control. There are three basic types of converter subsystems: series converter in which a voltage-controlled component is placed in series with the load; shunt converter in which a current-controlled component is placed in shunt with the load; and a switching converter in which a voltage-controlled component is turned on and off in series with the load. Converters employing any of these three types of subsystems can provide constant voltage, constant current, or constant impedance across the load. Design and application considerations, step-by-step design procedures, and the solution to sample design problems for the series, shunt, and switching types are presented.

Lalli, V. R.↗
NASA NTRS1973

Servomechanism design techniques and applications - Aerospace problems.

Transistorized alternating-current servomechanisms for a basic position servo with rate feedback or network compensation are reviewed. Studies of optimum methods of control position variables in aerospace applications show that no single method is best for all cases. The optimum method is very much dependent upon available devices, generating sources, and load parameters. These are constraints difficult to identify for future aerospace missions. Design and application considerations are discussed, along with step-by-step design procedures. For illustration, specific design problems are used to exemplify the approach to solutions.

Lalli, V. R.↗
NASA NTRS1973

Servomechanism design techniques and applications aerospace problems

A cryogenic oxygen flow control servomechanism subsystem is described that is typical for an auxiliary power unit fuel system. Three possible types of feedback for this type of subsystem are: position with velocity feedback accomplished by gear train and synchro-transformer, position with velocity feedback accomplished by adding a rate generator and position feedback with compensating network. Servomechanisms employing any of these three types of subsystems can provide the oxygen flow control desired. The differences in performance relate primarily to steadiness of flow with the companion heat modulation. The damping ratio parameter can be used to achieve a reasonable response time.

Lalli, V. R.↗
NASA NTRS1973

The application of standardized control and interface circuits to three dc to dc power converters.

Standardized control and interface circuits were applied to the three most commonly used dc to dc converters: the buck-boost converter, the series-switching buck regulator, and the pulse-modulated parallel inverter. The two-loop ASDTIC regulation control concept was implemented by using a common analog control signal processor and a novel digital control signal processor. This resulted in control circuit standardization and superior static and dynamic performance of the three dc-to-dc converters. Power components stress control, through active peak current limiting and recovery of switching losses, was applied to enhance reliability and converter efficiency.

Yu, Y.↗
NASA NTRS1972

ASDTIC - A feedback control innovation.

The ASDTIC (analog signal to discrete time interval converter) control subsystem provides precise output control of high performance aerospace power supplies. The key to ASDTIC operation is that it stably controls output by sensing output energy change as well as output magnitude. The ASDTIC control subsystem and control module were developed to improve power supply performance during static and dynamic input voltage and output load variations, to reduce output voltage or current regulation due to component variations or aging, to maintain a stable feedback control with variations in the loop gain or loop time constants, and to standardize the feedback control subsystem for power conditioning equipment.

Lalli, V. R.↗
NASA NTRS1972

Aerospace reliability applied to biomedicine.

An analysis is presented that indicates that the reliability and quality assurance methodology selected by NASA to minimize failures in aerospace equipment can be applied directly to biomedical devices to improve hospital equipment reliability. The Space Electric Rocket Test project is used as an example of NASA application of reliability and quality assurance (R&QA) methods. By analogy a comparison is made to show how these same methods can be used in the development of transducers, instrumentation, and complex systems for use in medicine.

Lalli, V. R.↗
NASA NTRS1972

ASDTIC duty-cycle control for power converters

The application of analog signal to discrete interval converter (ASDTIC), a hybrid micromodule, two loop control subsystem, to a switching, stepdown dc to dc converter is described. The power circuitry, interface and ASDTIC subsystems used in this switching regulator were developed to exhibit the improved regulation, transient performance, regulator stability and freedom from the effects of variations in parts characteristics due to environmental changes and aging. ASDTIC can be used with other types of power circuits that use duty-cycle control techniques by simple changes in the interface subsystem. The circuitry and performance characteristics of a +10V dc switching converter as well as that of the ASDTIC micromodule are described. Realization of the ASDTIC hybrid micromodule has been accomplished with a hermetically sealed, beam-lead, bonded/deposited nichrome thin film resistors, discrete capacitors and integrated circuits on dilithic, glazed alumina substrates using 22 feed through terminals in an integrated package.

Lalli, V. R.↗
NASA NTRS1972

ASDTIC duty-cycle control for power converters.

The application of analog signal to discrete interval converter (ASDTIC), a hybrid micromodule, two-loop control subsystem, to a switching, stepdown dc-to-dc converter is described. The power circuitry, interface and ASDTIC subsystems used in this switching regulator were developed to exhibit the improved regulation, transient performance, regulator stability, and freedom from the effects of variations in parts characteristics due to environmental changes and aging. The circuitry and performance characteristics of a +10-V dc switching converter as well as that of the ASDTIC micromodule are described. Realization of the ASDTIC hybrid micromodule has been accomplished with hermetically sealed, beam-lead, bonded/deposited nichrome thin film resistors, discrete capacitors, and integrated circuits on dilithic, glazed alumina substrates, using 22 feed through terminals in an integrated package.

Lalli, V. R.↗