9,456 research outputs found
Index to NASA Tech Briefs, 1975
This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs
Options for Control of Reactive Power by Distributed Photovoltaic Generators
High penetration levels of distributed photovoltaic(PV) generation on an
electrical distribution circuit present several challenges and opportunities
for distribution utilities. Rapidly varying irradiance conditions may cause
voltage sags and swells that cannot be compensated by slowly responding utility
equipment resulting in a degradation of power quality. Although not permitted
under current standards for interconnection of distributed generation,
fast-reacting, VAR-capable PV inverters may provide the necessary reactive
power injection or consumption to maintain voltage regulation under difficult
transient conditions. As side benefit, the control of reactive power injection
at each PV inverter provides an opportunity and a new tool for distribution
utilities to optimize the performance of distribution circuits, e.g. by
minimizing thermal losses. We discuss and compare via simulation various design
options for control systems to manage the reactive power generated by these
inverters. An important design decision that weighs on the speed and quality of
communication required is whether the control should be centralized or
distributed (i.e. local). In general, we find that local control schemes are
capable for maintaining voltage within acceptable bounds. We consider the
benefits of choosing different local variables on which to control and how the
control system can be continuously tuned between robust voltage control,
suitable for daytime operation when circuit conditions can change rapidly, and
loss minimization better suited for nighttime operation.Comment: 8 pages, 8 figure
Modeling and Energy Optimization of LDPC Decoder Circuits with Timing Violations
This paper proposes a "quasi-synchronous" design approach for signal
processing circuits, in which timing violations are permitted, but without the
need for a hardware compensation mechanism. The case of a low-density
parity-check (LDPC) decoder is studied, and a method for accurately modeling
the effect of timing violations at a high level of abstraction is presented.
The error-correction performance of code ensembles is then evaluated using
density evolution while taking into account the effect of timing faults.
Following this, several quasi-synchronous LDPC decoder circuits based on the
offset min-sum algorithm are optimized, providing a 23%-40% reduction in energy
consumption or energy-delay product, while achieving the same performance and
occupying the same area as conventional synchronous circuits.Comment: To appear in IEEE Transactions on Communication
Study of high voltage solar array configurations with integrated power control electronics
Solar array electrical configurations for voltage regulatio
Modeling and analysis of power processing systems: Feasibility investigation and formulation of a methodology
A review is given of future power processing systems planned for the next 20 years, and the state-of-the-art of power processing design modeling and analysis techniques used to optimize power processing systems. A methodology of modeling and analysis of power processing equipment and systems has been formulated to fulfill future tradeoff studies and optimization requirements. Computer techniques were applied to simulate power processor performance and to optimize the design of power processing equipment. A program plan to systematically develop and apply the tools for power processing systems modeling and analysis is presented so that meaningful results can be obtained each year to aid the power processing system engineer and power processing equipment circuit designers in their conceptual and detail design and analysis tasks
A program of research and development of low input voltage conversion and regulation First quarterly report, 14 Jun. - 14 Sep. 1965
Switching and circuit studies for development of low input voltage converter and regulato
Variance-constrained multiobjective control and filtering for nonlinear stochastic systems: A survey
The multiobjective control and filtering problems for nonlinear stochastic systems with variance constraints are surveyed. First, the concepts of nonlinear stochastic systems are recalled along with the introduction of some recent advances. Then, the covariance control theory, which serves as a practical method for multi-objective control design as well as a foundation for linear system theory, is reviewed comprehensively. The multiple design requirements frequently applied in engineering practice for the use of evaluating system performances are introduced, including robustness, reliability, and dissipativity. Several design techniques suitable for the multi-objective variance-constrained control and filtering problems for nonlinear stochastic systems are discussed. In particular, as a special case for the multi-objective design problems, the mixed H 2 / H ∞ control and filtering problems are reviewed in great detail. Subsequently, some latest results on the variance-constrained multi-objective control and filtering problems for the nonlinear stochastic systems are summarized. Finally, conclusions are drawn, and several possible future research directions are pointed out
Ant colony system-based applications to electrical distribution system optimization
Chapter 16, February 201
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