70,944 research outputs found
PMU-Based ROCOF Measurements: Uncertainty Limits and Metrological Significance in Power System Applications
In modern power systems, the Rate-of-Change-of-Frequency (ROCOF) may be
largely employed in Wide Area Monitoring, Protection and Control (WAMPAC)
applications. However, a standard approach towards ROCOF measurements is still
missing. In this paper, we investigate the feasibility of Phasor Measurement
Units (PMUs) deployment in ROCOF-based applications, with a specific focus on
Under-Frequency Load-Shedding (UFLS). For this analysis, we select three
state-of-the-art window-based synchrophasor estimation algorithms and compare
different signal models, ROCOF estimation techniques and window lengths in
datasets inspired by real-world acquisitions. In this sense, we are able to
carry out a sensitivity analysis of the behavior of a PMU-based UFLS control
scheme. Based on the proposed results, PMUs prove to be accurate ROCOF meters,
as long as the harmonic and inter-harmonic distortion within the measurement
pass-bandwidth is scarce. In the presence of transient events, the
synchrophasor model looses its appropriateness as the signal energy spreads
over the entire spectrum and cannot be approximated as a sequence of
narrow-band components. Finally, we validate the actual feasibility of
PMU-based UFLS in a real-time simulated scenario where we compare two different
ROCOF estimation techniques with a frequency-based control scheme and we show
their impact on the successful grid restoration.Comment: Manuscript IM-18-20133R. Accepted for publication on IEEE
Transactions on Instrumentation and Measurement (acceptance date: 9 March
2019
Interpolated-DFT-Based Fast and Accurate Amplitude and Phase Estimation for the Control of Power
The quality of energy produced in renewable energy systems has to be at the
high level specified by respective standards and directives. The estimation
accuracy of grid signal parameters is one of the most important factors
affecting this quality. This paper presents a method for a very fast and
accurate amplitude and phase grid signal estimation using the Fast Fourier
Transform procedure and maximum decay sidelobes windows. The most important
features of the method are the elimination of the impact associated with the
conjugate's component on the results and the straightforward implementation.
Moreover, the measurement time is very short - even far less than one period of
the grid signal. The influence of harmonics on the results is reduced by using
a bandpass prefilter. Even using a 40 dB FIR prefilter for the grid signal with
THD = 38%, SNR = 53 dB and a 20-30% slow decay exponential drift the maximum
error of the amplitude estimation is approximately 1% and approximately 0.085
rad of the phase estimation in a real-time DSP system for 512 samples. The
errors are smaller by several orders of magnitude for more accurate prefilters.Comment: in Metrology and Measurement Systems, 201
Indirect test of M-S circuits using multiple specification band guarding
Testing analog and mixed-signal circuits is a costly task due to the required test time targets and high end technical resources. Indirect testing methods partially address these issues providing an efficient solution using easy to measure CUT information that correlates with circuit performances. In this work, a multiple specification band guarding technique is proposed as a method to achieve a test target of misclassified circuits. The acceptance/rejection test regions are encoded using octrees in the measurement space, where the band guarding factors precisely tune the test decision boundary according to the required test yield targets. The generated octree data structure serves to cluster the forthcoming circuits in the production testing phase by solely relying on indirect measurements. The combined use of octree based encoding and multiple specification band guarding makes the testing procedure fast, efficient and highly tunable. The proposed band guarding methodology has been applied to test a band-pass Butterworth filter under parametric variations. Promising simulation results are reported showing remarkable improvements when the multiple specification band guarding criterion is used.Peer ReviewedPostprint (author's final draft
High Resolution Microimaging with Pulsed Electrically-Detected Magnetic Resonance
The investigation of paramagnetic species (such as point defects, dopants,
and impurities) in solid-state electronic devices is significant because of
their effect on device performance. Conventionally, these species are detected
and imaged using the electron spin resonance (ESR) technique. In many
instances, ESR is not sensitive enough to deal with miniature devices having
small numbers of paramagnetic species and high spatial heterogeneity. This
limitation can in principle be overcome by employing a more sensitive method
called electrically-detected magnetic resonance, which is based on measuring
the effect of paramagnetic species on the electric current of the device while
inducing electron spin-flip transitions. However, up until now, measurement of
the current of the device could not reveal the spatial heterogeneity of its
paramagnetic species. We provide here, for the first time, high resolution
microimages of paramagnetic species in operating solar cells obtained through
electrically-detected magnetic resonance. The method is based on unique
microwave pulse sequences for excitation and detection of the electrical signal
under a static magnetic field and powerful pulsed magnetic field gradients that
spatially encode the electrical current of the sample. The approach developed
here can be widely used in the nondestructive three-dimensional inspection and
characterization of paramagnetic species in a variety of electronic devices.Comment: 19 pages, 4 figures +S
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
- …