5,425 research outputs found
Smart Power Grid Synchronization With Fault Tolerant Nonlinear Estimation
Effective real-time state estimation is essential for smart grid synchronization, as electricity demand continues to grow, and renewable energy resources increase their penetration into the grid. In order to provide a more reliable state estimation technique to address the problem of bad data in the PMU-based power synchronization, this paper presents a novel nonlinear estimation framework to dynamically track frequency, voltage magnitudes and phase angles. Instead of directly analyzing in abc coordinate frame, symmetrical component transformation is employed to separate the positive, negative, and zero sequence networks. Then, Clarke\u27s transformation is used to transform the sequence networks into the αβ stationary coordinate frame, which leads to system model formulation. A novel fault tolerant extended Kalman filter based real-time estimation framework is proposed for smart grid synchronization with noisy bad data measurements. Computer simulation studies have demonstrated that the proposed fault tolerant extended Kalman filter (FTEKF) provides more accurate voltage synchronization results than the extended Kalman filter (EKF). The proposed approach has been implemented with dSPACE DS1103 and National Instruments CompactRIO hardware platforms. Computer simulation and hardware instrumentation results have shown the potential applications of FTEKF in smart grid synchronization
Improving the torque generation in self-sensing BLDC drives by shaping the current waveform
Brushless DC drives are widely used in different fields of application because of their high efficiency and power density. Torque ripple can be considered one of the drawbacks of these drives. This paper proposes a method to reduce the torque ripple in BLDC drives. For this reason, the current amplitude is adapted to the rotor position rather than to be kept constant as done in a conventional commutation method. This is done by computing an optimum reference current based on the phase back-EMF waveform. The proposed approach is implemented in a self-sensing drive so its applicability to self-sensing BLDC motor drives is verified. Simulation and experimental results are given and discussed to show that the proposed method actually is able to improve torque production
Edge pixel response studies of edgeless silicon sensor technology for pixellated imaging detectors
Silicon sensor technologies with reduced dead area at the sensor's perimeter are under development at a number of institutes. Several fabrication methods for sensors which are sensitive close to the physical edge of the device are under investigation utilising techniques such as active-edges, passivated edges and current-terminating rings. Such technologies offer the goal of a seamlessly tiled detection surface with minimum dead space between the individual modules. In order to quantify the performance of different geometries and different bulk and implant types, characterisation of several sensors fabricated using active-edge technology were performed at the B16 beam line of the Diamond Light Source. The sensors were fabricated by VTT and bump-bonded to Timepix ROICs. They were 100 and 200 μ m thick sensors, with the last pixel-to-edge distance of either 50 or 100 μ m. The sensors were fabricated as either n-on-n or n-on-p type devices. Using 15 keV monochromatic X-rays with a beam spot of 2.5 μ m, the performance at the outer edge and corners pixels of the sensors was evaluated at three bias voltages. The results indicate a significant change in the charge collection properties between the edge and 5th (up to 275 μ m) from edge pixel for the 200 μ m thick n-on-n sensor. The edge pixel performance of the 100 μ m thick n-on-p sensors is affected only for the last two pixels (up to 110 μ m) subject to biasing conditions. Imaging characteristics of all sensor types investigated are stable over time and the non-uniformities can be minimised by flat-field corrections. The results from the synchrotron tests combined with lab measurements are presented along with an explanation of the observed effects
Variable-Frequency Grid-Sequence Detector Based on a Quasi-Ideal Low-Pass Filter Stage and a Phase-Locked Loop
This paper proposes a filtered-sequence phase-locked loop (FSPLL) structure for detection of the positive sequence in
three-phase systems. The structure includes the use of the Park
transformation and moving average filters (MAF). Performance
of the MAF is mathematically analyzed and represented in Bode
diagrams. The analysis allows a proper selection of the window
width of the optimal filter for its application in the dq transformed
variables. The proposed detector structure allows fast detection
of the grid voltage positive sequence (within one grid voltage cycle).
The MAF eliminates completely any oscillation multiple of the
frequency for which it is designed; thus, this algorithm is not affected
by the presence of imbalances or harmonics in the electrical
grid. Furthermore, the PLL includes a simple-frequency detector
that makes frequency adaptive the frequency depending blocks.
This guarantees the proper operation of the FSPLL under large
frequency changes. The performance of the entire PLL-based detector
is verified through simulation and experiment. It shows veryPeer ReviewedPostprint (published version
Formation of Long Single Quantum Dots in High Quality InSb Nanowires Grown by Molecular Beam Epitaxy
We report on realization and transport spectroscopy study of single quantum
dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The
nanowires employed are 50-80 nm in diameter and the QDs are defined in the
nanowires between the source and drain contacts on a Si/SiO substrate. We
show that highly tunable QD devices can be realized with the MBE-grown InSb
nanowires and the gate-to-dot capacitance extracted in the many-electron
regimes is scaled linearly with the longitudinal dot size, demonstrating that
the devices are of single InSb nanowire QDs even with a longitudinal size of
~700 nm. In the few-electron regime, the quantum levels in the QDs are resolved
and the Land\'e g-factors extracted for the quantum levels from the
magnetotransport measurements are found to be strongly level-dependent and
fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted
from the magnetic field evolutions of a ground state and its neighboring
excited state in an InSb nanowire QD and is on the order of ~300 eV. Our
results establish that the MBE-grown InSb nanowires are of high crystal quality
and are promising for the use in constructing novel quantum devices, such as
entangled spin qubits, one-dimensional Wigner crystals and topological quantum
computing devices.Comment: 19 pages, 5 figure
Cancellation of crosstalk-induced jitter
A novel jitter equalization circuit is presented that addresses crosstalk-induced jitter in high-speed serial links. A simple model of electromagnetic coupling demonstrates the generation of crosstalk-induced jitter. The analysis highlights unique aspects of crosstalk-induced jitter that differ from far-end crosstalk. The model is used to predict the crosstalk-induced jitter in 2-PAM and 4-PAM, which is compared to measurement. Furthermore, the model suggests an equalizer that compensates for the data-induced electromagnetic coupling between adjacent links and is suitable for pre- or post-emphasis schemes. The circuits are implemented using 130-nm MOSFETs and operate at 5-10 Gb/s. The results demonstrate reduced deterministic jitter and lower bit-error rate (BER). At 10 Gb/s, the crosstalk-induced jitter equalizer opens the eye at 10^sup-12 BER from 17 to 45 ps and lowers the rms jitter from 8.7 to 6.3 ps
A Calibration System for Compton Polarimetry at Linear Colliders
Polarimetry with permille-level precision is essential for future
electron-positron linear colliders. Compton polarimeters can reach negligible
statistical uncertainties within seconds of measurement time. The dominating
systematic uncertainties originate from the response and alignment of the
detector which records the Compton scattered electrons. The robust baseline
technology for the Compton polarimeters foreseen at future linear colliders is
based on an array of gas Cherenkov detectors read out by photomultipliers. In
this paper, we will present a calibration method which promises to monitor
nonlinearities in the response of such a detector at the level of a few
permille. This method has been implemented in an LED-based calibration system
which matches the existing prototype detector. The performance of this
calibration system is sufficient to control the corresponding contribution to
the total uncertainty on the extracted polarisation to better than .Comment: 27 pages, 17 figure
Induction methods used in low temperature physics
A study has been made of induction bridges used in low temperature physics.\ud
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In Part 1 the design of a mutual inductance bridge of the Hartshorn type is discussed. This design is based on a critical analysis of impurity effects of the different parts of the Hartshorn bridge. With this equipment frequencies up to 0.5 MHz can be used. Two methods have been developed to examine the secondary signal. In one of these use has been made of AD conversion techniques. In the other one, the secondary signal, produced by a superconducting sample, which is generally distorted, is analysed by using a Fourier expansion.\ud
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In Part 2 equipment is described which enables us to measure the phase and amplitude of the harmonics of the output signal of the bridge. For synchronous detection a reference signal of the same frequency of the harmonic of interest is required. This reference signal is generated from the input signal of the bridge by means of a digital frequency multiplier with programmable multiplication factor N.\ud
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In Part 3 some experimental results, showing the possibilities of the equipment, on some superconductors are presented
Wavelet-based Islanding Detection in Grid-Connected PV Systems
Distributed Power Generation Systems (DPGS)
based on inverters require reliable islanding detection algorithms
(passive or active) in order to determine the electrical grid status
and operate the grid connected inverter properly. These methods
are based on the analysis of the DPGS voltage, current and power
in time or frequency domain.
This paper proposes a time-frequency detection algorithm
based on monitoring the DPGS output power considering the
influence of the PWM, the output LCL filter and of the employed
current controller. Wavelet analysis is applied to obtain time localization
of the islanding condition. Simulation and experimental
results show the performance of the proposed detection algorithm
also in comparison with existing methods
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