Phase-shifted Discontinuous Pulse-Width Modulation Methods for Multi-level Inverters Operated in Over-modulation Range

This article presents combinations of the generic phase-shifted pulse-width modulation method with conventional discontinuous pulse-width modulation methods operated in the over-modulation range. The treated discontinuous methods are the third harmonic injection, Depenbrock's DPWM1, and Ogasawara's DPWM2. The significant advantage of the present approach over the conventional phase disposition pulse-width modulation method is the equal power flow between the H-bridges and the improved distribution of the switching operations number between them. Furthermore, they provide improved linearity in the over-modulation range. The proposed pulse-width modulation methods are analyzed by extensive simulation results. Several aspects, such as the total harmonic distortion factor of the inverter output currents and voltages, harmonic content, frequency spectrum distribution, and switchings number, are studied.     

Multi-pulse Rectifiers Feeding H-bridge Inverter

This article presents a comparative analysis of 12-, 18-, 24-, and 36-pulse rectifier topologies supplying 3-phase three-level H-bridge inverters as active loads. The analysis comprises the total harmonic distortion data of the inverter and grid currents and voltages, including inter-modulation harmonics. This article shows that the rectifier-inverter connection produces inter-modulation harmonics between the grid and inverter frequencies. As a result, inter-modulation and sub-harmonics are present in the grid currents. This article presents an analysis and comparison of these inter-modulation effects for the mentioned topologies. Moreover, it is shown that the inter-modulation effects can be reduced by increasing the capacitance of DC-link capacitors, increasing grid series inductance, and using rectifiers with high number of pulses. The analysis is validated by extensive simulation results.     

CuInTe2 and In-rich telluride chalcopyrites thin films obtained by electrodeposition techniques

In order to obtain single-phase thin films of the system Cu–In–Te with optoelectronic properties adequate for solar cells, electrodeposition techniques were used on substrates of molybdenum supported by glass. Different annealings in Te atmosphere have been done that affect the Te concentration and In/Cu atomic ratio. Single chalcopyrite phase appears in two ranges of composition where the In/Cu atomic ratio varies between 0.21–0.76 and 0.90–3.46, respectively. Morphology, cell lattice parameters and electrical resistance for single-phase samples depend strongly on the composition in the annealed samples. The cell parameters ranges are a=6.141–6.183 Å and c=12.201–12.375 Å.     

Matrix pencil method for simultaneously estimating azimuth and elevation angles of arrival along with the frequency of the incoming signals

In this paper we describe a method for simultaneously estimating the direction of arrival (DOA) of the signal along with its unknown frequency. In a typical DOA estimation problem it is often assumed that all the signals are arriving at the antenna array at the same frequency which is assumed to be known. The antenna elements in the array are then placed half wavelength apart at the frequency of operation. However, in practice seldom all the signals arrive at the antenna array at a single pre-specified frequency, but at different frequencies. The question then is what to do when there are signals at multiple frequencies, which are unknown. This paper presents an extension of the matrix pencil method to simultaneously estimate the DOA along with the operating frequency of each of the signals. This novel approach involves approximating the voltages that are induced in a three-dimensional antenna array, by a sum of complex exponentials by jointly estimating the direction of arrival (both azimuth and elevation angles) along with the carrier frequencies of multiple far-field sources impinging on the array by using the three-dimensional matrix pencil method. The matrix pencil method is a direct data domain method for approximating a function by a sum of complex exponentials in the presence of noise. The variances of the estimates computed by the matrix pencil method are quite close to the Cramer–Rao bound. Finally, we illustrate how to carry out the broadband DOA estimation procedure using realistic antenna elements located in a conformal array. Some numerical examples are presented to illustrate the applicability of this methodology in the presence of noise. It is shown that the variance decreases as the SNR increases. The Cramer–Rao bound for the estimators are also provided to illustrate the accuracy and the computational efficiency of this new methodology.     

Detonation Energies from the Cylinder Test and CHEETAH V3.0

The cylinder test for deriving detonation energies is fully described and analyzed, including the relation between streak camera and Fabry‐Perot interferometer data. The 6, 12.5 and 19 mm scaled displacements are modified to represent average relative volumes of 2.2, 4.4 and 7.2. CHEETAH V3.0 is introduced with its new all‐Hugoniot calibration, which produces the most accurate detonation energies to date. Using CHEETAH V3.0 energies at the three cylinder volumes, we find that 107 cylinder shots show full burn. Of these, 52 are taken as standards with an error of ±2.6 %. Another 26 show higher energies, which cannot be explained. Finally, 111 shots show lower energies and these are taken to represent slow kinetics. The composite explosive PBXN‐111 is taken as a special problem, because unconfined and confined Size Effect data plus two different‐size cylinder tests have been done. The form of JWL++ with one fully‐reacted JWL, as copied from Ignition & Growth, failed to fit the data. The two rate constants interact too strongly, so that the form works for 90 % cylinder energies but not for the 25 % found in PBXN‐111. We, therefore, constructed a 2‐JWL form with the first, fast rate describing the detonation velocity and the second, slow rate the cylinder energies. This form of JWL++ isolates the rate constants and works for slow‐reacting explosives. The simple form of JWL++ allows the fast and slow rates to be estimated directly from the data. The Gurney velocity divided by the detonation velocity for the standard explosives is found to be 0.30, 0.33, 0.34 and 0.35 for the relative volumes v=2.2, 4.4, 7.2 and the maximum measured.     

A simple model of the wind turbine induction zone derived from numerical simulations

The induction zone in front of different wind turbine rotors is studied by means of steady‐state Navier‐Stokes simulations combined with an actuator disk approach. It is shown that, for distances beyond 1 rotor radius upstream of the rotors, the induced velocity is self‐similar and independent of the rotor geometry. On the basis of these findings, a simple analytical model of the induction zone of wind turbines is proposed.     

Autonomous tracking of an oceanic thermal front by a Wave Glider

Temporal variation in the structure and location of dynamic ocean features make them challenging to observe. Beyond requiring sufficient persistence and speed of the sensor platform, effective observation is augmented by autonomous feature detection coupled with adaptive localization of mapping effort. These capabilities enable observations to remain localized within and around features of interest, thereby enhancing spatial and temporal resolution in their depiction. A Wave Glider is a wave‐propelled unmanned surface vehicle with solar energy collection to support payload and a backup propeller in calm sea state. The efficiency of this platform enables persistence (months), and its propulsion system provides speed (~1 m/s). Building on these capabilities, we aim at enabling the Wave Glider to autonomously recognize and track oceanic features that have strong surface expressions, accessible to near‐surface sensors. We present a method of using a Wave Glider to autonomously track an oceanic thermal front known to have biological importance and dynamic evolution. In October 2017, this method was applied to tracking and mapping an upwelling front in Monterey Bay, CA, over 39 hr. The field result demonstrates adaptive localization of mapping based on autonomous feature detection.