Dual Input Z-source Indirect Matrix Converter for Grid Connected Hybrid Renewable Energy Systems

This paper presents a new converter topology for grid connected Hybrid Renewable Energy System (HRES). The proposed topology named Dual Input Z-source Indirect Matrix Converter (DIZIMC) consists of an Ultra Sparse Z-source Matrix Converter (USZMC) interfacing PV and Wind Turbine (WT) to the grid. The DC link of the proposed converter is replaced by Interconnection Sources System (ISS). The ISS operates according to whether the sources produce energy or not. It allows connecting the sources individually or simultaneously and even isolates them if necessary. In the other hand, the DIZIMC provides several advantages such as reduced number of IGBTs and compact size inherited from USZMC, the use of Z-sources instead of conventional DC/DC converters keep the matrix configuration of the global structure. The global model of the proposed system was tested by simulation under Matlab/Simpowersys environment. The obtained results show clearly freedom in connecting the operational sources, also a better quality of energy injected to the grid.

Big and Young Supermassive Black Holes in the Early Universe

Blazars are active galactic nuclei characterized by relativistic jets launched in the vicinity of the central engine (i.e., a supermassive black hole), which are oriented close to our line of sight. Their peculiar orientation makes them very efficient tracers of the overall jetted population, and due to their brightness they can be visible up to very high redshifts. A deep knowledge of these objects can provide fundamental clues to the models of formation and growth of the first supermassive black holes, but the search for them in the early Universe must be careful and follow a systematic approach. The discovery in the last ∼15 years of extremely massive blazars at very high redshifts (MBH>109M⊙, z>4) revolutionized our perception of their earliest evolution: there seem to be different formation epochs for extremely massive black holes hosted in jetted (z∼4) and non-jetted (z∼2.5) systems. This is not easy to explain, since one would expect jetted sources to accrete less efficiently. Small differences in the population are also derived from the search for such high-z sources. We will go through the open questions in order to understand where the common knowledge stands and which steps must be taken to better understand the formation and common evolution of supermassive black holes and jets in the early Universe.

Kilohertz quasi-periodic oscillations as probes of the X-ray color-color diagram and neutron star accretion-disk structure for Z sources

Based on the detected kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (NS-LMXBs), we investigate the evolution of the NS magnetosphere-disk structure along the Z track in the X-ray color-color diagram (CCD) for luminous Z sources, such as Cyg X-2, GX 5-1, GX 17+2, and Sco X-1. We find that the magnetosphere-disk radius r inferred by kHz QPOs for all the sources shows a monotonically decreasing trend along the Z track from the horizontal branch (HB) to the normal branch (NB), implying that the dominated radiation components may dramatically change as the accretion disk moves toward the NS surface. In addition, the specific radius that corresponds to the HB/NB vertex is found to be around r ∼ 20 km, implying a potential characteristic position of transiting for the X-ray radiation mode. Furthermore, we find that the NBs that occur near the NS surface have a radius of r ∼ 16−20 km, which is systematically smaller than those of HBs that have radii of r ∼ 20−29 km. To interpret the relation between the CCD properties and the special magnetosphere-disk radii of Z sources, we suggest that the magnetic field lines corresponding to NB are “frozen-in” to the plasma, and move further inward with the shrinking of the NS magnetosphere-disk radius and pile up near the NS surface. They then form a strong magnetic field region around r ∼ 16−20 km, where the high magnetic energy density and high plasma mass density may dominate the radiation process in NB.

AstroSat view of LMC X-2: evolution of broad-band X-ray spectral properties along a complete Z-track

ABSTRACT In this paper, we report the first results of the extragalactic Z-source Large Magellanic Cloud (LMC) X-2 obtained using the ∼140 ks observations with Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat. The Hardness-Intensity Diagram created with the LAXPC data revealed a complete Z-pattern of the source, showing all the three branches. We studied the evolution of the broad-band X-ray spectra in the energy range of 0.5–20.0 keV along the Z-track, a first such study of this source. The X-ray spectra of the different parts of the Z-pattern were well described by an absorbed Comptonized component. An absence of the accretion disc component suggests that the disc is most probably obscured by a Comptonized region. The best fit electron temperature (kTe) was found to be in the range of 1.7–2.1 keV and optical depth (τ) was found to be in the range of 13.2–17.5. The optical depth (τ) increased as the source moved from the normal/flaring branch (NB/FB) vertex to the upper part of the FB, suggesting a possible outflow triggered by a strong radiation pressure. The power density spectra (PDS) of HB and NB could be fitted with a pure power law of index α∼1.68 and 0.83, respectively. We also found a weak evidence of quasi-periodic oscillation (2.8σ) in the FB. The intrinsic luminosity of the source varied between (1.03–1.79) × 1038 erg s−1. We discuss our results by comparing with other Z-sources and the previous observations of LMC X-2.

Three-Phase Symmetric Cascading Z-Source Seven Levels Multilevel Inverter Excited by Multi Carrier Sinusoidal Pulse Width Modulation Scheme

The Multilevel Z sources Inverter have been documented as attractive topologies used for elevated voltage adaptation. As the digit of levels improved, the synthesized set of steps output waveform have many ladder, imminent the preferred sine waveform but the major weakness of MLI be its amplitude of ac output voltage is imperfect to DC input sources voltage summing up. To conquer this drawback seven level cascading symmetric multilevel inverter based Z source inverter have been projected. This work focuses on different multi-carrier sinusoidal PWM scheme for the seven level three phase Z source symmetric cascading inverter. Performance parameters of seven level three phase Z source symmetric cascading inverter has been analyzed. A simulation circuit model of seven level three phase Z source symmetric cascading inverter urbanized using MATLAB/SIMULINK and its presentation have been urbanized.

Optical Flow Estimation Using Total Least Squares Variants

The problem of recursively approximating motion resulting from the Optical Flow (OF) in video thru Total Least Squares (TLS) techniques is addressed. TLS method solves an inconsistent system Gu=z , with G and z in error due to temporal/spatial derivatives, and nonlinearity, while the Ordinary Least Squares (OLS) model has noise only in z. Sources of difficulty involve the non-stationarity of the field, the ill-posedness, and the existence of noise in the data. Three ways of applying the TLS with different noise conjectures to the end problem are observed. First, the classical TLS (cTLS) is introduced, where the entries of the error matrices of each row of the augmented matrix [G;z] have zero mean and the same standard deviation. Next, the Generalized Total Least Squares (GTLS) is defined to provide a more stable solution, but it still has some problems. The Generalized Scaled TLS (GSTLS) has G and z tainted by different sources of additive zero-mean Gaussian noise and scaling [G;z] by nonsingular D and E, that is, D[G;z] E makes the errors iid with zero mean and a diagonal covariance matrix. The scaling is computed from some knowledge on the error distribution to improve the GTLS estimate. For moderate levels of additive noise, GSTLS outperforms the OLS, and the GTLS approaches. Although any TLS variant requires more computations than the OLS, it is still applicable with proper scaling of the data matrix.