Sisir Kumar Nayak

Bio: Sisir Kumar Nayak is an academic researcher from Indian Institute of Technology Guwahati. The author has contributed to research in topics: Transformer oil & Photovoltaic system. The author has an hindex of 15, co-authored 101 publications receiving 713 citations. Previous affiliations of Sisir Kumar Nayak include Indian Institutes of Technology & Indian Institute of Science.

Maximizing the Power Generation of a Partially Shaded PV Array

Abstract: As per energy efficiency of a photovoltaic (PV) system is concerned, partial shading is an important issue. Under partial shading condition, the modules of a PV array receive different levels of solar irradiation, so the power generation of a PV system decreases. The power–voltage characteristic of a partially shaded PV array contains multiple local maxima, and the global maximum power point is one of them. The losses in a PV array depend on the shading pattern and the physical location of shaded modules. This paper presents the Futoshiki puzzle pattern for the arrangement of the modules of a PV array under partial shading condition, ensuring the enhancement of the power generation with respect to totally crossed tired (TCT) structure. In this method, the physical locations of modules in a TCT structure PV array are rearranged without changing the electrical connection of the modules. A comparison between the power generation in TCT and Futoshiki puzzle pattern configuration is presented. It is demonstrated that the power generated by a PV array in the Futoshiki configuration method is enhanced, and mismatch loss (ML) is minimized under different shading patterns by theoretical, simulation, and experimental results.

Extraction of Maximum Power From a PV Array Under Nonuniform Irradiation Conditions

Abstract: In this paper, a generalized algorithm for the physical relocation of the modules with a fixed electrical connection (PRM-FEC) in total cross tied (TCT) configuration of an $m\times n$ (where $m$ and $n$ are the number of rows and columns) photovoltaic array is presented for digit $m$ that is either odd or even number This rearrangement of the TCT configuration distributes the shadows over the array, and hence, it increases the power output of an array under partial shading conditions The proposed scheme is simple and cost effective The comparison of power generated by an array with the TCT, electrical array reconfiguration, and the PRM-FEC configuration is performed with MATLAB simulation and also the simulation results are validated with experimental results The performance of the PRM-FEC configuration is superior to the TCT configuration

Estimation of low-frequency modes in power system using robust modified Prony

Abstract: This study proposes to modify improved Prony method by suggesting to use robust covariance matrix for the identification of low frequency power system modes utilising the real time data obtained from phasor measurement unit. The methods reported in the current literature are many based on l 2-norm minimisation, the estimated modes from these methods are severely affected in the presence of an outlier or bad measurements. Hence, there is a need to develop the method which can provide a good estimate of the modes even in the presence of outliers in the measurements. In order to mitigate the effect of such bad data, this study proposes a robust Prony estimator for estimating the low frequency modes of power systems. The method is based on minimum covariance determinant technique to find the robust covariance followed by improved Prony to estimate the modes. In this study the proposed method is compared with other methods such as improved Prony, etc. on synthetic test signal at different signal-to-noise ratio in the presence of outliers. Furthermore, the effectiveness of the proposed method is also shown on two area system and real time probing data of the Western Electricity Coordinating Council network.

Linear-to-Cross-Polarization Transmission Converter Using Ultrathin and Smaller Periodicity Metasurface

Abstract: A novel ultrathin linear-to-cross-polarization transmission metasurface converter with a periodicity of 8 mm ( $\lambda _{0}\diagup$ 4.26, where $\lambda _{0}$ is free-space wavelength at 8.8 GHz) is proposed, which gives perfect transmission. The proposed MS is a single layer with a thickness of 0.8 mm (0.0235 $\lambda _{0}$ ). The conversion efficiency is near unity due to Fabry–Perot resonator-like condition formed, thus giving the perfect cross-polarized wave. The bandwidth of conversion efficiency greater than 80% is 4.21%. As the top and bottom surfaces have the same patterns, the proposed design shows the same conversion with x - or y -polarized incident wave. Due to the ease of fabrication and light weight, the proposed design is a better candidate for applications such as remote sensing and microwave communications than the multilayer transmission converters.

Magnetic compensation, field-dependent magnetization reversal, and complex magnetic ordering in Co 2 TiO 4

Abstract: The complex nature of magnetic ordering in the spinel Co2TiO4 is investigated by analyzing the temperature and magnetic field dependence of its magnetization (M), specific heat (C-p), and ac magnetic susceptibilities chi' and chi ''. X-ray diffraction of the sample synthesized by the solid-state reaction route confirmed the spinel structure whereas x-ray photoelectron spectroscopy shows its electronic structure to be Co2TiO4 = [Co2+][Co3+ Ti3+]O-4. From analysis of the temperature dependence of the dc paramagnetic susceptibility, the magnetic moments mu(A) = 3.87 mu(B) and mu(B) = 5.19 mu B on the A and B sites are determined with mu(B) in turn yielding mu(Ti3+) = 1.73 mu(B) and mu(Co3+) = 4.89 mu(B). Analysis of the dc and ac susceptibilities combined with the weak anomalies observed in the C-p vs T data shows the existence of a quasi-long-range ferrimagnetic state below T-N similar to 47.8K and a compensation temperature T-comp similar to 32 K, the latter characterized by sign reversal of magnetization with its magnitude depending on the applied magnetic field and the cooling protocol. Analysis of the temperature dependence of M (field cooled) and M (zero field cooled) data and the hysteresis loop parameters is interpreted in terms of large spin clusters. These results in Co2TiO4, significantly different from those reported recently in isostructural Co2SnO4 = [Co2+][Co2+ Sn4+]O-4, warrant further investigations of its magnetic structure using neutron diffraction.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Aerodynamics of wind turbines

Abstract: The study of rotor blade aerodynamic performances of wind turbine has been presented in this thesis. This study was focused on aerodynamic effects changed by blade surface distribution as well as grid solution along the airfoil. The details of numerical calculation from Fluent were described to help predict accurate blade performance for comparison and discussion with available data. The direct surface curvature distribution blade design method for two-dimensional airfoil sections for wind turbine rotors have been discussed with the attentions to Euler equation, velocity diagram and the factors which affect wind turbine performance and applied to design a blade geometry close to an existing wind turbine blade, Eppler387, in order to argue that the blade surface drawn by direct surface curvature distribution blade design method contributes aerodynamic efficiency. The FLUENT calculation of NACA63-215V showed that the aerodynamic characteristics agreed well with the available experimental data at lower angles of attack although it was discontinuities in the surface curvature distributions between 0.7 and 0.8 in x/c. The discontinuities were so small that the blade performance could not be affected. The design of Eppler 387 blade performed to reduce drag force. The discontinuities of surface distribution matched the curve of the pressure coefficients. It was found in the curvature distribution that the leading edge pressure side had difficulties to connect to Bezier curve and also the trailing edge circle was never be tangent to the lines of trailing edge pressure and suction sides due to programming difficulties.

Particle Swarm Optimization Based Solar PV Array Reconfiguration of the Maximum Power Extraction Under Partial Shading Conditions

Abstract: For large photovoltaic power generation plants, number of panels are interconnected in series and parallel to form a photovoltaic (PV) array. In this configuration, partial shade will result in decrease in power output and introduce multiple peaks in the P–V curve. As a consequence, the modules in the array will deliver different row currents. Therefore, to maximize the power extraction from PV array, the panels need to be reconfigured for row current difference minimization. Row current minimization via Su Do Ku game theory do physical relocation of panels may cause laborious work and lengthy interconnecting ties. Hence, in this paper, an alternative to physical relocation based on particle swarm optimization (PSO) connected modules is proposed. In this method, the physical location of the modules remains unchanged, while its electrical connections are altered. Extensive simulations with different shade patterns are carried out and thorough analysis with the help of I–V , P–V curves is carried out to support the usefulness of the proposed method. The effectiveness of proposed PSO technique is evaluated via performance analysis based on energy saving and income generation. Further, a comprehensive comparison of various electrical array reconfiguration based is performed at the last to examine the suitability of proposed array reconfiguration method.

A review on maximum power point tracking for photovoltaic systems with and without shading conditions

Abstract: This paper discusses maximum power point tracking (MPPT) methods of PV system for normal and partial shading conditions (PSC). The selected MPPT methods were classified as artificial intelligent, hybrid, and other MPPT methods. The comparison of researches on MPPT methods under normal condition and PSC reveals that researchers have concentrated more on shading conditions since the last few years mainly due to the need of power output and efficiency improvements. It is believed that the information contained in this piece of work will be of great use for the researchers in the field under consideration.