Sisir Kumar Nayak

Maximizing the Power Generation of a Partially Shaded PV Array

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.

Micro and small-scale HAWT blades airfoils study through CFD for low wind applications

In this paper, an analysis of basic airfoils profile for micro and small-scale horizontal axis wind turbine (HAWT) has been studied for different angle-of-attack α and fixed Reynolds number. For turbine blade modeling, the data used is from National advisory committee of aeronautics (NACA) of five digit airfoil series. The comprehensive relationship between optimal angle-of-attack α and Reynolds number has been analyzed. A low or high lift-to-drag ratio (Lc/Dc) can be identified at different angle-of-attack α. The computational fluid dynamics analysis of NACA 63-415 airfoil is carried out at different angle-of-attack α at wind speed 5 m/s using ANSYS/Fluent software. The pressure, turbulence and velocity distribution plots have been observed.

A robust TLS-ESPIRIT method using covariance approach for identification of low-frequency oscillatory mode in power systems

A robust spectral estimation technique for identifying low frequency oscillatory mode is presented in this paper. The effect of outliers is taken into account in the proposed method which occurs due to temporary fault in network or measuring instruments. In order to reduce the effect of such bad data the paper presents a robust covariance approach based TLS-ESPIRIT estimation using multivariate M (MM) estimator. Comparison of the modified TLS-ESPIRIT method with the proposed method are done on two test signals for mode identification at different signal-to-noise ratio (SNR). Efficiency of the proposed method is obtained in presence of outliers through Monte Carlo simulations. Comparison of the proposed method with the TLS-ESPIRIT method is also carried out on real time measurement data of Western Electricity Coordinating Council (WECC) network.

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

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 × 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.

A nonlinear filtering technique along with RD and TLS-ESPRIT for mode identification of ambient data

The analysis of electromechanical modes has become a major concern in power system. A spectral estimation technique using a nonlinear filter for identifying the inter-area oscillatory modes for ambient data is presented in this paper. The proposed method contains three steps: (1) non-linear filtering to remove the non-linear trends from the ambient signals (2) Random decrement (RD) technique for obtaining the free decay response from the pre-filtered ambient data and (3) TLS-ESPRIT method for estimating the frequency and damping from these impulse responses obtained using RD. The proposed method is compared with RDT-TLS-ESPRIT method using simulated test signals for ambient data. Comparison of the proposed method is further carried out for actual ambient signals received from a PMU connected to Indian grid. The results shows that the proposed method is able to identify the modes accurately, and hence is suitable for application in wide area monitoring of oscillatory modes.

Modeling and optimal design of small HAWT blades for analyzing the starting torque behavior

This paper presents a computational framework for an optimal aerodynamic blade design. Analysis of the wind turbine rotor is conducted using blade element momentum (BEM) theory. The geometric parameters of the wind turbine also have been calculated by BEM theory. The methodology and design approach is discussed in detail throughout this paper. A small three-bladed horizontal axis wind turbine (HAWT) is designed to improve its starting torque behaviour. The study of the starting torque behaviour, its analysis, and a new approach to smoothen it, is the important part of this work. The simulation results show that a turbine starts rotating with a smooth rising torque, and after ten seconds it gains a constant torque and a constant angular velocity which seems to be quite encouraging thus reducing the mechanical vibration of the system. The MATLAB is used to get the blade geometry parameters and aerodynamic forces along the blade span, the Pro/ENGINEER is used for the solid structure modeling of the wind turbine and ADAMS is being used for the simulation purpose.

Comparative study of mechanical and electrical strength of kraft paper in nanofluid based transformer oil and mineral oil

Transformer is a long run device in a power system network. The life of the transformer is affected by the insulating system provided to it. When transformer oil comes in contact with cellulosic paper, it generates oxides, peroxides and several other harmful gases that lead to the formation of sludge and impurities in the insulating oil. This sludge, not only affects the dielectric properties of the oil, at the same time it is also responsible for the formation of hot spots in the core and hence leads to failure in the winding. Adequate insulation in the winding is maintained by using insulating kraft paper, but sludge contamination degrades the electrical and mechanical strength of the cellulosic kraft paper. To understand the mechanism behind the formation of sludge and decay in the properties of the kraft paper, thermal ageing study has been performed followed by electrical and mechanical strength analysis. Keeping the same kraft paper, a comparative study of mechanical and electrical strength has been carried out after thermal ageing in two different insulating oils namely: mineral oil (MO) and exfoliated hexagonal boron nitride (Eh-BN) based nanofluid (NF). Initially the thermophysical and electrical properties of the MO are studied. However, non-biodegradable nature, inferior thermophysical and electrical properties of the MO motivate the researcher to develop a new class of NF (Eh-BN/MO) for transformer application. Eh-BN nanofiller are dispersed into the MO and extensively sonicated to avoid the agglomeration in the NF. Five different concentrations of Eh-BN nanofiller from 0.01–0.1wt.% are dispersed into the MO to prepare the Eh-BN/MO-NF. Due to enhanced stability and superior thermophysical and electrical properties, 0.01wt.% concentration is chosen to prepare Eh-BN/MO-NF for ageing study. It is also observed that thermophysical and electrical properties of 0.01wt.% of Eh-BN/MO-NF are far more superior to the existing MO. Hence to understand the effect of the preferred NF to the paper insulation inside the transformer, ageing study is necessary. Ageing study of both MO/kraft paper and 0.01wt% Eh-BN/MO-NF/kraft paper are performed in two different ageing vessels at same parametric conditions and the electrical and mechanical strength of the aged kraft paper are examined in different ageing duration. The moisture absorbances in both the cases are studied and lower moisture contamination and higher breakdown strength has been observed for kraft paper in NF. INSTRON tensile test measurement setup is used to measure the tensile strength of the virgin kraft paper, MO/kraft paper and 0.01wt.% NF/kraft paper. It is observed from the experimental results that both modulus and tensile strength of the aged kraft paper in the Eh-BN/MO-NF are superior to the aged kraft paper in MO. It is concluded that Eh-BN/MO-NF can reduce the effect of sludge formation and hence better insulation stability can be achieved for enhancing the life of the transformer.

Relay approach for parameter extraction of li-ion battery and SOC estimation using finite time observer

This paper proposes a novel integrated robust system identification and state of charge estimation of Li-ion battery. A finite time extended state observer is used for state of charge (SOC) estimation of Li-ion battery. A relay feedback test has been adopted to yield accurate battery parameters in noisy environment. New identification method using state space based relay feedback approach is employed with a disturbance nullifier to extract the parameters of battery model. Thereafter, the objective of SOC estimation is carried out by designing a novel finite time extended state observer based on higher order sliding modes. The unknown battery model parameters are determined first, followed by the estimation of SOC next, under both charging and discharging conditions. This investigation finds a high amount of accuracy in the proposed battery model identification method, besides an accurate and time bound estimation of SOC using the proposed observer scheme.

Comparative statistical analysis on AC breakdown voltage of thermally aged nanofluid with mineral oil

Insulating properties of the conventional transformer oil can be enhanced by the substation of appropriate nanofluid (NF). This study report based on the comparative analysis of statistical AC breakdown voltage (ACBDV) in mineral oil (MO) with a well dispersed TiO2 based NF after accelerated thermal ageing. The studies have been performed measuring 60 ACBDV data as per ASTM D1816 standard using spherical electrode under AC source for a specified ageing period of the liquid. The breakdown probabilities of both the oil are estimated using normal and Weibull distribution functions. Suitable distribution functions are used for this hypothesis. The ACBDV probabilities of the sample population are evaluated by seeking the histogram, frequency of distribution, mean and standard deviation. Thermal ageing of two different liquids namely MO and TiO2/MO-NF is carried out in two similar ageing vessels as per standard testing condition. Investigations of ACBDV are carried out for the four distinct ageing duration (100, 300, 500 and 1000 hour) of these two liquid. The effect of ageing on ACBDV of the two liquid at similar ageing duration are compared and analyzed. At upper aging duration, ACBDV of MO is drastically dropped compared to TiO2/MO-NF. Hydrophilic nature of MO may be the key reason of generating oxidative product such as oxide, peroxide and water in contact with cellulosic paper insulation and hence decrement in its BDV. It is observed that the measured ACBDV data follows better normal than Weibull distribution for both the liquid at each ageing durations. ACBDV at the level of risk 0.1%, 5% and 50% probability for U0.1%, U5%, and U50%, the dielectric tolerance of TiO2/MO-NF is far more superior to MO under homogeneous field of AC. It has been observed that AC withstand voltage of tested TiO2/MO-NF are well suited for the transformer application.

An efficient wavelet based technique for oscillatory mode identification of ambient data via RD and TLS-ESPRIT

This paper proposes a spectral estimation technique for identification of inter-area oscillatory modes using ambient data. In order to mitigate the effect of high noise level, the proposed method has used a combination of wavelet, random decrement (RD) and modified TLS-ESPRIT for mode identification. The main contribution of this paper is to find the optimal set of wavelet coefficients to represent the clean signal for mode estimation. The proposed method is compared with non-linear filtering and random decrement technique-Ibrahim time domain (RDT-ITD) method over the synthetic signals resembling ambient signals. The effectiveness of the proposed method is further validated for real time ambient data obtained from a PMU located in North Eastern Regional Electricity Board (NEREB) of India and on the probing data of the Western Electricity Coordinating Council (WECC).