Kumar V Jagadeesh

Abstract: An angle transducer that provides a linear output for full-circle range (0–360°) of operation is presented in this paper. The sensor part of the transducer is made of two pairs of Tunneling Magneto-Resistors (TMR) and the signal conditioning part consists of a couple of sinusoids having same frequency but differing in phase by 90° and a phase detector. The novel signal conditioning circuit proposed here operates on the sine/cosine outputs of the TMRs and provides a voltage that is linear to the angle being sensed. Simulation studies conducted using SPICE demonstrate the efficacy of the transducer in providing a linear output across the entire full-scale range with a worst case error less than ± 0.15 %. Results obtained from a prototype unit built and tested establish the practicality of the proposed transducer. The worst case error of the prototype was < ± 1 %.

Abstract: On line assessment of winding deformation in a power transformer can be performed via a bushing tap excitation with optimized high frequency excitation. A benchmark layer winding is used to validate the use of the specific high frequency excitation. Axial displacement, compression and buckling of the winding are simulated and the changes identified. Measurements are performed on a voltage transformer to verify the suitability of the technique. The procedure will result in a considerably shorter time for measurement.

Abstract: Comparative performance analysis of fixed or oriented (single axis or twin axis type) sun tracking systems in the field requires that the solar PV arrays mounted on the test tracker and the reference tracker, not only have to be identical, but also tested under identical operating conditions. In order to satisfy the above criteria as well as to extract the maximum output, the identical operating condition for a comparison test is chosen to be the maximum power point operation. Use of an electronic load, realized with a MOSFET serving as a variable load resistor, in conjunction with a microcontroller for maximum power point operation of a PV array during such comparative tests is presented in this paper. A prototype measurement system based on the proffered technique is developed to carryout comparison studies on sun tracker systems in the filed. Using the prototype, tests were conduced to compare the performances of a fixed PV array system and a two step, stepwise manual tracker. Simulation results and experimental results obtained using a prototype unit built and tested establish the efficacy of the proposed technique for proper comparison of sun tracking systems, in the field.

Abstract: A novel signal conditioning circuit that operates on a floating wiper resistive displacement sensor and provides a digital output proportional to the displacement of the wiper is presented here. Floating wiper resistive displacement sensors possess long operational life due to reduced wear and tear as the wiper does not rub against the resistive element. However, the air gap between the floating wiper and the resistance introduces a coupling capacitance whose value varies as the wiper moves, making it difficult to obtain an output proportional to the displacement of the wiper. The successive approximation logic-based method presented here, operates on a floating wiper resistive displacement sensor and provides a digital output that is linear to the displacement of the wiper. More importantly the output is independent of the value of coupling capacitance. The efficacy of the scheme has been established through simulation studies, the results of which are also presented here.

Abstract: An online method for the assessment of moisture in a power transformer is presented in this paper. It is experimentally tested on simple insulating materials as well as on a sample bushing insulation. It is finally tested during the drying of a 110 kV transformer. The results are presented and show that the method is clearly able to distinguish between levels of moisture in the range of interest.

Abstract: This paper presents the current status and future trends in the application of the frequency-response analysis (FRA) technique with the transformer in service (online) through bibliographic review and analysis. As a result, three basic stages of the online FRA test have been identified and defined: injection and excitation signal measurement; recording, filtering and processing of measured signals; and curve analysis and interpretation. This work presents an overview of the online FRA technique, useful for subsequent research in this area.

Abstract: This paper is an attempt to investigate the performance of existing and some proposed solar photovoltaic (PV) array configurations comprehensively. Based on the MATLAB/Simulink model of single diode solar cell, performance of PV array configurations such as series-parallel (SP), total-cross-tied (TCT), bridge-link (BL), honey-comb (HC) and proposed hybrid SP–TCT, BL–TCT and non-symmetrical puzzle pattern based configurations such as NS-1 (non-symmetrical-1) and NS-2 (non-symmetrical-2) is comprehensively reported. The performance of all these configurations has been investigated using P–V characteristics, power loss due to shading, fill factor and shading dispersion effect on maximum power point (MPP) for various shading patterns namely pattern-1 (vertical shading), pattern-2 (horizontal shading) and pattern-3 (diagonal shading). Extensive simulations are carried out on these configurations for these shading patterns by considering several cases of shading. The performances of proposed configurations are found superior for some cases of shading patterns.

Abstract: This paper describes a novel and high-performance phase-locked loop (PLL) resolver converter for the measurement of mechanical angles. The proposed method does not require the use of demodulators, voltage-controlled oscillator, digital-to-analog converter, counter, and lookup tables, that are associated with conventional PLL converters. The proposed method employs full-wave rectifiers to obtain the absolute values of the modulated resolver signals. This scheme results in a triangular output voltage and two binary outputs that represent a measure of the input angle. The required sine and cosine of the estimated angle, which are needed for PLL converters, are determined using simple approximation techniques. The proposed method can be used to measure angles in the full 360° range, is simpler than the available techniques, and may be easily implemented using digital or basic analog electronic circuitry. This paper describes the proposed method, full details of its implementation using standard electronic components, and experimental results. The performance of the proposed converter is comparable with that of a commercial product.

Abstract: Sinusoidal encoders are used for the measurement of angular position and linear displacement. These provide electrical signals dependent on the sine and cosine of the position $\theta $ of their moving part relative to the stationary one. Conventional tangent/cotangent converters for determining $\theta $ from the encoder signals produce alternating highly non-linear segments of tangent and cotangent. Lookup tables are used for determining $\theta $ . This paper presents a novel converter for estimating $\theta $ without the lookup table. The method is based on dividing the circle angular interval into $N$ sections. A crude or coarse measure $\theta _{C}$ of the unknown angle $\theta $ is first determined by identifying the section in which $\theta $ is located. This is followed by the determination of a fine measure $\theta _{F}$ . These measures are combined to yield a precise measure of $\theta $ ; the maximum error of the method depends on $N$ . The converter has been implemented on a dSPACE set and has been successfully tested both with a sensor emulator and a real Hall-Effect sinusoidal encoder. This paper describes full details of the theory, simulation, and experimental results. The experimental results demonstrate excellent agreement with theory and simulation.

Abstract: This paper investigates performance of seven photovoltaic (PV) array topologies experimentally under cumulative impact of partial shading and deposition of aerosols at different irradiance levels and aerosol types at their different concentration levels. Different array topologies respond differently with regard to their mismatch power loss and fill factor under partial shaded condition. However, a comprehensive analysis of their behavior under the influence of other environmental phenomena is neglected so far by the researchers. The topologies studied in the present work, include four conventional topologies viz. series-parallel (SP), honey comb (HC), bridge link (BL) and total cross-tied (TCT) along with three novel hybrid topologies proposed in this paper (CT-SP, CT-BL and CT-HC). The complex and large amount of data generated from the experimental study have been analyzed using combined Shannon's entropy and data envelopment analysis to quantify the relative performances of different PV array topologies under different environmental conditions. The proposed methodology of comprehensive analysis will help the policy makers and researchers to enhance the performance ratio of PV projects by leveraging on the environmental factors and thereby increase techno-commercial viability of the PV projects.