Srf Theory Revisited” To Control Self-Supported Dynamic Voltage Restorer (Dvr) For Unbalanced And Nonlinear Loads

In this paper a fuzzy controller based DVR is proposed for the protection of the sensitive unbalanced nonlinear loads from sag/swell, distortion, and unbalance in supply voltage is achieved. A simple generalized algorithm based on basic synchronous reference frame theory has been developed for the generation of instantaneous reference compensating voltages for controlling a DVR. This novel algorithm makes use of the fundamental positive sequence phase voltages extracted by sensing only two unbalanced and/or distorted line voltages. In addition to this a fuzzy logic controller have been developed to reduce the % THD compared with the conventional method. The compensating voltages when injected in series with a distribution feeder by three single-phase H-bridge voltage-source converters A capacitor-supported DVR does not need any active power during steady-state operation because the injected voltage is in quadrature with the feeder current. The proposed control strategy is validated through simulation results with the help of MATLAB/SIMULINK software

Monitoring the Progression of Spontaneous Articular Cartilage Healing with Infrared Spectroscopy

Objective. Evaluation of early compositional changes in healing articular cartilage is critical for understanding tissue repair and for therapeutic decision-making. Fourier transform infrared imaging spectroscopy (FT-IRIS) can be used to assess the molecular composition of harvested repair tissue. Furthermore, use of an infrared fiber-optic probe (IFOP) has the potential for translation to a clinical setting to provide molecular information in situ. In the current study, we determined the feasibility of IFOP assessment of cartilage repair tissue in a rabbit model, and assessed correlations with gold-standard histology. Design. Bilateral osteochondral defects were generated in mature white New Zealand rabbits, and IFOP data obtained from defect and adjacent regions at 2, 4, 6, 8, 12, and 16 weeks postsurgery. Tissues were assessed histologically using the modified O’Driscoll score, by FT-IRIS, and by partial least squares (PLS) modeling of IFOP spectra. Results. The FT-IRIS parameters of collagen content, proteoglycan content, and collagen index correlated significantly with modified O’Driscoll score (P = 0.05, 0.002, and 0.02, respectively), indicative of their sensitivity to tissue healing. Repair tissue IFOP spectra were distinguished from normal tissue IFOP spectra in all samples by PLS analysis. However, the PLS model for prediction of histological score had a high prediction error, which was attributed to the spectral information being acquired from the tissue surface only. Conclusion. The strong correlations between FT-IRIS data and histological score support further development of the IFOP technique for clinical applications, although further studies to optimize data collection from the full sample depths are required

Electrically tunable microwave devices using BST-LTCC thick films

Abstract The thesis describes electrically tunable microwave devices utilising low sintering temperature, screen printable Barium Strontium Titanate (BST) thick films. The work has been divided into two parts. In the first section, the fabrication and microwave characterisation of BST material based structures compatible with Low Temperature Cofired Ceramic technology (BST-LTCC) are presented. Three different fabrication techniques, namely: direct writing, screen printing and via filling techniques, were used for the realisation of the structures. A detailed description of these fabrication techniques is presented. The dielectric properties such as relative permittivity, static electric field dependent tunability and loss tangent of BST-LTCC structures at microwave frequencies were characterised using coplanar waveguide transmission line and capacitive element techniques. The measured dielectric properties of BST-LTCC structures realised with the different fabrication methods are presented, compared and discussed. The second section describes tunable microwave devices based on BST-LTCC structures. A frequency tunable folded slot antenna (FSA) with a screen printed, integrated BST varactor is presented. The resonant frequency of the FSA was tuned by 3.2% with the application of 200 V external bias voltage. The impact of the BST varactor on the total efficiency of the antenna was studied through comparison with a reference antenna not incorporating the BST varactor. A compact, frequency tunable ceramic planar inverted-F antenna (PIFA) utilising an integrated BST varactor for mobile terminal application is presented. The antenna's resonant frequency was tuned by 3% with an application of 200 V bias voltage. Frequency tunable antennas with a completely integrated electrically tunable BST varactor with silver metallisation are introduced in this work for the first time. The integration techniques which are described in this thesis have not been previously reported in scientific literature. The last part of the thesis presents a microwave delay line phase shifter operating at 3 GHz based on BST-LTCC structures. The figure of merit (FOM) of the phase shifter was measured to be 14.6 °/dB at 3 GHz and and the device employs a novel structure for its realisation that enabled the required bias voltage to be decreased, while still maintaining compliance with standard screen printing technology. The performance of the phase shifter is compared and discussed with other phase shifters realised with the BST thick film process. The applications of BST-LTCC structures were demonstrated through frequency tuning of antennas, varactors, and phase shifters. The low sintering temperature BST paste not only enables the use of highly conductive silver metallisation, but also makes the devices more compact and monolithic

Optimizing real power loss and voltage stability limit of a large transmission network using firefly algorithm

This paper proposes a Firefly algorithm based technique to optimize the control variables for simultaneous optimization of real power loss and voltage stability limit of the transmission system. Mathematically, this issue can be formulated as nonlinear equality and inequality constrained optimization problem with an objective function integrating both real power loss and voltage stability limit. Transformers taps, unified power flow controller and its parameters have been included as control variables in the problem formulation. The effectiveness of the proposed algorithm has been tested on New England 39-bus system. Simulation results obtained with the proposed algorithm are compared with the real coded genetic algorithm for single objective of real power loss minimization and multi-objective of real power loss minimization and voltage stability limit maximization. Also, a classical optimization method known as interior point successive linear programming technique is considered here to compare the results of firefly algorithm for single objective of real power loss minimization. Simulation results confirm the potentiality of the proposed algorithm in solving optimization problems

Voltage stability assessment of a power system incorporating FACTS controllers using unique network equivalent

AbstractVoltage instability is considered as a main threat to stability, security, and reliability in the modern power systems. Prediction of voltage stability limit of multi-bus system through its two-bus equivalent model is a hot topic of the research in the field of power system operation and control. This paper presents a novel method to assess voltage stability status using a unique two-bus π-network equivalent derived with OPF solution of the actual system at different operating conditions. As the FACTS controllers are now an ineluctable part of power system, this paper considers an SVC and a TCSC in OPF formulation to assess voltage stable states of any interconnected power system in terms of its reduced two-bus integrated π-equivalent system. Simulation results for a practical power system establish that the proposed methodology is highly promising to assess voltage stability in a better way as compared to existing series equivalent model