Triac Based Novel Single Phase Step-Down Cycloconverter with Reduced THDs for Variable Speed Applications

In variable speed applications, the cycloconverter-based AC to AC power conversion technique has gained more attention among researchers and academics than the traditional rectifier-inverter-based AC to AC power conversion process. The conventional rectifier-inverter-based AC to AC power conversion process has several disadvantages. It uses multi-power stages that increase the converter power conversion losses and increase the cost, volume, and weight of power losses. Besides high conduction and switching losses, the electromagnetic interference problems also accompany the above issues. In this regard, this paper proposes a novel step-down Triac based cycloconverter for variable speed control applications. The proposed topology uses only five Triac devices for one-third and one-fourth frequency conversion of 50 Hz with reduced total harmonics distortion without using any pulse width modulation techniques. The proposed model is designed in the MATLAB/SIMULINK environment. The simulation results show that around 18.85% and 23.67% of total harmonics distortions are reduced in the proposed converter for one-third and one-fourth frequency conversion of 50 Hz, respectively. Two physical experiments are carried out to prove the validity of the simulation results.

A Comprehensive Three-Phase Step Voltage Regulator Model with Efficient Implementation in the Z-Bus Power Flow

<p>This paper presents a comprehensive three-bus equivalent circuit model of three-phase step voltage regulators. The proposed model can be efficiently integrated in the Z-bus power flow method and can accurately simulate any configuration of step voltage regulators. In contrast to the conventional step voltage regulator models that include the tap variables inside the Y_BUS matrix of the network, the proposed model simulates them in the form of current sources, outside the Y_BUS matrix. As a result, the re-factorization of the Y_BUS matrix is avoided after every tap change reducing significantly the computational burden of the power flow. Furthermore, possible convergence issues caused by the low impedance of step voltage regulators are addressed by introducing fictitious impedances, without, however, affecting the accuracy of the model. The results of the proposed step voltage regulator model are compared against well-known commercial softwares such as Simulink and OpenDSS using the IEEE 4-Bus and an 8-Bus network. According to the simulations, the proposed model outputs almost identical results with Simulink and OpenDSS confirming its high accuracy. Furthermore, the proposed 3-bus equivalent model is compared against a recently published conventional step voltage regulator model in the IEEE 8500-Node test feeder. Simulation results indicate that the proposed step voltage regulator model produces as accurate results as the conventional one, while its computation time is significantly lower. More specifically, in the large IEEE 8500-node network consisting of four SVRs, the proposed model can reduce the computation time of power flow around one minute for every tap variation. Therefore, the proposed step voltage regulator model can constitute an efficient simulation tool in applications where subsequent tap variations are required. </p>

Hybrid solar/wind/diesel water pumping system in Dubai, United Arab Emirates

This paper proposes a hybrid power system design for water pumping system in Dubai (Latitude 25.25 &deg;N and Longitude 55 &deg;E), United Arab Emirates using solar photovoltaic (PV) panels, wind turbines, and diesel generator. The proposed design considers the changes in weather conditions (humidity percentage, temperature in celsius, and wind speed in m/s) that directly affect solar irradiance values which alter the performance of the hybrid system. The proposed design deals with the problem of rare rainy days in Dubai between December and March and the high temperature throughout the year since that makes providing water to rural and isolated zones essential. The proposed system uses voltage regulator to maintain stable DC voltage from the solar power system, battery bank to store the voltage from solar PV panels, three-phase rectifier to convert the AC voltage from wind power system to DC, three-phase step-down transformers to reduce the AC voltage of the wind turbine and diesel generator, and DC electric motor for water pumping output. The system used neural network for solar irradiance forecasting over an interval of 10 years (from 2009 to 2019). The proposed system will be demonstrated using Simulink to show the stability and performance under different weather conditions.

Measurement of the diffusion coefficient in liquids using Fresnel diffraction from a phase step

Fresnel diffraction from a phase step for measuring diffusion coefficient in transparent liquids is investigated. When a transparent glass plate immersed vertically in a cell containing two diffusing liquids is illuminated by a parallel beam of light, the diffraction pattern of the plate edge forms on a screen perpendicular to the beam direction and varies by diffusion. The gradient of the refractive index in the liquids is then obtained by analyzing the diffraction patterns at different times after the beginning of the diffusion process, from which the diffusion coefficient is determined. Using this method, we study the diffusion process of the sucrose-water solution and report the diffusion coefficient with a reliable accuracy.