Iranian Journal of Science and Technology-Transactions of Electrical Engineering最新文献

A nonlinear circuit element called a memristor has become a popular research area today. Circuits that mimic the behavior of a memristor are called memristor emulators. There are many different types of memristor emulators made. There are also optoelectronic memristor emulators in the literature, albeit in small numbers. In this study, a microcontroller-controlled memristor emulator with a hand-made optocoupler was designed. The circuit is made using an inexpensive microcontroller, the STM32F103RB microcontroller. The emulator made was used in the design of an LP filter with an adjustable cutoff frequency of low and high pass. The operation of the emulator and the filter has been studied experimentally. Experimental results show that the emulator and the LP filter circuits perform well.

The adjustment of DC bus voltage is one of the most critical challenges in DC microgrids. Any changes in power generation or load leads to voltage fluctuation. Recently, the DC electric spring (DCES) has been suggested for bus voltage adjustment and maintaining the DC network stability. An electric spring is a power electronic converter that adjusts the voltage of critical loads (sensitive loads) by utilizing the variations in the power of non-critical loads (insensitive loads). In this paper, a new structure of DCES, based on a fully isolated three-port converter (TPC), is presented. The proposed structure not only solves the issues associated with conventional structures, but it also provides isolation between critical and non-critical loads, as well as the battery energy storage system. Furthermore, the separate control of each port converter ensures that DCES has the required dynamic performance to keep a stable critical load voltage. Utilizing the suggested DCES structure produces an adequate voltage range for non-critical loads, reducing battery sizing and minimizing converter losses. The performance and feasibility of the three-port DC electric spring (TP-DCES) and its control method are acknowledged by the simulations carried out by the MATLAB/SIMULINK software for various scenarios.

Rectifiers are generally categorized as passive and active rectifiers. Compared to the active rectifiers (e.g. pulse width modulated (PWM) rectifiers), passive rectifiers (i.e., diode rectifiers) result in higher total harmonic distortion (THD) in the input current. However, passive rectifiers are simpler than the active rectifiers in their hardware and control structure. Therefore, passive rectifiers are still considered with different THD minimization schemes. In industry, three-phase diode rectifiers are used in 6-pulse, 12-pulse, 18-pulse, and 24-pulse configurations with THD values of 30%, 15%, 10%, and 6%, respectively. Single-phase diode rectifiers result in a higher THD of 48%. Minimization of THD for single-phase rectifiers is a conspicuous need for increasing DC appliances for domestic use. This paper proposes a novel rectifier using a conventional diode bridge followed by a series chopper. A controlled conduction angle of the chopper significantly reduces the THD from 48 to 28%. The THD is further reduced to 16.4% on the primary side of the distribution transformer after the elimination of triple-n harmonics in a balanced configuration. The proposed topology uses a single switch operating at the line frequency making the circuit and control much simpler than a PWM rectifier, and the dynamic power loss is also low. So, the proposed topology is better suited for single-phase applications requiring circuit and control simpler than a PWM rectifier, and THD much lower than a conventional diode bridge rectifier. A comprehensive analytical analysis, circuit simulations, power loss analysis, and experimental results are presented for the proposed topology to validate its working and evaluate its performance.

Abstract

As the world increasingly turns to renewable energy sources, the integration of solar photovoltaic (PV) systems into the grid has emerged as a pivotal solution. Effective control methods are paramount to harnessing the full potential of these grid-connected PV systems. While existing control methods have laid a foundation, there persists a compelling need for innovative approaches capable of surpassing the limitations of conventional methods. This paper introduces a novel nonlinear control approach utilizing an enhanced Lyapunov function for a single-phase PV/grid electric power system. High-performance operation of the solar PV system, interfacing with a grid-connected single-stage inverter, is achieved through the control of maximum PV voltage using predictive voltage control for MPPT. The enhanced Lyapunov function maintains PV voltage stability at the dc-bus by treating the difference between PV voltage and its reference as a controlled state error. Notably, this approach ensures the stability of the closed-loop PV system even under varying solar irradiances. To achieve full active power injection into the grid with high quality, the proposed enhanced Lyapunov function is augmented by integrating an LCL filter with virtual resistance as an active damping circuit for grid current feedback control. This integration introduces an opposing current to the grid-side inductance current. This compensation mechanism corrects the q-axis grid current using the dq-SRF mathematical model of the global PV/grid system. The LCL parameters and virtual resistance design methods are provided. The effectiveness of the enhanced Lyapunov function is demonstrated through simulations using MATLAB/Simulink software. The results showcase outstanding performance when compared to conventional Lyapunov function and sliding mode control strategies in achieving key objectives, including zero state errors, global stability, and the generation of a sinusoidal grid current signal with low total harmonic distortion and the unit power factor at the point of common coupling.

Waveguide directional couplers are fundamental microwave devices that are commonly used in routing RF signals to different ports within a waveguide network. Waveguides are coupled through apertures in a common wall between them. The shape and size of these apertures can be varied for certain coupling factors and to produce specific directivity patterns. This research applies the superformula in transitioning from circular apertures to square ones. Additionally, a novel approach to using the Legendre polynomials in sizing the apertures is discussed. Comparisons of the simulation results of Chebyshev and Legendre couplers show that Legendre couplers generally give a flatter directivity pattern for an equivalent coupling factor at 17.4 dB and bandwidth of 4 GHz centered at around 9 GHz. Moreover, square apertures are found to be noticeably superior to circular ones in their frequency response as they maintain a similar bandwidth of and higher directivity at an average of over 50 dB, but suffer poorer coupling factors, which increase by 6 dB.

This paper proposes sliding mode pulse-width modulation (SMPWM) for the nine-switch inverter (NSI) as solution for the main drawback of voltage and current distortion. The proposed modulation is based on Lyapunov approach and can directly trigger the nine switches without restrictions and regardless of the operation frequency modes. SMPWM along with modified direct torque control-based sliding mode approach is designed for NSI driving dual-induction motor to obtain fixed switching frequency and low torque ripple. Stability analysis is carried out for each proposed method, and convergence condition depends on the value of dc-bus voltage that can be achieved. The feasibility of the proposed control is verified under load and speed conditions through simulation results.

The Fermatean fuzzy set (FFS) is an effective and robust technique for handling ambiguity, to deal with issues that can’t be resolved using the concepts of Intuitionistic fuzzy set and Pythagorean fuzzy set. Due to its essential uses and crucial significance in solving insoluble real-world problems in a variety of sectors, FFS has generated a maze of research since its inception. In this elaborative study, we establish a clear definition for the concept of similarity measures along with their essential qualities in the context of FFS. Additionally, we introduced a group decision-making algorithm grounded in the suggested similarity measures to tackle the issues. The attribute weights are determined by utilizing the newly introduced similarity measures as part of the process. The credibility of the algorithm is demonstrated through a case of dengue diseases and a comparison of its results with some of the existing studies.

In the following manuscript, an original microwave sensor is planned to detect the meat's dielectric changes, as a type of tissue. The presented sensor is created in the model of a microstrip structure and consists of U-shaped, meander, and waterfall parts. If a liquid sample is located on the sensor at the sensing location, it can measure permittivity changes. For this, a resonance is formed in the free-load sensor at 3.2 GHz frequency then when the sample touches the sensor, according to the amount of relative dielectric changes of the desired sample, the sensor resonance frequency is shifted. To determine the sensitivity of the proposed sensor, water–methanol solution samples are used and as a result, its Q-factor and sensitivity are 5346 and 2.36%, respectively. Then, three samples of sheep, fish, and chicken meats are measured by the proposed sensor, and with time, the measurement is repeated, and the results are analyzed. With this method, the freshness of the meat is evaluated. It is possible to use the proposed sensor in the food production industry and can determine the exact postmortem time of all types of meat with high speed and accuracy.

Analog and digital circuits are used to make memristor emulators. Power electronics circuits use switching to obtain the desired waveforms. A single-phase power factor corrector circuit is a well-known power electronics circuit. This study shows that a single-phase power factor corrector circuit can be used as a memristor emulator. To the best of our knowledge, there is no memristor emulator circuit made in this way in literature yet. This circuit employs a boost converter placed after the full-wave bridge rectifier. The power switch of the converter is controlled to obtain the desired memristive behavior by a microcontroller, STM32F429ZIT6. The circuit operation is examined using simulations and experiments. Also, a comparison is given between the proposed emulator and the other memristor emulators in the literature. Although the proposed emulator is able to emulate different memristor models described with varying window functions, only the results of the Biolek model are given due to space considerations. The circuit performs well and can easily emulate other memristor models after modification of its firmware for their window functions.

Correct diagnosis in medicine is of great importance as it is one of the most important issues in medicine. Today, researchers have embarked on many new searches to make an accurate medical diagnosis. In order for any disease to be cured, it is necessary to define it precisely early and accurately. In this study, a new method was proposed to make a more accurate medical diagnosis. This method is based on automatically selecting the fold with the best accuracy rate after k-fold crossvalidation is performed in any database. In this way, scientific studies that lead to more accurate results will be carried out by using the fold with the highest accuracy in both classification and medical diagnosis procedures. This method has been applied on two different databases, Ecoli and Wisconsin Breast Cancer Diagnostic (WBCD) databases, which are used in scientific studies by many researchers in the literature. The statistical measurements of each fold values of both databases used have been examined in detail. Diagnostics for these databases were carried out using 7 different Machine Learning Algorithms (MLA), (k nearest neighbor (k-NN), Decision Tree (DT), Random Forest (RF), Multinominal Logistic Regression (MLR), Naive Bayes (NB), Support Vector Machine (SVM), Minumum (Mean) Distance Classifier (MMDC)). In the test procedures for Ecoli dataset, the following accuracy values were obtained for k-NN, DT, RF, MLR, NB, SVM, MMDC, respectively; 0.8485, 0.8358, 0.9848, 0.8182, 0.6667, 0.8636, 0.7424. For the WBCD database, the following accuracy values were obtained for k-NN, DT, RF, MLR, NB, SVM, MMDC, respectively; 0.9856, 0.9568, 0.9784, 0.9856, 0.9856, 0.9856, 0.9784. Other results were given in detail in the experimental studies section. It is of great importance to choose the most accurate MLAs to be used in medical diagnosis for human life. Thus, in the studies to be done with MLAs in medicine or any field in the literature, how the best score that can be obtained from MLAs will be introduced to the literature. In this study, an original study was conducted on how to make the correct medical diagnosis, which is one of the most important issues for human life.