Ebrahim Afjei

Bio: Ebrahim Afjei is an academic researcher from Shahid Beheshti University. The author has contributed to research in topics: Switched reluctance motor & Rotor (electric). The author has an hindex of 25, co-authored 257 publications receiving 2120 citations. Previous affiliations of Ebrahim Afjei include Yahoo! & K.N.Toosi University of Technology.

New Double-Layer-per-Phase Isolated Switched Reluctance Motor: Concept, Numerical Analysis, and Experimental Confirmation

Abstract: This paper presents a new configuration for switched reluctance motor (SRM) which can be proposed as a suitable candidate for high-torque and low-flux-leakage SRMs. Unlike the conventional SRMs, this configuration has no direct windings wrapped on the stator poles. This motor consists of three different sets, and each set has one concentric independent winding, two layers of the stator poles, and three layers of the rotor poles in which the middle rotor layer acts as a core for phase winding. To evaluate the motor performance, two types of analysis, namely, numerical technique and experimental study, have been utilized. In the numerical analysis, the 3-D finite-element method is employed, whereas in the experimental study, a prototype motor has been fabricated and tested in the laboratory. Finally, experimental results are compared to conventional SRM to verify the advantages of the proposed motor and show its applicability.

Static, Dynamic, and Mixed Eccentricity Faults Diagnosis in Switched Reluctance Motors Using Transient Finite Element Method and Experiments

Abstract: This paper presents a new method for noninvasive diagnosis of static, dynamic, and mixed eccentricity faults in switched reluctance motors (SRMs). This method makes it possible to precisely determine the eccentricity fault features. The proposed signature in this algorithm is based on the analysis of produced current with a particular variation pattern. It is theoretically shown that the occurrence and growth of the fault level cause an increase in amplitude of the produced current signature (PCS), which can be employed to diagnose the fault and extract its details. In this method, first, occurrence of the fault and its location are detected by utilizing eccentricity level detection pattern. Afterward, a new index to precisely determine the fault level is introduced. Then, a novel strategy based on the proposed pattern and index is offered to detect the type of eccentricity as well as the exact location of the faulty phase. For this purpose, an SRM under eccentricity fault is modeled using three dimensional transient finite element method (TFEM). This precise model considers all complex motor geometry, nonlinear characteristics of the motor, end effects and axial fringing effects. A test bed in the laboratory is established to perform various measurements on the eccentric motor with different fault levels. The experimental results validate the numerical analysis outcomes. Fault detection and analysis in SRM demonstrate that the algorithm presented can assure the reliability of detection as well as the sensitivity of eccentricity fault in a SRM.

Comprehensive Detection of Eccentricity Fault in Switched Reluctance Machines Using High-Frequency Pulse Injection

Abstract: This paper presents a comprehensive method for eccentricity fault diagnosis in switched reluctance machine (SRM) during offline and standstill modes. In this method, the fault signature is achieved by processing the differential currents resulted from injected high-frequency diagnostic pulses to the motor windings. For feasibility assessment of the proposed method, the correlation between differential current and eccentricity occurrence is analytically demonstrated. A 3-D transient finite-element method is utilized to analyze the proposal, and its results are validated by experimental tests on a prototype machine in the laboratory. According to the obtained results by experimental as well as numerical analysis, a pattern is introduced in order to detect fault presence. In this stage, an algorithm with two methods is proposed for the detection of fault location or faulty phase. Furthermore, the direction of fault is recognized by a simple comparative technique. Next, a normalized indicator is proposed in order to estimate the eccentricity fault severity as well as its occurrence. This indicator is not dependent of the healthy motor information, which makes it reliable and applicable tool for all sizes of SRMs. Finally, a simple procedure based on achieved pattern and indicator is implemented to distinguish the static, dynamic, and mixed eccentricity in the SRM.

High-Frequency Oscillations and Their Leading Causes in DC Microgrids

Abstract: A comprehensive analysis is carried out to investigate the high-frequency (HF) oscillations and their leading causes in dc microgrids. The analysis relies on the impedance-based stability criterion. It is shown for the first time that all types of DGs and loads contribute to the HF oscillations in a dc microgrid. This is in contrast with the previous studies that designate constant-power loads as the main cause for the interaction dynamics in dc microgrids. It is noted that different factors including number of DGs, load dynamics, load powers, and the type of resonances affecting the HF voltage/current oscillations are taken into account in our studies. A closed-form expression is derived for the estimation of the damping factor of dominant HF modes of dc microgrids. Moreover, a proper damping approach is proposed to reduce the HF oscillations. Various simulation studies are presented to evaluate the effectiveness of the proposed analysis approach.

High-performance hybrid photovoltaic -battery system based on quasi-Z-source inverter: application in microgrids

Abstract: This study presents a high-performance photovoltaic (PV)-battery hybrid power conversion system (HPCS) which is integrated to a microgrid using a quasi-Z-source inverter (qZSI). The battery system is directly connected to the intermediate dc link of the qZSI without any extra converter which reduces the size and the cost of the power electronic interface. A controller equipped with a harmonic compensator is designed to control the battery current in the grid-connected mode and to regulate the microgrid voltage in the islanded mode in the presence of unbalanced and non-linear loads. Furthermore, the proposed controller adjusts the shoot-through duty cycle of the qZSI to regulate the PV voltage to its reference value provided through the maximum power point tracking algorithm. Moreover, the proposed controller provides the microgrid with the capability to transfer between the two operation modes. A new strategy is adopted to keep the HPCS operational in case of severe reduction in the available power of the PV modules and its consequent voltage drop. The performance of the proposed control system is evaluated for the control of a typical microgrid simulated in MATLAB/SIMULINK environment.

Introduction to the Finite Element Method

Abstract: This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

A Brief Review of Nature-Inspired Algorithms for Optimization

Abstract: Swarm intelligence and bio-inspired algorithms form a hot topic in the developments of new algorithms inspired by nature. These nature-inspired metaheuristic algorithms can be based on swarm intelligence, biological systems, physical and chemical systems. Therefore, these algorithms can be called swarm-intelligence-based, bio-inspired, physics-based and chemistry-based, depending on the sources of inspiration. Though not all of them are efficient, a few algorithms have proved to be very effi cient and thus have become popular tools for solving real-world problems. Some algorithms are insuffici ently studied. The purpose of this review is to present a relatively comprehensive list of all the algorithms in the literature, so as to inspire further research.

Review of Energy Storage System Technologies in Microgrid Applications: Issues and Challenges

Abstract: A microgrid (MG) is a local entity that consists of distributed energy resources (DERs) to achieve local power reliability and sustainable energy utilization. The MG concept or renewable energy technologies integrated with energy storage systems (ESS) have gained increasing interest and popularity because it can store energy at off-peak hours and supply energy at peak hours. However, existing ESS technology faces challenges in storing energy due to various issues, such as charging/discharging, safety, reliability, size, cost, life cycle, and overall management. Thus, an advanced ESS is required with regard to capacity, protection, control interface, energy management, and characteristics to enhance the performance of ESS in MG applications. This paper comprehensively reviews the types of ESS technologies, ESS structures along with their configurations, classifications, features, energy conversion, and evaluation process. Moreover, details on the advantages and disadvantages of ESS in MG applications have been analyzed based on the process of energy formations, material selection, power transfer mechanism, capacity, efficiency, and cycle period. Existing reviews critically demonstrate the current technologies for ESS in MG applications. However, the optimum management of ESSs for efficient MG operation remains a challenge in modern power system networks. This review also highlights the key factors, issues, and challenges with possible recommendations for the further development of ESS in future MG applications. All the highlighted insights of this review significantly contribute to the increasing effort toward the development of a cost-effective and efficient ESS model with a prolonged life cycle for sustainable MG implementation.