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fault-detection
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Fast Failure Detection in Modular Multilevel Converter Power Switches for Fault Tolerant Operation
, Ph.D. Dissertation Sharif University of Technology ; Zolghadri, Mohammad Reza (Supervisor)
Abstract
Multilevel converters are the best solution in medium and high voltage applications because of their better output votage quality, redundant structure, less power semiconductor losses and common-mode voltages. Modular multilevel converters (MMCs) have additional advantages such as higher degree of modularity, transformerless operation capability and using a single common DC-bus. All these useful features make MMC the first alternative for HVDC systems. Fault detection, defected cells insulation and post fault operation control are necessary to ensure MMC continouse service. A simple, fast and accurate fault detection method is proposed for MMC semiconductor power switches in this thesis....
Fault Detection of Rotary System with Signal Processing and Intelligent Systems
, M.Sc. Thesis Sharif University of Technology ; Behzad, Mehdi (Supervisor)
Abstract
Condition monitoring and fault detection is an important way to provide economy in both time and costs. Many methods are developed for this purpose. Vibration analysis is one of the most important ways in this field. In this thesis, fault detection of mechanical rotary systems with nonlinear and non-stationary nature has been developed by use of empirical mode decomposition (EMD) and Hilbert transform. Firstly the measured signal is transformed into some intrinsic mode functions (IMF’s) by EMD, and then the Hilbert transform is implemented on each IMF. With Hilbert transform, the instantaneous frequency of system and then the mean frequency are obtained. Mean frequency is a key definition...
Fault Diagnosis of Crack Growth in Power Transmission Systems, using Neural Network
, M.Sc. Thesis Sharif University of Technology ; Selk Ghafari, Ali (Supervisor) ; Khayyat, Amir Ali Akbar ($item.subfieldsMap.e)
Abstract
Nowadays, industrial companies deal with a wide range of serious problems in the field of power transmission maintenance and also fault detection. A large amount of money and time is spent on these issues in order to solve them; consequently, there is an essential need for this subject. In this thesis, in order to tackle those major issues which were referred above, an artificial neural network is trained with only one hidden layer. Also, a suitable database for training an efficient neural network is needed. Thus, a one-stage gearbox system with appropriate degrees of freedom is used to set up referred database. In this system, a crack is imposed to a tooth of spur gear with different sizes...
Fault Detection in Plant Wide
,
Ph.D. Dissertation
Sharif University of Technology
;
Bozorgmehry, Ramin
(Supervisor)
;
Shahrokhi, Mohammad
(Supervisor)
Abstract
The accurate fault diagnosing system design helps the process safety and also helps increasing the products quality of the process. In this project, the fuzzy system and neural network have been used for fault detection and diagnosis of a yeast fermentation bioreactor. In one case, parameters of membership functions are selected in a conventional manner. In second case, the optimal values of these parameters have been obtained using the genetic algorithm. In another case, the neural network system is used for fault detection. These three cases are compared based on their performances in fault diagnosis of a yeast fermentation bioreactor for three different conditions. The results indicate...
Fault-Tolerant Operation of Three-Phase Dual Active Bridge Converter Against Semiconductor Power Switches Fault
, M.Sc. Thesis Sharif University of Technology ; Zolghadri, Mohammad Reza (Supervisor)
Abstract
The three-phase Dual Active Bridge DC-DC converter, by virtue of its various advantages, has been widely used in numerous industrial and sensitive applications. However, this converter includes a large number of power switching devices, which are the most fragile components in Power Electronics, and therefore, can pose a threat to appropriateness of the converter for such applications. Accordingly, introducing a fault-tolerant scheme for this converter is necessary, in order to meet the demands of high reliability and service continuity in aforementioned applications. In this thesis, firstly, the converter is studied during normal operation as well as under switch open-circuit fault, and the...
Leak Detection and Location in Oil Transmission Lines by Closed Form Solution and Linear Observer
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohammad (Supervisor)
Abstract
In this paper, an approach is proposed to estimate the location of the leaks in oil pipelines. The pipeline possesses a system of Partial Differential Equations (PDE). First, a closed-form solution is applied to the pipeline equations and the leakage location is found solving the steady-state equations. To tackle the case where the pressure and flowrate do not reach constant values, the initial estimations are provided by the closed-form solution. Then, the pressures, flow rates, and leakage coefficient are estimated by solving the system of differential equations. This system is then discretized with respect to the location variable to yield the system state equations which, in turn, are...
An Accurate Algorithm for Power Transformer Turn to Turn Fault Detection to Enhance the Performance of Differential Relay
, Ph.D. Dissertation Sharif University of Technology ; Vakilian, Mehdi (Supervisor) ; Hajipour, Ehsan (Co-Supervisor)
Abstract
Power transformer is one of the most important equipment in the power system which plays a key role in the reliability and quality of power delivery. Among numerous failure modes of a typical power transformer, the turn-to-turn fault (TTF) is one of the most prominent reasons for its unplanned outage. A turn-to-turn fault quite often begins with the degradation of the winding insulation between two adjacent turns, then in a short time, this low-level fault can progress to a large number of turns and results in the transformer costly damages. Therefore, it is vital to detect TTF at an early stage and prevent its progression to a catastrophic disaster. The conventional percentage differential...
Geometric-Based Fault Diagnosis in a Grid-Connected Inverter
, Ph.D. Dissertation Sharif University of Technology ; Namvar, Mehrzad (Supervisor)
Abstract
Inverters are the main utility in transmitting power from distributed generation (DG) systems toward grid and their safe and immune performance has become a major concern among the system designers. In addition to poor power transmittance, faults in inverter can harm other equipment such as DG and local load. Consequently different protections has been considered to increase the reliability of these systems. Some of these protections like fuses and varistors are implemented in the hardware while others are considered in the processor. In the later class of protections, fault detection and isolation (FDI) system has been the subject of intense investigation in inverters over the past two...
Design and Implementation of a Fault Detecting Algorithm for a High Voltage Underground Cable Using UHF Wireless Measuring Method
, M.Sc. Thesis Sharif University of Technology ; Vakilian, Mehdi (Supervisor)
Abstract
One of the common problems in using high voltage network is the occurrence of partial electrical discharge in high voltage equipment such as cables. This problem may not be serious at first, but over time it can cause wear, corrosion, or reduction of equipment life, and eventually, if not prevented in a timely manner, can cause electrical sparks, larger problems, and possibly equipment and network become irreparable. On the one hand, due to very clear reasons, we need the voltage level to be high, and on the other hand, due to the application of high voltage level and the need to optimally design the insulation system to reduce their dimensions and construction costs, there will be the...
Turn-to-Turn Fault Detection in Power Transformers in the Presence of Inrush Current
, M.Sc. Thesis Sharif University of Technology ; Hajipour, Ehsan (Supervisor)
Abstract
One of the most critical equipments in power grids are power transformers, which are vulnerable to damage due to the possibility of faults in its various components. A very common category of such faults is turn-to-turn fault in its winding. This fault initiates by the aging of the winding insulation with a short circuit of several adjacent loops to each other and if it is not detected quickly by the transformer protection, it will spread rapidly and can lead to irreparable failure in the transformer. Traditionally, turn-to-turn fault should be detected by mechanical pressure relays, however, due to the poor performance of these relays in the rapid detection of this type of fault, in the...
An Ensemble Approach for Fault Analysis in Internet of Things
, M.Sc. Thesis Sharif University of Technology ; Hessabi, Shahin (Supervisor)
Abstract
Today, data analysis has become a valuable tool in various fields in order to discover the forms or abnormal behavior of the system. For example, detecting credit card fraud, network intrusion, or detecting defects in sensors. In this thesis, a method for fault analysis is presented, which can be used as a monitoring tool to monitor the data that is received in a time series from an Internet of Things system and understand the behavior of the system. This method is designed in such a way that by matching the components with the input data, in general, it is applicable for our desired time series. The presented algorithm is implemented in an unsupervised environment using a statistical...
Speed Estimation for Fault Diagnosis in Machinery Using Vibration Signal
, M.Sc. Thesis Sharif University of Technology ; Behzad, Mehdi (Supervisor) ; Arghand, Hesamaddin (Co-Supervisor)
Abstract
Nowadays, condition monitoring and fault diagnosis are considered as one of the most important maintenance and diagnosis strategies in state-of-the-art industries. Serious damage such as machine and coupled equipment failure, machine failure in a neighborhood in case of severe damage, and production loss will be resulted in late fault detection. One of the critical information in condition monitoring is the machine's rotating speed. In many cases of condition monitoring, the rotating speed, and the machine's technical information (such as bearing characteristic frequency )is not available. In this study, a ruled-base model and an intelligent model are developed for machine running speed...
Nonlinear Geometric Approach to Fault Detection in Mechanical Systems
, M.Sc. Thesis Sharif University of Technology ; Namvar, Mehrzad (Supervisor)
Abstract
The demand for safety operating systems is growing with the new developments in technology. One of the important and critical issues in system monitoring is the capability of the system to detect probable faults and hazards. In model-based fault detection one specific diagnostic signal called residual should be generated for each fault that is only sensitive to a particular fault and independent of other faults and disturbances. In this thesis we try to investigate the nonlinear geometric approach in fault detection of a class of mechanical systems. After a brief introduction to geometric tool for nonlinear inputaffine systems and conditions in which output is decoupled from input, we...
Develop a Monitoring Center Conceptual Framework for Chain Stores
, M.Sc. Thesis Sharif University of Technology ; Rajabi Ghahnaviyeh, Abbas (Supervisor)
Abstract
Among the equipment used in supermarkets, refrigeration systems should be the focus of energy efficiency initiatives; Because they are the biggest consumers of energy and refrigerant with significant maintenance costs. Fault detection and diagnosis (FDD) can provide considerable potential for energy savings as well as reduced maintenance costs. Although there have been numerous investigations of FDD for HVAC systems, there has been very little research on the application of FDD for supermarket refrigeration systems. Therefore, this thesis focuses on the application of FDD to these systems and helps to fill these research gaps. The studied system is a commercial refrigerator system on a...
Evaluating Effectiveness of Machine Learning Approaches in Oscillation Detection in Control Loops
, M.Sc. Thesis Sharif University of Technology ; Tavazoei, Mohammad Saleh (Supervisor)
Abstract
Oscillation in control loops is a common problem in industrial processes. To ensure proper system performance, oscillation in control loops must first be properly detected and then eliminated. Various non-machine learning methods have been used in oscillation detection for years, with the development of machine learning algorithms, hardware improvements and easy access to diverse data, these methods have also been used for oscillation detection in recent years. In the research conducted the field of oscillation detection with machine learning, the focus has been on the advantages of machine learning methods compared to other methods. In this thesis, the aim is to examine and compare...
Fault Detection of Offshore Wind Turbines Using Data Driven Methods
, M.Sc. Thesis Sharif University of Technology ; Sadati, Nasser (Supervisor)
Abstract
Technology systems are vulnerable to various defects. Acuator failures reduce the performance of control systems and even they can damage the entire system. Incorrect reading from the sensors is the cause of many inefficiencies, because errors can reduce the quality and efficiency of a product line. In addition, failure of a single system's component can cause a system failure. Electromechanical energy conversion devices are composed of hundreds different components and subunits that are subject to varying adverse environmental conditions, and that is why the sensors, actuators, and components are likely to malfunction. Unexpected defects and unplanned repairs result in high operating costs...
Satellite Attitude Actuator Fault Detection and Identification Using Adaptive Neuro-Fuzzy Inference System (ANFIS)
, M.Sc. Thesis Sharif University of Technology ; Asadian, Nima (Supervisor)
Abstract
This thesis focuses on the detection and estimation of faults occurring in one of the reaction wheel axes of a three-axis stabilized satellite. The wheel axes are aligned with the satellite's body axes, and the emphasis is on the attitude (rather than position) of the satellite. The primary goal of the subsystem is to determine and control the satellite's attitude, transitioning from its initial state to a desired Earth-pointing state. It is assumed that environmental disturbances, including gravitational disturbances and Drag related disturbances, are considered. Based on this, a PID controller is designed after modeling the nonlinear kinematics and dynamics of the satellite using Euler...
Robust Reconstruction of Medical Ultrasound Images in The Presence of Transducer Faults
, Ph.D. Dissertation Sharif University of Technology ; Jahed, Mehran (Supervisor)
Abstract
Medical ultrasound imaging is one of the common imaging methods in modern medicine, which is used to diagnose and even treat some diseases due to its cheapness and harmlessness. Medical ultrasound transducer arrays have a significant error rate. They are a major cause of failure in ultrasound imaging systems. This problem causes a noticeable decrease in the quality of the images and medical misdiagnoses. The topics of accurate detection of the location and severity of the error or failure, as well as the compensation for weak transducers by signal processing methods, have received less attention from predecessor researchers. In this thesis, an innovative method for accurate error detection...
Transmission Grid Fault Location by Optimal Placement of Phasor Measurement Units (PMU)
, M.Sc. Thesis Sharif University of Technology ; Ranjbar, Ali Mohammad (Supervisor)
Abstract
In this thesis, the problem of placing a minimum number of phasor measurement units (PMUs) in a transmission system is considered so that faults on all lines of the network can be diagnosed and located irrespective of their locations. For this purpose, a PMU placement algorithm is proposed to calculate the required data for impedance-based fault-location of any fault line in the network, achieving the full potential of the circuit laws throughout the system. Another algorithm is then proposed to compute the voltage and current values of the fault line for fault-location purposes. Moreover, as many networks are already equipped with PMUs, the proposed algorithm makes it possible to locate...
RT-Level Test Pattern Generation with Horner Expansion Model
, Ph.D. Dissertation Sharif University of Technology ; Tabandeh, Mahmoud (Supervisor) ; Navabi, Zainalabedin (Co-Advisor)
Abstract
Increasing in size and complexity of digital designs has made manufacturing process more complex and enforces more complexity in verification of designs. This makes it essential to address critical verification issues at the early stages of design cycle. Such a complicated designs needs to be tested for fabrication faults as well as functional faults. Several attempts have been made to raise the quality of testing methods with automatic test pattern generation (ATPG) and design for testability (DFT) methods in logic and lower levels. Although these techniques try to increase the testability of a circuit considerably, but there are always some overheads in area, power and performance....