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Total 131 records

    Actuator failure-tolerant control of an all-thruster satellite in coupled translational and rotational motion using neural networks

    , Article International Journal of Adaptive Control and Signal Processing ; 2018 ; 08906327 (ISSN) Tavakoli, M. M ; Assadian, N ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    Abstract
    The nonlinear model predictive control (MPC) approach is used to control the coupled translational-rotational motion of an all-thruster spacecraft when one of the actuators fails. In order to model the dynamical response of the spacecraft in MPC, instead of direct integration, a neural network (NN) model is utilized. This model is built of a static NN, followed by a dynamic NN. The static NN is used to find the changes of the mapping of “the demanded forces to the thrusters” and “the real torques/forces produced by the remaining thrusters” after the failure occurrence through online training. In this manner, the effect of failed thruster on the dynamics can be found and the need for... 

    Online identification of aircraft dynamics in the presence of actuator faults

    , Article Journal of Intelligent and Robotic Systems: Theory and Applications ; Volume 96, Issue 3-4 , 2019 , Pages 541-553 ; 09210296 (ISSN) Emami, A ; Banazadeh, A ; Sharif University of Technology
    Springer  2019
    Abstract
    In this paper, a multiple model-based nonlinear identification approach is introduced for a conventional aircraft in the presence of different types of actuator faults. Occurrence of actuator faults can obviously reduce the validity of a predetermined dynamic model of nonlinear systems. In such cases, use of multi-model structures can be an effective choice. However, determining the optimal validity functions of the local models in a multi-model structure is still a challenging problem. This problem becomes even more challenging in case of unpredictable faults, which are not considered in training the local models. In this paper, two effective techniques are proposed for online determination... 

    A unified framework for passive–active fault-tolerant control systems considering actuator saturation and L ∞ disturbances

    , Article International Journal of Control ; Volume 92, Issue 3 , 2019 , Pages 653-663 ; 00207179 (ISSN) Khatibi, M ; Haeri, M ; Sharif University of Technology
    Taylor and Francis Ltd  2019
    Abstract
    This paper presents a unified passive–active fault-tolerant control strategy to compensate the loss of actuators’ effectiveness. The proposed approach is capable of handling the system in pre- and post-fault diagnosis intervals by passive and active approaches, respectively. The stability of the designed system is independent of the accuracy of information provided by the fault detection and diagnosis unit, however, a precise estimation could improve the conservation. Actuator saturation and L ∞ disturbances effects are considered in the design stage. The trade-off between maximising the domain of attraction and minimising the effects of L ∞ disturbances is tackled by developing a... 

    Transmission Grid Fault Location by Optimal Placement of Phasor Measurement Units (PMU)

    , M.Sc. Thesis Sharif University of Technology Rezaei Jegarluei, Mohammad (Author) ; 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... 

    Fault Diagnosis in Power Systems by Wide-area Measurement System

    , Ph.D. Dissertation Sharif University of Technology Salehi Dobakhshari, Ahmad (Author) ; Ranjbar, Ali Mohammad (Supervisor)
    Abstract
    A power transmission system includes transmission lines that are interconnected for economic and security reasons. Power systems are often prone to faults at the transmission level, since transmission lines are spread over vast geographical areas. Being the most serious events in power systems, blackouts are often initiated by a fault and a sequence of events afterward leads to partial or complete power outage. In this condition, fault diagnosis is the first step for power system restoration. In this research work, a new approach utilizing impedance-based fault location is introduced for fault diagnosis. By developing wide-area measurements in the context of smart grids, accurate... 

    Nonlinear Geometric Approach to Fault Detection in Mechanical Systems

    , M.Sc. Thesis Sharif University of Technology Mashreghi, Ali (Author) ; 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... 

    Introducing a Supervisory Hardware Platform for Wireless Body Area Sensor Network with an Anomaly Detection Ability

    , M.Sc. Thesis Sharif University of Technology Zare Dehabadi, Mohammad Saeed (Author) ; Jahed, Mehran (Supervisor)
    Abstract
    Wireless Body Area Network (WBAN) is a set of various physiological sensors for remote monitoring and controlling of the patient’s health status. Detection of anomalies, containing faults and physiological stresses, and distinguishing between them can eliminate the need for constant presence of specialists and decrease the occurrence of False Alarm Rate (FAR).A supervisory hardware platform for WBAN architecture is introduced and implemented in this thesis. The proposed architecture contains three sensors for recording of biomedical signals, heart rate, SpO2 and body temperature simultaneously and transmitting them to central node wirelessly through Wi-Fi standard. This proposed architecture... 

    Implementation of Lean Management Principles in the Banking System a Case Study: Middle East Bank

    , M.Sc. Thesis Sharif University of Technology Ghasemi, Pedram (Author) ; Houshmand, Mahmoud (Supervisor)
    Abstract
    Lean Management is a set of modern procedures that uplifted Japanese manufacturers' status in global markets. The core principle of lean management is to eliminate every process or operation which creates no value, directly and indirectly. To this day, lean has been more focused on production. But eliminating the wastes in service organizations in crucial, due to nature of service. In this thesis, first the lean concept and the Middle East bank is discussed and a literature review on lean studies is presented. Then a vision for the future is envisioned and a questionnaire for conducting a Corporate Diagnosis is developed. In the next step, a lean management system for the bank is implemented... 

    Performance Improvement of Cascaded H-bridge Multilevel Inverter under Faulty Conditions

    , Ph.D. Dissertation Sharif University of Technology Ouni, Saeed (Author) ; Zolghadri, Mohammad Reza (Supervisor) ; Oraee Mirzamani, Hashem (Supervisor) ; Rodriguez, Jose (Co-Advisor)
    Abstract
    Fault-tolerant ability is more subjected in Cascaded H-Bridge Multilevel Inverter due to its high-power medium-voltage applications and large number of semiconductors switches used in its structure. In this thesis, the goal is performance improvement of Cascaded H-bridge Multilevel Inverter under faulty conditions. Since to achieve the post-fault ability two steps; fault detection and post-fault control are required, both steps are considered in the improving process. In this dissertation, first operation of Cascaded H-Bridge Multilevel Inverter in normal and faulty condition is surveyed. Then, the conventional fault detection methods are mentioned and post-fault control methods are... 

    Applying of Data Fusion Method for Improving the Protection System of the High Voltage DC Power Supply

    , M.Sc. Thesis Sharif University of Technology Ayoubi, Ramin (Author) ; Kaboli, Shahriyar (Supervisor)
    Abstract
    Short-circuit fault detection is mandatory in a high voltage DC power supply to prevent fatal damage. The majority of converters employ a single sensor to detect the short-circuit fault. This attribute increases the interference vulnerability of the fault detection system in the presence of noise. Therefore, miss detections and false alarms are possible to occur. Miss detections and false alarms are harmful catastrophes in most applications. A commonly used method to suppress the noise impacts is using a low-bandwidth low-pass filter. However, the use of the low-bandwidth low-pass filter reduces the speed of fault detection due to the filter delay. This paper proposes a fast fault detection... 

    Energy Efficient Concurrent Test of Switches and Links for Networks-On-Chip

    , M.Sc. Thesis Sharif University of Technology Alamian, Sanaz (Author) ; Hessabi, Shahin (Supervisor)
    Abstract
    Nowadays by increasing the number of processing cores in system-on-chip, using networks-on-chip, as an optimized interconnection foundation for transferring data between processing cores is inevitable .Based on this, the necessity of designing and implementing an optimized structure for testing network-on-chip, considering various overheads such as power consumption, latency, bandwidth and area, becomes an important issue in designing network-on-chip. The purpose of this project is to design an optimized structure for testing routers and connecting links in network, which considers power consumption overhead, latency and area overhead on one hand, and fault coverage on the other hand.... 

    Improvement of Inverter-based AC Microgrids Protection Against Short Circuit

    , Ph.D. Dissertation Sharif University of Technology Zarei, Fariborz (Author) ; Mokhtari, Hossein (Supervisor) ; Blaabjerg, Frede (Co-Supervisor)
    Abstract
    Inverter-based distributed generations (IBDGs) have gained special interest in the electricity supply chain due to the advancements in power electronics technology. Power electronic inverters provide high-efficiency energy conversion with full controllability over a wide operating range, and ancillary services such as reactive power support and active filtering. Considering the voltage and frequency control capability of power inverters, supplying inverter-based micro-grid (IBMG) loads is now pissible. Despite the significant opportunities associated with such sources, they introduce new challenges that should be addressed properly. Reliable and accurate protection against short circuit... 

    Fast Failure Detection in Modular Multilevel Converter Power Switches for Fault Tolerant Operation

    , Ph.D. Dissertation Sharif University of Technology Haghnazari, Saeed (Author) ; 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 Tebyanian, Afshin (Author) ; 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 Delavari, Mohammad Mohsen (Author) ; 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 Tayyebi, Shokoufe (Author) ; 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... 

    Leak Detection and Location in Oil Transmission Lines by Closed Form Solution and Linear Observer

    , M.Sc. Thesis Sharif University of Technology Derakhshan, Masoud (Author) ; 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 Farzin, Nima (Author) ; 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 Mashreghi, Ali (Author) ; 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... 

    Fault effect analysis of the exhaust manifold leakage for a turbocharged spark ignition engine

    , Article Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering ; Vol. 228, issue. 8 , 2014 , pp. 970-984 ; ISSN: 09544070 Salehi, R ; Vossoughi, G ; Alasty, A ; Sharif University of Technology
    Abstract
    Fault monitoring in internal-combustion engines is crucial for keeping the vehicle performance within the acceptable standards of emission levels and drivers' demands. This paper analyses how a vehicle's performance and engine variables are affected by a leakage fault in the exhaust manifold. The threshold leakage that causes the vehicle to exceed the emission standards is determined for a class M1 vehicle tested on a chassis dynamometer over the New European Driving Cycle. It is shown that, when a leakage of 6 mm diameter on the exhaust manifold is introduced, the vehicle emissions exceed those specified in the European 2013 on-board diagnostics standard. In addition, the effects of the...