Sharif Digital Repository

Rolling element bearings (REBs) are one of the most critical components in rotating ma-chines. Failure of these components may lead to fatal and costly breakdowns in rotating machinery. Therefore, it is significant to detect faults at early stage accurately. The pur-pose of this study is to compare vibration analysis and shock pulse method (SPM) in early detection of fault and remaining useful life prediction of REBs. To the aim, a set of ac-celerated life tests on REBs was planned. Vibration and shock pulse values accelerated life tests of the REBs were simultaneously measured from the moment of start to the end of the failure by two vibration and shock pulse sensors and their changes were... 

AC/DC/AC converters are widely being used in a variety of power applications. Continuity of service of these systems, as well as their reliability and performance are now of the major concerns. Indeed, the failure of the converter can lead to the total or partial loss of the control of the phase currents and can cause serious system malfunction or even shutdown. Thus, uncompensated faults can quickly endanger the system. Therefore, to prevent the spread of the fault to the other system components and to ensure continuity of service, fault tolerant converter topologies associated with quick and effective fault detection and compensation methods must be implemented. In this thesis, the... 

Five-Level Active-Neutral-Point -Clamped (5L-ANPC) converter is used for medium-voltage and high-power applications. In many of these applications, availability and robustness against fault are the most important issues. On the other hand, this converter is made of a large number of power semiconductor switches, diodes and capacitors which could increase the failure probability. Thus, fault detection of power circuit elements is necessary for fault tolerant operation of the converter. In this thesis, following an introduction to the topology and operation principles of Five-Level Active Neutral point clamped converter, a novel open-circuit fault detection and localization method is... 

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.... 

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... 

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... 

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... 

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...