Sharif Digital Repository

Today the need for fault diagnosis in polymer electrolyte membrane fuel cells (PEMFCs) is felt more than ever to increase the useful life and durability of the cell. The present study proposes an indirect in-situ experimental-based algorithm for diagnosing the moisture content issues in a three-cell stack. Three adaptive neuro-fuzzy inference systems (ANFIS) approximate the system outputs (cells voltages, cathodic and anodic pressure drop) in normal conditions. The values of Pearson's correlation coefficients (0.998, 0.983, and 0.995 for outputs, respectively) show the high quality of the modeling. In unknown operating conditions, the residuals of experimental and ANFIS values are compared... 

Vacuum arc is one of the most important failure factors of the vacuum tubes. The amount of delivered energy from the high-voltage dc power supply to the vacuum tube is an important issue during the vacuum arc in the tube. Vacuum arc acts as a short-circuit fault (SCF) at the power supply output. The majority of converters use a single current sensor to measure only the converter output current for detecting the SCF. However, the sensor may provide unreliable data because of the noise effect. Application of a low-pass filter reduces the noise effect. Regarding the delay of the low-pass filter, the interval of arc detection increases and more energy is delivered to the tube. In this article, a... 

Inverter driven electrical machines need resolver for position estimation and efficient electronic commutations. In this paper, the resolver signals are also used for the purpose of mechanical fault diagnosis. Therefore, a comprehensive procedure based on winding function (WF) method is presented to propose a noninvasive index to identify the mechanical fault's type (static/dynamic eccentricity) and even its percentage. In this regard, once the resolver signals are measured and saved in health condition. Then, during the operation of the motor, calculating the proposed index using the healthy and faulty signals leads to predict the fault type and its percentage. The success of the proposed... 

Rolling-element bearing (REB) Failure is one of the most common failure in rotary machines in industry. Therefore, this concern draws attention to the concept of diagnostic and the prediction of REB failure. The efficacy of vibration analysis in this area has led many researchers to focus on this topic in recent decades. Defective bearings such as fatigue, surface roughness, and corrosion can lead to disastrous accidents. Therefore, providing an algorithm for the detection and classification of bearing defects is valuable and useful. The prediction of the bearing's lifetime is important to ensure the planned production in an industrial unit. In this paper, different models for performance... 

Short-circuit fault (SCF) detection is mandatory in a high voltage DC power supply (HVPS) to prevent fatal damage. The majority of converters employ a single sensor to detect the SCF. This attribute increases the interference vulnerability of the fault detection (FD) 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 FD due to the filter delay. This paper proposes a fast FD algorithm based on... 

Due to several advantages, three-phase Dual Active Bridge (DAB) converter is widely used in numerous applications nowadays. On the other hand, this converter is very vulnerable to Transistor Open-Circuit Fault (TOCF). Therefore, a fault-tolerant (FT) scheme has been proposed in this paper to solve the problem. First, normal and faulty conditions are investigated, and according to the results, a fault-diagnosis (FD) approach is introduced. Using the outcomes of FD unit, a new post-fault strategy is proposed for the converter. The FD method is based on the DC component of transformer phase currents, and the basis of FT technique is shedding the faulty phase. Some benefits of the proposed... 

The ceramic fracture in output RF window is one of the most important failure factors in high power microwave sources. Fast protection systems are used to protect the source. The methods for determining the required protection response time are conservative and rough. In this paper, an investigation is presented about the twin growth in the ceramic of RF window in faulty condition. It is shown that the twin growth in ceramic can be a reliable figure of merit for the response time calculation of the microwave source protection system  

Vacuum tubes are widely used for various applications. These vacuum tubes are supplied by high voltage power supplies. The amount of delivered energy from the high voltage power supply to the vacuum tube is an important issue during the vacuum arc in the tube. The protection mechanism consists of a shunt crowbar which diverts the fault current from the tube to itself as a parallel path. Detection of the vacuum arc is crucial and only one sensor is usually employed to detect the vacuum arc. This characteristic intensifies the interference susceptibility of the vacuum arc diagnosis system in a noisy environment. As a result of the noise, the arc detection system can report false alarms. False... 

In this paper, a fast and practical method is proposed for open-circuit (OC) fault diagnosis (FD) in a three-phase quasi-Z-source inverter (q-ZSI). Compared with the existing fast OC FD techniques in three-phase voltage source inverters, this method is more cost-effective since no ultrafast processor or high-speed measurement is required. Additionally, the method is independent of the load condition. The proposed method is only applicable to Z-source family inverters and is based on observing the effect of shoot-through intervals on the system variables during switching periods. The proposed algorithm includes two consecutive stages: OC detection and fault location identification. When both... 

Augmenting the security of cryptographic algorithms by protecting them against side-channel active attacks (and natural faults) is essential in cryptographic engineering. BLAKE algorithm is an efficient hash function which has been developed based on Bernstein's ChaCha stream cipher. Because of the fact that Google has chosen ChaCha along with Bernstein's Poly1305 message authentication code as a replacement for RC4 in TLS for Internet security, BLAKE's implementation is of paramount importance. In this paper, we present high-performance fault detection schemes for BLAKE. Specifically, for the round function, two fault diagnosis approaches are developed and analyzed in terms of error... 

In this paper, a fast and practical method is proposed for open-circuit (OC) fault diagnosis (FD) in a three-phase quasi-Z-source inverter (q-ZSI). Compared to the existing fast OC FD techniques in three-phase voltage-source inverters (VSIs), this method is more cost-effective since no ultra-fast processor or high-speed measurement is required. Additionally, the method is independent of the load condition. The proposed method is only applicable to Z-source family inverters and is based on observing the effect of shoot-through (SH) intervals on the system variables during switching periods. The proposed algorithm includes two consecutive stages: OC detection and fault location identification.... 

Statistical process control provides useful tools to improve the quality of multistage machining processes, specifically in continuous manufacturing lines, where product characteristics are measured at the final station. In order to reduce process errors, variation source identification has been widely applied in machining processes. Although statistical estimation and pattern matching-based methods have been utilized to monitor and diagnose machining processes, most of these methods focus on stage-by-stage inspection using complex models and patterns. However, because of the existence of high rate alarms and the complexity of the machining processes, a surrogate modelling is needed to solve... 

Abnormal operating conditions for the timing belt can lead to cracks, fatigue, sudden rupture and damage to engines. In this study, an intelligent system was developed to detect and classify high-load operating conditions and high-temperature operating conditions for timing belts. To achieve this, vibration signals in normal operating conditions, high-load operating conditions and high-temperature operating conditions were collected. Time-domain signals were transformed to the frequency domain and the time-frequency domain using the fast Fourier transform method and the wavelet transform method respectively. In the data-mining stage, 25 statistical features were extracted from different... 

Fast and accurate fault detection is the primary step and one of the most important tasks in fault tolerant converters. In this paper, a fast and simple method is proposed to detect and diagnosis the faulty cell in a cascaded H-bridge multilevel inverter under a short circuit fault. In this method, the reference voltage is calculated using switching control pulses and DC-Link voltages. The comparison result of the output voltage and the reference voltage is used in conjunction with active cell pulses to detect the faulty cell. To achieve this goal, the cell which is active when the Fault signal turns to “0” is detected as the faulty cell. Furthermore, consideration of generating the active... 

Fault detection (FD) in power electronic converters is necessary in embedded and safety critical applications to prevent further damage. Fast FD is a mandatory step in order to make a suitable response to a fault in one of the semiconductor devices. The aim of this study is to present a fast yet robust method for fault diagnosis in nonisolated dc-dc converters. FD is based on time and current criteria which observe the slope of the inductor current over the time. It is realized by using a hybrid structure via coordinated operation of two FD subsystems that work in parallel. No additional sensors, which increase system cost and reduce reliability, are required for this detection method. For... 

Detection and isolation of faults in the exhaust gas path of a turbocharged spark ignition (SI) engine is an essential part of the engine control unit (ECU) strategies to minimize exhaust emission and ensure safe operation of a turbocharger. This paper proposes a novel physics-based strategy to detect and isolate an exhaust manifold leakage and a closed-stuck wastegate fault. The strategy is based on a globally optimal parameter estimation algorithm which detects an effective hole area in the exhaust manifold. The estimation algorithm requires prediction of the exhaust manifold's input and output flows. The input flow is predicted by a nonlinear Luenberger observer which is analytically... 

Fault diagnosis following a disturbance in a power system is of great importance for the operators in the control center as a prerequisite for system restoration. In this article, for the first time, an analytic method for fault diagnosis, using the wide area measurement system (WAMS) and employing circuit rules, is developed. Instead of conventional information about status of protective relays and circuit breakers, voltage and current phasors at different points of the power network after fault occurrence are utilized. Because most of the power systems will be equipped with WAMS consisting of high-speed sampling features, the proposed method introduces a new application of WAMS for fault... 

While the importance of wide area measurement system (WAMS) consisting of phasor measurement units (PMUs) is recognized, there are still unidentified applications that can be addressed with the advance of technology. Traditionally, power system operators diagnosed the fault point through the status of protective relays and circuit breakers of the protection system. In large blackouts, however, the malfunction of protection system has itself often been among the suspects of the disaster. This paper proposes an alternative fault diagnosis approach independent of the function of protection system, utilizing PMU data and bus impedance matrix (Zbus). First, the proposed method diagnoses the fault... 

This paper introduces a novel approach for power system fault diagnosis based on synchronized phasor measurements during the fault. The synchronized measurements are obtained in real time from Phasor Measurement Units (PMUs) and compared with offline thresholds determined by decision trees (DTs) to diagnose the fault. The DTs have already been trained offline using detailed power system analysis for different fault cases. While the traditional methods for fault diagnosis use the status of protective relays (PRs) and circuit breakers (CBs) to infer the fault section in the power system, the proposed method uses the available signals following the fault and thus can be trusted even in case of... 

Journal-bearings play a significant role in industrial applications and the necessity of condition monitoring with nondestructive tests is increasing. This paper deals a proper fault detection technique based on power spectral density (PSD) of vibration signals in combination with K-Nearest Neighbor and Support Vector Machine (SVM). The frequency domain vibration signals of an internal combustion engine with three journal-bearing conditions were gained, corresponding to, (i) normal, (ii) corrosion and (iii) excessive wear. The features of the PSD values of vibration signals were extracted using statistical and vibration parameters. The extracted features were used as inputs to the KNN and...