Sharif Digital Repository

This paper develops a general framework for reliability assessment of multi-microgrid (MMG) distribution systems. It also investigates reliability impacts of coordinated outage management strategies in a MMG distribution network. According to the proposed reliability evaluation framework, which is based on sequential Monte Carlo simulation method, distribution system is divided into smaller sections/microgrids based on protection system configuration and operating measures are efficiently simulated considering different operation modes. In order to demonstrate the role of outage management strategy in reliability performance of MMG distribution systems, at first, the required features of an... 

Solid-State Drives (SSDs) are recently employed in enterprise servers and high-end storage systems in order to enhance performance of storage subsystem. Although employing high speed SSDs in the storage subsystems can significantly improve system performance, it comes with significant reliability threat for write operations upon power failures. In this paper, we present a comprehensive analysis investigating the impact of workload dependent parameters on the reliability of SSDs under power failure for variety of SSDs (from top manufacturers). To this end, we first develop a platform to perform two important features required for study: A) a realistic fault injection into the SSD in the... 

Nowadays position sensors are increasingly used in many applications. One of the most commonly used sensors are resolvers. There are different types of resolvers including Wound Rotor (WR) resolvers, Variable Air-gap Length Variable Reluctance (VAGL-VR) resolvers, and Sinusoidal Rotor Variable Reluctance (SR-VR) resolvers. Regardless of the resolvers’ configurations, including linear, cylindrical and disk type, finite element analysis (FEA) is inseparable part of design and performance evaluation of these magnetic sensors. The scope of this study is to discuss challenges in the FEA of resolvers. The influence of mesh quality, time steps, stop time, excitation methods including volt-age... 

Nowadays, position sensors are increasingly used in many applications. One of the most commonly used sensors are resolvers. There are different types of resolvers including wound rotor resolvers, variable air-gap length variable reluctance resolvers, and sinusoidal rotor variable reluctance resolvers. Regardless of the resolvers' configurations, including linear, cylindrical and disk type, finite element analysis (FEA) is inseparable part of design and the performance evaluation of these magnetic sensors. The scope of this study is to discuss challenges in the FEA of resolvers. The influence of mesh quality, time steps, stop time, excitation methods including voltage source and current... 

In this paper, reliability of conventional pulse width modulation buck-boost converter is analyzed, where the effects of duty cycle, input voltage, output power, voltage gain and time duration are evaluated. These analyses are performed in both continuous and discontinuous conduction modes and Markov process model is utilized to obtain the results. In addition, mean time to failure of this converter is obtained with respect to the aforementioned parameters. In this paper, detailed analyses of reliability in buck-boost converter with different evaluation parameters are presented. Moreover, the plots of MATLAB software are prepared to have complete evaluation in each operating state  

Due to the system-level power constraints, it is encountered that not all cores in a multicore chip can be simultaneously powered-on at the highest voltage/frequency levels. Also, in the future technology nodes, reliability issues due to the susceptibility of systems to transient faults should be considered in multicore platforms. Therefore, two major objectives in designing multicore embedded systems are low energy/power consumption and high reliability. This letter presents an energy management system that optimizes the energy consumption such that it satisfies reliability target and meets timing, thermal design power (TDP) and thermal safe power (TSP) constraints. Toward the... 

Continuity of supply plays a significant role in modern distribution system planning and operational studies. Accordingly, various techniques have been developed for reliability assessment of distribution networks. However, owing to the complexities and restrictions of these methods, many researchers have resorted to several heuristic optimization algorithms for solving reliability-constrained optimization problems. Therefore, solution quality and convergence to global optimality cannot be guaranteed. Aiming to address this issue, two salient mathematical models are introduced in this paper for topology-variable-based reliability evaluation of both radial and radially-operated meshed... 

Cost, durability and reliability are three critical issues in electrical/hybrid electrical vehicles (EV/HEV). In this regard, resolvers are often used as position and speed sensors in such applications. In this paper design and analysis of a novel multi-turn resolver is discussed to address all the mentioned issues. The proposed resolver has got one stator core and one rotor core. Double sets of signal windings on the stator and a special excitation winding on the rotor are designed to achieve both absolute and multi-speed operations. Mathematical model of the proposed resolver is verified using time stepping finite element analysis and experimental measurements. © 1967-2012 IEEE  

In this article, a new soft switching isolated push-pull dc-dc converter using a three-winding transformer is proposed. The proposed hybrid resonant and pulse width modulated converter employs a conventional push-pull structure in the primary side, a voltage doubler in the secondary side, and a bidirectional switch besides the transformer, altogether help offering a high efficiency over a wide range of input and output voltage signals with an unsophisticated fixed-frequency control mechanism. The primary-side switches are commutated under zero voltage switching with low switching current and the secondary-side diodes are commutated under zero current switching. In this article, we first... 

This article offers a holistic model and approach on reliability assessment of conventional isolated multiswitch pulsewidth modulation dc-dc (IMSDC-DC) power electronic converters with conventional half-bridge, full-bridge, and push-pull dc-dc topologies. The proposed reliability assessment analytics encapsulate correlated effects of several conditions (e.g., open- and short-circuit faults) and prevailing parameters (e.g., duty cycle, input voltage, output power, transformer turns ratio, voltage gain, switching frequency, operation time duration, and components characteristics) on the overall reliability performance of IMSDC-DC converters. Such insights are then harnessed within a Markov... 

Reliability of routing mechanisms in wireless networks is typically measured with Packet Delivery Ratio (PDR). Basically, PDR is reported with an optimistic assumption that the topology is fully constructed, and the nodes have started their packet transmission. This is despite the fact that prior to being able to transmit packets, nodes must first join the network, and then try to keep connected as much as possible. This is a key factor in the overall reliability provided by the routing protocols, especially in mobile IoT applications, where disconnections occur frequently. Nevertheless, there is a lack of appropriate metrics, which could evaluate the routing mechanisms from this... 

This paper provides a general methodology for evaluating the reliability of microgrids embedding conventional and renewable energy sources (RESs), as well as energy storage systems (ESSs). The developed reliability assessment model is then leveraged to investigate the impact of different resource scheduling methods on the reliability. The technique applied in this article to assess microgrid reliability is based on the sequential Monte Carlo simulation. In this approach, the coincidence of faults is considered, aside from the annual generation pattern of RESs, i.e., wind and photovoltaic, and the network load profiles. For the sake of considering priority of the microgrid loads, two... 

In addition to meeting the real-time constraint, power/energy efficiency and high reliability are two vital objectives for real-time embedded systems. Recently, heterogeneous multicore systems have been considered an appropriate solution for achieving joint power/energy efficiency and high reliability. However, power/energy and reliability are two conflict requirements due to the inherent redundancy of fault-tolerance techniques. Also, because of the heterogeneity of the system, the execution of the tasks, especially real-time tasks, in the heterogeneous system is more complicated than the homogeneous system. The proposed method in this paper employs a passive primary/backup technique to... 

The increasing use of power electronic equipment and the importance of their continuous and correct operation have attracted remarkable attention to the condition monitoring of power electronic converters. Since capacitors are the leading cause of power electronic converters failure, this paper attempts to attain a solution to monitor the condition of the DC-link capacitor in a three-phase back-to-back converter using the stimulated measurable transients. The proposed method works based on the temporary change of switching logic and the measurement of the DC-link voltage and converter input phase current transients. By processing the measured signals, the capacitance of the capacitor is... 

Reliability of the power distribution unit (PDU) is very important in electrical systems. Since any failure in this unit leads to system failure. A commonly used method for increasing the reliability of a dc PDU is using the redundant modules. If a fault occurs in a voltage regulator of PDU, it is replaced by its redundant module. In conventional redundancy, each dc voltage regulator has its exclusive redundant modules. Therefore, if both a regulator and its redundant modules fail, the system is stopped. It is an important drawback since the exclusive redundant modules of other voltage regulators may not be used, but, the PDU cannot use them instead of faulty regulators. In this paper, the... 

To cope with the unprecedented growth of mobile data traffic, we investigate the performance gains obtained from unifying coverage-centric 4G mobile networks and capacity-centric fiber-wireless (FiWi) broadband access networks based on data-centric Ethernet technologies with resulting fiber backhaul sharing and WiFi offloading capabilities. Despite recent progress on backhaul-aware 4G studies with capacity-limited backhaul links, the performance-limiting impact of backhaul latency and reliability has not been examined in sufficient detail previously. In this paper, we evaluate the maximum aggregate throughput, offloading efficiency, and in particular, the delay performance of FiWi enhanced... 

Editor's note: Due to increasing process, voltage, and temperature (PVT) variability, reliability is becoming a growing worry. This article addresses this concern with a combination of software and hardware hardening modes while considering power, performance, and overhead constraints. Similar to other examples in this special issue, this work illustrates that complex management tasks that have to integrate multiple objectives, goals, and constraints require a comprehensive understanding of the system's state. - Axel Jantsch, TU Wien - Nikil Dutt, University of California at Irvine. © 2013 IEEE  

I/O caching techniques are widely employed in enterprise storage systems in order to enhance performance of I/O intensive applications in large-scale data centers. Due to higher performance compared to Hard Disk Drives (HDDs) and lower price and nonvolatility compared to Dynamic Random-Access Memories (DRAM), Flash-based Solid-State Drives (SSDs) are used as a main media in the caching layer of storage systems. Although SSDs are known as non-volatile devices but recent studies have reported large number of data failures due to power outage in SSDs. To overcome the reliability implications of SSD-based I/O caching schemes, RAID-1 (mirrored) configuration is commonly used to avoid data loss... 

I/O caching techniques are widely employed in enterprise storage systems in order to enhance performance of I/O intensive applications in large-scale data centers. Due to higher performance compared to Hard Disk Drives (HDDs) and lower price and nonvolatility compared to Dynamic Random-Access Memories (DRAM), Flash-based Solid-State Drives (SSDs) are used as a main media in the caching layer of storage systems. Although SSDs are known as non-volatile devices but recent studies have reported large number of data failures due to power outage in SSDs. To overcome the reliability implications of SSD-based I/O caching schemes, RAID-1 (mirrored) configuration is commonly used to avoid data loss... 

Analysis of reliability, power, and performance at hardware and software levels due to heterogeneity is a crucial requirement for heterogeneous multicore embedded systems. Escalating power densities have led to thermal issues for heterogeneous multicore embedded systems. This paper proposes a peak-power-aware reliability management scheme to meet power constraints through distributing power density on the whole chip such that reliability targets are satisfied. In this paper, we consider peak power consumption as a system-level power constraint to prevent system failure. To balance the power consumption, we also employ a Dynamic Frequency Scaling (DFS) method to further reduce peak power...