Sharif Digital Repository

This paper presents a capacitor cross-coupled gm-boosting scheme for differential implementation of common-gate transimpedance amplifier (CG-TIA). A differential transimpedance amplifiers (DTIA) is designed by this scheme using two modified floating-biased CG stage with improved low corner frequency. Despite conventional methods for single-ended to differential conversion that increase the power and the noise for the same gain, the new DTIA gives a higher gain and hence reduces the input-referred noise power. Design of the DTIA circuit using 0.13 μm CMOS technology illustrates near 1.7 dB improvement in the circuit sensitivity and 5.2 dB enhancement in transimpedance gain compared to its... 

In this paper, we describe an innovative method to model and solve spatio-temporal behavior of nuclear reactor cores via three-dimensional multilayer cellular neural networks. This method uses electrical elements and the existing duality between neutronic and thermal-hydraulic parameters of nuclear reactors. The relevant electrical circuit can be simulated by existing professional electrical circuit software. This research goes beyond our previous efforts to use a neural computing approach in the nuclear field. Modeling and solving simple nuclear reactor kinetic equations is now expanded to a complete dynamic calculation, integrating the core thermal-hydraulic models and the relevant... 

Measurement of partial discharges (PDs) current pulses is found to be one of the most efficient methods to evaluate the high voltage electrical equipment insulation condition. Generators, transformers, cables and transmission lines are especially tested for the presence of PDs. In AC, the solution is well known. Phase-resolved method can be used to detect and determine partial discharge activities. Although phase-resolved method works well under AC voltage; due to lack of a cyclic variation in DC voltage and current this cannot be used when studying partial discharges in DC voltage systems. Therefore, other methods are employed to interpret the partial discharge in DC. For this purpose, the... 

CT saturation is a phenomenon that can cause inaccurate fault current measurement and may result in related protective relay failure to block the high current flow under a fault condition in a power system. Hence, it is required to develop a method to detect occurrence of CT saturation with a good accuracy under presence of noise in a power system. In this paper, a new method having the afore-mentioned characteristics is presented. The main benefit of exploiting the introduced approach here for detecting CT saturation is its high level of reliability as well as its reasonable operational speed in CT saturation detection. In other words, these two properties are implemented to this method.... 

Nowadays power electronic devices have a wide usage in the industries and different electrical equipment for power conditioning. As a point of view, reliability is one of important figure of merits that should be considered to have long life time and also have more probability to do exactly the proposed mission. In this paper some methods are presented to improve the reliability of power electronic components. Also some methods of system reliability improvement are reviewed. One group of converters is DC-DC step down converter which is used in different applications such as battery charger and voltage regulator. In this paper as an example, reliability of a DC-DC step down converter with... 

Recently, an increasing concern has been raised about turn-to-turn faults (TTFs) in power transformers, because these faults can lead to severe transformer insulation failure and consequently, its outage. Generally, it is impossible to experimentally analyze the transformer behavior under such faults, since the implementation of those experiments may be substantially destructive. Therefore, computer-aided models should be developed to investigate the performance of transformer protective relays under turn-to-turn faults. So far, existing transformer models are mainly formulated to implement in the EMTP-based softwares. However, most of power system protection engineers and researchers... 

Despite the significant research efforts devoted to the microgrid and smart grid areas, numerous problems related to real world implementations still remain unsolved. The present special issue was announced with the objective of addressing and disseminating state-of-the-art R&D results on microgrids to bring together researchers from both academia and industry with the goal of fostering interactions among stakeholders. In response, 190 two-page extended abstracts were received and considered for the first round of reviews. Authors of about 60 selected abstracts were then invited to submit the full papers in the second round and out of them 27 high-quality manuscripts were ultimately approved... 

In this paper an analytical approach is proposed to formulate the proper set of phase currents reference to ride the permanent magnet synchronous generator (PMSG)-based wind turbine (WT) through faults properly, regardless of fault type. Hence, the WT is forced to inject required reactive current by grid codes together with active power injection, to help support grid frequency during faults and reduce the energy storage system (ESS) power rating. Moreover, it prevents pulsating active power injection to the grid. During grid faults, the DC-link voltage is controlled by the ESS instead of the grid-side converter (GSC) and the GSC controller applies calculated reference currents. The ESS... 

This paper proposes effective approach for determining appropriate crowbar resistance value to be able to improve the brushless doubly fed induction generator ride through capability during any asymmetrical voltage dip scenarios. The brushless DFIG has great potential for wind power plants particularly in offshore applications where maintenance is a major concern. Dynamic behavior of the machine is studied using two axis model and a more precise equivalent circuit model is extracted for analyzing machine behavior under fault conditions. Important limits and constraints in the use of crowbar are identified and discussed in detail. It is shown that large crowbar values can lead to considerable... 

Quality and continuity of electrical power to sensitive loads especially in power plants and industrial sectors is of great importance. For this reason, bus transfer is used. During the bus transfer interval, sensitive loads especially motors will be interrupted, and may encounter difficulties. So, it is used reactive power compensator and custom power devices to mitigate stress in motors and improve power quality indices. This paper presents the effect of reactive power compensator and custom power devices paralleling with motor in process of bus transfer which is done in two methods: EMTS and STS. Also, it is investigated dynamic performance of induction motor and spin-down curves in... 

Extraction of thermal heat from a salinity-gradient solar pond (SGSP) as a way of accumulating solar energy, stockpiling and taking merit of it for medium and low temperature demands is presented as an interesting topic in recent decades. This reliable supply of heat can be used for low-temperature refrigeration systems to yield cooling load for residential applications. For this purpose, theoretical investigation of ejector refrigeration cycle (ERC) driven by a SGSP is carried out to produce cooling output. Also, thermoelectric generator (TEG) is used as a potential device replacing condenser of the ERC for the sake of bolstering performance of the fundamental system by producing power,... 

The integration of renewable energy (RE)-based distributed generation (DG) with electric power distribution systems (DSs) in association with smart grid technology has numerous benefits, however, due to their intermittent nature, the utilisation of RE-based DG may pose threats to the proper operation of conventional overcurrent (OC) protection schemes. The resulting threats, malfunctions, and non-selective actions could occur by relays within the DS, and the development of efficient protection schemes is necessary. The objective of this study is to propose and simulate an adaptive OC protection scheme in DSs in the presence of doubly-fed induction generator (DFIG) wind turbines based on wind... 

Wind turbines are generally controlled for the objectives of the turbine protection and generation of the acceptable power for the utility grid. In this paper, a nonlinear multivariable model of the wind turbine with a DFIG generator is considered. The rotor speed and the d-axis rotor current, as the controlled variables, are controlled via manipulation of the two generator voltages, as the control signals. Two robust control strategies including the sliding mode control and H∞ robust control, designed via μ-synthesis based on DK-iteration algorithm, are presented for switching between various operating modes. Development of an acceptable dynamic model and two innovative control strategies... 

This paper presents a priority based dynamic programming approach for long term maintenance scheduling of overhead distribution networks. The proposed approach is based on risk management approach and utilizes the model of decoupled risk factors. Two heuristic factors are defined and utilized in order to establish a maintenance priority list and to curtail the dynamic programming search space. The proposed methodology yields a significant computational saving compare to the previously reported dynamic programming. Risk management approach enables the asset managers to consider the actual condition of electrical equipments and expected consequence of their failures. Furthermore, the decoupled... 

This paper presents an efficient mixed-integer linear formulation for long term maintenance schedule of overhead lines. The proposed formulation is based on risk management approach and utilizes the model of decoupled risk factors. The proposed methodology yields a significant computational saving comparing to the previously reported dynamic programming. Risk management approach enables the asset managers to consider the actual condition of electrical equipment and expected consequence of their failures. Furthermore, the decoupled risk strategy in conjunction with the mixed-integer linear programming formulation establishes a precise description of time-dependent deterioration failure rate... 

Failure statistics of most utilities indicate that distribution systems make the greatest individual contribution to the unavailability of supply to customers. Optimal capacitor placement in distribution systems has a number of advantages such as reducing losses, improving voltage profile, improving power factor and so on. The conventional objective function of the optimal capacitor placement consists of the total cost of losses and investments. Since capacitors supply reactive loads locally, they improve the load-carrying capability of the lines and therefore play the same role as redundant lines. Thus, optimal capacitor placement can also improve the reliability indices of a distribution...