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    Nondetection zone assessment of an active islanding detection method and its experimental evaluation

    , Article IEEE Transactions on Power Delivery ; Volume 26, Issue 2 , 2011 , Pages 517-525 ; 08858977 (ISSN) Bahrani, B ; Karimi, H ; Iravani, R ; Sharif University of Technology
    2011
    Abstract
    This paper analytically determines the nondetection zone (NDZ) of an active islanding detection method, and proposes a solution to obviate the NDZ. The method actively injects a negative-sequence current through the interface voltage-sourced converter (VSC) of a distributed generation (DG) unit, as a disturbance signal for islanding detection. The estimated magnitude of the corresponding negative-sequence voltage at the PCC is used as the islanding detection signal. In this paper, based on a laboratory test system, the performance of the islanding detection method under UL1741 anti-islanding test conditions is evaluated. Then, determining the NDZ of the method and proposing the... 

    Effect of customer demand type on optimization of distributed generation for minimization of energy loss

    , Article International Review of Electrical Engineering ; Volume 7, Issue 2 , Oct , 2012 , Pages 4113-4122 ; 18276660 (ISSN) Ebrahimi, R ; Ehsan, M ; Nouri, H ; Sharif University of Technology
    Praise Worthy Prize  2012
    Abstract
    The problem of distributed generation (DG) optimization in distribution systems has normally been assessed by assuming a constant power (real and reactive) load model. Such assumptions may lead to inconsistent and misleading results about loss reduction, DG optimization and other subsequent calculations. In this paper, the effect of different types of demand, e.g. industrial, residential and commercial, and its time varying effects on distribution networks is investigated. Customer demand type is defined by the load model that is voltage dependent and the load patterns from real life hourly demand data. The study shows that by defining the energy loss minimization as the objective function,... 

    Automatic image annotation using semi-supervised generative modeling

    , Article Pattern Recognition ; Volume 48, Issue 1 , January , 2015 , Pages 174-188 ; 00313203 (ISSN) Amiri, S. H ; Jamzad, M ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    Image annotation approaches need an annotated dataset to learn a model for the relation between images and words. Unfortunately, preparing a labeled dataset is highly time consuming and expensive. In this work, we describe the development of an annotation system in semi-supervised learning framework which by incorporating unlabeled images into training phase reduces the system demand to labeled images. Our approach constructs a generative model for each semantic class in two main steps. First, based on Gamma distribution, a generative model is constructed for each semantic class using labeled images in that class. The second step incorporates the unlabeled images by using a modified EM... 

    Distributed generation planning for losses, voltage profile, line congestion and total system cost improvement

    , Article International Review of Electrical Engineering ; Volume 4, Issue 3 , 2009 , Pages 434-440 ; 18276660 (ISSN) Porkar, S ; Poure, P ; Abbaspour Tehrani fard, A ; Saadate, S ; Sharif University of Technology
    2009
    Abstract
    The main goal of this paper is to obtain the optimal Distributed Generation (DG) investments as well as purchase additional power from Transmission Companies (TRANSCOs). To do this, a new mathematical modeling and a new software package interfacing between the two powerful softwares MATLAB and GAMS are used. The proposed model optimizes total system planning costs and consequently costumers' bills, reduces total system losses, guaranties system voltage profiles and prevents feeders' congestion. This new model and software package have been executed in two different cases depending if system voltage profiles are in their permissible margin or not; in each case, three different scenarios are... 

    Control of a microgrid with unbalanced loads using virtual negative-sequence impedance loop

    , Article PEDSTC 2014 - 5th Annual International Power Electronics, Drive Systems and Technologies Conference ; 2014 , p. 78-83 Hamzeh, M ; Karimi, H ; Mokhtari, H ; Mahseredjian, J ; Sharif University of Technology
    Abstract
    This paper presents an effective control strategy for autonomous operation of a multi-bus medium voltage (MV) microgrid (MG) consisting of several dispatchable distributed generation (DG) units. Each electronically-coupled DG unit supplies the loads which can be unbalanced due to the inclusion of single-phase loads. The proportional resonance (PR) and droop controllers are, respectively, used to regulate the load voltage and share the average powers among the DG units. The virtual negative-sequence impedance controller (VNSIC) is proposed to effectively compensate the negative-sequence currents of the unbalanced loads. Moreover, the VNSIC minimizes the negative-sequence currents in the MV... 

    A stochastic framework for short-term operation of a distribution company

    , Article IEEE Transactions on Power Systems ; Volume 28, Issue 4 , 2013 , Pages 4712-4721 ; 08858950 (ISSN) Safdarian, A ; Fotuhi Firuzabad, M ; Lehtonen, M ; Sharif University of Technology
    2013
    Abstract
    This paper presents a stochastic framework for short-term operation of a distribution company (disco). The proposed framework optimizes disco's operational decisions in two hierarchical stages. The first stage, called day-ahead operation stage (DAOS), deals with the operational decisions on purchases from the day-ahead market and commitment of distributed generation (DG) units. The objective of this stage is to minimize the expected operating cost while the financial risk exposed by uncertain real-time prices and loads is restricted to a given level. The model associated with this stage is based on the mixed-integer programming (MIP) format. The second stage, named real-time operation stage... 

    A new decentralized voltage control scheme of an autonomous microgrid under unbalanced and nonlinear load conditions

    , Article Proceedings of the IEEE International Conference on Industrial Technology ; February , 2013 , Pages 1812-1817 ; 9781467345699 (ISBN) Paridari, K ; Hamzeh, M ; Emamian, S ; Karimi, H ; Bakhshai, A ; Sharif University of Technology
    2013
    Abstract
    This paper presents an effective voltage control strategy for the autonomous operation of a medium voltage (MV) microgrid under nonlinear and unbalanced load conditions. The main objectives of this strategy are to effectively compensate the harmonic and negative-sequence currents of nonlinear and unbalanced loads using distributed generation (DG) units. The proposed control strategy consists of a multi-proportional resonant controller (MPRC) whose parameters are assigned with particle swarm optimization (PSO) algorithm. The optimization function is defined to minimize the tracking error at the specific harmonics considering the stability limitations. In this paper the performance of the... 

    IGDT based robust decision making tool for DNOs in load procurement under severe uncertainty

    , Article IEEE Transactions on Smart Grid ; Volume 4, Issue 2 , 2013 , Pages 886-895 ; 19493053 (ISSN) Soroudi, A ; Ehsan, M ; Sharif University of Technology
    2013
    Abstract
    This paper presents the application of information gap decision theory (IGDT) to help the distribution network operators (DNOs) in choosing the supplying resources for meeting the demand of their customers. The three main energy resources are pool market, distributed generations (DGs), and the bilateral contracts. In deregulated environment, the DNO is faced with many uncertainties associated to the mentioned resources which may not have enough information about their nature and behaviors. In such cases, the classical methods like probabilistic methods or fuzzy methods are not applicable for uncertainty modeling because they need some information about the uncertainty behaviors like... 

    Optimal allocation of distributed generation using a two-stage multi-objective mixed-integer-nonlinear programming

    , Article European Transactions on Electrical Power ; Volume 21, Issue 1 , 2011 , Pages 1072-1087 ; 1430144X (ISSN) Porkar, S ; Poure, P ; Abbaspour Tehrani Fard, A ; Saadate, S ; Sharif University of Technology
    Abstract
    Cost is one of the most essential factors that influence many decisions taken in the distribution system planning. In general, cost can be defined as everything that should be sacrificed to gain the desired results. This paper proposes a new two-stage methodology for distributed generation (DG) placement as an attractive option for distribution system planner. This method aims to minimize cost and maximize total system benefit (TSB). Optimal placement and size are obtained from total cost minimization mathematical problem which is solved in the first stage. For each DG cost characteristics and for each investment payback time, there is an optimal location and size. Then the optimal DG... 

    Day-ahead resource scheduling in distribution networks with presence of electric vehicles and distributed generation units

    , Article Electric Power Components and Systems ; Volume 47, Issue 16-17 , 2019 , Pages 1450-1463 ; 15325008 (ISSN) Shafiee, M ; Ghazi, R ; Moeini Aghtaie, M ; Sharif University of Technology
    Taylor and Francis Inc  2019
    Abstract
    In this paper a new framework for scheduling of available resources in the distribution networks is developed. In this respect attempts are focused on interactions between charging/discharging profiles of electric vehicles (EVs) and output power of distributed generation units. To reach this goal, the proposed framework is designed as a two-stage optimization procedure. In the first stage, the charging/discharging schedules of EVs are extracted running a linear programing optimization problem taking into account the EV users' constraints and requirements. The usage profiles of the DG units, strategy of buying electricity from the market and also the final charging/discharging patterns of the... 

    Micro-Grid Protection in Presence of Inverter Based Distributed Generation

    , M.Sc. Thesis Sharif University of Technology Zarei, Fariborz (Author) ; Parniani, Mostafa (Supervisor)
    Abstract
    In this study, control and protection of low voltage microgrids have been analyzed. Studied microgrid takes the advantages of inverter based distributed generation. One of the most important issues in inverter based microgrids is the control of its distributed generation. Since, the low voltage networks have single phase loads and many imbalances, these imbalances can affect the control of IBDGs (inverter based distributed generations). This issue in the islanded mode of operation is the most important, because in this mode of operation, IBDGs control the network voltage and frequency.
    In this thesis, the different control strategies of IBDGs are reviewed, and then modified to address... 

    Developing an Framework for Efficient Usage of Distributed Generation Expansion Plans in Distribution Network Considering the Effects of Reward-Penalty Mechanism

    , M.Sc. Thesis Sharif University of Technology Mirkhaef, Farzan (Author) ; Abbaspour Tehrani Fard, Ali (Supervisor)
    Abstract
    Based on codification and implementation of regulations of supporting from development of distributed generation sources, it is expected that in future years, investment in distributed generation scheme will be welcomed by private investors impressively. Under this circumstances, distribution Company will be faced with new chances for improving quality level of their services and optimal management of penalty-reward schemes. Penalty-reward schemes is set by legislator for distribution Company in order to improve their network. One of the pioneer ways is using distributed generators. So first, distribution Companies have to find optimum places for using these generators and in the second step... 

    Improvement of Control of Hybrid AC-DC Microgrid in Islanded Mode

    , Ph.D. Dissertation Sharif University of Technology Khorsandi, Amir (Author) ; Mokhtari, Hossein (Supervisor)
    Abstract
    A microgrid is a collection of loads, sources, and power storage units that operates as a single controllable system and can operate in grid-connected or islanded mode. From the generating side, renewable energy resources such as photovoltaic system, fuel cell and power storage units are inherently DC. From the load side, electronic loads such as computers, data centers and most of the variable speed motor drives require a DC supply. Therefore, DC Microgrids have gained widespread attention in recent years. On the other hand, since existing distribution systems are mostly AC, a hybrid microgrid is more likely. The hybrid microgrid is composed of two AC and DC subgrids interlinked by power... 

    Load Shedding in Microgrids to preserve System Stability In The Islanded Operation Mode

    , M.Sc. Thesis Sharif University of Technology Jamshidi, Mohammad Hossein (Author) ; Parniani, Mustafa (Supervisor)
    Abstract
    In the near future, it is expected that the microgrids become widespreed due to issues such as reliability, increased penetration of renewable energy sources and distributed generation, environmental concerns and shortage of fossil fuels. Different control methods have been suggested to regulate the frequency and voltage of the system so that these quantities remain in their permissible range upon islanding and in the islanded operation mode. However, in emergency conditions, such as shortage of generated power compared to the load of microgrid, frequency or voltage reduction occures due to imbalance. In this situation, it is invitable to shed extra load to maintain the stability and... 

    Hybrid AC/DC Microgrid Planning

    , M.Sc. Thesis Sharif University of Technology Shariat, Maryam (Author) ; Fotouhi Firuzabad, Mahmoud (Supervisor) ; Rajabi Ghahnavie, Abbas (Co-Advisor)
    Abstract
    Nowadays, due to the increasing importance and penetration of microgrids, solving the microgrid optimal sizing problem has become more important. The current utility grid and conventional energy sources are mainly ac, however, increasing rate of the replacement of the ac load with dc load lead to a more efficient dc system. So choosing the optimal type of microgrid as a way to increase efficiency of these systems would be a serious issue. This thesis establishes a planning model which finds the optimal size and type of a microgrid to minimize total cost. Total cost includes investment, operation and reliability cost of the microgrid. Sizes of DGs, converters and transformer linking the... 

    A comprehensive digital protection scheme for low-voltage microgrids with inverter-based and conventional distributed generations

    , Article IEEE Transactions on Power Delivery ; Volume 32, Issue 1 , 2017 , Pages 441-452 ; 08858977 (ISSN) Zarei, S. F ; Parniani, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    Microgrid (MG) protection is one of the main challenges in proliferation of microgrids. Due to limited fault current feeding of inverter-based distributed generations (DGs), in islanded operation of MG, protection problems become more complicated; and, therefore, conventional protection strategies cannot be applied. Hence, new protection methods that are applicable in islanded and grid-connected modes of operation are necessary. In this paper, a comprehensive digital-relay based protection is introduced for the protection of MGs. The proposed method includes protection of lines, distributed generations, and the point of common coupling. The structure and graphical schematic of the proposed... 

    Distribution system planning considering integration of distributed generation and load curtailment options in a competitive electricity market

    , Article Electrical Engineering ; Volume 93, Issue 1 , 2011 , Pages 23-32 ; 09487921 (ISSN) Porkar, S ; Abbaspour Tehrani Fard, A ; Poure, P ; Saadate, S ; Sharif University of Technology
    Abstract
    Distribution systems management is becoming an increasingly complicated issue due to the introduction of new technologies, new energy trading strategies and new deregulated environment. In the new deregulated energy market and considering the incentives coming from the technical and economical fields, it is reasonable to consider distributed generation (DG) as a viable option to solve the lacking electric power supply problem. This paper presents a mathematical distribution system planning model considering three planning options to system expansion and to meet the load growth requirements with a reasonable price as well as the system power quality problems. DG is introduced as an attractive... 

    Distribution loss allocation for radial systems including dgs

    , Article IEEE Transactions on Power Delivery ; Vol. 29, issue. 1 , 2014 , pp. 72-80 ; ISSN: 08858977 Ghofrani-Jahromi, Z ; Mahmoodzadeh, Z ; Ehsan, M ; Sharif University of Technology
    Abstract
    Due to the liberalization of the electricity market and the introduction of distributed generation (DG), the importance of distribution loss allocation (LA) has increased. This paper presents a new method for distribution power LA in radial systems. The proposed method, which is based on the results of power flow and considers active and reactive power flows of lines for LA, is composed of three steps. In the first step, starting from the source nodes (i.e., the nodes whose generation is more than their load), the power loss allocated to all nodes is calculated and then the power loss allocated to the loads connected to each node is obtained. In the next step, the total power loss is... 

    Imperialist competition algorithm for distributed generation connections

    , Article IET Generation, Transmission and Distribution ; Volume 6, Issue 1 , January , 2012 , Pages 21-29 ; 17518687 (ISSN) Soroudi, A ; Ehsan, M ; Sharif University of Technology
    2012
    Abstract
    This study proposes an imperialist competition algorithm (ICA) to maximise the benefits of distribution network operators (DNOs) because of the existence of distributed generation (DG) units. The sum of active loss reduction and network investment deferral incentives has been considered as the objective function to be maximised in this study. The optimal location and size of DG units in the network are found considering various techno-economical issues. The application of the proposed methodology in the UK under current Ofgem financial incentives for DNOs is investigated. The ability of the proposed approach in finding the optimal solution is validated by comparing the obtained results with... 

    Stability analysis and experimental evaluation of a control strategy for islanded operation of distributed generation units

    , Article IEEJ Transactions on Industry Applications ; Volume 131, Issue 8 , 2011 , Pages 1013-1022 ; 09136339 (ISSN) Bahrani, B ; Karimi, H ; Iravani, R ; Sharif University of Technology
    2011
    Abstract
    This paper presents stability analysis of a distributed generation (DG) controller (1), in an islanded mode, based on the Mapping Theorem and the Zero Exclusion Condition, and validates the results based on a laboratory scale experimental setup. The DG unit is interfaced to the host system through a voltage-sourced converter (VSC). The control strategy regulates the load voltage at the desired value in the islanded mode, despite uncertainties in the load parameters. The frequency of the island is controlled in an open loop manner by an internal oscillator. The experimental results show that the controller provides robust voltage control for a wide range of load parameters, and even maintains...