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    Assessment and Performance Improvement of Hierarchical Voltage Control System

    , M.Sc. Thesis Sharif University of Technology Davoodi, Ehsan (Author) ; Parniani, Mostafa (Supervisor)
    Abstract
    Hierarchical voltage control is one of the conventional kinds of coordinated voltage control schemes which has been studied in some countries in the last decades. In this method network is divided into several voltage control regions and in each region voltage profile is controlled near optimal level, satisfying the economic and secure goals of the network performance. In this thesis, after the explanation of the main concepts of this scheme, its effects on the network voltage control is assessed and its performance is improved. First the primary concepts of hierarchical voltage control are explained. Then, the methods of the control regions determination and pilot nodes selection are... 

    Power and voltage control in a grid-connected microgrid system with a back-to-back converter

    , Article 6th Annual International Power Electronics, Drive Systems, and Technologies Conference, PEDSTC 2015, 3 February 2015 through 4 February 2015 ; 2015 , Pages 468-473 ; 9781479976539 (ISBN) Sekhavatmanesh, H ; Mokhtari, H ; Hamzeh, M ; Asbafkan, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    This paper proposes to use a back-to-back converter as the interlink between a utility grid and a microgrid. To justify this proposal, two modes of operation are explained and the benefits of the back-to-back converter over conventional static switches are shown. In mode-1, the inter-link converter injects prespecified amounts of active and reactive power to the microgrid. This mode is identified as PQ control mode. Mode-2 is the voltage control mode in which, the back to back converter controls the voltage of the microgrid and maintains the power quality of the current drawn from the utility grid in spite of nonlinear and unbalanced loads in the microgrid  

    Enhanced control of grid forming VSCs in a micro-grid system under unbalanced conditions

    , Article 9th Annual International Power Electronics, Drive Systems, and Technologies Conference, PEDSTC 2018, 13 February 2018 through 15 February 2018 ; Volume 2018-January , April , 2018 , Pages 380-385 ; 9781538646977 (ISBN) Zarei, S. F ; Mokhtari, H ; Ghasemi, M. A ; SHarif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    Abstract
    Due to the technical advances in power electronic industry, employing inverter-based distributed energy resources (IBDERs) are increased in electric power systems. Distributed generators (DGs) with the rating capacity of few megawatts are commonly connected to the distribution level of power systems which are inherently unbalanced. A cluster of IBDERs and loads form a small-scale grid called microgrid (MG) which can operate independent of the main grid. In a MG, grid forming voltage source converters (VSCs) are used to control the voltages and frequency of the MG. However, grid forming VSCs with conventional control schemes cannot do this task properly when the MG is unbalanced. In this... 

    Power quality improvement in three-phase four-wire systems using shunt active filters

    , Article 9th IEEE International Power Electronics Congress, CIEP 2004, Celaya, Gto, 17 October 2004 through 22 October 2004 ; 2004 , Pages 193-197 Esfandiari, A ; Parniani, M ; Mokhtari, H ; Sharif University of Technology
    2004
    Abstract
    This paper presents a shunt active filter control using the instantaneous power theory on a rotating reference frame for power quality improvement in 3-phase 4-wire system. By current space vector mapping on rotating reference frame, three linearly independent components are derived. The defined powers can be controlled by current vector components. The in-phase current vector component to voltage vector is used for compensating oscillatory load active power and controlling dc voltage. Two other components are used to compensate for reactive power and to eliminate neutral current. Advantage of this control strategy is that synchronizing circuit is not required. Simulation results verify... 

    A power-efficient LC quadrature VCO for RFID, zigbee and bluetooth standards

    , Article Advances in Electrical and Computer Engineering ; Volume 9, Issue 3 , 2009 , Pages 34-38 ; 15827445 (ISSN) Torkzadeh, P ; Atarodi, M ; Sharif University of Technology
    2009
    Abstract
    A multi-band CMOS LC Quadrature Voltage Control Oscillator (QVCO) with minimum power consumption is developed to meet the phase noise and frequency band requirements of RFID, Zigbee and Bluetooth standards. To accomplish the multi-band receiving architecture at low power consumption, current switching technique with optimized cross-coupled transistor sizes has been used. A comprehensive analysis of small signal model for complementary architecture including transistor noise sources and their effects on output phase noise amount has been discussed. Using extracted small signal model, coupled and coupling transistor sizes for minimum power consumption and the least achievable phase noise have... 

    An 8-bit switched-resistor pipeline ADC

    , Article 2007 IEEE International Symposium on Circuits and Systems, ISCAS 2007, New Orleans, LA, 27 May 2007 through 30 May 2007 ; 2007 , Pages 1963-1966 ; 02714310 (ISSN) Sedighi, B ; Sharif Bakhtiar, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2007
    Abstract
    In this paper a new technique called switched-resistor is used as an alternative to switched-capacitor circuits in a low-voltage low-power high-speed A/D converter. Simulation results for an 8-bit 150MS/s pipeline ADC are presented. This converter consumes 20mW from a 1.8V supply and provides an ENOB of 7.5bit. © 2007 IEEE  

    Voltage regulation through smart utilization of potential reactive power resources

    , Article Proceedings - UKSim 5th European Modelling Symposium on Computer Modelling and Simulation, EMS 2011, 16 November 2011 through 18 November 2011, Madrid ; 2011 , Pages 293-298 ; 9780769546193 (ISBN) Kazari, H ; Abbaspour Tehrani Fard, A ; Dobakhshari, A. S ; Ranjbar, A. M ; Sharif University of Technology
    Abstract
    The introduction of demand response concept, in addition to increment of penetration of distributed generation (DG) based on renewable energies, make opportunities for the novel control schemes to be integrated in power system on a smart grid framework. Voltage control methods in power systems needs proper coordination among reactive power resources and conventional volt/var control equipments. In this work, potential reactive power resources are investigated and then, reactive power output of renewable DG units and controllable loads along with operation of conventional voltage controllers are optimized using a centralized control scheme. Considering the variability of demand and... 

    Immune-based selection of pilot nodes for secondary voltage control

    , Article European Transactions on Electrical Power ; Volume 20, Issue 7 , 2010 , Pages 938-951 ; 1430144X (ISSN) Amraee, T ; Ranjbar, A. M ; Feuillet, R ; Sharif University of Technology
    2010
    Abstract
    Secondary voltage control is used to re-adjust the reference values of automatic voltage regulators of generators. The performance of the secondary voltage control strongly depends on pilot node selection. In this paper the two proposed control laws for secondary voltage control are discussed and then an immune based algorithm is proposed to solve the optimal pilot node selection problem. The proposed algorithm is based on the clonal selection theory. The merit of immune algorithm lies in pattern recognition and memorization capabilities. Also, to provide independency of electrical zones a decoupling factor based on electrical distance concept is proposed. To verify the network observability... 

    Robust backstepping control of an interlink converter in a hybrid AC/DC microgrid based on feedback linearisation method

    , Article International Journal of Control ; 2016 , Pages 1-15 ; 00207179 (ISSN) Mahdian Dehkordi, N ; Sadati, N ; Hamzeh, M ; Sharif University of Technology
    Taylor and Francis Ltd 
    Abstract
    This paper presents a robust dc-link voltage as well as a current control strategy for a bidirectional interlink converter (BIC) in a hybrid ac/dc microgrid. To enhance the dc-bus voltage control, conventional methods strive to measure and feedforward the load or source power in the dc-bus control scheme. However, the conventional feedforward-based approaches require remote measurement with communications. Moreover, conventional methods suffer from stability and performance issues, mainly due to the use of the small-signal-based control design method. To overcome these issues, in this paper, the power from DG units of the dc subgrid imposed on the BIC is considered an unmeasurable... 

    Control of grid-following inverters under unbalanced grid conditions

    , Article IEEE Transactions on Energy Conversion ; Volume 35, Issue 1 , 2020 , Pages 184-192 Zarei, S. F ; Mokhtari, H ; Ghasemi, M. A ; Peyghami, S ; Davari, P ; Blaabjerg, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    Abstract
    This paper proposes a new control scheme to eliminate the 3rd harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical 3rd harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a... 

    Design of Medium Voltage Cascaded H Bridge Multilevel Inverter with Reliability Consideration

    , M.Sc. Thesis Sharif University of Technology Balador, Ayoub (Author) ; Zolghadri, Mohammad Reza (Supervisor)
    Abstract
    Today, with the development of power electronics and the emergence of various multilevel converters, possibility of operation at the voltage and powers higher than the rated value of components is provided. The reliability of these converters due to their high power is important. In this project, design of multilevel inverter with cascaded H-bridge structure have been studied for a medium voltage and high power 3.3 KV, 1MVA application, due to its advantages over other structures. This converter is composed of several cascaded low voltage full-bridge cells. Therefore, the converter is composed of many semiconductor elements that the reliability of them depends on the physical stresses such... 

    A fast local index for online estimation of closeness to loadability limit

    , Article IEEE Transactions on Power Systems ; Volume 25, Issue 1 , December , 2010 , Pages 584-585 ; 08858950 (ISSN) Parniani, M ; Vanouni, M ; Sharif University of Technology
    2010
    Abstract
    Closeness to the nose point of P-V curve, or loadability limit (LL), and voltage instability is one of the main concerns of modern power systems. Hence, online evaluation of LL has attracted the interest of researchers in recent years. This letter introduces a simple local index for online estimation of closeness to LL, using two consecutive scalar local measurements. This index is achieved based on the fact that variation of the load apparent power is zero at LL. The index is suitable for implementation in numerical relays to stimulate local control actions to prevent voltage instability, and in the system control center for system-wide coordinated analysis and control measures. Simulation... 

    Autonomous power management in LVDC microgrids based on a superimposed frequency droop

    , Article IEEE Transactions on Power Electronics ; 2017 ; 08858993 (ISSN) Peyghami, S ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
    Abstract
    In this paper a novel droop approach for autonomous power management in low voltage dc microgrids based on a master-slave concept is presented. Conventional voltage-based droop approaches suffer from poor power sharing due to line resistance effects on a virtual resistance, which is solved a by introducing a communication system to increase the current sharing accuracy. In this paper, a virtual frequency is superimposed by the master units, and slave units determine their output power according to the corresponding frequency-based droop characteristics. Unlike the voltage-droop methods, the proposed virtual frequency-droop approach can be applied for proportional power management among the... 

    A high-speed and low-power voltage controlled oscillator in 0.18-μm CMOS process

    , Article 2007 IEEE International Symposium on Circuits and Systems, ISCAS 2007, New Orleans, LA, 27 May 2007 through 30 May 2007 ; 2007 , Pages 933-936 ; 02714310 (ISSN) Savadi Oskooei, M ; Afzali Kusha, A ; Atarodi, S. M ; Sharif University of Technology
    2007
    Abstract
    In this paper, we propose a new voltage controlled oscillator (VCO) with a high oscillation frequency yet low power consumption. The oscillator which is a single stage circuit has a low phase noise due to reduced noise sources. To evaluate the performance parameters, the oscillator was simulated in a 0.18-μm standard CMOS process. The results show that the oscillation frequency of VCO may vary between 4.66-5.9 GHz. Also, the phase noise of the VCO at oscillation frequency of 5.6 GHz is -99.7 dBc at 1 MHz offset frequency. Also, the power consumption was 4.8 mW at the same oscillation frequency. © 2007 IEEE  

    Electric arc furnace power quality improvement using shunt active filter and series inductor

    , Article IEEE TENCON 2004 - 2004 IEEE Region 10 Conference: Analog and Digital Techniques in Electrical Engineering, Chiang Mai, 21 November 2004 through 24 November 2004 ; Volume D , 2004 , Pages D105-D108 Esfandiari, A ; Parniani, M ; IEEE Region 10 ; Sharif University of Technology
    2004
    Abstract
    This paper presents an investigation of power quality problems arising from electric arc furnace (EAF) operation, and the required compensating system capabilities. It also proposes a compensation system using a shunt active filter and a series inductor. A shunt active filter compensates for the reactive power and the current harmonics of the highly varying load. Reference signals for the compensation logic are obtained from the instantaneous current vector components on a rotating reference frame. Due to noninteger harmonics on voltages at the point of common coupling, conventional methods for the inverter dc bus voltage regulation fail to perform properly. Hence, a new method is introduced... 

    A very low power CMOS, 1.5V, 2.5GHz prescaler

    , Article 2002 45th Midwest Symposium on Circuits and Systems, Tulsa, OK, 4 August 2002 through 7 August 2002 ; Volume 3 , 2002 , Pages III378-III380 Mirzaei, A ; Sharif University of Technology
    2002
    Abstract
    A very low power CMOS, 1.5V, 2.5GHz prescaler was designed. Implemented in 0.25u standard CMOS technology, this prescaler can operate up to 3GHz range. The prescaler consists of three delay flip flops (DFF) that work synchronously with RF sinusoidal clock and divides by 4 or 5 according to control signal  

    A 5 GHz, 1.5 Volt and very low-power cmos frequency synthesizer for wireless communications

    , Article 2002 45th Midwest Symposium on Circuits and Systems, Tulsa, OK, 4 August 2002 through 7 August 2002 ; Volume 3 , 2002 , Pages III536-III539 Mirzaei, A ; Sharif University of Technology
    2002
    Abstract
    A 5GHz, 1.5 Volt and low power CMOS frequency synthesizer with LC-tuned VCO (voltage controlled oscillator) is presented. The synthesizer consists of an LC-tuned VCO, an injection-lock frequency divider, a very low power prescaler which brings 2.5GHz range frequency to 11 MHz, a phase-frequency detector and charge-pump with improved architecture. Spiral inductors with Q-factor of 9 are used for the LC-tuned 5 GHz VCO. A fixed 2 frequency divider based on injection-locking phenomenon is used to bring 5 GHz VCO frequency to 2.5GHz. Both VCO and injection-locked divider's oscillators are tuned with NMOS varactors with their bodies are grounded, resulting in about 700 MHz tuning range.... 

    Reinforcing fault ride through capability of grid forming voltage source converters using an enhanced voltage control scheme

    , Article IEEE Transactions on Power Delivery ; 2018 ; 08858977 (ISSN) Zarei, F ; Mokhtari, H ; Ghasemi, M. A ; Blaabjerg, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    Abstract
    Medium power distributed energy resources (DERs) are commonly connected to medium voltage distribution systems via voltage source converters (VSCs). Several guidelines and standards have been developed to establish the needed criteria and requirements for DERs interconnections. In this respect, it is preferred to reinforce the VSC fault ride through (FRT) capability, which considerably minimizes the DG outage period and reconnection time and results in a resilient system against short circuits. Considering the significant number of asymmetrical faults in distribution systems, the VSC response in such conditions must be investigated, and consequently, its FRT capability must be reinforced. In... 

    Reinforcing fault ride through capability of grid forming voltage source converters using an enhanced voltage control scheme

    , Article IEEE Transactions on Power Delivery ; Volume 34, Issue 5 , 2019 , Pages 1827-1842 ; 08858977 (ISSN) Zarei, S. F ; Mokhtari, H ; Ghasemi, M. A ; Blaabjerg, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    Medium power distributed energy resources (DERs) are commonly connected to medium voltage distribution systems via voltage source converters (VSCs). Several guidelines and standards have been developed to establish the needed criteria and requirements for DERs interconnections. In this respect, it is preferred to reinforce the VSC fault ride through (FRT) capability, which considerably minimizes the DG outage period and reconnection time and results in a resilient system against short circuits. Considering the significant number of asymmetrical faults in distribution systems, the VSC response in such conditions must be investigated, and consequently, its FRT capability must be reinforced. In... 

    Design and Implementation of a Programmable VCO for DVB-H Application

    , M.Sc. Thesis Sharif University of Technology Alizadeh Arand, Saralah (Author) ; Medi, Ali (Supervisor)
    Abstract
    Recent growth in wireless communications leads to higher demand for smaller and cheaper wireless products. This increasing demand for high speed wireless products and therefore development of new modulation techniques, results in higher sensitivity to phase deviations. This means that the voltage controlled oscillator or VCO circuit must has lower phase noise. VCO is an important part in Phase Lock Loop or PLL that has been used in most of transceivers. This thesis focuses on design of a Programmable VCO for DVB-H Application in 0.18um TSMC process. A VCO is an oscillator designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation is varied by the...