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    Narrowband Interference Cancellation in Wireless Ultra Wideband Communication Systems via Three-Level Spread Time Codes

    , Ph.D. Dissertation Sharif University of Technology Mashhadi, Saeed (Author) ; Salehi, Javad (Supervisor)
    Achieving various data rates over a wide range of applications and in a multiple-access scenario should be done under certain power and bandwidth constraints. Emerging UWB communications has opened a novel perspective against different wireless network challenges, especially overwhelming data rates. In the research field, we begin our thesis with exposition of UWB, narrowband interference and spread time codes. We elaborate on the properties of spread time codes through frequency domain analysis of a reusable multiple-access scheme. Evaluating the variance of ISI, MAI and RUI, we demonstrate the spread time codes behave in an optimum manner, i.e., the most RUI resistibility, along with all... 

    An Extremely low ripple high voltage power supply for pulsed current applications

    , Article IEEE Transactions on Power Electronics ; Volume 35, Issue 8 , 2020 , Pages 7991-8001 Zarghani, M ; Mohsenzade, S ; Hadizade, A ; Kaboli, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    This article describes the development of an 18 kV, 30 kW power supply for a pulsed current load with the maximum current of 20 A and a di/dt equal to 100 A/μs. The achieved output ripple is less than 0.01%. In such a high level of precision, the most important issues are considerable difference between the instantaneous and average output powers, as well as insufficient reaction speed of the converter to the fast load change. Very low level of the voltage feedback and its sensitivity to the noise. The first issue necessitates a notable overdesign of the converter switches if the output voltage precision is dedicated to the converter. The second issue raises the problems relevant to... 

    Applying portfolio theory-based modified ABC to electricity generation mix

    , Article International Journal of Electrical Power and Energy Systems ; Volume 80 , 2016 , Pages 356-362 ; 01420615 (ISSN) Adabi, F ; Mozafari, B ; Ranjbar, A. M ; Soleymani, S ; Sharif University of Technology
    Elsevier Ltd  2016
    Portfolio theory has found its model in numerous engineering applications for optimizing the electrical generation mix of an electricity area. However, to have better performance of this theory, this paper presents a new heuristic method as known modified artificial bee colony (MABC) to portfolio optimization problem. Moreover, we consider both dis-patchable and non-dis-patchable constrains variables and energy sources. Note that the proposed MABC method uses a Chaotic Local Search (CLS) to enhance the self searching ability of the original ABC algorithm. Resulting, in this paper a portfolio theory-based MABC model that explicitly distinguishes between electricity generation (energy),... 

    A new control method of three-phase PMSG wind turbine connected to single-phase network through a Back-to-Back converter

    , Article Asia-Pacific Power and Energy Engineering Conference, APPEEC ; 2011 ; 21574839 (ISSN) ; 9781424462551 (ISBN) Shamsnia, A ; Hojabri, H ; Mokhtari, H ; Chang, L ; Sharif University of Technology
    In this paper, a new control strategy is proposed to improve the performance of a wind generator system composed of a three-phase PMSG and a Back-to-Back three-phase to single-phase converter. With the use of the large inductance of the synchronous generator, the control method minimizes the generator torque ripple when the system supplies a single-phase load. The problem arises from the fact that the instantaneous power of a single-phase load is pulsating at the double of the system frequency. This paper tries to minimize the effect of this pulsating power on the PMSG torque without using a large capacitor on the DC link. Simulation results show the effectiveness of the proposed method. ©... 

    Efficient control scheme of wind turbines with doubly fed induction generators for low-voltage ride-through capability enhancement

    , Article IET Renewable Power Generation ; Volume 4, Issue 3 , May , 2010 , Pages 242-252 ; 17521416 (ISSN) Rahimi, M ; Parniani, M ; Sharif University of Technology
    As the penetration of wind power in electrical power systems increases, it is required that wind turbines remain connected to the grid and actively contribute to the system stability during and after grid faults. This study proposes an efficient control strategy to improve the low-voltage ride-through (LVRT) capability in doubly fed induction generators (DFIGs). The proposed scheme consists of passive and active LVRT compensators. The passive compensator is based on a new crowbar arrangement located in series with stator windings. It considerably reduces the rotor inrush current at the instants of occurring and clearing the fault. The active LVRT compensator is realised through rotor voltage... 

    Novel probabilistic bounds on power level profile of spectrally-encoded spread-time CDMA signals

    , Article IEEE Transactions on Wireless Communications ; Volume 8, Issue 5 , 2009 , Pages 2296-2301 ; 15361276 (ISSN) Mashhadi, S ; Salehi, J ; Sharif University of Technology
    In this letter we introduce an effective tool to demonstrate signal power behavior of a typical spectrallyencoded spread-time (SE/ST) CDMA system using probabilistic approach. By denning power level profile (PLP), as the probability of stretching instantaneous power from a pre-specified threshold, we can find novel upper bounds on the signal power profile. We discuss various properties owing to PLP and elaborate on the main parameters affecting the PLP value. We present three theorems, propose some simple upper bounds on the PLP, and give an insight on the main contributions of the results. We introduce a fundamental parameter, namely β, as a key design parameter which relates the most... 

    The design of a low-power high-speed current comparator in 0.35-μm CMOS technology

    , Article Proceedings of the 10th International Symposium on Quality Electronic Design, ISQED 2009, 16 March 2009 through 18 March 2009, San Jose, CA ; 2009 , Pages 107-111 ; 9781424429530 (ISBN) Ziabakhsh, S ; Alavi Rad, H ; Alavi Rad, M ; Mortazavi, M ; International Society for Quality Electronic Design, ISQED ; Sharif University of Technology
    A novel low power with high performance low current comparator is proposed in this paper which comprises of low input impedance using a simple biasing method. It aimed for low power consumption and high speed designs compared with other high speed designs. The simulation results from HSPICE demonstrate the propagation delay is about 0.7 ns and the average power consumption is 130 μW for 100 nA input current at supply voltage of 1.8 V using 0.35 micron CMOS technology. © 2009 IEEE  

    A new control strategy of shunt active filters for power quality improvement of highly and randomly varying loads

    , Article 2004 IEEE International Symposium on Industrial Electronics, IEEE-ISlE, 4 May 2004 through 7 May 2004 ; Volume 2 , 2004 , Pages 1297-1302 Esfandiari, A ; Parniani, M ; Mokhtari, H ; Sharif University of Technology
    This paper presents a newr control strategy for the shunt active filter in three-phase three-wire svstems with zero sequence voltages. An extended method based on instantaneous power theory in a rotating reference frame is developed for extracting the compensating signals for highlv/randomly varying loads. Since voltages at the point of common coupling contain low frequency interharmonics, conventional methods can not be used for dc voltage regulation. Therefore, a new method is introduced for this purpose. A three-phase electric arc furnace model is used to showT power quality improvement through reactive power and harmonic compensation by a shunt active fi'lter using the proposed method....