Sharif Digital Repository

This paper presents a robust decentralized proportional-integral (PI) control design as a solution of the load frequency control (LFC) in a multi-area power system. In the proposed methodology, the system robustness margin and transient performance are optimized simultaneously to achieve the optimum PI controller parameters. The Kharitonov's theorem is used to determine the robustness margin, i.e., the maximal uncertainty bounds under which the stable performance of the power system is guaranteed. The integral time square error (ITSE) is applied to quantify the transient performance of the LFC system. In order to tune the PI gains, the control objective function is optimized using the... 

In most of the existing studies, the frequency response in the variable speed wind turbines (VSWTs) is simply realized by changing the torque set-point via appropriate inputs such as frequency deviations signal. However, effective dynamics and systematic process design have not been comprehensively discussed yet. Accordingly, this paper proposes a proportional-derivative frequency controller and investigates its performance in a wind farm consisting of several VSWTs. A band-pass filter is deployed before the proposed controller to avoid responding to either steady state frequency deviations or high rate of change of frequency. To design the controller, the frequency model of the wind farm is... 

Due to the proliferation of wind turbines in power networks, participation of doubly-fed induction generator (DFIG)-based wind turbines in the frequency regulation task is attracting more attention during recent decades. It is a challenge to design an effective DFIG's auxiliary frequency controller, since back-to-back converters used in DFIG make the possibility of large deviations in current and speed of rotor during frequency support period. Hence, it is necessary to use exact expression of DFIG's output power in the frequency-related studies. This paper addresses this challenge by developing a nonlinear dynamic model for the DFIG's output power integrated into the dynamic model of power... 

This study investigates the dynamic participation of wind power plants (WPPs) in the automatic generation control (AGC) task. The pre-specified model of wind farm in the AGC studies has been used. It is shown that operating of WPPs at the command mode results in a significant improvement in the frequency behaviour of power system due to their faster response. However, the WPPs may change their operation mode from the command mode to the maximum power point mode according to the wind speed conditions and load variations. This reduces the improvement in the frequency response. In this condition, the shortage in the wind power should be compensated by the conventional units. Thus, the share of... 

In this paper, the participation of wind farms in load frequency control (LFC) is studied. A previously proposed macromodel for the wind farm is employed to regulate its output power. The wind farm including its proposed control strategy is incorporated into the conventional LFC model. The proposed LFC structure is able to dynamically maintain the system frequency at the nominal value against the power imbalances. To achieve proper transient response, the integral control parameter of the LFC controller is optimized using the genetic algorithm (GA). To verify the effectiveness of the proposed method, several simulation case studies are carried out. The results show that the wind farm can... 

With increasing the share of wind farms in generation profile, their contribution to frequency regulation has become crucial. This study presents an optimal robust first-order frequency controller in the wind farms, which collectively emulates the inertial response as well as governor droop of synchronous generators. To account for various uncertainties associated with system inertia, damping, and doubly-fed induction generator (DFIG)-based wind turbine's parameters, the robustness of controller is verified through the 16-plant theorem. An analytic method based on the small-signal model of the system is utilised to determine the stability region of the first-order controller. To evaluate the... 

Synthetic inertial frequency response has attracted increasing attention due to the paradigm shift in power generation from synchronous generators toward wind turbines. This paper presents a novel nonlinear controller to enable inertial response of a variable speed wind turbine (VSWT). The VSWT has a nonlinear model which cannot efficiently be dealt with by linear control techniques as it may experience large deviations from its operating point during the frequency support period. To design the controller, a nonlinear model for the wind turbine together with power system is utilized. The output power of the wind turbine is expressed in terms of the state variables, and its exact Taylor... 

This article proposes a bang-bang auxiliary frequency control scheme for doubly-fed induction generator (DFIG)-based wind turbines. It results in the DFIGs emulate the primary frequency control of conventional units and, thus, increases the power system frequency stability. Indeed, the suggested hysteresis controller causes to deliver the maximum extractable kinetic energy of DFIGs to the grid and consequently further enhance the power system frequency. This is accomplished using different frequency deviation indices, which determine the size of power mismatch and lead to an appropriate frequency response by the DFIGs. The operational constraints of the DFIGs are taken into account in the... 

Several methods have been developed in the past for analyzing the porosity and other types of well logs for large-scale porous media, such as oil reservoirs, as well as their permeability distributions. We developed a method for analyzing the porosity logs φ(h) (where h is the depth) and similar data that are often nonstationary stochastic series. In this method one first generates a new stationary series based on the original data, and then analyzes the resulting series. It is shown that the series based on the successive increments of the log y(h)=φ(h+δh)-φ(h) is a stationary and Markov process, characterized by a Markov length scale hM. The coefficients of the Kramers-Moyal expansion for... 

Yeh et al. have recently proposed a mutual authentication protocol based on EPC Class-1 Gen.-2 standard. They claim their protocol is secure against adversarial attacks and also provides forward secrecy. In this paper we show that the proposed protocol does not have cited security features properly. A powerful and practical attack is presented on this protocol whereby the whole security of the protocol is broken. Furthermore, Yeh et al.'s protocol does not assure the untraceabilitiy and backwarduntraceabilitiy attributes. We also will propose our revision to safeguard the Yeh et al.'s protocol against cited attacks  

In this paper, we show how time-sharing method may reduce transmission delay in the dynamic index coding scenario. We propose a novel time-shared dynamic index coding transmission scheme that achieves the maximum index coding gain for a complete bi-directional side information graph and formulate a constrained optimization problem to tune the transmission scheme for the minimum transmission delay. A closed-form solution is presented for the special case of two-user. We also use analytical and simulation results to provide graphical intuition for the obtained results  

Dynamic index coding is a practical generalization of conventional index coding that deals with real dynamic traffic streams. We identify the code-constrained capacity region of a dynamic index coding problem with a complete bi-directional side information graph and introduce the performance metric of dynamic index coding gain to measure how dynamic index coding reduces the required data transmissions. A greedy dynamic index coding scheme is proposed that achieves the maximum coding gain almost everywhere in the identified capacity region. Although the greedy scheme attains the maximum coding gain, its selfish nature may unacceptably increase transmission delay. To address this issue, a... 

This paper suggests methods for improving efficiency of a high step up high efficiency converter based on three state commutation cells. A loss analysis has been performed to identify the source of power loss. Based on this analysis, methods are presented to reduce losses in the most power dissipating elements. These methods include replacing some power diodes with large conduction losses with MOSFETs having small on-state resistance. Efficiency improvement up to %1.25 percent is verified in simulation and experimental results  

Locally multipath adaptive routing (LMAR) protocol, classified as a new reactive distance vector routing protocol for MANETs is proposed in this paper. LMAR can find an ad-hoc path without selfish nodes and wormholes using a random search algorithm in polynomial-time. Also when the primary path fails, it discovers an alternative safe path if network graph remains connected after eliminating selfish/malicious nodes. The main feature of LMAR to seek safe route free of selfish and malicious nodes in polynomial time is its searching algorithm and flooding stage that its generated traffic is equiloaded compared to single-path routing protocols but its ability to bypass the attacks is much better... 

von Willebrand factor (VWF) is a naturally collapsed protein that participates in primary haemostasis and coagulation events. The clotting process is triggered by the adsorption and conformational changes of the plasma VWFs localized to the collagen fibres found near the site of injury. We develop coarse-grained models to simulate the adsorption dynamics of VWF flowing near the adhesive collagen fibres at different shear rates and investigate the effect of factors such as interaction and cooperativity of VWFs on the success of adsorption events. The adsorption probability of a flowing VWF confined to the receptor field is enhanced when it encounters an adhered VWF in proximity to the... 

A general regression neural network technique was applied to design optimization of a liquid-liquid coaxial swirl injector. Phase Doppler Anemometry measurements were used to train the neural network. A general regression neural network was employed to predict droplet velocity and Sauter mean diameter at any axial or radial position for the operating range of a liquid-liquid coaxial swirl injector. The results predicted by neural network agreed satisfactorily with the experimental data. A general performance map of the liquid-liquid coaxial swirl (LLCS) injector was generated by converting the predicted result to actual fuel/oxidizer ratios. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA  

Development of Smart Grid and deployment of smart meters in large scale has raised a lot of concerns regarding customers’ privacy. Consequently, several schemes have been proposed to overcome the above mentioned issue. These schemes mainly rely on data aggregation as a method of protecting users’ privacy from the grid operators. However, the main problem with most of these schemes is the fact that they require a large amount of processing power at the meter side. This, together with the fact that smart meters don't usually have a powerful processor, can cause the unavailability of smart meter data at the required time for operators of the grid, and at the same time prevents smart meters from...