Sharif Digital Repository

This article investigates optimization of long-term operation of hydrothermal power systems consisting of cascaded reservoirs. Due to stochasticity of reservoir inflows, demand for energy, and unit forced outages, the uncertainty of this system is so significant that reliability of demand satisfaction becomes an indispensable component of the modelling process. On the other hand, existence of stochastic parameters, especially in the case of cascaded reservoirs, makes the problem very difficult to solve by applying existing optimization techniques. A hybrid genetic algorithm with dynamic tuning of its control parameters is developed that incorporates real number encoding and an analytical... 

This chapter describes performance of the power system stabilizer (PSS) of a large thermal power plant as tuned by the manufacturer. The stabilizer was redesigned based on extended phase compensation of the exciter input-the electrical torque transfer function and root locus analysis; and its effect on local, interplant, and interarea electromechanical oscillations was thoroughly analyzed. Participation factors and mode shapes were effectively employed to identify local, interplant, and interarea modes, as well as their characteristics. The PSS designed with extended phase compensation improves the damping of local and interplant oscillation modes considerably, and has some positive damping... 

A special hybrid genetic algorithm (GA) is designed to solve the long-term coordination of hydro-thermal power systems with cascaded reservoirs and stochastic inflows. Since decision variables are continuous, in the proposed GA we employ real number rather than binary encoding. To create superior children we introduce dynamic tuning of the weights of operators. An exponential normalization is also developed such that better chromosomes have more chance to reproduce. To test the proposed method, 16 GAs are investigated which differ based on real or binary encoding, dynamic tuning or fixed weights for operators, inverse or exponential normalization and mixed or pure random initial populations.... 

Memristor is the fourth fundamental passive circuit element which has potential applications in development of analog memristive memories, neuroscience, and brain simulation. In all of these applications the memristance of the device should be adjusted to the desired value, which is currently performed by trial and error. The aim of this paper is to propose a new method and develop a circuit for automatic adjustment of the memristance of memristive devices. The proposed method is based on the sliding mode control and numerical simulations show that it can be used for tuning the memristance of such devices with a high accuracy  

In this paper, important issues that could come up in practice of Active Disturbance Rejection Control (ADRC) due to a common assumption and some inevitable practical restrictions are investigated. The main idea behind ADRC is modeling effects of both internal uncertainties and external disturbances as an extra state called the total disturbance which is timely estimated. In the majority of recent works, it is assumed that time derivative of total disturbance is bounded. First we prove that, beside the system characteristics, the validity of this assumption strongly depends on the tuning parameters, even in the case of simple classes of linear second order systems. Thus, one should be... 

We introduce a novel probabilistic framework to achieve robust non-fragile tuning methods in control of processes with parametric uncertainties. We consider probability distributions to model the process parameters' uncertainties. First, we propose the tuning framework in a general setting. Then, as an illustration, we apply it to PD control of IPD-modeled processes. It is noteworthy that the proposed tuning method is robust against the considered parametric uncertainties. Also, to empower the proposed robust tuning method in the viewpoint of non-fragility, we utilize a centroid approach. Selecting the form of the probabilistic framework, we empirically observe some of the popular tuning... 

This paper presents an approach to improve the sliding mode controller performance. Accordingly, a fuzzy controller is designed based on a limited number of rules and independent of the sliding mode controller complexity. To enhance the performance, this controller will continuously optimize the sliding mode controller parameters including hitting control gain, boundary layer thickness, sliding surface slope and intercept. The controller is applied to a two-degree-of-freedom robot and the experimental results are compared with a QFT based and a PID controller. The results demonstrate the significant performance improvement of the proposed controller. © 2005 IEEE  

In this paper we offer a tuning method for the design of stabilizing PI controllers that utilizes the stability region centroid in the controller parameter space. To this end, analytical formulas are derived to describe the stability boundaries of a class of relative-degree-one linear time invariant second-order systems, the stability region of which has a closed convex shape. The so-called centroid stable point is then calculated analytically and the resultant set of algebraic formulas are utilized to tune the controller parameters. The freedom to choose the surface density function in the calculation of centroid stable point provides the designer with the possibility to incorporate optimal... 

In this paper, an algebraic tuning rule is presented for fractional PI controllers to control first order plus dead-time processes. By using the performance map (PM) method, this tuning rule is derived in order to set the gain margin of the control system close to 3 and the phase margin close to 60 degrees. The robustness and performance of this tuning rule are compared with some well-known PI tuning rules. Simulation results are brought to demonstrate the effectiveness and robustness of this tuning formula against process dynamic uncertainties in comparison with the other tuning methods  

In this paper we propose a new paradigm for a Differential Service (DiffServ) network consisting of two-color marking at the edges of the network using TSW2CM coupled with self tuning adaptive controller (STAC) in the core. This scheme exploits online estimates of the network parameters in the controller parameters adjustment. The performance demonstrates that the new scheme is able to admit traffic fairly and achieve edge-to-edge QoS under heavy traffic conditions and network state changes. We illustrate our results using ns-2 simulations and demonstrate the practical impact of self tuning control on managing queue utilization and delay. © 2006 ICASE  

Fractional order models have been widely used in modeling and identification of thermal systems. General model in this category is considered as the model of thermal systems in this paper, and a fractional order controller is proposed for controlling such systems. The proposed controller is a generalization for the traditional PI controllers. The parameters of this controller can be obtained by using a recently introduced tuning method which can simultaneously ensure the following three requirements: desired phase margin, desired gain crossover frequency, and flatness of the phase Bode plot at this frequency. In this paper, it is found whether simultaneously achieving the mentioned... 

A new approach for PID tuning, based on GA (Genetic algorithm) and Internal Model Control (IMC) technique, is presented in this paper. PID tuning is based on using Method. The IMC technique reduces the number of parameters that must be tuned for a multivariable system using PID controller. The algorithm uses GA for optimal determination of IMC variables. Simulation results present the good performance of the proposed method. © 2007 IEEE  

Various types of passive control systems have been used to suppress the seismic response of structures in recent years. Among these systems, Tuned Liquid Column Dampers (TLCDs) dissipate the input earthquake energy by combining the effects of the movement of the liquid mass in the container, the restoring force on the liquid due to the gravity loads and the damping due to the liquid movement through orifices. In this study, the effects of seismic excitation characteristics such as frequency content and soil condition on the seismic performance of TLCDs are investigated using nonlinear time-history analyses. In this regard, among the past earthquake ground motion records of Iran, 16 records... 

A new, ultra low-voltage, linear CMOS OTA will be described. A 4th order, 18 MHz low pass Butterworth Gm-C filter has been designed with this new OTA stage for video applications. In this filter a new, fully digital approach has been used for frequency tuning. The THD of the filter for input signal 0.5 VPPis better than -60 dB. All of circuits are designed based on 0.25 um CMOS process technology with a single 1-volt power supply  

A Prototype Thyristor Controlled Reactor (a kind of Static Var Compensator) has been designed and implemented to balance load and correct power factor in distribution systems. This article aims at presenting the steps of designing along with some new aspects which are employed. Double Tuned Filters has been developed and used to remove current harmonics due to TCR. Exact relations for load balancing and power factor correction were obtained, ft new method for measurement of the active and reactive component of current or active and reactive power is presented. Implementation results indicate the proper functioning of TCR in load balancing along with power factor correction. Both transient... 

The power control of horizontal axis wind turbines can affect significantly the vibration loads and fatigue life of the tower and the blades. In this paper, we both consider the power control and vibration load mitigation of the tower fore-aft vibration. For this purpose, at first, we developed a fully coupled model of the NREL 5MW turbine. This model considers the full aeroelastic behaviour of the blades and tower and is validated by experiment results, comparing the time history data with the FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code which is developed by NREL (National Renewable Energy Lab in the United States). In the next, novel sensorless control algorithms are... 

Employing dampers to control wave-induced and seismic vibrations of offshore jacket platforms is an attractive method in order to mitigate fatigue and seismic damage. However, adjustable parameters of a damper are designed by considering only one type of environmental loads; either normal-condition load or extreme-condition load. So, it is important to investigate effectiveness of damping system, for both of two main categories of environmental loads. Also it is ideal for the system to have an acceptable performance in both normal and extreme conditions. The idea investigated in the current study is to use a friction damper device (FDD) and a tuned mass damper (TMD) simultaneously in... 

This paper deals with introducing non-fragile algebraic tuning rules for fractional-order PD controllers where they are used in controlling processes modeled in Integral Plus Delay (IPD) forms. These tuning rules are obtained based on a recently introduced approach, named as the centroid approach, which results in non-fragile tuning methods. Based on this approach, the centroids of two-dimensional admissible regions or the center of gravity of three-dimensional admissible regions in controller parameter space give non-fragile options for choosing controller parameters. © 2013 IFAC