Sharif Digital Repository

Electric networks often consist of remote cities or villages with low population densities, which consume a considerably small amount of energy. This can be in the order of a few megawatts for places that are up to 100 km away from the source. Typical uncompensated primary distribution lines are not an effective option for these situations, since line loadability drastically decreases as the line length is increased. Increasing the voltage level, on the other hand, is not cost effective. This paper investigates different reactive compensation techniques for increasing the loadability of these lines. Effect of series capacitors, shunt capacitors and voltage regulating transformers in such... 

This paper presents a new approach for controlling SMA actuators with hysteresis compensation by using two energy based semi active controllers. SMA actuators exhibit severe hysteresis that is often responsible for position inaccuracy in a regulation or tracking system. In this paper, a SMA actuator model is recalled from [Alasty A, Shameli E. Dynamic modeling of a new varying stress SMA actuator for precise applications. In: Proceedings of 2004 IEEE international conference on mechatronics (ICM'04). Istanbul, Turkey, June 3-5, 2004]. Then, a PID and a novel PID-P3 controllers have been suggested to perform a position control. To investigate the stability of controlled system the... 

In this paper, we focus on adaptive and wavelet based systems in radar signal processing, and a new algorithm to Doppler compensation is developed. The new wavelet-based method for ambiguity surface smoothing that applies the three dimensions dual tree wavelet transform and adapt constant false alarm rate, is proposed. The model captures the dependence between a wavelet coefficient and its parent. Simulation results show that new approach is better than older algorithms. We have simulated this new method for bistatic FM-based passive coherent receiver  

Motion estimation and compensation is an essential part of existing video coding systems. Compared to the widely used block-matching algorithms (BMA), the mesh-based motion estimation (MME) produces better subjective and objective qualified image sequences in many cases, especially at low bitrates. However, the iterative refinement step of the MME is computationally too expensive. In this paper, we propose a fast MME scheme, which adjusts its interpolation patterns to the motion features of image sequences to achieve higher quality reconstructed results. Experimental results show notable rate-distortion improvement over both the BMA and the conventional non-iterative MME schemes, especially... 

Stator resistance PI compensator is one of the simplest methods proposed to estimate stator resistance. This method is based on the real time stator resistance correction regarding the variations of the stator current magnitude, which must be a constant value when the stator flux and motor torque are constant. This reference value can be calculated using the flux and torque commands and motor parameters. In this paper, it is shown that for DTC systems using digital controller with limited sampling frequency, stator current vector amplitude varies as a function of speed, sampling period, and switching strategy. Effects of sampling frequency, motor speed, and switching strategy on this current... 

Advanced static VAR compensators (ASVCs) are used to improve the transient stability of electric power systems. In this paper we present a new control strategy, which has superior performances compared to the conventional control techniques for these systems. The proposed method utilizes a novel current reference based on the transient energy function (TEF) approach. It also includes the voltage limits in the optimizing process using the Lyapunov theory and linear programming. In addition, it is optimized considering the permissible system conditions. A continuous control of the reactive power flow is also achieved. The proposed ASVC is modeled in single-machine and multimachine systems. In... 

Input nonlinearities of many physical systems due to their actuator constraints are important points which have to be considered by designers. One of the recent method for dealing with this problem is to use compensation after controller. In this paper, a new approach based on fuzzy sets theory, as a solution, has been proposed. The main objective of the proposed method is to provide a feasible controller output if it is not in the legal ranges to keep the system output performance as high as possible. © 2002 IEEE  

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... 

In this paper, a compact algorithm for balancing the load and correction of power factor in three-phase three-wire system is presented. Susceptances of SVC in each phase are computed as a function of real and imaginary parts of line current. This calculation is based on unity power factor and elimination of negative sequence of currents. A laboratory prototype of Thyristor Switched Capacitor (TSC) at 380V and 45KVAR is designed and implemented. Also, a new approach for measuring active and reactive power, power factor and voltage is presented. This measuring technique is based on integration of current signal over a specific part of voltage signal period. Finally, a brief description of... 

In this paper we propose a new fault location algorithm for power transmission lines based on one terminal voltage and current data. A distributed time domain model of the line is used as a basis for algorithm development. The suggested technique only takes advantage of post-fault voltage and current samples taken at one end of the line and does not require filtering of DC offset and high-frequency components of the recorded signals, which are present during transient conditions. Another advantage of the proposed method is the application of a very narrow window of data i. e. less than 1/4 of a cycle. The paper also proposes two different algorithms for lossless and lossy line models.... 

In this paper, an accurate fault location algorithm for series compensated power transmission lines is presented. A distributed time domain model is used for modeling of the transmission lines. The algorithm makes use of two subroutines for estimation of the fault distance-one for faults behind the series capacitors and another one for faults in front of the series capacitors. Then a special procedure to select the correct solution is utilized. Samples of voltages and currents at both ends of the line are taken synchronously and used to calculate the location of the fault. The proposed algorithm is independent of fault resistance and does not require any knowledge of source impedance. The... 

One of the most critical issues in manufacturing systems is the operator management. In this paper, the operator assignment problem is studied within a cellular manufacturing system. The most important novelty of this research is the consideration of operator learning and forgetting effects simultaneously. The skill level of an operator can be increased/decreased based on the time spent on a machine. Moreover, the issues related to operators like hiring, firing, and salaries are considered in the proposed model. The parameters are considered to be uncertain in this model, and a robust optimization approach is developed to handle it. Using this approach, the model solution remains feasible... 

In this paper, several new control strategies for employing the battery energy storage systems (BESSs) and demand response (DR) in the load frequency control (LFC) task are proposed. In this way, first, the unit commitment problem considering the BESSs’ constraints in presence of wind farms and responsive loads is solved and the best location and the optimal size of the BESSs as well as the regulation power of the responsive loads are obtained. A rule-based plan is then suggested to improve the frequency regulation considering participation of wind farms. This plan is takes into account different states associated with power system frequency response as well as BESSs’ state of charge (SOC)....