Sharif Digital Repository

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  

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... 

This paper deals with the problem of simultaneous compensation of the gain, phase, and phase-slope at an arbitrary frequency by using a fractional-order lead/lag compensator. The necessary and sufficient conditions for feasibility of the problem are derived. Also, the number of existing solutions (i.e., the number of distinct fractional-order lead/lag compensators satisfying the considered compensation requirements) is analytically found. Moreover, as a sample application, it is shown that the obtained results for the considered compensation problem are helpful in tuning fractional-order lead/lag compensators for simultaneously achieving desired phase margin, desired gain cross frequency,... 

Nowadays, design and tuning of controllers with predefined structures are among the most popular topics in control system theory. During the last decade, many studies have focused on designing fixed-structure fractional-order compensators. This paper presents a generalized version of fractional-order compensators to achieve the required magnitudes and phases at two given frequencies (for example, to achieve desired phase and gain margins with adjustable cross frequencies). In this generalization, at first some basic analysis of the phase behaviour of this introduced type of fractional-order compensators is presented. Also, exact formulas are found for designing this family of compensators in... 

The sampling process in electrical devices includes non-linear distortion which needs to be compensated to boost up the system efficiency. In this paper, a blind method is suggested for non-linear distortion compensation. The core idea is to leverage the sparsity of the signal to cope with the ill-posedness of the distortion compensation task. The proposed scheme is an iterative method based on out of support energy minmization where the support information is not available. An adaptive thresholding operator is used to give a rough approximation of the support according to the estimated signal at each iteration. Various simulation scenarios have validated the capability of the suggested... 

The sampling process in electrical devices includes nonlinear distortion that needs to be compensated to boost up the system efficiency. In this brief, a blind method is suggested for nonlinear distortion compensation. The core idea is to leverage the sparsity of the signal to cope with the ill-posedness of the distortion compensation task. The proposed scheme is an iterative method based on out of support energy minimization, in which the support information is not available. An adaptive thresholding operator is used to give a rough approximation of the support according to the estimated signal at each iteration. Various simulation scenarios have validated the capability of the suggested... 

The common and traditional method for optical dispersion compensation is concatenating the transmitting optical fiber by a compensating optical fiber having a high-negative dispersion coefficient. In this Letter, we take the opposite direction and show how an optical fiber with a high-positive dispersion coefficient is used for dispersion compensation. Our optical dispersion compensating structure is the optical implementation of an iterative algorithm in signal processing. The proposed dispersion compensating system is constructed by cascading a number of compensating sub-systems, and its compensation capability is improved by increasing the number of embedded sub-systems. We also show that... 

This paper deals with robust frequency compensation in control of fractional-order plants with an uncertain fractional pole/zero (or specially in control of integer-order plants with an uncertain pole/zero). The specifications yielding a robust compensation are introduced, and fractional-order compensators are proposed for satisfying these specifications in the set-point tracking control of the above-mentioned plants. Also, the infinite ranges for the uncertain parameter of the plant, in which satisfying robust compensation specifications is possible by the obtained compensators, are exactly specified. Furthermore, the stability of the obtained control system is analytically analyzed.... 

Depending on the reference frame, a proportional integral (PI) or proportional resonant (PR) controller is often utilized for current control in the three-phase PWM rectifiers. Due to the fact that the controller bandwidth is either smaller than the frequency of a specific order harmonic or the controller gain at that frequency is too low the harmonics cannot be effectively eliminated. Among all approaches introduced for harmonic elimination, selective harmonic compensation is believed to have a better performance. Selective harmonic compensation can successfully compensate for harmonics. It, however, forces a considerable computation burden on DSP. This paper proposes a new compensation... 

The ability of static VAr compensators (SVC) to reduce the flicker caused by electric arc furnaces and other variable VAr loads depends on their speed, which is limited by delays in reactive power measurement and thyristor ignition. In this paper, a predictive method is proposed to compensate the delay time and, hence, to improve the SVC performance. Previous samples of the load reactive power are used to predict its future values. Predicted VAr is then applied as a reference for reactive power compensation. © 2006 IEEE  

An assessment study of two different shunt FACTS devices for compensating disturbances due to voltage variation in power systems is presented in this paper. Namely, Static Compensator (STATCOM) and Static Var Compensator (SVC) are Considered in this study. Eigen Value analysis and nonlinear time domain simulations for starting motor, motor in load varying state and short circuit on motor terminals show that STATCOM DC Voltage regulation has a better performance Compared to that of SVC. The result that will be presented in the paper will prove the superiorly of STATCOM over SVC in increasing motor speeding up and improving system voltage profile particularly at starting. © 2005 IEEE  

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 study deals with a generalised version of lead/lag compensators known as fractional-order lead/lag compensators. Exact and simple formulas are found for designing this introduced type of fractional-order compensators in order to provide the required magnitude and phase at a given frequency. Also, the region in the phase-magnitude plane, which is accessible by these compensators, is analytically found. Moreover, numerical examples and experimental results are presented to show the applicability of the achievements of this study in control system design  

This paper presents a novel flexible control strategy for Unified Power Quality Conditioner (UPQC), which achieves more flexibility in compensation of power quality disturbances as compared to the existing methods. The proposed control strategy provides priority-based compensation as well as full and standard-based compensation considering the rating of series and shunt parts of a UPQC. The priority-based compensation is done based on the compensation priority among different power quality disturbances. In this control strategy, an on-line estimation of different voltage and current disturbances is required. For this purpose, a Unified Adaptive Power Quality Estimator (UAPQE) has been... 

In this study, kernel least mean square (KLMS) algorithm with fractionally spaced equalizing structure is proposed for electrical compensation of chromatic dispersion (CD) and nonlinear phase noise (NLPN) in a dual polarization optical communications system with coherent detection. We consider single mode fiber channel. At the receiver, the additive optical noise is represented as additive white Gaussian noise. Phase modification is utilized at high signal powers to maintain the validity of Gaussian model of noise. We consider QAM and PSK modulations and evaluate the performance of the proposed method in terms of error rate, phase error, and error vector magnitude (EVM). The results are... 

Static pre-compensators are used in industrial applications to reduce interactions of a multivariable system to facilitate implementation of decentralised single-loop control systems. Whilst a wide range of techniques exist for the design of static pre-compensators, not all types of system interactions will yield to a static design. Outlined is a simple test which constitutes a necessary condition for a solution to exist  

This paper introduces the modeling of Static Series Voltage Regulator (SSVR) in the load flow calculations for steady-state voltage compensation and loss reduction. For this approach, an accurate model for SSVR is derived to use in load flow calculations. The rating of this device as well as direction of required reactive power injection to compensate voltage to the desired value (1p.u.) is derived, discussed analytically, and mathematically using phasor diagram method. Since performance of SSVR varies when it reaches to its maximum capacity, modeling of SSVR in its maximum rating of reactive power injection is derived. The validity of the proposed model is examined using two standard...