فصلنامه روشهای هوشمند در صنعت برق
پیاپی 12 (زمستان 1391)

In this study، a system has been designed and simulated to track sunlight، which identifies sun location based on the exact relations of solar angles and without any optical sensor. In fact the relations which have been used in this study are far more accurate compared to similar cases، because of using the «equation of time» and reducing the tracking time of every 15 minutes. In this system، an economical micro-controller has been used to generate the necessary orders to control system and two stepper motors for powering solar array. By adding a real-time clock IC (RTC) to angle differentiation circuit، dynamic plane has improved.

In this paper، a new nonisolated bidirectional buck–boost dc–dc converter is introduced. The proposed converter can be operated under ZVS condition and fixed switching frequency regardless of the direction of power flow. To provide ZVS condition for switches a simple auxiliary circuit is used، that consists of an auxiliary inductor and a coupled winding to main inductor. Due to ZVS operation of switches، the reverse recovery problem of the body diode of the switches does not occur. Moreover، to provide soft switching any extra switch is not used in this converter، so its implementation and control is very simple. The experimental and simulation results of the proposed bidirectional converter are given to confirm the theoretical analysis.

The idea of using fractional order calculus in control became apparent when this kind of calculus was accepted as a powerful tool in many applications. This resulted in a new generation of PID controller called fractional order PID Controller، named as Controller. controller is more flexible and provides a better response with larger stability region as compared with standard PID controller. This paper presents a simple and reliable method for finding the family of controllers. The required calculations are done in frequency domain based on frequency response of the system and the stability region is specified in the parameters space. This method can be used for time-delay systems and، more generally، for any system with no transfer function.

In various applications، such as speech recognition and automatic teleconferencing، the recorded speech signals may be corrupted by both noise and reverberation. Reverberation causes a noticeable change in speech intelligibility and quality. In this research، firstly reverberation is described. There are some de-reverberation enhancement algorithms that use only one microphone. They mostly use inverse filtering and spectral subtraction as their sub-systems. On the other hand، there are many multi-microphone speech enhancement systems; Delay-and-sum beam former is the most famous amongst them. Moreover، several efficient approaches have been also reported that use linear prediction (LP) residual signal، inverse filtering، and phase error. Despite the improvements and benefits gained by the use of several input microphones، considering the tradeoff between these gains and the complexity and computational cost forced by the use of more microphones، many researchers have focused on dual-microphones systems. So، a review on Microphone array signal processing is explained and then an arrangement for two microphones systems is proposed. As we want to evaluate these algorithms for Farsi speech signals، the problem of speech intelligibility assessment has been explained and a Farsi word list for Diagnostic Rhyme Test (DRT) is presented. The structure of presented word list is similar to that of English DRT words. In this research، after a brief study of above-mentioned methods، we propose and implement some hybrid techniques to benefit from the advantages of several methods and achieve significant improvement in output signals. It will be shown that the proposed method performs superior to the state-of-the-art dereverberation algorithms.

One of the most important power quality aspects in wind farms is voltage fluctuation or flicker which should be investigated due to the nature of wind speed variations. These variations result in power and voltage fluctuations at the load bus. Moreover، the wind generation systems may be assumed as a harmonics source because of their power electronic converters. There are numerous factors that affect flicker and harmonic emission of grid-connected wind turbines during continuous operation، such as wind characteristics (e. g. mean wind speed، turbulence intensity)، type of generator and grid conditions (e. g. short circuit capacity، grid impedance angle). In this paper، an IEC based flickermeter is first modeled and then a variable speed wind turbine has been simulated by Matlab/Simulink software. The flicker and harmonics emissions of wind turbines equipped with DFIG during continuous operation and using output reactive control are investigated. The simulation results show that control of wind turbine output reactive power is an effective means for flicker mitigation during continuous operation. However، there should be a compromise between flicker reduction and harmonics level increase to enhance the whole power quality of wind turbine.

The congestion management system is a systematic approach، collaboratively developed and implemented throughout a metropolitan region that provides for the safe and effective management and operation of new and existing transportation facilities through the use of demand reduction and operational management strat­e­gies. In this paper we try to present some points which should be investigated in congestion management problems. We calculate different kinds of congestion problems which may be occurred in our network. Here، the hybrid model is used to solve problems in the electricity market to solve the congestion problem in the network and Benders techniques is used together with an optimal power flow (OPF). In fact، by using of Benders algorithm the problem is divided into two major and minor problems. Therefore، the major problem related to the economy sector and no network is included and the minor problem is to solve the network and examine the accuracy of the network. Benders algorithm has been tested on a standard network IEEE 24 bus and Matlab software is used to implement the algorithm.

This paper presents a control approach to the fuzzy-adaptive control scheme for rigid manipulators with unknown parameters. Lagrange’s method is employed for computing robot motion dynamics. Stability analysis guaranteed through Lyapunov’s theory using some suitable adaptive rules that make sure all signals in the closed-loop system are bounded and tracking error ones asymptotically reaches to zero. Compared with other controllers، there are some numerical simulations that verify effectiveness of the proposed method. Also، simulation results verify that the proposed controller can deal with uncertainties in the system.

One of the most effective strategies for steam generator efficiency enhancement is to improve the control system. For such an improvement، it is essential to have an accurate model for the steam generator of power plant. In this paper، an industrial steam generator is considered as a nonlinear multivariable system for identification. An important step in nonlinear system identification is the development of a nonlinear model. In recent years، artificial neural networks have been successfully used for identification of nonlinear systems in many researches. Wavelet neural networks (WNNs) also are used as a powerful tool for nonlinear system identification. In this paper we present a time delay neural network model and a WNN model in order to identify an industrial steam generator. Simulation results show the effectiveness of the proposed models in the system identification and demonstrate that the WNN model is more precise to estimate the plant outputs.