Iranian Journal of Electrical and Electronic Engineering

---

The concepts of robust classification and intelligently controlling the search process of genetic algorithm (GA) are introduced and integrated with a conventional genetic classifier for development of a new version of it, which is called Intelligent and Robust GA-classifier (IRGA-classifier). It can efficiently approximate the decision hyperplanes in the feature space. It is shown experimentally that the proposed IRGA-classifier has removed two important weak points of the conventional GA-classifiers. These problems are the large number of training points and the large number of iterations to achieve a comparable performance with the Bayes classifier, which is an optimal conventional classifier. Three examples have been chosen to compare the performance of designed IRGA-classifier to conventional GA-classifier and Bayes classifier. They are the Iris data classification, the Wine data classification, and radar targets classification from backscattered signals. The results show clearly a considerable improvement for the performance of IRGA-classifier compared with a conventional GA-classifier.

---

In this paper, two vector control systems for investigating the performance of Static Synchronous Series Compensators (SSSC) in steady state conditions are presented that are based on famous d-q axis theory. The workability of proposed method to simplify the SSSC mathematical expressions is shown. The performance of SSSC with two different vector controllers, first based on d-q line currents(indirect control) and the second a heuristic vector control based on real and reactive line powers (direct control), are investigated through simulation. It is found that the new introduced direct control produces better performance in controlling AC power system. Finally the simulation results of an elementary two-machine system with SSSC in different cases are investigated.

---

In this paper, a new field oriented control scheme with maximum torque for permanent magnet hysteresis synchronous (PMHS) motor has been presented. Vector control method provides significant improvement to the dynamic performance of ac motors but in this method d- axis current is controlled such as the ratio of motor torque to motor current is a maximum, then the dynamic performance will be very fast. Furthermore, d and q axis currents are limited such as stator winding currents remain in the allowed range. Feedback method is used for the decoupling the torque-current component from the fluxcurrent component so these two components can be independently controlled. Simulation results for the motor are given and test results validate the theoretical performances.

---

Hunting is a flutter associated with the synchronous speed that gives rise to the gyro drifting errors and may cause objectionable time-displacement errors in video head wheel drives and other precision scanning systems. In this paper, dynamic characteristics of permanent Magnet hysteresis motors are presented and hunting is explained. New damping techniques have been developed using optimized eigenvalues calculation. They are calculated from LQR optimization method. In this damping method, a distinct reduction in hunting has been archived. Furthermore field oriented control result of motor is presented that have good effect on Hunting. Nearest agreement between simulated and measurement results shows the accuracy of motor model. Comparison between this paper results and other measured damping methods result are shown its success.

---

The operation of Fuel Cell Distributed Generation (FCDG) systems in distribution systems is introduced by modeling, controller design, and simulation study of a Solid Oxide Fuel Cell (SOFC) distributed generation (DG) system. The physical model of the fuel cell stack and dynamic models of power conditioning units are described. Then, suitable control architecture based on fuzzy logic control for the overall system is presented in order to active power control and power quality improvement. A MATLAB/Simulink simulation model is developed for the SOFC DG system by combining the individual component models and the controllers designed for the power conditioning units. Simulation results are given to show the overall system performance including active power control and voltage regulation capability of the distribution system.

---

This paper describes a DC isolated network which is fed with Distributed Generation (DG) from photovoltaic (PV) renewable sources for supplying unbalanced AC loads. The battery energy storage bank has been connected to the DC network via DC/DC converter to control the voltage of the network and optimize the operation of the PV generation units. The PV arrays are connected to the DC network via its own DC/DC converter to ensure the required power flow. The unbalanced AC loads are connected to the DC network via its own DC/AC converter. This paper proposes a novel control strategy for storage converter which has a DC voltage droop regulator. Also a novel control system based on Park rotating frame has been proposed for DC/AC converters. In this paper, the proposed operation method is demonstrated by simulation of power transfer between PV arrays, unbalanced AC loads and battery unit. The simulation results based on PSCAD/EMTDC software show that DC isolated distribution system including PV generation systems can provide the high power quality to supplying unbalanced AC loads.

---

New equations are proposed for frequency and amplitude of a ring oscillator. The method is general enough to be used for all types of delay stages. Using exact largesignal circuit analysis, closed form equations for estimating the frequency and amplitude of a high frequency ring oscillator are derived as an example. The method takes into account the effect of various parasitic capacitors to have better accuracy. Based on the loop gain of the ring, the transistors may only be in saturation or experience cutoff and triode regions. The analysis considers all of the above mentioned scenarios respectively and gives distinct equations. The validity of the resulted equations is verified through simulations using TSMC 0.18 µm CMOS process. Simulation results show the better accuracy of the proposed method compared with others.

---

The main theme of this paper is to present novel controller, which is a genetic based fuzzy Logic controller, for interior permanent magnet synchronous motor drives with direct torque control. A radial basis function network has been used for online tuning of the genetic based fuzzy logic controller. Initially different operating conditions are obtained based on motor dynamics incorporating uncertainties. At each operating condition, a genetic algorithm is used to optimize fuzzy logic parameters in closed-loop direct torque control scheme. In other words, the genetic algorithm finds optimum input and output scaling factors and optimum number of membership functions. This optimization procedure is utilized to obtain the minimum speed deviation, minimum settling time, zero steady-state error. The control scheme has been verified by simulation tests with a prototype interior permanent magnet synchronous motor.

---

The use of directional antennas in wireless ad hoc networks can significantly improve global performance due to a high spatial channel reuse. Nevertheless, its introduction poses new location dependent problems related to the MAC protocol. In this paper, the Balanced Incomplete Block Design theory has been exploited to develop a new MAC protocol for wireless ad hoc networks using directional antennas. It is a time slotted protocol, which is highly scalable. Moreover, it can provide a high number of concurrent communications, depending on the number of directional antennas mounted on each node, great fairness in bandwidth sharing and significant energy saving. In particular, energy saving provided by our scheme is consistently higher compared to those of usual directional MAC protocols for the following reasons. Firstly, control packets are sent only over fairly selected beams rather than over all the available ones. Secondly, our protocol provides a filtering, i.e. a fair selection, of the nodes that can try the access to the medium in each time slot. Simulation results validate the advantages of our protocol by proving high spatial reuse, great fairness and significant energy saving and by showing that it improves the overall system performance.

---

An adaptive online flux-linkage estimation method for the sensorless control of switched reluctance motor (SRM) drive is presented in this paper. Sensorless operation is achieved through a binary observer based algorithm. In order to avoid using the look up tables of motor characteristics, which makes the system, depends on motor parameters, an adaptive identification algorithm is used to estimate of the nonlinear flux-linkage parameters. This method makes position and speed estimation more accurate and robust towards any model uncertainty, also it is suitable replacement for a priori knowledge of motor characteristics.

---

A switched Reluctance motor (SRM) has several desirable features, including simple construction, high reliability and low cost. However, it suffers from large torque ripple, highly non-uniform torque output and magnetization characteristics and large noise. Several studies have succeeded in torque ripple reduction for SRM using Direct Torque Control (DTC) technique. DTC method has many advantages over conventional voltage control and current chopping mode control such as simple algorithm, less torque ripple and instantaneous response to the torque command. In this paper, DTC method is proposed for a 5-phase 10/8 SRM. The performance of the motor is demonstrated through the computer simulation in Mtalab/Simulink. Then, the obtained results are verified by comparison with the corresponding results of a 3-phase 6/4 motor performance.

---

Robust performance controller design for duty-cycle controlled series resonant converter (SRC) is proposed in this paper. The uncertainties of the converter are analyzed with load variation and power circuit components tolerances are taken into consideration. Additionally, a nominal performance (NP) controller is designed. Closed-loop system is simulated with Orcad and simulation results of robust controller are compared with nominal performance controller. Although nominal performance controller has better performance for nominal plant, the robust performance controller is advantageous in dealing with uncertainties.

---

New control circuits and algorithms are frequently proposed to control the impedance (Z) source inverter in efficient way with added benefits. As a result, several modified control techniques have been proposed in recent years. Although these techniques are clearly superior to the simple boost control method which was initially proposed along with the Z-source inverter (ZSI), little or conflicting data is available about their merits relating to each other. In this paper, it is shown how the shoot-through periods are inserted in the switching waveforms of the power switches and the performances of them are analyzed based on the operation of ZSI. Simple boost control, maximum boost control, constant boost control and space vector modulation based control methods given in the literature has been illustrated with their control characteristics. A critical investigation on ripples of the impedance source elements, output voltage controllability, output harmonic profile, transient response of the voltage across the impedance source capacitor and voltage stress ratio etc has been presented with the simulation results. The simulation results are experimentally verified in the laboratory with digital signal processors (DSP). DSP coding for the above all control techniques has been generated by interfacing Matlab/Simulink with DSP C6000 tool box and signal processing block set.

---

Here, a new fuzzy direct torque control algorithm for induction motors is proposed. As in the classical direct torque control, the inverter gate control signals directly come from the optimum switching voltage vector look-up table, the best voltage space vector selection is a key factor to obtain minimum torque and flux ripples. In the proposed approach, the best voltage space vector is selected using a new fuzzy method. A simulation model is built up and the torque and flux ripples of basic direct torque control and the proposed method are compared. The simulation results show that the torque and flux ripples are significantly decreased and in addition, the switching frequency can be fixed.

---

In this paper, we propose smart step closed-loop power control (SSPC) algorithm and base station assignment based on minimizing the transmitter power (BSAMTP) technique in a direct sequence-code division multiple access (DS-CDMA) receiver in the presence of frequency-selective Rayleigh fading. This receiver consists of three stages. In the first stage, with conjugate gradient (CG) adaptive beamforming algorithm, the desired users’ signal in an arbitrary path is passed and the inter-path interference is canceled in other paths in each RAKE finger. Also in this stage, the multiple access interference (MAI) from other users is reduced. Thus, the matched filter (MF) can be used for the MAI reduction in each RAKE finger in the second stage. Also in the third stage, the output signals from the matched filters are combined according to the conventional maximal ratio combining (MRC) principle and then are fed into the decision circuit of the desired user. The simulation results indicate that the SSPC algorithm and the BSA-MTP technique can significantly improve the network bit error rate (BER) in comparison with other algorithms. Also, we observe that significant savings in total transmit power (TTP) are possible with our proposed methods.

---

The role of waveform design is central to effective radar resource management for state-of-the art radar systems. The waveform shape employed by any radar system has always been a key factor in determining the performance and application. The design of radar waveform to minimize mean square error (MSE) in estimating the target impulse response is based on power allocation using waterfilling. This paper shows the effect of various power control strategies in the MMSE performance of the waveform design. We find that the truncated power control strategy exhibits a good MMSE performance. The performance improvement results from the fact that with the truncated power control no power is wasted in poor quality modes.

---

Bayesian Networks (BN) provides a robust probabilistic method of reasoning under uncertainty. They have been successfully applied in a variety of real-world tasks but they have received little attention in the area of load-frequency control (LFC). In practice, LFC systems use proportional-integral controllers. However since these controllers are designed using a linear model, the nonlinearities of the system are not accounted for and they are incapable to gain good dynamical performance for a wide range of operating conditions in a multi-area power system. A strategy for solving this problem due to the distributed nature of a multi-area power system, is presented by using a BN multi-agent system. This method admits considerable flexibility in defining the control objective. Also BN provides a flexible means of representing and reasoning with probabilistic information. Efficient probabilistic inference algorithms in BN permit answering various probabilistic queries about the system. Moreover using multi-agent structure in the proposed model, realized parallel computation and leading to a high degree of scalability. To demonstrate the capability of the proposed control structure, we construct a BN on the basis of optimized data using genetic algorithm (GA) for LFC of a three-area power system with two scenarios.

---

this work studies the effect of neutral earth resistance on the controlling ferroresonance oscillation in the power transformer including MOV surge arrester. A simple case of ferroresonance circuit in a three phase transformer is used to show this phenomenon and the three-phase transformer core structures including nonlinear core losses are discussed. The effect of MOV surge arrester and neutral earth resistance on the onset of chaotic ferroresonance and controlling chaotic transient in a power transformer including nonlinear core losses has been studied. It is expected that these resistances generally cause into ferroresonance control. Simulation has been done on a power transformer rated 50 MVA, 635.1 kV with one open phase. The magnetization characteristic of the transformer is modelled by a single-value two-term polynomial with q=7, 11. The core losses are modelled by third order in terms of voltage. The simulation results reveal that connecting the MOV arrester and neutral resistance to the transformer, exhibits a great impact on ferroresonance over voltages. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved.

---

When the process is highly uncertain, even linear minimum phase systems must sacrifice desirable feedback control benefits to avoid an excessive ‘cost of feedback’, while preserving the robust stability. In this paper, the problem of supervisory based switching Quantitative Feedback Theory (QFT) control is proposed for the control of highly uncertain plants. According to this strategy, the uncertainty region is suitably divided into smaller regions. It is assumed that a QFT controller-prefilter exits for robust stability and performance of the individual uncertain sets. The proposed control architecture is made up by these local controllers, which commute among themselves in accordance with the decision of a high level decision maker called the supervisor. The supervisor makes the decision by comparing the candidate local model behavior with the one of the plant and selects the controller corresponding to the best fitted model. A hysteresis switching logic is used to slow down switching for stability reasons. Besides, each controller is designed to be stable in the whole uncertainty domain, and as accurate in command tracking as desired in its uncertainty subset to preserve the robust stability from any failure in the switching.

---

Torque ripple minimization of switched reluctance motor drives is a major subject based on these drives’ extensive use in the industry. In this paper, by using a well-known cascaded torque control structure and taking the machine physical structure characteristics into account, the proposed energy-based (passivity-based) adaptive sliding algorithm derived from the view point of energy dissipation, control stability and algorithm robustness. First, a nonlinear dynamic model is developed and decomposed into separate slow and fast passive subsystems which are interconnected by negative feedbacks. Then, an outer loop speed control is employed by adaptive sliding controller to determine the appropriate torque command. Finally, to reduce torque ripple in switched reluctance motor a high-performance passivity-based current controller is proposed. It can overcome the inherent nonlinear characteristics of the system and make the whole system robust to uncertainties and bounded disturbances. The performance of the proposed controller algorithm has been demonstrated in simulation, and experimental using a 4KW, four-phase, 8/6 pole SRM DSP-based drive system.