Amirkabir International Journal of Electrical & Electronics Engineering
Volume:45 Issue: 2, Summer - Autumn 2013

This paper introduces a new method for accelerating current sluggish FEM and improving memory demand in FEM problems with high node resolution or bulky structures. Like most of the numerical methods, FEM results to a matrix equation which normally has huge dimension. Breaking the main matrix equation into several smaller size matrices, the solving procedure can be accelerated. For implementing this matter, the meshing process should be changed. Here, a multi-step meshing process is proposed which consists of both posterior and main levels. The posterior level is used for separating matrix equations from each other and the main level for field computation in the problem. The proposed approach is compatible with other optimizing method for increasing speed in FEM. Therefore, combining this method with other methods creates a powerful asset for solving complex FEM problems. The results show that the proposed method speeds up FEM and decreases the memory capacity. In addition, it brings the facility of parallel computation which is of great importance in fast computational algorithm

Decentralized control strategies are popular candidates in microgrids control because of their reliability and performance. Conventionally, droop control (as a main decentralized strategy) is been utilized in order to prevent permanent droop of voltage and frequency after change in loads and also to share generated power between distributed generation units. In this paper, a new droop control strategy was introduced to control the voltage and frequency of autonomous microgrids. Following a review of the basic droop equations, it was concluded that the new form of droop equations enhanced the voltage and frequency control performance better than conventional droop equations. The voltage control behavior in the proposed method was within the acceptable range, and the frequency also returned to the nominal value after a change in loads. The simplicity and accurateness of the proposed method is a unique characteristic compared with the other recent control methods. Simulation studies showed the effectiveness of the proposed control strategy in different scenarios.

This paper proposes a new smart antenna beamforming scheme based on electronically steerable parasitic array radiator (ESPAR). The proposed method is capable of providing better capacity compared to the conventional ESPAR. The termination of each antenna element in this structure comprises a PIN diode in addition to a varactor. Using PIN diode besides the varactor provides more degrees of freedom which lead to better interference suppression. Moreover, in the proposed method the required tunable impedance range of the varactors is dramatically reduced. The optimal values of the tunable loads in each simulation scenario repetition are attained iteratively using steepest descent method with a maximum cross correlation coefficient criterion. Simulation results show that the proposed scheme outperforms the conventional ESPAR technique with respect to interference suppression and capacity enhancement. To further validate the beamforming ability of the proposed method, a testbed was fabricated. Measurement results confirm that the proposed method can provide an acceptable beamforming capability close to the simulated beam.

In this paper satellite wave propagation at Ku and Ka band is considered. The design and simulation of a typical satellite beacon receiver at Ka band is designed and simulated for the future works. Also rain attenuation prediction at Ku band using satellite signal beacon measurement and simulations for Iran Telecommunication Research Center (ITRC) are presented. The measurement setup consists of two simultaneous measurement stations: satellite signal beacon measurement station and automatic weather measurement station. Within the period of January to June 2012, beacon signal level and rain rate were simultaneously recorded, collected and analyzed. The results of these measurement are compared with ITU-R attenuation model. The comparison shows that there are some differences between ITU-R and measured data. The main conclusion of this paper is that using global rain attenuation prediction models is not suitable solution in local satellite link design and detailed satellite wave propagation study at local points are necessary. Finally design and implementation of the propagation software is described.

Biomedical datasets usually include a large number of features relative to the number of samples. However, some data dimensions may be less relevant or even irrelevant to the output class. Selection of an optimal subset of features is critical, not only to reduce the processing cost but also to improve the classification results. To this end, this paper presents a hybrid method of filter and wrapper feature selection that takes advantage of a modified method of sequential forward floating search (SFFS) algorithm. The filtering approach evaluates the features for predicting the output and complementing the other features. The candidate subset generated by the filtering approach is used by k-fold cross validation of support vector machine (SVM) with user-defined classification margin as a wrapper. Applications of the proposed SFFS method to five biomedical datasets illustrate its superiority in terms of classification accuracy and execution time relative to the conventional SFFS method and another previously improved SFFS method.

This paper presents a delay compensator fuzzy control for trajectory tracking of omni-directional mobile robots. Fuzzy logic control (FLC) of the robots is a suitable strategy for dealing with model uncertainties, nonlinearities and disturbances. On the other hand, in many robotic applications such as mobile robots, delay phenomenon is able to substantially deteriorate the behavior of system's performance if not considered in the controller design. In this work, a delay compensator strategy is employed in order to eliminate the influence of dead time problem. On the other hand, a discrete-time kinematic model is presented for high level control of SSL soccer robots. Also, the model uncertainties are considered as multiplicative parameters and external random disturbances are noticed as additive parameters. The simulation experiments as well as real system experiments demonstrate that the proposed method handles both constant time delay and uncertainties with a small tracking error in comparison with pure fuzzy control.