Iranian Journal of Electrical and Electronic Engineering
Volume:9 Issue: 3, Sep 2013

In this article, three new green''s functions are presented for a narrow strip line (not a thin wire) inside or on a homogeneous dielectric, supposing quasi-TEM dominant mode. These functions have no singularity in contrast to so far presented ones, so that they can be used easily to determine the capacitance matrix of multi-layer and single-layer homogeneous coupled microstrip lines. To obtain the green’s functions, the Laplace’s equation is solved analytically in Fourier integral or Fourier series expressions, taking into account the boundary conditions including the narrow strip. The validity and accuracy of three presented green’s functions are verified by some examples.

In this article, a novel concept is introduced to improve the radio frequency (RF) linearity of partially-depleted (PD) silicon-on-insulator (SOI) MOSFET circuits. The transition due to the non-zero body resistance (RBody) in output conductance of PD SOI devices leads to linearity degradation. A relation for RBody is defined to eliminate the transition and a method to obtain transition-free circuit is shown. 3-D Simulations of various body-contacted devices are carried out to extract the transition-free body resistances. To identify the output conductance transition-free concept and its application to RF circuits, a 2.4 GHz low noise amplifier (LNA) is analyzed. Mixed mode device-circuit analysis is carried out to simultaneously solve device transport equations and circuit spice models. FFT calculations are performed on the output signal to compute harmonic distortion figures. Comparing the conventional body-contacted and transition-free SOI LNAs, third harmonic distortion (HD3) and total harmonic distortion (THD) are improved by 16% and 24%, respectively. Two-tone test is used to analyze third order intermodulation distortions. OIP3 is improved in transition-free SOI LNA by 17% comparing with the conventional body-contacted SOI LNA. These results show the possibility of application of transition-free design concept to improve linearity of RF SOI MOSFET circuits.

In this paper, the continuous optimal control theory is used to model and solve the maximum entropy problem for a continuous random variable. The maximum entropy principle provides a method to obtain least-biased probability density function (Pdf) estimation. In this paper, to find a closed form solution for the maximum entropy problem with any number of moment constraints, the entropy is considered as a functional measure and the moment constraints are considered as the state equations. Therefore, the Pdf estimation problem can be reformulated as the optimal control problem. Finally, the proposed method is applied to estimate the Pdf of the hourly electricity prices of New England and Ontario electricity markets. Obtained results show the efficiency of the proposed method.

In this paper, an approach is proposed for accurate locating of single phase faults in transmission lines using voltage signals measured at one-end. In this method, harmonic components of the voltage signals are extracted through Discrete Fourier Transform (DFT) and are normalized by a transformation. The proposed fault locator, which is designed based on Random Forests (RF) algorithm, is trained based on these normalized harmonic components. RF algorithm has the capability of learning patterns with a large number of features. The proposed approach only requires voltage signals measured at one-end; hence, there are not problems of transmitting and synchronization of two-end data. In addition, current measurement is not required and the proposed approach is sheltered against current transformer errors and its saturation. No need for very high sampling frequency is another advantage of the proposed approach. Numerous tests carried out on a sample system indicate that accuracy of the proposed fault locator is secure against changing fault location, fault inception angle, fault resistance, and magnitude and direction of pre-fault load current. An average of 0.11% is obtained for the fault locating test errors.

Nowadays, the doubly-fed induction generators (DFIGs) based wind turbines (WTs) are the dominant type of WTs connected to grid. Traditionally the back-to-back converters are used to control the DFIGs. In this paper, an Indirect Matrix Converter (IMC) is proposed to control the generator. Compared with back-to-back converters, IMCs have numerous advantages such as: higher level of robustness, reliability, reduced size and weight due to the absence of bulky electrolytic capacitor. According to the recent grid codes it is required that wind turbines remain connected to the grid during grid faults and following voltage dips. This feature is called low voltage ride-through (LVRT) capability. In this paper the linear quadratic regulator (LQR) controller is used for optimal control of the DFIG. The weighting matrices of the LQR are obtained using the genetic algorithm (GA) technique. With the LQR controller the intention is to improve the LVRT capability of the DFIG wind turbines to satisfy the new LVRT requirements. Compared to the PI controller, the superiority of the LQR controller in improving the transient stability and LVRT performance of the DFIG wind turbines is evident. Simulation results confirm the efficiency of the proposed controller.

Fault classification in distance protection of transmission lines, with considering the wide variation in the fault operating conditions, has been very challenging task. This paper presents a probabilistic neural network (PNN) and new feature selection technique for fault classification in transmission lines. Initially, wavelet transform is used for feature extraction from half cycle of post-fault three phase currents at one end of line. In the proposed method three classifiers corresponding with three phases are used which fed by normalized particular features as wavelet energy ratio (WER) and ground index (GI). The PNNs are trained to provide faulted phase selection in different ten fault types. Finally, logic outputs of classifiers and GI identify the fault type. The feasibility of the proposed algorithm is tested on transmission line using PSCAD/EMTDC software. Variation of operating conditions in train cases is limited, but it is wide for test cases. Also, quantity of the test data sets is larger than the train data sets. The results indicate that the proposed technique is high speed, accurate and robust for a wide variation in operating conditions and noisy environments.

In this paper, a robust Maximum Power Point Tracking (MPPT) for PV array has been proposed using sliding mode control by defining a new formulation for sliding surface which is based on increment conductance (INC) method. The stability and robustness of the proposed controller are investigated to load variations and environment changes. Three different types of DC-DC converter are used in Maximum Power Point (MPP) system and the results obtained are given. The simulation results confirm the effectiveness of the proposed method in the presence of load variations and environment changes for different types of DC-DC converter topologies.