نشریه مهندسی برق
سال چهل و چهارم شماره 2 (پیاپی 68، تابستان 1393)

Due to growing demand of the electric energy, the need to generation expansion planning is inevitable. In this paper at first effective criteria in Generation Expansion Planning (GEP) are determined and a novel approach for GEP is proposed. In this approach Fuzzy-Analytical Hierarchy Process (FAHP) is utilized for GEP. The Fuzzy is one of the techniques that uses for weight assessment in decision making in Multi Criteria Decision Making (MCDM) model. For this purpose, five criteria are introduced and then by utilization of the FAHP, the optimization of GEP problem is implemented. In the first stage, the Local Marginal Price (LMP) of each bus is calculated by Optimal Power Flow (OPF) execution. In the next stage, base on the criteria that will describe, the candidate places for power plants installation are determined. Finally, the FAHP is used to assign a value to each criterion and by using these values the optimal place for installation of power plant among the candidate places is determined. The IEEE 14 bus network is used to simulate and evaluate the effectiveness of the proposed method.

Discrete torque generation mechanism and inherently nonlinear magnetic characterization of switched reluctance motors lead to unacceptable torque ripple and reduce the variety of applications in industry. In this paper, a phase current profiling technique and torque sharing function are proposed considering magnetic saturation effects as well as minimizing power loss during the commutation area between the adjacent phases. Constant torque trajectories are considered in incoming and outgoing phase currents plane based on nonlinear T-i-theta curves which are obtained from experimental measurements. Optimum points on constant torque trajectories are selected based on improving drive efficiency and minimizing copper loss in each rotor position. In order to implement the proposed method, experimental measurements were undertaken to obtain the motor operational characterizations. A modification scheme based on logical rules will be introduced to enhance maximum speed with torque free operation. Experimental and simulation results on four phase, 4Kw 8/6 SRM, validate the effectiveness of the proposed method.

In this paper, a scheme is presented for the control of Dynamic Voltage Restorer using Adaptive Notch Filter (ANF) and PD controller. In order to increase the speed of dynamic response and reduce system losses, the resistor of the output LC filter is eliminated and the oscillations in the control system are actively damped. For this purpose, the current of the output filter capacitor is used as feedback to the control system and current mode control is implemented in the inner loop, which is more stable system. Frequency, amplitude and phase of the main component of voltage is extracted using the ANF. In addition to the use of frequency response correction, PD controller is used to improve the speed of dynamic response. Correct functioning under frequency deviation, faster response in the case of voltage sag/swell and harmonics mitigation are among the merits of this type of controller. Simulations in the MATLAB software environment demonstrate the effectiveness performance of the DVR in test system under different conditions.

In this paper, the single mode operation of a DFB Raman Fiber laser with /2 phase shift is analyzed theoretically at threshold condition. The effects of length and coupling coefficient on the modal gain, threshold pump power of the main mode and side mode are investigated. The presented model is based on the combination of three nonlinear coupled wave equations including self phase modulation and cross phase modulation effects. Computer simulation is carried out by solving the self-consistent of three nonlinear coupled wave equations to evaluate the steady-state of pump, forward and backward stokes waves. Numerical results show that the threshold pump power of main mode and side mode decreases by increasing the coupling coefficient and fiber length. So it can be expected that for some values of these parameters the side mode appears in the output of laser. The presented algorithm in this paper enables us to get the optimized values of fiber length and coupling coefficient of DFB Raman Fiber laser for single mode operation. Numerical calculations are carried out for characteristics of an UHNA4 SiO2 fiber. The theoretical calculations are validated by the experimental data of similar structures.

One of the most important objectives in Reactive Power Planning (RPP) is to select optimal location and size of var sources for maintaining the required voltage stability margin under normal and single-contingency cases. To meet this objective, an optimization problem must be formulated considering N-1 contingencies constrained for a set of predetermined contingencies. In optimization problem, all the contingencies must simultaneously be considered. This may cause the convergence of solution in a large power system to make impossible. This paper uses two voltage stability indices to select a small number of contingencies instead of all ones in optimization problem, so that the allocated var sources cover all of the contingencies. The contingencies divided into some groups, each group affects one part of power system. Then the worst contingency from each group is selected. The method is tested on IEEE 57-bus test system and the results are compared with the ones when all the contingencies are included in the optimization problem.

High peak-to-average-power ratio (PAPR) is a weakness of orthogonal frequency division multiplexing (OFDM). Selected mapping (SLM) is one of the well-known techniques to reduce the PAPR. In this method, transmitter is obliged to send several bits named side information (SI). Such side information causes bandwidth efficiency to be decreased; in addition, incorrect detection of SI by receiver make whole data block be lost. In this paper, we propose a technique on the base of linear congruential generator (LCG) by which side information bits are not explicitly sent. We simulate our method for an OFDM system through the use of 16-QAM modulation. It is shown that our proposed scheme, from the view point of bit error rate (BER), probability of detection failure (Pdf) and PAPR reduction, performs very well.