NASHRIYYAH -I MUHANDISI -I BARQ VA MUHANDISI -I KAMPYUTAR -I IRAN, A- MUHANDISI -I BARQ
Year:2016 | Volume:14 | Issue:2|Papers Count:10

This paper offers a modified circuit for improving linearization of power amplifier with based on the model of the Feed Forward circuit amplifier. With the help of mathematical model for the single power amplifier, the circuit is simulated und a demonstrator is built and measured. it is used a complex Taylor series for modeling the power amplifier by the approximation of the amplitude transfer function and the level-dependence of the transmission-phase of the power amplifier and can be understood as a simplified form of Volterra series. In our proof of concept experiment, we verified the concept but also found that the adjustment of the circuit is critically dependent on the drive conditions and linearization is achieved only for a narrow range of drive power. The simulation of the total circuit is largely determined by the models for the transmission characteristics of the two power amplifiers. The new circuit in compare with the conventional Feed Forward amplifier, in addition a significant increase in efficiency to minimize the power of the distortion signal 3IMD for large driving amplitude (large signals).

In order to improve power quality, the detection and identification of factors involved in reducing power quality are paramount. One of the main factors in creating flicker and harmonics in the system connected to the wind turbines are wind aerodynamic turbulences and wind turbines mechanical errors. In this paper the mathematical equations of turbulence wind shadow and wind shear and mechanical equations of Gear Tooth Breaks in Wind Turbine Gearboxes have been evaluated accurately using the MATLAB simulation. The continued impact of the disturbances on the output parameters of the network is observed. Also, it is shown that these disturbances can be identified and classified properly by wavelet function.

Transient mechanical force in transformer induced critical mechanical stress on windings and transformers in radial and axial directions. In this paper, impact of force’s within transient inrush current duration on MV three phase transformer with propose novelty winding configuration (S-P-S) to considered. In order to forces analysis, a 3-D model of three phase transformer developed by use Ansoft Maxwell V15.0. Magnetic vector potential, Magnetic flux density and electro-mechanical force’s of SPS-type and conventional-type of configuration windings and transformer calculated from a 3D finite element model. Based on the comparison and result analysis, proposed an optimal configuration for transformer winding in order to trade-off and minimization of electromechanical force’s in the transient inrush current state.

Smart grid is the result of enabling consumers in the power system in order to play an effective role in the power system planning and operation processes. The communication, control, and measurement infrastructures create a two-way intelligent communication between users and the network which facilitates the effective implementation of demand response programs (DRPs) such as the direct load control (DLC). In this paper, optimal power flow as an important research topic in the power systems is presented based on DLC and a new voltage stability index. Simple calculations, voltage dependence, indirect dependence to the load and network topology, and also not reducing the network into a two-bus equivalent model, have made the proposed voltage stability index more applicable to real-time calculations considering the load pattern changes. In the proposed method, the optimal load curtailment in some selected loads of the network, with the aim of improving the voltage stability index of the weakest bus is evaluated. Finally, in order to show the effectiveness of the suggested method, it is applied to a 69-bus radial distribution network as an intelligent system.

We present an analytical method for the calculation of cogging torque in surface permanent-magnet (PM) motors. The cogging torque is calculated by integrating the Maxwell stress tensor inside the air gap. The stator design techniques are applied to reduce the cogging torque in SPM motors. The used techniques are stator dummy slots, teeth pairing and stator slot skewing. The direct search method is used to find the optimum geometry in the mentioned methods. Finally, the validity of the proposed model and the obtained results are verified with Finite Element Analysis.

In the presented work an analytical model is developed for the pole-shifting method in the surface-mounted PM machine at no-load condition. The machine cogging torque and the harmonic spectrum of the air gap flux density are most no-load indexes of the machine performance. It is shown that, although, the pole-shifting reduces the machine cogging torque; it destroyed the half-odd symmetry in the PMs and produces even harmonics in the air gap flux density. The even harmonics of the air gap flux density, results in undesired torque pulsations. Using the developed analytical model and the direct search method a multi-objective optimization is carried out for the machine cogging torque and the total harmonic distortion of the air gap flux density. Since, the considered variables are not in a same unite; a normalized technique is applied. Finally, the developed model and the obtained results are verified by finite element analysis.

In this paper, a Wide-Area protection system to deal with rotor angle instabilities is proposed. Firstly, a system blackout model is developed and secondly the extreme contingencies that lead to large blackouts are extracted. Initiating events that ultimately lead to rotor angle instabilities are determined by artificial neural network (ANN). Coherent generators are detected by an algorithm using the data presented by phasor measurement units (PMUs). Based on identification of coherent generators, the power system is split into stable islands by disconnecting the weak interconnecting lines and load shedding. The performance of the proposed strategy is verified by simulations on the IEEE 39-bus sample power system.

Abstract-In this paper, we study the inter carrier interference (ICI) in fractional Fourier transform based orthogonal frequency division multiplexing (FrFT-OFDM) systems. In this analysis, we derive tight upper and lower bounds for ICI power of FrFT-OFDM systems in doubly dispersive channels. These bounds have considerably simpler expressions than the exact ICI formula. Thus, they provide deep and useful insight into the effect of Doppler frequency, symbol duration, channel delay spread, and angle of transform on the ICI power. This analysis confirms that in the special case of flat fast fading channels the FrFT-OFDM and Fourier transform based OFDM (FT-OFDM) systems exhibit analogous performance while in doubly dispersive channels FrFT-OFDM can achieve better performance than single carrier (SC) and FT-OFDM, if the angle of transform is selected accurately.

Energy harvesting (EH) has emerged as a promising technique for green communications and it is a novel technique to prolong the lifetime of the wireless networks with replenish able nodes. In this paper, we investigate the online resource allocation for a large class of objective functions in the EH communication systems, which are asymptotically optimal. It is shown that the solution is obtained by only considering the average EH pattern, irrespective of its stochastic dynamics. This optimal solution neither has the complexity of dynamic programming solutions, nor uses the non-causal knowledge about EH pattern. Also, some practical numerical examples for objective functions, which are utilized in communication systems, are considered and general results are derived for them. Moreover, simulation results validate our theoretical findings and show the accuracy of asymptotic theoretical curves for the transmission periods, which are used in practice.

Photonic crystal fibers (PCFs) as waveguides with low dispersion, low confinement loss, and low nonlinearity can be used in optical telecommunication systems. In this paper, a hexagonal-circular photonic crystal fiber is proposed. In the first design, we present a hexagonal PCF with 70 ps/nm.km dispersion at 1550 nm wavelength. The confinement loss and nonlinearity of this structure are respectively obtained as 0.6´10-12dB/cm and 8.988 W-1km-1. In the second design, by improving th e primary structure as hexagonal-circular PCF, the nearly zero dispersion is obtained. The simulation results show that the confinement loss and nonlinearity of the improved structure are 8´10-11 dB/cm and 7.956 W-1km-1, respectively.