NASHRIYYAH -I MUHANDISI -I BARQ VA MUHANDISI -I KAMPYUTAR -I IRAN, A- MUHANDISI -I BARQ
Year:2018 | Volume:16 | Issue:1 |Papers Count:9

One of the most important problems in power networks is the presence of resonance at some of the buses which leads to an unwanted increase in voltage and current and damage to equipment. Since with installing a capacitor bank in the network, frequency characteristic of the system is changed and resonance is increased, it is necessary to consider this point in allocation of capacitors in the network. In this paper, a new index for evaluating the resonance is presented. Applying the proposed resonance index, a new two-step method for optimal placement of capacitors in a harmonic system is provided. In the first step, a sensitivity analysis is used, then in the second step, the objective function considering technical constraints is optimized using a fuzzy technique. The proposed method is implemented with the MSPSO algorithm on the IEEE 18-bus network. The results show the efficiency of this method in comparison with other methods.

By using usual industrial switching methods, two new multicarrier PWM (MCPWM) methods are proposed in this paper to improve the output voltage characteristics for eleven levels diode-clamped inverter. DC component and Even harmonic orders of the output voltage are totally eliminated in the proposed VFCBOD and COOD methods by applying the phase shift in the carrier wave (carrier-based); so total harmonic distortion (THD) and torque ripple are reduced. By using the both proposed methods, the number of pulses per cycle equally are distributed and increased the lifetime of the switches. In this paper, a full bridge has been series with each phase of eleven levels diode-clamped inverter to change the polarity of the voltage to produce more switching patterns to generate the specified voltage levels. Then, by determining suitable switching patterns, the inverter can be driven with the least of switches when there is a failure and finally increased the reliability of the whole system.

Modular Multilevel Converters, by increasing the number of voltage levels the quality of output waveform is improved and the semiconductor switches tolerate low voltage values. However, design of switching strategy in these complicated circuits is challenging. In this paper, based on sphere decoding algorithm, a predictive controller with finite control set is proposed to regulate load current while minimizing both capacitor voltage variations and circulating currents. The suggested scheme decreases the computational burden of optimization stage which is considerable for long prediction horizons and modular converters with high number of voltage levels. The suggested scheme is simulated for a practical modular multilevel converter to demonstrate its performance compared to some rival methods.

Optimum design of electrical motors may be considered as a complex optimization problem due to the wide variety of mechanical, electrical, electromagnetics parameters, although recently it can be accomplished utilizing heuristic optimization algorithms. In this paper optimum design of an out-runner PM BLDC motor for flywheel energy storage applications is performed. The optimization utilized particle swarm optimization (PSO) algorithm to achieve maximum torque density. Accordingly, the motor design equations are employed in the fitness function of the algorithm. Based on the random initial values and respecting the designs constraints, the optimum design is achieved. Effectiveness of the algorithm results are verified by finite element analysis (FEA) and motor operating parameters are obtained and analyzed. Finally, the prototype of the motor is fabricated and experimental results are demonstrated to show the applicability of the model and analysis.

Scaling the channel length leads to the increased leakage current of double gate junctionless field effect transistor (DGJL-FET) and, as a result, the increased power consumption in OFF-state. The present paper proposes a new structure for reducing the leakage current in DGJL-FET, which is called modified DGJL-FET. In this structure, the channel doping under the gate is the same as the drain and source doping but higher than the mid-channel doping. The simulation results indicated that reducing the thickness of the doped layer under the gate, D, resulted in the reduced OFF-state current. For the proposed device with 10 nm channel length, the OFF-state current is less than that in the regular DGJL-FET by two orders of magnitude. Performance of the regular DGJL-FET and modified DGL-FET for different channel lengths is compared based on the IOFF/ION ratio, sub-threshold slope (SS), and intrinsic gate delay. For modified DGJL-FET, the mid-channel doping and Dare considered as additional parameters for improving the device’s performance in nanometer regime. The simulation results indicated that in the proposed device with channel length of 15 nm, values of SS and IOFF/ION ratio are improved compared to the regular DGJL-FET by 14% and 106 orders of magnitude, respectively.

In this paper a novel branch line coupler (BLC) with size reduction and performance improvement at 2.4 GHz is proposed. The proposed branch line coupler suppresses the second harmonic with 38.55 dB attenuation level. The scattering parameters of the proposed BLC are given as follows: S11= -67.67 dB, S12= -2.95 dB, S13= -3.09 dB and S14= -49.78 dB. The bended line structures and open-ended stubs are used in design process. The proposed BLC has 45.4% size reduction compare to the conventional one. The proposed device fabricated on RT/Duroid 5880 substrate.

Due to the lack of measurement in distribution systems, state estimation has particular importance. Different methods are presented to improve the accuracy of system state with limited measurements. In this paper a new state estimator in distribution systems are offered. This estimator bases on backward forward load flow estimates system state with adjusting load consumption at each step. Voltage measurements in slack bus, loads and zero injection measurements are inputs of estimator. This estimator is compared with weight least square estimator and its results are shown. The estimator calculates voltage magnitude with less error and also faster than WLS estimator. 85-bus system is presented in this paper.

Harmonic pollution of source currents and poor power factor are the main challenges of rectifiers. In this paper using one cycle control strategy, rectifiers can be operated at unity power factor. For performance analysis of this method harmonic injection and unbalanced load applied to the source side considered. Simulation results show that combination of three phase four leg rectifier with one cycle control can be improved power factor and harmonic pollution reduction especially in nonlinear and unbalanced loads in the source side.

Severe saturation of the magnetic core is the most influential factor in ferroresonance that leads to distorted currents and voltages., modeling the nonlinear behavior of the magnetic core is the most important challenge in ferroresonance study. In this paper, finite element method in conjunction with the inverse Jiles-Atherton (JA) hysteresis model of the steel core, is employed for modeling of a single-phase transformer accurately. Then, ferroresonance is studied by inserting different capacitors in series with the unloaded transformer, and the corresponding variation of copper losses and iron losses are obtained and discussed. Ferroresonance affects the shape of the hysteresis loop that necessitates the retuning of the parameters of the JA hysteresis model. The numerical results agree well with the experimental ones.