Showing papers in "iranian journal of electrical and electronic engineering in 2010"

Application of Fuzzy and ABC Algorithm for DG Placement for Minimum Loss in Radial Distribution System

Abstract: Distributed Generation (DG) is a promising solution to many power system problems such as voltage regulation, power loss, etc. This paper presents a new methodology using Fuzzy and Artificial Bee Colony algorithm (ABC) for the placement of Distributed Generators (DG) in the radial distribution systems to reduce the real power losses and to improve the voltage profile. A two-stage methodology is used for the optimal DG placement. In the first stage, Fuzzy is used to find the optimal DG locations and in the second stage, ABC algorithm is used to find the size of the DGs corresponding to maximum loss reduction. The ABC algorithm is a new population based meta heuristic approach inspired by intelligent foraging behavior of honeybee swarm. The advantage of ABC algorithm is that it does not require external parameters such as cross over rate and mutation rate as in case of genetic algorithm and differential evolution and it is hard to determine these parameters in prior. The proposed method is tested on standard IEEE 33 bus test system and the results are presented and compared with different approaches available in the literature. The proposed method has outperformed the other methods in terms of the quality of solution and computational efficiency.

Pole shape optimization of permanent magnet synchronous motors using the reduced basis technique

Abstract: In the present work, an integrated method of pole shape design optimization for reduction of torque pulsation components in permanent magnet synchronous motors is developed. A progressive design process is presented to find feasible optimal shapes. This method is applied on the pole shape optimization of two prototype permanent magnet synchronous motors, i.e., 4-poles/6-slots and 4-poles-12slots.

Implementation and Critical Investigation on Modulation Schemes of Three Phase Impedance Source Inverter

Abstract: New control circuits and algorithms are frequently proposed to control the impedance (Z) source inverter in efficient way with added benefits. As a result, several modified control techniques have been proposed in recent years. Although these techniques are clearly superior to the simple boost control method which was initially proposed along with the Z-source inverter (ZSI), little or conflicting data is available about their merits relating to each other. In this paper, it is shown how the shoot-through periods are inserted in the switching waveforms of the power switches and the performances of them are analyzed based on the operation of ZSI. Simple boost control, maximum boost control, constant boost control and space vector modulation based control methods given in the literature has been illustrated with their control characteristics. A critical investigation on ripples of the impedance source elements, output voltage controllability, output harmonic profile, transient response of the voltage across the impedance source capacitor and voltage stress ratio etc has been presented with the simulation results. The simulation results are experimentally verified in the laboratory with digital signal processors (DSP). DSP coding for the above all control techniques has been generated by interfacing Matlab/Simulink with DSP C6000 tool box and signal processing block set.

A heuristic approach to distributed generation source allocation for electrical power distribution systems

Abstract: The recent trends in electrical power distribution system operation and management are aimed at improving system conditions in order to render good service to the customer. The reforms in distribution sector have given major scope for employment of distributed generation (DG) resources which will boost the system performance. This paper proposes a heuristic technique for allocation of distribution generation source in a distribution system. The allocation is determined based on overall improvement in network performance parameters like reduction in system losses, improvement in voltage stability, improvement in voltage profile. The proposed Network Performance Enhancement Index (NPEI) along with the heuristic rules facilitate determination of feasible location and corresponding capacity of DG source. The developed approach is tested with different test systems to ascertain its effectiveness.

Improved Direct Torque Control for Induction Machine Drives Based on Fuzzy Sector Theory

Abstract: Here, a new fuzzy direct torque control algorithm for induction motors is proposed. As in the classical direct torque control, the inverter gate control signals directly come from the optimum switching voltage vector look-up table, the best voltage space vector selection is a key factor to obtain minimum torque and flux ripples. In the proposed approach, the best voltage space vector is selected using a new fuzzy method. A simulation model is built up and the torque and flux ripples of basic direct torque control and the proposed method are compared. The simulation results show that the torque and flux ripples are significantly decreased and in addition, the switching frequency can be fixed.

Design Modification of Rogowski Coil for Current Measurement in Low Frequency

Abstract: The principle object of this paper is to offer a modified design of Rogowski coil based on its frequency response. The improvement of the integrator circuit to nullify the phase difference between the waveforms of the measured-current and the corresponding terminal voltage is a further object of this investigation. This paper addresses an accurate, yet more efficient measuring and protecting device for low frequency applications. This requires verification for the simulations by physical descriptions and experimental results. These validate the superior performance of Rogowski coils over conventional current transformers.

Long-Term Peak Demand Forecasting by Using Radial Basis Function Neural Networks

Abstract: Prediction of peak loads in Iran up to year 2011 is discussed using the Radial Basis Function Networks (RBFNs). In this study, total system load forecast reflecting the current and future trends is carried out for global grid of Iran. Predictions were done for target years 2007 to 2011 respectively. Unlike short-term load forecasting, long-term load forecasting is mainly affected by economy factors rather than weather conditions. This study focuses on economical data that seem to have influence on long-term electric load demand. The data used are: actual yearly, incremental growth rate from previous year, and blend (actual and incremental growth rate from previous years). As the results, the maximum demands for 2007 through 2011 are predicted and is shown to be elevated from 37138 MW to 45749 MW for Iran Global Grid. The annual average rate of load growth seen per five years until 2011 is about 5.35%.

Reliability Model of Power Transformer with ONAN Cooling

Abstract: Reliability of a power system is considerably influenced by its equipments. Power transformers are one of the most critical and expensive equipments of a power system and their proper functions are vital for the substations and utilities. Therefore, reliability model of power transformer is very important in the risk assessment of the engineering systems. This model shows the characteristics and functions of a transformer in the power system. In this paper the reliability model of the power transformer with ONAN cooling is obtained. The transformer is classified into two subsystems. Reliability model of each subsystem is achieved. Markov process representation and the frequency/ duration approach are employed to obtain a complete reliability model of the subsystems. By combining these models reliability model of power transformer is obtained. The reliability model associated with the transformer is then proposed combining the models of subsystems. The proposed model contains five states. To make the model more applicable, the 5-state model is alleviated to a 3-state one. Numerical analysis and sensitivity analysis relevant to the proposed reliability model are performed for evaluating the numerical values of the model parameters and the impact of different components on the reliability of the model.

Multi-Objective Design Optimization of a Linear Brushless Permanent Magnet Motor Using Particle Swarm Optimization (PSO)

Abstract: In this paper a brushless permanent magnet motor is designed considering minimum thrust ripple and maximum thrust density (the ratio of the thrust to permanent magnet volumes). Particle Swarm Optimization (PSO) is used as optimization method. Finite element analysis (FEA) is carried out base on the optimized and conventional geometric dimensions of the motor. The results of the FEA deal to the significant improvement of the all objective functions.

Stochastic congestion management considering power system uncertainties

Abstract: Congestion management in electricity markets is traditionally done using deterministic values of power system parameters considering a fixed network configuration. In this paper, a stochastic programming framework is proposed for congestion management considering the power system uncertainties. The uncertainty sources that are modeled in the proposed stochastic framework consist of contingencies of generating units and branches as well as load forecast errors. The Forced Outage Rate of equipment and the normal distribution function to model load forecast errors are employed in the stochastic programming. Using the roulette wheel mechanism and Monte-Carlo analysis, possible scenarios of power system operating states are generated and a probability is assigned to each scenario. Scenario reduction is adopted as a tradeoff between computation time and solution accuracy. After scenario reduction, stochastic congestion management solution is extracted by aggregation of solutions obtained from feasible scenarios. Congestion management using the proposed stochastic framework provides a more realistic solution compared with the deterministic solution by a reasonable uncertainty cost. Results of testing the proposed stochastic congestion management on the 24-bus reliability test system indicate the efficiency of the proposed framework.

Application of Neural Space Mapping for Modeling Ballistic Carbon Nanotube Transistors

Abstract: In this paper, using the neural space mapping (NSM) concept, we present a SPICE-compatible modeling technique to modify the conventional MOSFET equations, to be suitable for ballistic carbon nanotube transistors (CNTTs). We used the NSM concept in order to correct conventional MOSFET equations so that they could be used for carbon nanotube transistors. To demonstrate the accuracy of our model, we have compared our results with those obtained by using open-source software known as FETToy. This comparison shows that the RMS errors in our calculated IDS, under various conditions, are smaller than the RMS errors in IDS values calculated by the existing analytical models published by others.

Determination of Electric Field at Inception Based upon Current-Voltage Characteristics of AC Corona in Rod-Plane Gaps

Abstract: This paper deals with the measurement of AC corona inception voltage, Vincp, at the tip of a rod electrode using a hemispherically-capped rod-plane electrode configuration for various rod radii with a short air gap. Effects of atmospheric pressure and temperature variation on Vincp are investigated experimentally. An empirical equation for the field form factors of the hemispherically capped rod-plane electrodes is proposed with its range of applicability. The obtained results are analyzed to derive a more accurate analytical equation for the calculation of the electric field at corona inception voltage, Eincp, and the average of electric field distribution, Emean.

Joint closed-loop power control and base station assignment for ds-cdma receiver in multipath fading channel with adaptive beamforming method

Abstract: In this paper, we propose smart step closed-loop power control (SSPC) algorithm and base station assignment based on minimizing the transmitter power (BSA- MTP) technique in a direct sequence-code division multiple access (DS-CDMA) receiver in the presence of frequency-selective Rayleigh fading. This receiver consists of three stages. In the first stage, with conjugate gradient (CG) adaptive beamforming algorithm, the desired users' signal in an arbitrary path is passed and the inter-path interference is canceled in other paths in each RAKE finger. Also in this stage, the multiple access interference (MAI) from other users is reduced. Thus, the matched filter (MF) can be used for the MAI reduction in each RAKE finger in the second stage. Also in the third stage, the output signals from the matched filters are combined according to the conventional maximal ratio combining (MRC) principle and then are fed into the decision circuit of the desired user. The simulation results indicate that the SSPC algorithm and the BSA-MTP technique can significantly improve the network bit error rate (BER) in comparison with other algorithms. Also, we observe that significant savings in total transmit power (TTP) are possible with our proposed methods.

A Simple Analytic Method to Model and Detect Non-Uniform Air-Gaps in Synchronous Generators

Abstract: The air-gap of electrical machines may become non-uniform due to low accuracy of the manufacturing machinery, in assembling processes, or by aging. Detection and monitoring of this phenomenon is very important and of interest. There are several methods to model non-uniform air-gaps and to detect them by monitoring systems. One of the most widely used methods is by the analysis of the line currents. In this paper a new, simple and comprehensive method is presented to model and detect non-uniform air-gaps in synchronous generators with skewed rotors. The influence of non-uniform air-gaps on the harmonics of the induced voltage of the stator is investigated by the proposed method. Simulations are performed for three cases: uniform air-gap, static rotor eccentricity, and stator ovality in a two phase generator. The experimental results are also presented. The good correspondence between the simulation and the experimental results clearly validates the theoretical findings put forward in this paper.

A Low-Voltage, Low-Power, Two-Stage Amplifier for Switched-Capacitor Applications in 90 nm CMOS Process

Abstract: A novel low-voltage two-stage operational amplifier employing resistive biasing is presented. This amplifier implements neutralization and correction common mode stability in second stage while employs capacitive dc level shifter and coupling between two stages. The structure reduces the power consumption and increases output voltage swing. The compensation is performed by simple miller method. For each stage an independent common- mode feedback circuits has been used. Simulation results show that power consumption is 2.1 mW at 1 V supply. The dc gain of the amplifier is about 70 dB while its output swing is as high as around 1.2 V.

Using modular pole for multi-objective design optimization of a linear permanent magnet synchronous motor by particle swarm optimization (pso)

Abstract: In this paper particle swarm optimization (PSO) is used for a design optimization of a linear permanent magnet synchronous motor (LPMSM) considering ultra low thrust force ripples, low magnet consumption, improved efficiency and thrust. The influence of PM material is discussed, too and the modular poles are proposed to achieve the best characteristic. PM dimensions and material, air gap and motor width are chosen as design variables. Finally 2-D finite element analyses validate the optimization results.

A Modified Proportional Navigation Guidance for Accurate Target Hitting

Abstract: When a detector sensitive to the target plume IR seeker is used for tracking airborne targets, the seeker tends to follow the target hot point which is a point farther away from the target exhaust and its fuselage. In order to increase the missile effectiveness, it is necessary to modify the guidance law by adding a lead bias command. The resulting guidance is known as target adaptive guidance (TAG). First, the pure proportional navigation guidance (PPNG) in 3-dimensional state is explained in a new point of view. The main idea is based on the distinction between angular rate vector and rotation vector conceptions. The current innovation is based on selection of line of sight (LOS) coordinates. A comparison between two available choices for LOS coordinates system is proposed. An improvement is made by adding two additional terms. First term includes a cross range compensator which is used to provide and enhance path observability, and obtain convergent estimates of state variables. The second term is new concept lead bias term, which has been calculated by assuming an equivalent acceleration along the target longitudinal axis. Simulation results indicate that the lead bias term properly provides terminal conditions for accurate target interception.

Transmission Cost Allocation in Restructured Power Systems Based on Nodal Pricing Approach by Controlling the Marginal Prices

Abstract: This paper presents a method to allocate the transmission network costs to users based on nodal pricing approach by regulating the nodal prices from the marginal point to the new point. Transmission nodal pricing based on marginal prices is not able to produce enough revenue to recover the total transmission network costs. However, according to the previous studies in this context, this method recovers only a portion of transmission costs. To solve this problem, in this paper a method is presented in which by considering the direction and amount of injected power in each node the marginal price is regulated to the new price, in such a way as the nodal pricing can recover the total transmission network costs. Also the proposed method is able to control the cost splitting between loads and generators in accordance with the pre-specified ratio. The proposed method is implemented on both IEEE 24-bus and 118-bus test systems and the obtained results are reported.

Design of a resonant suspended gate mosfet with retrograde channel doping

Abstract: High Q frequency reference devices are essential components in many Integrated circuits. This paper will focus on the Resonant Suspended Gate (RSG) MOSFET. The gate in this structure has been designed to resonate at 38.4MHz. The MOSFET in this device has a retrograde channel to achieve high output current. For this purpose, abrupt retrograde channel and Gaussian retrograde channels have been investigated.

A New ZVZCS Isolated Dual Series Resonant DC-DC Converter with EMC Considerations

Abstract: A novel ZVZCS isolated dual series-resonant active-clamp dc-dc converter is proposed to obtain high efficiency. The proposed converter employs an active-clamp technique, while a series-resonant scheme controls the output voltage with the complementary pulse width modulation controller. The active-clamp circuit serves to recycle the energy stored in the leakage inductance or the magnetizing inductance and provides zero-voltage and zero-current turn-on and turn off switching. The voltage stresses of the main switch are clamped. The voltage transient spikes across the dual series active clamp circuit and the current stress of the current-fed side switches are limited by auxiliary active clamping circuits on both sides, and ZVZCS is achieved. The operating principles and design considerations are discussed and verified by simulations using PSIM software. Also, the EMI reduction techniques from EMC point of view in the circuits related to converters has been pointed out.

Dual Z-Source Network Dual-Input Dual-Output Inverter

Abstract: This paper presents a modified nine switch inverter with two inputs and two Z- source networks. This inverter has two DC inputs and two AC outputs. Input DC voltages can be boosted to the required level. Amplitude, frequency and phase of AC output voltages can be controlled, independently. The proposed converter can be used in applications with two unregulated DC sources, which require feeding two independent loads. Compared to the conventional structure, the proposed converter requires reduced number of semiconductor switches hence improved converter reliability and less volume. While the authors have already presented a similar inverter (single z-source network dual-input dual-output inverter) with the above features, new inverter has some differences in the topology, control strategy and operation. In this paper, a new control strategy of space vector modulation for the new inverter is proposed. Also a new switching method utilizing carrier-based modulation concept is presented for both dual (proposed) and single z-source network dual-input dual-output inverters. Performance of the proposed inverter is verified by simulation and experimental results.

Effects of non-ideal pre-distorter high power amplifiers in wcdma using multi-user detectors

Abstract: Wide band code division multiple access (WCDMA) signals, transmitted by the base station high power amplifiers (HPAs), show high peak to average power ratios (PAPR), which results in nonlinear distortions. In this paper, using computer simulations effect of using a predistorted HPA on the symbol error rate (SER) of multi-user detectors in terms of output back-off (OBO) in the transmit power is analyzed. As well, using polynomials for modeling predistorters to remove nonlinear distortions of traveling wave tube amplifiers (TWTAs) and of solid state power amplifiers (SSPAs), effect of different degrees of polynomials on the SER is investigated. Simulation results show that a polynomial of degree 4 is a sufficient degree polynomial, which fits to the AM/AM characteristic of the predistorter for TWTAs. As well, for solid state power amplifiers (SSPAs) with different p values, different approximations are considered and sufficient degree polynomials are found.

Discrimination of the heart ventricular and atrial abnormalities via a wavelet-aided adaptive network fuzzy inference system (anfis) classifier

Abstract: The aim of this study is to address a new feature extraction method in the area of the heart arrhythmia classification based on a metric with simple mathematical calculation called Curve-Length Method (CLM). In the presented method, curve length of the under study excerpted segment of signal is considered as an informative feature in which the effect of important geometric parameters of the original signal can be found. To show merits of the presented method, first the original electrocardiogram (ECG) in lead I is pre- processed by removing its baseline wander then by scaling it in the (-1,1) interval. In the next step, using a method, discrete wavelet scales 2 3 and 2 4 and smoothing function scale 2 2 are extracted. Afterwards, segments including samples of the QRS complex, P and T waves are estimated via an approximation criterion and CLM is implemented to extract corresponding features from aforementioned scales, smoothing function and also from each original segment. The resulted feature vector (including 12 components) is used to tune an Adaptive Network Fuzzy Inference System (ANFIS) classifier. The presented strategy is applied to classify four categories found in the MIT-BIH Arrhythmia Database namely as Atrial Premature Beat (APB), Left Bundle Branch Block (LBBB), Right Bundle Branch Block (RBBB) and Premature Ventricular Contraction (PVC) and average values of Se = 99.81%, P+ = 99.80%, Sp = 99.81% and Acc = 99.72% are obtained for sensitivity, positive predictivity, specifity and accuracy respectively showing marginal improvement of the heart arrhythmia classification performance.

Mathematical Proof for the Minimized Stray Fields in Transformers Using Auxiliary Windings Based on State Equations for Evaluation of FEM Results

Abstract: Stray magnetic field is one of the main issues in design of transformers, since it causes non-ideal behavior of transformers. One of the techniques is usually adopted to mitigate the unwanted stray magnetic field is the use of auxiliary windings creating a magnetic field opposite to the incident one giving rise to the reduction of the total magnetic fields. This paper presents a new mathematical proof for optimized parameters such as connection resistance and leakage inductance of the auxiliary windings based on state equations. Some numerical examples for various types of practical transformers are given to demonstrate the validity of the presented mathematical proof and a comparison is made with the results of transformers behavior which is obtained with the help of finite element method. The proposed method is successfully implemented on three different types of transformers: current injection transformer, pulse transformer and superconductor transformers.

Multiarea transmission cost allocation in large power systems using the nodal pricing control approach

Abstract: This paper proposes an algorithm for transmission cost allocation (TCA) in a large power system based on nodal pricing approach with multiarea scheme. The nodal pricing approach is introduced to allocate the transmission costs using the nodal pricing control in a single area network. As the number of equations is dependent on the number of buses and generators, this method will be very time consuming for large power systems. To solve this problem, the present paper proposes a new algorithm based on multiarea approach for regulating the nodal prices, so that the simulation time is greatly reduced and therefore the nodal pricing approach can be applicable for large power systems. In addition, in the proposed method, the transmission costs are allocated to the users more equitable than the single area method. Since the higher transmission costs of an area due to its higher reliability are paid only by users of that area in contrast with the single area method, in which these costs are allocated to all users regardless of their locations. The proposed method was implemented on the IEEE 118 bus test system having three areas. The obtained results show that with the application of multiarea approach, the simulation time is greatly reduced and the transmission costs are also allocated to users with less variation in new nodal prices with respect to the single area approach.

Detection and Classification of Heart Premature Contractions via α-Level Binary Neyman-Pearson Radius Test: A Comparative Study

Abstract: The aim of this study is to introduce a new methodology for isolation of ectopic rhythms of ambulatory electrocardiogram (ECG) holter data via appropriate statistical analyses imposing reasonable computational burden. First, the events of the ECG signal are detected and delineated using a robust wavelet-based algorithm. Then, using Binary Neyman-Pearson Radius test, an appropriate classifier is designed to categorize ventricular complexes into "Normal + Premature Atrial Contraction (PAC)" and "Premature Ventricular Contraction (PVC)" beats. Afterwards, an innovative measure is defined based on wavelet transform of the delineated P-wave namely as P-Wave Strength Factor (PSF) used for the evaluation of the P-wave power. Finally, ventricular contractions pursuing weak P-waves are categorized as PAC complexes; however, those ensuing strong P-waves are specified as normal complexes. The discriminant quality of the PSF-based feature space was evaluated by a modified learning vector quantization (MLVQ) classifier trained with the original QRS complexes and corresponding Discrete Wavelet Transform (DWT) dyadic scale. Also, performance of the proposed Neyman-Pearson Classifier (NPC) is compared with the MLVQ and Support Vector Machine (SVM) classifiers using a common feature space. The processing speed of the proposed algorithm is more than 176,000 samples/sec showing desirable heart arrhythmia classification performance. The performance of the proposed two-lead NPC algorithm is compared with MLVQ and SVM classifiers and the obtained results indicate the validity of the proposed method. To justify the newly defined feature space (σi1, σi2, PSFi), a NPC with the proposed feature space and a MLVQ classification algorithm trained with the original complex and its corresponding DWT as well as RR interval are considered and their performances were compared with each other. An accuracy difference about 0.15% indicates acceptable discriminant quality of the properly selected feature elements. The proposed algorithm was applied to holter data of the DAY general hospital (more than 1,500,000 beats) and the average values of Se = 99.73% and P+ = 99.58% were achieved for sensitivity and positive predictivity, respectively.

Analysis of Electric Field and Polarization of SF6 Circuit Breaker to Approach a Suitable Structure

Abstract: The application of electric field theory to widely different aspects of electrical insulation has led to more understanding the phenomena. Electric fields may be considered as the main reason for insulation failure. The purpose of this paper is to modify importance of analyzing electric field in insulation design. The SF6 circuit breaker is chosen as case study that encounters critical situations during its application. The other phenomena affects insulation is the presence of polar species in a non-polar molecular material locally modifies the polarization energy, thus creating local states (traps) on neighboring molecules. Results of calculations carried out for arrays of spatially connected dipoles indicating that local states of a considerable density may be created, modifying the density- of-states function, and therefore influencing the effective mobility of charge carriers. The main result of polarization during application in circuit breaker is loss of life. In this paper the reduction of negative effects of electric field and polarization by choosing a suitable insulation structure in a 33 kV SF6 circuit breaker according to calculation in critical areas is investigated that can also be studied in other types of circuit breakers.