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International Review of
Electrical Engineering
(IREE)
December 2013
(Vol. 8 N. 6)




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    Soft-Switching Buck PFC Converter for a High-Efficiency AC-DC LED Driver

    by Jae-Won Yang, Hyun-Lark Do

     

    Abstract - In this paper, a soft-switching buck power-factor-correction (PFC) converter for a high-efficiency AC-DC light-emitting-diode (LED) driver is proposed. By replacing a freewheeling diode with a self-driven synchronous rectifier (SR), efficiency improvement is achieved due to the reduced conduction loss on the SR. In addition, there is no switching loss on switching devices because zero-voltage-switching (ZVS) operations of both switches are easily performed. Since the SR is self-driven without an additional control circuit, the proposed converter has competitive price. In order to verify efficiency improvement of the proposed converter, it is compared with a conventional critical-conduction-mode (CRM) buck PFC converter. The efficiency of the proposed converter is measured maximum 95.61% at 170 [vac] and improved maximum 0.23% at 240 [vac]. For verifying soft-switching and efficiency improvement of the proposed converter, theoretical analysis, design consideration, and experimental results from a 48-[V] and 1.4-[A] prototype for a high-efficiency LED driver are presented.

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    Keywords: Buck Converter, Power-Factor-Correction (PFC), Zero-Voltage-Switching (ZVS), Synchronous Rectifier, LED Driver.

     

    A Bridgeless SEPIC PFC Rectifier with Reduced Conduction Losses

    by Jae-Won Yang, Hyun-Lark Do

     

    Abstract - A bridgeless single-ended primary inductor converter (SEPIC) power factor correction (PFC) rectifier is introduced in this paper. In order to maximize its efficiency more than a conventional bridgeless SEPIC PFC Rectifier, a new driving scheme is proposed. In the proposed converter, conduction losses are reduced by eliminating bridge diodes. In addition, the impedance of the return current paths is lowered and conduction losses are reduced by applying a gate-on signal which is maintained during half line cycle to inactive switches. Consequently, the conduction losses of the proposed converter are significantly reduced and high efficiency is achieved. Besides high efficiency, the proposed converter provides high power factor (PF) and a continuous input current. Input current ripple can be easily removed by a simple filter capacitor. The operational principles, steady-state analysis and design equations of the proposed converter are described in detail. Experimental results from a 130 W prototype at a constant switching frequency of 100 kHz are presented to verify the performance of the proposed converter.

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    Keywords: Bridgeless Converter, Power-Factor-Correction (PFC), SEPIC, Conduction Losses.

     

    A Novel High-Efficiency High-Power-Factor Single-Stage Converter for Small-Scale Wind Power Generation System

    by Yi-Hung Liao, Yi-Jyhn Cheng, Li-Ching Yang

     

    Abstract - In this paper, a novel single-stage ac/dc converter for small-scale wind power generation system is proposed. The power factor correction of line currents for wind power is achieved so as to reduce the harmonic currents and decrease the wind turbine noise. The proposed converter has both zero-voltage switch in the primary-side switches and zero-current transition in the secondary-side diodes. Compared with a traditional two-stage converter, high efficiency and high set-up voltage ratio are also accomplished in the proposed single-stage three-phase converter. In addition, based on the proposed wind converter, only the MPPT control algorithm needs to be considered to achieve both power factor correction and MPPT functions. Finally, a prototype system is constructed by utilizing the controller DSP 28335. The simulation and experimental results verified the validity of the proposed converter.

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    Keywords: Single-Stage Ac/Dc Converter, Power Factor Correction, Zero-Voltage Switch, Zero-Current Transition, High Set-Up Voltage Ratio.

     

    Trapezoidal PWM with Direct Modulation Technique (TPWM-DM) Using a Low Cost Microcontroller with High Signal Quality for Power Inverters

    by P. J. Sotorrío-Ruiz, F. J. Sánchez-Pacheco, F. Pérez-Hidalgo, J. R. Heredia-Larrubia

     

    Abstract - This paper presents a high signal quality PWM modulation technique for power inverters that can be implemented by means of a low cost microcontroller. The proposed modulation technique is a mixture between generated and calculated techniques that allows the voltage and frequency of the output signal to be modified on line within a broad margin. Moreover, the quality of the signals generated exceeds that of already existing modulation techniques; hence, better performance is achieved in the system as a whole, reducing the size of the filters at the inverter output which represents an important cost reduction. Additionally, the implementation by means of a low cost microcontroller helps to reduce the cost of the final application.

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    Keywords: PWM, TPWM-DM, Inverter, Microcontroller.

     

    A Review on Power Quality Enhanced Converter of Permanent Magnet Synchronous Wind Generator

    by Navdeep Singh, Vineeta Agrawal

     

    Abstract - The extraction of wind energy has been essential to fulfill the load demand which is not supplied by conventional sources at the end of 2012. In India, total capacity of wind power is very high, approximately 102,788 MW, in comparison to installed capacity. This paper reviews different permanent magnet synchronous generator (PMSG) operated in wind energy systems. A complete survey has been made towards the new contributions for harmonic compensation and new efficient topologies in the last five years to improve the efficiency, reliability and cost of the wind energy system. Different power electronic converters, which are connected between generator and the load/ grid, have been investigated on based on harmonic compensation, efficient working, and high power rating conversion. The wind generation system is still a challenge to extract smooth power from wind. To improve the power quality of the system such as islanding problem and power variation, different renewable storage systems are discussed and compared. Finally, discussion about the different controller is presented to fulfill the load or grid requirement.

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    Keywords: Energy Storage System, Generator, Power Electronics Converter, Power Quality Improvement Controller, Wind Energy System .

     

    A New Boost DC-DC Converter Exhibiting Low Stresses and High Efficiency

    by Aurel Cireşan, Daniel Drăghici, Mircea Gurbină, Dan Lascu

     

    Abstract - The paper proposes a new boost-type switching dc-dc converter. Compared to the classical boost topology it exhibits lower semiconductor voltage stresses and the same current stresses at the cost of only three components: one diode, a capacitor and an inductor. Its operation is similar to that of the hard-switched pulse width modulated converters, except for the fact that the first topological state includes also a resonant interval. Continuous conduction mode operation is analyzed in detail focusing on dc conversion parameters and design equations. The theoretical results were first verified through computer simulations and finally the experiments accurately confirmed the feasibility of the new proposed topology.

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    Keywords: Boost Converter, Efficiency, Resonant Stage, Static Conversion Ratio, Zero Current Switching.

     

    Inverter with Passive/Active Regenerative Snubbers

    by P. Radika

     

    Abstract - An inverter with passive and active regenerative snubbers is presented in this paper. A single phase full bridge inverter with passive regenerative snubber uses a diode and capacitor for each main switch to provide low dv/dt, low switching stresses and to achieve zero voltage switching (ZVS) turn-off. A snubber inductor is used to obtain low di/dt and zero current switching (ZCS) turn-on for the switches. Further, the energy recovery circuit which uses a resonant inductor and a diode to recover the snubber capacitor stored energy into the input side. In addition, a high frequency inverter (HFI) with active regenerative snubber reduces the voltage spike across the main switches of the transformer and at the same time recovers the snubber energy into the output side. The obtained simulation and experimental results are discussed.

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    Keywords: Inverter, Passive Snubber, Active Snubber, Regenerative Snubber, Snubber Capacitor, High Frequency Inverter, High Frequency Transformer, Leakage Inductance, Spike Suppression.

     

    Modeling, Design and Simulation of Multilevel Inverter Based Active Power Filter

    by Madhukar M. Waware, Pramod Agarwal

     

    Abstract - This paper presents mathematical modeling, design and simulation of a three-phase MLI based APF for compensation of current harmonics present in a high voltage system. A PI controller is designed to control DC link voltage. Complete design methodology for the selection of power and control circuit parameters is developed. The simulation results show that MLI based APF eliminates harmonics in high voltage system.

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    Keywords: Active Power Filter, Multilevel Inverter.

     

    Model of Double-Star IPM Machines with General Mutual Inductance Relationships between the Two Three-Phase Winding Sets

    by S. Kallio, M. Andriollo, J. Karttunen, P. Peltoniemi, P. Silventoinen

     

    Abstract - This paper proposes a decoupled d–q model of double-star interior permanent magnet (IPM) machines, whose stator consists of two three-phase winding sets displaced by an arbitrary angle. The model is based on the elaboration of the inductance parameters and is obtained by deriving a transformation that diagonalizes the original 6 × 6 stator inductance matrix of the machine. In the derivation of the transformation, the common assumption of the regularity of the mutual inductances between the two three-phase sets is omitted. Thus, the transformation diagonalizes the stator inductance matrix even if the mutual inductances do not have specific symmetry. It is demonstrated that in order to obtain decoupled reference frames in such a case, the transformation depends on the machine parameters. The validity of the machine model is verified by experimental tests with a double-star IPM machine, in which the two three-phase winding sets are displaced by 30 electrical degrees.

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    Keywords: Double-Star, Interior-Permanent-Magnet (IPM) Machine, Modelling, Mutual Inductances.

     

    Permanent Magnet Synchronous Generator Design Solution for Large Direct-Drive Wind Turbines

    by Y. Alexandrova, R. S. Semken, J. Pyrhönen

     

    Abstract - Turbine power generation in the range of 8-12 MW and beyond will be needed to accelerate the global growth of wind energy production and meet renewable energy targets. Described here is a theoretical framework for a compact, high-power, direct-drive permanent magnet synchronous generator (DD PMSG) that uses direct liquid cooling (LC) of the stator windings to efficiently manage generator cooling, and therefore the temperature of the windings and permanent magnets. Direct liquid cooling enables a significantly lighter weight generator, and this lower mass design promises reliable and efficient power generation at substantially lower cost. It is clear that much improved cooling will become a necessity for DD-PMSGs targeting wind turbine applications as power ratings continue to grow. Discussed first here is the analysis of air gap tangential stress and its effect on generator torque density and efficiency. Major LC DD-PMSG design issues are presented along with a suggested integrated design solution in the form of an 8 MW example. Next, a fabricated, instrumented, and tested cooling loop is described. This prototype features a pair of typical LC tooth coils embedded in a lamination stack attached to a forced recirculation liquid cooling loop. Finally, operating characteristics are evaluated for a large wind turbine equipped with the proposed 8 MW LC DD-PMSG revealing annual energy output and load factor calculated for typical North Sea wind conditions. Ultimately, the higher partial load efficiency inherent in the LC DD PMSG design results in more efficient total electricity production.

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    Keywords: Directly Cooled Winding, Permanent Magnet, Synchronous Generator, Wind Turbine.

     

    The Process of Self Excitation in Dual Three-Phase Induction Generator

    by Marwa Ben Slimene, Med Arbi Khlifi, Mouldi Benfredj, Habib Rehaoulia

     

    Abstract - In this paper the phenomenon of self excitation in dual three-phase induction generator (DTPIG) is examined and a physical interpretation of how self excitation occurs is presented. The proposed steady-state model of a dual three phase self-excited induction generator for stand-alone renewable generation dispenses with the segregating real and imaginary components of the complex impedance of the induction generator. Steady state performances and characteristics of different configurations are clearly examined and compared. The analytical results are found to be in good agreement with experimental results.

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    Keywords: Dual Three-Phase Induction Generator, Self-Excited DTPIG, Steady-State Analysis, Experimental Validation.

     

    Performance of High-Power, High-Speed Induction Motor with Slitted-Rotor

    by Sarika Kalra, Vineeta Agarwal

     

    Abstract - An attempt has been made to analyze the methods to improve the electromagnetic properties of a solid-rotor induction motor. The slip of the solid rotor is reduced notably if the solid rotor is axially slitted. The slitting patterns of the solid rotor are examined. It is shown how the slitting parameters affect the produced torque. Finite element analysis is used to numerically analyze the effect of axial slitted rotor on the electromagnetic performance characteristics of a 180 kW, 170 Hz 3-phase induction motor. The paper considered the effect of variation of slit depth, variation of no of rotor slits and the variation of air gap length on the performance of 3-phase induction motor using Flux-2D Maxwell software package from ANSYS. It is found that larger and deeper slit of the rotor with minimum valve of air gap gives the better and higher operating torque. It is also found that deeper slit gives the higher efficiency of the slitted rotor, high speed induction motor.

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    Keywords: Slit, Operating Torque, Air Gap, Induction Motor.

     

    Finite Element Observer for Induction Machine in Electric Vehicle Power Train

    by Mohamed Radhouan Hachicha, Moez Ghariani, Rafik Neji

     

    Abstract - Sensorless control allows lower cost and higher reliability of the induction machine "IM" drives. The performance of an IM drive remains dependent on the rapidity and the accuracy of the submitted parameters values. In electric vehicle "EV" applications, the IM parameters may widely vary owing to the external disturbances and the snippy control variations. Some solutions are already available, such as intelligent controllers, but they still need to improve their reactivity and their accuracy level. Nowadays, the finite element methods provide very accurate information on electrical machines. In this paper an IM finite element model "IMFEM" is developed using the finite element method magnetics numerical tool "FEMM" to identify the IM parameters. Practice tests are carried out and results are compared to those obtained from simulation. The IMFEM is then integrated in a complete EV power train model using an IM observer. Trials are performed and results are compared with those obtained by the EV power train model using an IM constant parameters controller.

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    Keywords: Finite Element Method, Induction Motor, Electric Vehicle, Power Train, Parameters Identification.

     

    Modeling Electric Vehicle Charging Flexibility for the Maintaining of Power Balance

    by A. Alahäivälä, E. Saarijärvi, M. Lehtonen

     

    Abstract - Maintaining the power balance between electricity consumption and generation might become more challenging in the near future due to intermittent electricity generation. The decrease in flexibility on the generation side may at least to some extent be compensated by managing demand. Therefore, this paper concentrates on modeling the flexibility electric vehicles (EVs) are able to offer to the maintaining of power balance over a typical weekday. The modeling rests on real mobility behavior data utilized in the dynamic simulations of an EV fleet. Of particular interest are the hourly powers and energies available when a portion of the EV battery capacity is reserved for the maintaining of the balance. Employing the estimated flexibility, EV contribution to the power system frequency control and hourly regulation is analyzed in the Finnish power system. The results indicate that EVs are able to contribute to the maintaining of power balance, but this depends greatly on the reserved energy content of the batteries.

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    Keywords: Electric Vehicle, Demand Response, Frequency Control, Regulation Market.

     

    On the Choice of Three-to-Four-Phase Transformers for Four-Phase Power Transmission

    by Davide Lauria, Giovanni Mazzanti, Stefano Quaia

     

    Abstract - Four-phase transmission systems, which have been deeply investigated in several recent papers, are recognized as a possible alternative to traditional three-phase transmission lines. However, the problem of the phase transformation between the three-phase and the four-phase section, which is not a new theme in the relevant literature, exhibits some troubles especially in the choice of the most convenient typology of the needed special transformers. First of all the paper examines the underlying principles of the old Parton’s theory of phase transformation. Second, according to this theory new potential solutions are derived and investigated. Hence the (double) Scott connection which, in any case, continues to be familiar to most electrical engineers, is examined and framed in the theory of phase transformation. In the last section, all the examined solutions are compared resorting to different aspects and parameters connected with the wiring connections.

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    Keywords: Power Transmission, Three-To-Four Phase Transformation, Special Power Transformers.

     

    Innovative Magnetic Field Calculation from Multiple-Circuit Twisted Three-Phase Lines

    by Giovanni Mazzanti, Effrosyni Kandia, Marco Landini

     

    Abstract - Multiple-circuit twisted three-phase cable lines are typically used for connecting renewable resources (e.g. photovoltaic and wind power) to the power grid. The magnetic field generated by such lines should be evaluated carefully whenever connecting such renewables to the network. This paper examines for the first time the calculation of the magnetic field generated by such lines. In the framework of a worst-case approach, the paper extends to multiple-circuit twisted three-phase cables both the exact treatment derived from the literature about single-circuits and a simple innovative formula developed for single and double circuits by the authors, that resulted a good approximation of the rigorous analytical treatment and much more accurate than an approximated formula found in literature. The paper shows that the “worst case” approach yields an approximate yet conservative expression for the total magnetic field generated by multiple twisted three-phase power cables, whose effectiveness is further enhanced by the use of the simple innovative formula, as proved by case-studies examined here for triple-circuit twisted three-phase cables in various configurations.

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    Keywords: Heuristic Algorithms, Magnetic Fields, Power Distribution Lines.

     

    Demand Response Pricing Strategies for Islanded Microgrids

    by E. Riva Sanseverino, G. Zizzo, L. Dam Khanh

     

    Abstract - In this paper, Time of Use and Critical Peak Pricing policies are designed and their effects on optimized operation is evaluated. For this purpose, an optimal operation algorithm is employed and the relevant production costs are derived. As far as the Time of Use policy is concerned, such costs are observed to be different in two time intervals of the day, due to the loads changing effect and the production of renewable energy. Whereas in the Critical Peak Pricing Policy, a peak time interval is identified to set up different pricing rates. The optimization algorithm used to carry out the work described above minimizes the microgrid’s energy losses, the production costs and the Green House Gas emissions and controls the power exchange with the main distribution grid. Loads control is indeed also another control variable that may help to get these objectives through active demand.

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    Keywords: Microgrids, Demand Response, Time of Use, Critical Peak Pricing .

     

    Novel Wavelet Transform based Islanding Detection Algorithms

    by H. Laaksonen

     

    Abstract - In this paper two novel discrete wavelet transform based islanding detection algorithms for distributed generation units are presented. One of the proposed algorithms is based on the use of all phase-to-phase voltages and the other on use of negative sequence voltage. Both new methods are able to detect islanding very fast and selectively near perfect power balance situations also with relatively low sampling frequencies. In addition, the proposed algorithms are applicable to both directly and converter connected distributed generation units. One main benefit of the developed wavelet based islanding detection methods is also related to their determination and calculation which enables the choosing of appropriate setting thresholds. Simulation results show that islanding detection operate times are a bit shorter with the proposed method using negative sequence voltage than with the method using phase-to-phase voltages when same timer time delays are applied.

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    Keywords: Distributed Generation, Islanding Detection, Loss-of-Mains Protection, Anti-Islanding, Islanding, Wavelet Transform, Smart Grids.

     

    Optimal DG Placement and Sizing in Radial Distribution Systems Using NSGA-II for Power Loss Minimization and Voltage Stability Enhancement

    by R. D. Mohammedi, A. Hellal, S. Arif, M. Mosbah

     

    Abstract - The present paper describes a multi-objective optimization approach to determine the optimal placement and sizing of Distributed Generation (DG) units in radial distribution systems. The main objectives are to minimize the active power loss and to enhance the voltage stability. Non-dominated Sorting Genetic Algorithms II (NSGA-II) is used to obtain the set of Pareto optimal solutions, which form a numerous set of non-dominated solutions and will be employed by the Decision Maker (power system operator) to select the best compromise solution. A detailed performance analysis is applied on 12, 33, 69 and 85 bus systems to illustrate the effectiveness of the proposed method.

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    Keywords: Distributed Generation, Non-Dominated Sorting Genetic Algorithm-II (NSGA-II), Multi-Objective, Power Losses, Voltage Stability, Stability Index, Radial Distribution Systems.

     

    Joint Optimization between Power Sources and Transmission Expansion Planning Considering Integration of Large Scale Wind Power

    by Jian-ping Zhang, Hao-zhong Cheng, Zhen-dong Wan, Liang-zhong Yao

     

    Abstract - Renewable energy sources such as wind power have been rapidly developed worldwide. However, due to the intermittence of wind power, the large scale exploitation and grid integration of wind power have imposed many challenges in planning of both power sources and transmission expansion. To maximize the penetration of wind power in the transmission system, it not only needs to have enough transmission capacity which can be achieved from the transmission expansion, but also optimal power source configuration. Therefore, there is a requirement for joint optimization method that can achieve simultaneously both optimal power source configuration with peak regulation capacity and optimal transmission planning, in order to reduce the total cost for the integration of large wind power. In this context, this paper mainly focuses on the development of optimization method with joint considering both power source configuration and transmission expansion requirement. A complicated nonlinear mixed integer planning model is proposed for this problem and Benders Decomposition technique together with QPSO algorithm is used to solve this model. The proposed method and model are applied to both a modified IEEE 39-bus test system and an actual power system in China. The results show that the method and model are correct and effective.

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    Keywords: Wind Power, Power Sources, Transmission Expansion Planning, Joint Planning, Non-Linear Mixed Integer Planning Model, Benders Decomposition, QPSO Algorithm.

     

    A Novel Fault Section Location Method Based on Energy Spectrum Entropy of EMD and Fuzzy C-Means Algorithm for Small Current to Ground System

    by Wang Xiaowei, Zhang Tao, Tian Shu

     

    Abstract - A fault location method of small current to ground system is proposed in this essay. First, the IMF component is obtained through the EMD of the transient zero-mode current at each detection device or FTU when fault occurs. Second, the definition of EMD energy spectrum entropy is put forward to measure the distribution of signal energy in the scale domain, based on which the energy spectrum entropy factor value reflecting the highest frequency IMF component is obtained. Third, FCM algorithm is adopted to cluster analyze the first IMF component spectrum entropy factor from the two feature matrixes of local and global variables. Finally, the fault section is accurately judged through the evaluation of the fuzzy membership degree matrix. In addition, the analysis of global variable clustering center matrix can show the slight differences between the IMF1 power spectrum entropy factor value of health section and that of fault section. A good many simulation calculations show that, this method can accurately and reliably judge fault sections at any time under any grounding resistance value whether it is in the neutral point ungrounded system or arc suppression coil grounded system.

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    Keywords: Empirical Mode Decomposition, Fuzzy C-Means Algorithm, Energy Spectrum Entropy Factor, Variable Matrix, Fault Location.

     

    Stochastic Characteristics of Load Profiling in Distribution Systems based on AMR measurements

    by M. Z. Degefa, M. Lehtonen

     

    Abstract - In order to enable the key applications provided by smart grid, a dynamic distribution system state estimator has to function properly giving the real time knowledge of a distribution network load profiles. However, due to unavailability of enough measurements and lagging communication of the measured data, the current system cannot readily access measurements in real time. Therefore a practical load modeling technique has to be applied to provide real time distribution system load profile estimates with the respective confidence intervals. Nevertheless, modeling individual customer loads is far statistically complicated and computationally prohibitive for real time application. The customer loads are not always normally distributed but rather a combination of normal distribution, lognormal distribution, generalized pareto and many others. In this study, models of primary heating type load classes are used to represent individual customers. A statistical formulation based on clustered customer groups’ hourly consumption model is used to calculate aggregated substation loads and day ahead load forecasts with the respective confidence intervals. The stochasticity of customer loads when aggregated at distribution substation is investigated for four customer type load classes.

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    Keywords: Confidence Interval, Correlation, Load Profiling, AMR, Normal Distribution, Load Modeling, Distribution State Estimation.

     

    Particle Swarm Optimization Technique for the Coordination of Optimal Wind and Thermal Generation Dispatch

    by K. Dhayalini, S. Sathiyamoorthy, C. Christober Asir Rajan

     

    Abstract - This paper discusses a Particle Swarm Optimization Technique to obtain optimal wind and thermal generation dispatch. As wind power penetrations increase in current power systems, its impact to conventional thermal unit should be investigated due to the intermittency and unpredictability of wind power generation. Development of better wind thermal coordination economic dispatch is necessary to determine the optimal dispatch scheme that can integrate wind power reliably and efficiently. In this paper Particle Swarm Optimization (PSO) is utilized to coordinate the wind and thermal generation dispatch and to minimize the total production cost in the economic dispatch considering wind power generation and valve effect of thermal units. To demonstrate the effectiveness of the proposed approach, the numerical studies have been performed for three different test systems, i.e., six, thirteen and forty generating unit systems, respectively. Different simulations with and without wind power production are simulated. Simulation result shows the performance of the proposed approach reveal the efficiency of wind power generation in reducing total fuel cost.

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    Keywords: Particle Swarm Optimization, Wind – Thermal Coordination Dispatch, Valve Point Effect.

     

    Determination of Dynamic Available Transfer Capability Using Potential Energy Boundary Surface based Transient Energy Function

    by A. Srinivasan, P. Venkatesh, B. Dineshkumar, N. Ramkumar

     

    Abstract - This paper proposes the application of potential energy boundary surface (PEBS) based transient energy function (TEF) method to evaluate fast and dynamically secured real time available transfer capability (DATC ) for the effective power transactions in the deregulated electricity market. With the involvement of various power transactions in this electricity market at the same time, the system may subject to severe disturbances. Transient stability analysis is a valuable tool for the system operator to maintain the system operating conditions under severe disturbances. In this paper, PEBS method of transient energy function is used to avoid the computational complexities in the transient stability analysis for the highly stressed power systems. The proposed method involves in assessing maximum Dynamic ATC at the critical point of energy margin. The prescreening of line outages using energy margin values is also carried out to reduce the computational burden in determining DATC. The proposed approach has been analyzed and tested on WSCC 3-machine 9-bus system and New England 10-machine 39-bus system.

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    Keywords: Available Transfer Capability, Deregulated Electricity Market, Energy Margin, Potential Energy Boundary Surface, Transient Energy Function.

     

    Distributed Generation Optimal Placement and Sizing to Enhance Power Distribution Network Performance Using MTLBO

    by Manas Ranjan Nayak, Chinmay Kumar Nayak

     

    Abstract - Integrating distributed generation (DG) into an electric radial distribution system has an overall positive impact on the system. The power injections from renewable DG units located close to the load centers provide an opportunity for system power loss reduction, cost reduction, voltage profile improvement, voltage stability improvement, environmental friendliness, postponement system upgrading and increasing reliability. This impact can be enhanced via optimal DG placement and sizing. The optimal DG placement and sizing problem is formulated as a mixed integer nonlinear optimization problem subject to highly nonlinear equality and inequality constraints. Evolutionary methods are used to solve this problem because of their independence from type of the objective function and constraints. In this paper, a Modified Teaching Learning Based Optimization Algorithm (MTLBO) for placement and sizing of multi-DGs in a radial distribution system is proposed. The objective function is considered to minimize the network active power losses, to improve the voltage profile and to improve the voltage stability index within the frame work of system operation and security constraints. A detailed performance analysis is carried out on 33 and 69 bus radial distribution system to demonstrate the effectiveness of the proposed methodology. Besides this, it has also been carried out a comparison using several results available in other published articles.

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    Keywords: Distributed Generation (DG), Radial Distribution System (RDS), Modified Teaching Learning Based Optimization Algorithm (MTLBO), Active Power Loss, Voltage Deviation, Voltage Stability Index.

     

    Conducted EMI Propagation Paths in DC-AC Hard Switching Converter

    by Piotr Musznicki

     

    Abstract - In order to limit the electromagnetic interference (EMI) in power electronics devices, knowledge about the phenomena connected with EMI generation and propagation is necessary. This papers describes the propagation paths in the 3 phase voltage source inverter using wide-band simulation and laboratory test with the signal processing method Wiener filtering, where the transfer functions between voltage across switches and the perturbation are measured for different inverter states. Definition of the voltage source inverter switching states is presented for more accurate EMI analysis.

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    Keywords: DC-AC Power Conversion, Propagation, Wiener Filtering.

     

    The High-Temperature Effect on the Breakdown Voltage of an Air-Gap at Atmospheric Pressure with Reference to Paschen Curve

    by Mohamed F. Abdel-Fattah, Matti Lehtonen

     

    Abstract - The breakdown voltage of an air-gap was determined as a function of gap pressure-spacing product as given by Paschen curve at 20 °C. This was followed by experimental research on the effect of temperature on the breakdown voltage. In this paper, a family of Paschen curves is calculated as a function of the temperature and gap-spacing. A comparison between the corresponding calculated Paschen curves and the recorded test data is then made. The results validate the theory presented and confirm its limitations at higher temperatures.

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    Keywords: Air Gaps, Dielectric Breakdown, Electric Breakdown, Spark Gaps.

     

    Analysis of Partial Discharge Characteristics of Olive and Castor Oil as Dielectric Medium for HV Applications

    by S. Banumathi, S. Chandrasekar

     

    Abstract - Mineral oils are preferred liquid insulating medium for high voltage power apparatus applications for a long period. However, the search for alternate insulating oil comes in mind of researchers because the mineral oil is non-biodegradable, toxic in nature and non-renewable. Recent times, many research works are being carried out to replace mineral oil with suitable vegetable oil. Partial discharge characteristics play a vital role in determining the long term electrical insulation strength of liquid dielectric medium. However, reports on partial discharge characteristics of vegetable oils, such as extra virgin olive oil and castor oil are scanty. To confirm the suitability of extra virgin olive oil and castor oil as a high voltage insulating medium, it is important to carry out in-depth analysis about their partial discharge activity and characteristics. In this paper, partial discharge tests were performed on extra virgin olive oil and castor oil at different electrode configurations as per IEC test procedures. Partial discharges such as corona discharge and surface discharge activities were simulated in the laboratory experimental setup and the results were compared with the conventionally used mineral oil. Partial discharge inception voltage and phase resolved partial discharge (PRPD) pattern of olive oil and castor oil were evaluated and compared with the mineral oil. Time/frequency map and repetition rate analysis of PD signals were performed. PD source identification was carried out using fuzzy inference engine. Results show that olive oil and castor oil has better PD characteristics than mineral oil and it could be used as an alternate for mineral oils for high voltage insulation applications.

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    Keywords: Partial Discharge, Vegetable Oil, Transformer, Mineral Oil, Insulation Strength.

     







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