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Home>Products>Journal and Reviews>I.R.E.E.>Latest issue
International Review of Electrical Engineering - April 2009 - Papers
International Review of Electrical Engineering - Papers
by M. Delshad, H. Farzanehfard Vol. 4. n. 2, pp. 159-167
Abstract - In this paper a new zero voltage switching current-fed push-pull converter with an active clamp circuit is proposed. The active clamp circuit not only absorbs the voltage surge across switches at turn off instance, but also provides soft switching condition for all the semiconductor elements. Implementation of control circuit is very simple since the converter is PWM controlled and the auxiliary switches turn on are complementary with respect to main switches. In this paper the proposed converter operating modes are analyzed and simulation results are presented. To verify the converter operation a 200W laboratory prototype operating at 100 kHz is implemented and the experimental results confirm the theoretical analysis. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Push-pull current-fed converter, Zero voltage switching (ZVS), DC-DC converter, Pulse width modulation (PWM), Active clamp.
Vol. 4. n. 2, pp. 168-173
Abstract - An induction heating appliance used for cooking can include more than one inductor each being controlled by a separate inverter system. The main aim of this paper is to control each coil separately at a different frequency and power output by using same inverter system. This paper describes a new triple half bridge series resonant inverter circuit (THB-SRI) for induction heating appliances with three loads. The proposed topology allows the control of three outputs, simultaneously and independently, up to their rated powers saving component count compared with the three half bridge solution. An exact analysis, operation principle and the design procedure of the proposed system with the proposed control scheme are described. Also, the simulation results are shown as compared with the experimental results for a prototype induction cooking system with three loads. It is shown that the experimental results are very similar to the theoretical predictions. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Induction cooker, Series resonant inverter, Time sharing control.
Vol. 4. n. 2, pp. 174-183
Abstract - In this research, an investigation of the fault modes of the rectifier of the subsynchronous cascade drive is carried out. It is shown that faults in the power electronic converter cause electromagnetic torque pulsations with amplitudes much higher than usual and with frequencies near the natural frequencies of the mechanical subsystem. This type of fault must be immediately detected in order to avoid damages in the mechanical subsystem, something which has also been proven by experience in service. Towards this goal, a novel approach for real-time fault detection and accurate diagnosis is investigated, based on the monitoring of the rotor current space vector angle, in order to extract features which indicate the specific fault modes of operation. The merits of this approach are demonstrated through simulation and experimental results. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Subsynchronous cascade drive, Electromagnetic torque pulsation, Torsional vibration, Condition monitoring, Fault diagnosis.
Vol. 4. n. 2, pp. 184-190
Abstract - A zero-voltage switching (ZVS) isolated converter is presented in this paper. The active clamp circuit is connected in parallel with the primary side of transformer which is not only to absorb the energy of leakage inductor, but also achieve ZVS for all power switches. Moreover, the transformer can be reset and the voltage stresses of secondary diodes are clamped to output voltage automatically. Hence, the proposed converter has reduced switching losses, the voltage stresses on the secondary diodes and transformer size. The operational principles, steady state analyses and design consideration are discussed. Finally, experimental results from a 50W prototype are presented to confirm the effectiveness of the proposed converter. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Zero-voltage switching (ZVS), Active clamp circuit.
Vol. 4. n. 2, pp. 191-198
Abstract - This paper presents a distributed computing approach for piecewise analysis of simultaneous fault in transient stability (T/S) studies of large-scale electrical networks using Diakoptics and large change sensitivity (LCS) concepts. Diakoptics is a general term standing for piecewise solution of large-scale physical systems , while LCS is a kind of sensitivity analysis making it possible to evaluate system responses for arbitrary changes in the values of parameters. The combination of these two concepts will be used here to develop an accurate piecewise method for linear equation solutions. The proposed distributed T/S method is implemented successfully and its performance is studied using a 14 bus IEEE test system. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Transient stability, Distributed computing, Simultaneous fault, Large change sensitivity.
Vol. 4. n. 2, pp. 199-205
Abstract - The unit commitment is one of the most important problems in power system operation. Restructured power system operation is performed as a single area in most countries. In this environment, GENCOs compete in order to contribute in power market. Generation scheduling in a power system considers network security constraints and system’s reliability indices. Hence, economic operation of the network is in the second preference. One of the methods to enhance the reliability of a power system is incorporating the adjacent units through tie-lines. In this paper, security constrained unit commitment problem of interconnected power systems is modeled and the results are evaluated using the IEEE 118-bus network. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Benders decomposition, Interconnected power systems, SCUC.
Vol. 4. n. 2, pp. 206-210
Abstract - This
paper proposes a virtual instrument (VI) for the electric power quality
monitoring - frequency aiming to act in real-time for monitoring and
recording all typical variations imposed on the ideal electrical network
signal delivered in any country belonging to the UCTE Organization; it
is based on IEC standards 61000-4-30 [1] and also on CEI EN 50610 [2].
According to the above mentioned regulations, the proposed VI acquires
line frequency for electrical network in case of home appliances, for
different sampling frequencies due to the A/D converter and DSP board
used, the readings being made at different moments of time decided by
the user. Harmonic analyzer is used in order to get the fundamental
frequency of the electrical network. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Power Frequency, Power Quality, Harmonic Analysis, Virtual Instrument, Expert System, Database, User Interface.
Vol. 4. n. 2, pp. 211-219
Abstract - As the electricity dependence has increased and is still increasing, many major disturbances have taken place in distribution networks. Because most of the disturbances in the overhead network are weather-related, the probable climate change may have its own impact, too, in the future. Thus, a higher reliability of electricity distribution is required. In this paper, a few major disturbances and their societal consequences, mainly in Finland, are presented. Moreover, the present state of preparedness for major disturbances of both Finnish utilities and some critical end users is described. Although the consequences of wide and long-lasting interruptions are realized, the preparation for those events is not always adequate. This paper gives a few proposals for improving the current situation. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Major Disturbance, Blackout, Consequences of Outages, Preparedness for Outages, Recovery Organization.
Vol. 4. n. 2, pp. 220-227
Abstract - This paper presents a spanning tree-based genetic algorithm (st-GA) to solve optimal multistage distribution network planning. According to the topological characteristic of distribution network, it is derived that the target network contains the message of each building stage for every candidate branch and its size. Thus, the multistage distribution network planning can be transformed into a problem of searching the optimal target network with the minimum total costs in the whole planning horizon. Moreover, st-GA with two specialized genetic operators can guarantee the topological feasibility and high heritability of each solution generated and overcome the deficiencies of existing GAs applied for distribution network planning. Finally, the case study is implemented to demonstrate the usefulness and effectiveness of the proposed method. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Distribution network planning, Multistage planning, Target network, Spanning tree, Genetic algorithm.
Vol. 4. n. 2, pp. 228-234
Abstract - This paper suggests the use of synchronous frame harmonic elimination technique in distributed power systems consisting of inverters with nonlinear loads. Inverters of the distributed system are controlled to share the active power. Power sharing is achieved without any communication between the units. To eliminate the harmonics caused by nonlinear loads, synchronous frame controller is used. The technique is explained in detail and simulation results for a system consisting of two inverters are given. The results show that the technique can be successful to eliminate the harmonics caused by nonlinear load while the active power sharing is achieved. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Distributed operation, Harmonic elimination, Load-frequency droop, Synchronous reference frame.
Vol. 4. n. 2, pp. 235-241
Abstract - The practical aspects of constructing an ironless axial flux direct-drive generator for wind applications are presented in this paper. In other words, the design procedure for this 50 kW-generator is discussed in details as well as the construction procedure. This generator provides various advantages which are distinctly discussed in this work. In this structure, both rotor and stator are designed without any ferromagnetic materials. Because of the absence of ferromagnetic materials and gearbox, the total mass of system is less than equivalent designs based on iron-cored magnetic circuits. The genetic algorithm is used to optimize machine structure and to achieve high power density and efficiency. As a result, the constructed 50kW-generator has been found to have a proper volume as well as an appropriate efficiency. Unlike other generator structures, the iron losses are completely omitted in this structure. This issue contributes to achieve high efficiency. In addition, the armature reaction effect is considerably reduced because of the significant decrease in the synchronous reactance. In this structure, like slotless machines, there is no cogging torque. The generator operation is investigated in both simulation and implementation. The validity of this generator structure is demonstrated by great agreement between simulation and implementation results. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Axial Flux Permanent Magnet Synchronous Generator, Finite Element Method, Ironless Generator, Wind Power.
Vol. 4. n. 2, pp. 242-248
Abstract - For determination the number of broken rotor bars in squirrel-cage induction motors when these motors are working, this paper presents a new method based on an intelligent processing of the stator transient starting current. In light load condition, distinguishing between safe and faulty rotors is difficult, because the characteristic frequencies of rotor with broken bars are very close to the fundamental component and their amplitudes are small in comparison. To overcome this problem, an advanced technique based on the wavelet transform and artificial neural network is suggested for processing the starting current of induction motors. In order to increase the efficiency of the proposed method, the results of the wavelet analysis, before applying to the neural networks are processed by Principal Component Analysis (PCA). Then the outcome results are supposed as neural network's training and testing data set. The trained neural networks undertake of determining the number of broken rotor bars. The given statistical results, announce the proposed method’s high ability to determine the number of broken rotor bars. The proposed method is independent from loading conditions of machine and it is useable even when the motor is unloaded. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Broken rotor bars, Fault detection, Wavelet, Principal component analysis (PCA), Neural networks.
Vol. 4. n. 2, pp. 249-259
Abstract - This paper presents an optimal advanced discontinuous pulse width modulation (ADPWM) based direct torque control (DTC) technique for the induction motor drives operating at high line side voltages. Unlike the existing discontinuous pulse width modulation (DPWM) methods the proposed ADPWM method uses a special category sequences which not only reduces the switching losses but also reduces the line current distortion during high speed operations. The known sequences of this category are 0121 and 7212. This category of DPWM sequences are referred as double switching clamping sequences as they switch individual phase twice in every sub cycle. It can be observed that only the zero state is different in these two sequences. In this paper it is shown that utilizing these two double switching DPWM sequences and by changing the zero state at any spatial angle where is between 00 and 600an infinite number of ADPWM methods can be generated which are categorized as “continual clamping” and “split clamping” sequences. Also, the proposed method will be compared both analytically and through simulation. It will be shown that the proposed ADPWM method is most suitable for the drives operating near rated speeds (voltages) as steady state line current distortion at higher line side voltages is reduced significantly compared with the conventional DTC (CDTC), conventional space vector pulse width modulation (CSVPWM) based DTC as well as the existing DPWM based DTC. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Advanced DPWM techniques, Double switching clamping sequences, DPWM, CSVPWM, Continual clamping, Harmonic distortion factor, Split clamping, Switching sequences, Space vector approach.
Vol. 4. n. 2, pp. 260-268
Abstract - A hybrid method for detecting motor bearing fault conditions via discrete wavelet packet decomposition (DWPD) of induction motor current with spectral post processing is presented in this paper. This method involves the decomposition of motor current into equally spaced frequency bands by using an all-pass implementation of elliptic IIR half-band filters in the filter bank structure to obtain wavelet packet coefficients (WPC) in a computationally efficient way. Then, the bias in WPCs for each frequency band is removed to suppress both power system harmonics and leakage from adjacent frequency bands. Finally, Fourier analysis is applied to WPCs to provide higher frequency resolution within each frequency band. The hybrid approach provides better results in early detection of bearing faults. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Motor current signature analysis, Bearing faults, Spectral post processing, Induction motors, Wavelet packet decomposition.
Vol. 4. n. 2, pp. 269-277
Abstract - Interbar currents exist in healthy and faulty squirrel cage induction machines. In previous works, based on winding function approach, the squirrel cage induction machine analysis was carried out excluding interbar currents. This paper presents a multilayer model for inclusion of interbar currents in a coupled electromagnetic model of skewed rotor induction machines. This model has been used to simulate an induction motor with broken rotor bars. For calculation of inductances, considering radial and axial nonuniformity, a variant of modified winding function theory is presented. Simulation results have been verified by three-dimensional magnetic equivalent circuit method and finally with experimental results. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Iinduction machine, Interbar currents, Winding function approach.
by K. Kouzi, M – S. Naϊt-Saϊd, M.Hilairet, E. Berthlot Vol. 4. n. 2, pp. 278-283
Abstract - MRAS-based sensorless vector control induction motor schemes discussed in the literature suffer from pure integration problems, instability problems and sensitivity to parameter variations mismatch at low speed operation. This paper describes the improvement in sensorless vector control of induction motor drive through the use of fuzzy logic in a standard rotor flux Model Reference Adaptive System (MRAS) based estimator. The rotor flux and speed estimator based on a fuzzy mechanism is developed. The error in the instantaneous phase position of the two rotor flux estimates is utilized for rotor speed estimation. The proposed scheme is recommended for applications requiring robust speed control even in presence of some key parameters deviation. Experimental results for a 1.1-kW induction motor are presented and analyzed by using a dSpace system with DS1104 controller board. Digital simulation and experimental results are presented to show the improvement in performance of the proposed method. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Field-oriented control, Induction motor, Speed sensorless control, Fuzzy Logic regulator,. Fuzzy MRAS estimator.
by F. H. Slaoui , S. Georges, P. J. Lagace,Yasser M. Mohanna Vol. 4. n. 2, pp. 284-291
Abstract - Grounding
electrode resistance plays an important role in the design of power
substations and transmission towers. The prediction of this resistance
is very complicated in some situations especially when the soil is
represented by an n-layer horizontal model with different resistivities. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Electrical grounding parameters, n-layer soil, Apparent resistivity, Resistivity measurements interpretation.
Vol. 4. n. 2, pp. 292-295
Abstract - In the context of ultra-low-power and ultra-low-voltage operational transconductance amplifiers (OTAs), there is the inconvenience of low unity-gain frequency and DC gain. In this paper, we presented a 0.5-V improved ultra-low-power OTA using the transistors operate in weak inversion. The proposed topology based on a bulk-driven input differential pair employed an under-weak-inversion gain-stage in the Miller capacitor feedback path to improve the “pole-splitting” effect. Simulations in a standard 0.18 µm CMOS process resulted on considerable enhancement in the unity-gain bandwidth and the DC gain as well. The topology presents rail-to-rail input and output swings and consumes only 1 μW. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Bulk-Driven Differential Pair, Full Swing, Miller Compensation, Operational Transconductance Amplifier (OTA), Right Half-plane Zero Control, Ultra-Low-Voltage, Ultra-Low-Power.
Vol. 4. n. 2, pp. 296-304
Abstract - In this paper, a fully integrated 900-MHz CMOS differential power amplifier (PA) with new power combiner is designed and fabricated in a 0.18- um technology. For the high power CMOS PA design, new transformer network and the number of power stages is fully analyzed and optimized to find inductors dimensions. A parallel combination of the Class AB and the Class C amplifier or multiple gated common source transistors in power stages was used to improve both the linear operating range and the power efficiency simultaneously. The PA delivers an output power of 29 dBm and a power-added efficiency of 24% with a power gain of 20 dB, including the losses of the bond-wires. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Power amplifier, Power combiner, Transformer, Efficiency optimization, Class AB, CMOS process.
Vol. 4. n. 2, pp. 305-311
Abstract - Electro-Mechanical Batteries have important advantages compared with chemical batteries, especially in Low Earth Orbit satellites applications. High speed, slotless, external rotor, halbach array permanent magnet machines are used in these systems as Motor/Generator. Proper material and structure for space applications are introduced; a simplified analytic design method is given for this type of machines and finally, the optimization of machine in order to have maximum efficiency and minimum volume and weight are given in this paper. Particle swarm optimization (PSO) is used as the optimization algorithm and the finite element-based simulations are used to confirm the design and optimization process and show less than 4.3% error in parametric design. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Flywheel, Electromechanical, Battery, Energy storage, Slotless, Halbach, PSO.
Vol. 4. n. 2, pp. 312-319
Abstract - In this paper, a novel architecture of sigma-delta modulator for maximum achievable signal-to-noise ratio, analytical aspects, noise transfer function optimization and its implementation by switched-capacitor circuits using double sampling technique will be presented. Integrator non-idealities and interferer parameters effects on modulator stability and signal-to-noise ratio have been explained elaborately. Designed 3rd order sigma-delta modulator has been implemented by CMOS transistors using 0.18um CMOS technology in ADS environment. 7th order all pole filter cascaded by 3rd order FIR filter has been implemented by digital circuits as a digital low pass filter and signal-to-noise ratio of 84dB for signal band-width of 10MHz corresponding to 14 bits of resolution has been achieved. Simulation results on implemented modulator validate the implemented ADC and its main parameters such as stability and signal-to-noise plus distortion ratio. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Sigma-Delta modulator ADC, Maximum achievable SNR, Switched-capacitor circuits, Double sampling technique.
Vol. 4. n. 2, pp. 320-326
Abstract - In the radar systems, Forward Scattering Radar (FSR) is special mode of bistatic radar which can be used for target detection and classification .This paper analyzed the electromagnetic signal scattered from the target crossing the FSR system. The aim of the analysis was to extract the Doppler signal of the target, under the presence of high ground clutter and noise interference. This paper is dedicated to the detection of ground target. Two signal processing methods, namely Hilbert Transform and Wavelet Technique, were used for target detection. The results in this study showed that the detection using Hilbert Transform was only applicable for some conditions and it was used to confirm the wavelet efficiency in the detection process. Similarly, it was also found that the detection using Wavelet Technique became more robust to higher clutter and noise level. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Forward Scattering Radar, Hilbert Transform, Wavelet De-noise.
Vol. 4. n. 2, pp. 327-334
Abstract - In signal processing, signal acquisition and reconstruction is based on the principle of Nyquist theory. However, an emerging theory known as, “compressed sensing” or “compressive sampling”, tends to show that the conventional wisdom might not be totally accurate. It shows that if a signal has a sparse representation in some basis, then it is possible to capture the signal information via a small number of projections. Furthermore, the signal can be accurately reconstructed using low complexity algorithms. Although the information encoding process may be agnostic to the signal type – random projections can capture the information with high probability – accurate reconstruction of the signal often depends on proper selection of a reconstruction basis. In this paper, we evaluate techniques for measuring sparseness, including some not traditionally used in signal processing such as the Gini Index, and apply them to compressive sampling with the goal of selecting the best basis for signal reconstruction, in the presence and absence of noise. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Compressive sampling, compressed sensing, wavelet transform, discrete cosine transform, sparseness.
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