Emerald | COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering | Table of Contents http://www.emeraldinsight.com/0332-1649.htm Table of contents from the most recently published issue of COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering Journal en-gb Tue, 26 Aug 2014 00:00:00 +0100 2013 Emerald Group Publishing Limited editorial@emeraldinsight.com support@emeraldinsight.com 60 Emerald | COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering | Table of Contents http://www.emeraldinsight.com/common_assets/img/covers_journal/compelcover.gif http://www.emeraldinsight.com/0332-1649.htm 120 157 Special Issue on Electric Machines and Systems: Design, Analysis, and Control http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115908&show=abstract <strong>Abstract</strong><br /><br />Not available. Article literatinetwork@emeraldinsight.com (Ahmed Masmoudi) Tue, 26 Aug 2014 00:00:00 +0100 Torque ripple and magnetic forces on teeth in IPM machines http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115913&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The purpose of this paper is to investigate torque ripple and magnetic force on the teeth in interior permanent magnet machines over a wide range of speed operation for electrical power steering applications.<B>Design/methodology/approach</B> - The flux-weakening capability of interior permanent magnet machines has been analysed by finite element method considering the effect of cross-coupling between d- and q-axis current. The traditional method of analysing torque ripple is based on constant torque and flux-weakening region. However, the cross-coupling need to be considered when applying this technique to flux-weakening region. Meanwhile, the torque ripple with current amplitude and angle and with different speed in the flux-weakening region is also investigated. In addition, the magnetic force on the teeth due to the separated teeth with stator yoke is also investigated during the constant torque and flux-weakening region.<B>Findings</B> - The torque ripple and magnetic force on teeth in IPM machine are dependent on current and current angle. Both the lowest torque ripple and magnetic force on teeth exist over the whole torque-speed region. <B>Research limitations/implications</B> - The purely sinusoidal currents are applied in this analysis and the effects of harmonics in the current on torque ripple and magnetic force on teeth are not considered in this application. The 12-slot/10-pole IPM machine has been employed in this analysis, but this work can be continued to investigate different slot/pole number combinations.<B>Originality/value</B> - This paper has analysed the torque ripple and magnetic force on the teeth in IPM machines for EPS application over a wide range of operation speed, which are the main cause of vibration and acoustic noise. The variation of torque ripple with current amplitude and angle as well as speed in the flux-weakening region is also investigated. In addition, the magnetic force on the teeth is also investigated over the whole torque-speed region. Article literatinetwork@emeraldinsight.com (Kai Wang, Zi-Qiang Zhu, G Ombach, W Chlebosz) Tue, 26 Aug 2014 00:00:00 +0100 On the investigation of the magnetic forces of CWPMM: comparison between surface and interior PM topologies http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116122&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The paper is aimed at the investigation of the magnetic forces generated by a 12 slot/10 pole concentrated winding PM machines, considering a comparative study between two topologies: (i) a surface mounted PM machine and (ii) an interior PM machine.<B>Design/methodology/approach</B> - Following a description of the main characteristics of the concentrated winding permanent magnet machines (CWPMMs) under comparison, an investigation of the magnetic forces developed by both machines under study is carried out using finite element analysis (FEA).<B>Findings</B> - A 2D FEA-based investigation has highlighted that the surface-mounted PM machine develops higher magnetic forces than the interior PM one. However, and following a 3D FEA, it has been found that the distribution of the magnetic forces along the air gap of the surface-mounted PM machine is almost homogenous while it is concentrated in two opposite positions in the air gap of the interior PM machine.<B>Research limitations/implications</B> - This work has treated almost all features of the machines under comparison, except the power losses. These should be investigated with emphasis on the PM eddy current losses is so far as the harmonic content of the armature air gap MMF is high.<B>Practical implications</B> - The list of the selection criteria of concentrated winding permanent magnet machines should be extended to the magnetic force cancellation in order to fulfill the requirements of many applications such as the automotive ones.<B>Originality/value</B> - The paper proposes a combined electromagnetic-mechanical approach to investigate the magnetic forces generated by concentrated winding permanent magnet machines using 2D and 3D FEA. Article literatinetwork@emeraldinsight.com (Imen Abdennadher, Ahmed Masmoudi) Tue, 26 Aug 2014 00:00:00 +0100 Torque Ripple Analysis for IPM AC Motors http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115912&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper is to investigate a new cause of torque ripple in interior permanent magnet (IPM) alternating current (AC) motors, which is common but has hardly been studied. The paper also proposes a new method to suppress the total torque ripple.<B>Design/methodology/approach</B> - Besides the well-known cogging torque and mutual torque ripple, a new ripple which exists in the reluctance torque is found. It is verified with both analytical model and finite element analysis (FEA). Also, a novel method is proposed to reduce the reluctance torque ripple, with experimental validation.<B>Findings</B> - It is usually said that the winding inductances of an IPM AC motor vary sinusoidally with the rotor position, thus, the d-axis and q-axis inductances are constant, whilst the reluctance torque is smooth. However, in most practical motors, the inductances vary irregularly, causing a significant ripple in the reluctance torque. Moreover, in machine design, it is always desirable to suppress the cogging torque as much as possible. However, in this paper, it is proved that the cogging torque can remain and be used to cancel the reluctance torque ripple.<B>Originality/value</B> - Torque ripple in the IPM AC motors is usually reduced by suppressing the cogging torque and making both back electromotive forces (EMFs) and currents sinusoidal. However, this paper reveals the new cause of the torque ripple due to the irregular variation of winding inductances. Moreover, the paper gives a new method to cancel the reluctance torque ripple with the cogging torque. Article literatinetwork@emeraldinsight.com (Jianxin Shen, Dan Shi, Canfei Wang, Peng Li, Kang Wang, Mengjia Jin) Tue, 26 Aug 2014 00:00:00 +0100 Optimal design of low-cost IPM AC motor http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115951&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper presents the optimal design of a low-cost interior permanent magnet (IPM) alternating current (AC) motor. It examines the influence of the permanent magnet (PM) materials, and proposes a simple and practical method of optimizing the air-gap field to achieve sinusoidal back electromotive force (EMF) and to reduce the cogging torque.<B>Design/methodology/approach</B> - IPM AC motors with different magnet materials and various topologies are comparatively studied. Finite element method (FEM) is used to predict the performances of these designs. Material costs and manufacture costs are both taken into account. Finally, an optimized design is prototyped and tested, validating the design considerations.<B>Findings</B> - In an IPM AC motor, even if the rotor outer profile is round, the air-gap field distribution can be fined, while the cogging torque can be significantly reduced, by properly shaping the stator tooth tips. Nevertheless, this technique is usually applicable to motor configurations with concentrated windings, but not to those with distributed windings.<B>Originality/value</B> - While using ferrite magnets for PM AC motors with a kilo-watts power, interior magnets are usually inserted in V-shaped slots, and the rotor outer profile is often shaped in order to enhance the air-gap field distribution. However, such a rotor configuration usually increases the manufacture costs, and also deteriorates the consistency of mass production. Therefore, a new motor configuration with a round rotor outer profile and shaped stator tooth tips is proposed. It can not only overcome the aforementioned problems, but also improve the motor performance. Article literatinetwork@emeraldinsight.com (Jianxin Shen, Kang Wang, Dan Shi, Canfei Wang, Mengjia Jin) Mon, 21 Jul 2014 00:00:00 +0100 An approach to the sizing of electric motors devoted to aerospace propulsion systems http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115916&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper deals with the design and optimization of PM synchronous motors devoted to aeronautic applications.<B>Design/methodology/approach</B> - A design approach as well as a performance investigation, based on two-dimensional finite element analysis of selected electromagnetic and thermal features, are applied to chosen PM synchronous machine topologies which differ by their number of phases.<B>Findings</B> - It has been found that the initial set of geometrical parameters does not fulfill the torque/weight compromise required by a ronautic applications since it leads to an average temper- ature rise higher than the authorized limit(class H: 155K). Therefore, the sizing has been rethought in an attempt to meet the constraints of the considered application.<B>Research limitations/implications</B> - Several continuations of the developed works shall be treated in the future, such as: (i) the prototyping of the designed machines, (ii) extending the optimization procedure to the whole drive including the motor and the associated static converter, and (iii) the synthesis and implementation of a dedicated control strategy with a suitable emulation of the load.<B>Practical implications</B> - The studied machines could be integrated in aerospace propulsion systems.<B>Originality/value</B> - The paper develops a design procedure of PM synchronous motors dedicated to aerospace applications where the compromise between torque/weight/temperature represents a crucial design challenge. Article literatinetwork@emeraldinsight.com (Ikhlas Bouzidi, Nicola Bianchi, Ahmed Masmoudi) Tue, 26 Aug 2014 00:00:00 +0100 Influence of rotor design on performance of PM machines for heavy-duty traction applications http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115955&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - To study the performance and efficiency of two different permanent magnet (PM) machine rotor configurations under magnetic core saturation conditions. <B>Design/methodology/approach</B> - Since the accuracy of conventional analytical methods is limited under saturation conditions, a Finite Element Model of the machine is built; which is used to predict the various losses over its operating range such as eddy current, hysteresis, copper and magnet losses. Using this model, the efficiency map of the machine is derived which is used to investigate its efficiency corresponding to a heavy-vehicle drive cycle. The performance of two different rotor designs are studied and the efficiency of each design is compared under the considered drive cycle.<B>Findings</B> - It has also been proved that the performance advantage due to reluctance torque in the v-shaped Interior PM machine (IPM) is offset by its core steel saturation at higher current/torque levels. The magnitude of iron losses in the IPM is higher than that in the surface PM machine (SPM), however, the magnet loss in the SPM is higher than in the IPM. <B>Originality/value</B> - An investigation of the performance of the IPM design in comparison with the SPM~design under magnetic saturation conditions is not known to the authors. Hence, in this paper, it will be determined if the assumed performance advantage of the IPM over the SPM still holds true under these conditions. Article literatinetwork@emeraldinsight.com (Jubin Jacob, Johannes J.H. Paulides, Elena A. Lomonova) Tue, 26 Aug 2014 00:00:00 +0100 Air gap MMF based prediction of eddy current loss in the PMs of concentrated winding brushless machines http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116011&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper aims at an analytical approach-based prediction of the eddy current loss in the PMs of a concentrated winding machine equipped with 12 slots in the stator and 10 poles in the rotor.<B>Design/methodology/approach</B> - The investigation of the PM eddy current loss has been carried out using an analytical model and a 2D time-stepped transient finite element analysis (FEA).<B>Findings</B> - It has been found, in the case of the treated machine, that just the subharmonic of rank one and the harmonic of rank seven have significant contributions to the eddy current loss in the PMs.<B>Research limitations/implications</B> - A shift between the results yielded by the developed analytical model and those computed by FEA has been noticed. This limitation is mainly due to the slotting effect which has been omitted in the analytical model.<B>Practical implications</B> - Fractional slot PM machines are currently given an increasing attention in automotive applications. The prediction of their iron loss in an attempt to rethink their design represents a crucial efficiency benefit.<B>Originality/value</B> - The analytical prediction of the eddy current loss in each PM then in all PMs and their validation by FEA represent the major contribution of this work. Article literatinetwork@emeraldinsight.com (Asma Masmoudi, Ahmed Masmoudi) Tue, 26 Aug 2014 00:00:00 +0100 Optimal design of synchronous reluctance machine – a feasible solution to eliminating rare earth permanent magnets for vehicle traction applications http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115915&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - Optimally designed synchronous reluctance machine is presented to demonstrate the feasibility of eliminating the use of rare earth permanent magnet (PM) in electric machine for vehicle traction applications.<B>Design/methodology/approach</B> - A typical rare earth Interior Permanent Magnet machine is used as the benchmark to conduct the optimal design study. Based on the flux distribution, major changes are made to the rotor lamination design. Enhanced torque production and lower torque ripple are specifically targeted as the two main objectives of the proposed design approach.<B>Findings</B> - As a result, the optimally designed synchronous reluctance machine can achieve performance very close to that of the benchmark permanent magnet machine with a potential for further improvement.<B>Originality/value</B> - Discussions of IPM replacement by optimally designed SynRM in electrical and hybrid electrical vehicles are given in terms of performance and cost. Article literatinetwork@emeraldinsight.com (Haiwei Cai, Bo Guan, Longya Xu, Woongchul Dan Choi) Mon, 21 Jul 2014 00:00:00 +0100 Comparative analysis of the SRM as an alternative to the PM motor for automotive applications http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115919&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper presents comparative analysis of several configurations of the switched reluctance motor (SRM) for an in-wheel drive for a heavy-duty automotive series hybrid system. The SRM motor is regarded as one of the primary candidates for possible replacement of the permanent magnet (PM) motor.<B>Design/methodology/approach</B> - Three SRMs of 10/8, 12/10 and 12/8 configurations have been analysed, where the last two motors had the stator lamination profile taken from the existing PM motor. The analysis is performed using magnetostatic FEM and transient modelling techniques.<B>Findings</B> - The maximum developed electromagnetic torque of the two analysed motors of 12/10 and 12/8 SRM configurations with the stator lamination profile taken from the existing PM motor is limited due to saturation of the stator yoke. Both motor configurations are capable to provide the specified power within the same outer dimensions due to extended speed in the field-weakening region and position independent starting torque. A redesigned stator results in substantial increase in torque developed by the machine and, consequently, ability to provide similar torque-speed performance as the existing PM motor, at cost of increased copper loss at the low-speed regime.<B>Originality/value</B> - The paper proposes several structures of SRMs for the in-wheel drive for a heavy-duty automotive series hybrid system converted from the present expensive PM machine, having the same power density. The "bottleneck" of the direct conversion of the PM machine into the SRM is highlighted. Article literatinetwork@emeraldinsight.com (Konstantin Boynov, Johannes J.H. Paulides, Elena A. Lomonova) Tue, 26 Aug 2014 00:00:00 +0100 Research on New Hybrid Excitation PM Synchronous Generators with Tooth Harmonic Excitation http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116014&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - In order to keep the advantages of PM generators and eleminate its disadvantage--difficulty in regulating the magnetic field, hybrid excitation is an effective way. This paper proposed a novel way to achieve hybrid excitation by use of tooth harmonic field.<B>Design/methodology/approach</B> - Unlike weakening the tooth harmonics field and EMF in traditional machines, in this paper the tooth harmonics filed is proposed to form a novel hybrid excitation permanent magnet synchronous generator.<B>Findings</B> - The generation mechanism of tooth harmonic electromotive force (EMF) of rotor winding is introduced, and its influencing factors are discussed in detail. The matching design of tooth harmonic winding and field winding for maximum output field current of tooth harmonic excitation system is analyzed.<B>Practical implications</B> - This machine can achieve not only effective adjustment of the air-gap magnetic field, but also elimination of the brushes and slip rings.<B>Originality/value</B> - Unlike weakening the tooth harmonics field and EMF in traditional machines, in this paper the tooth harmonics filed is proposed to form a novel hybrid excitation permanent magnet synchronous generator. This machine can achieve not only effective adjustment of the air-gap magnetic field, but also elimination of the brushes and slip rings. Article literatinetwork@emeraldinsight.com (Shanming Wang, Yonghong Xia, Shaogang Huang, Arui Qiu, Xiangheng Wang) Tue, 26 Aug 2014 00:00:00 +0100 Vibration signature analysis for monitoring rotor broken bar in double squirrel cage induction motors based on wavelet analysis http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115872&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The purpose of this paper is to present a diagnosis technique, for rotor broken bar in double cage induction motor, based on advanced use of Wavelet Transform Analysis. The proposed technique is experimentally validated.<B>Design/methodology/approach</B> - The proposed approach is based on a combined use of Frequency Sliding (FS) and Wavelet Transform (WT) analysis, to isolate the contribution of the rotor fault components issued from vibration signals in a single frequency band.<B>Findings</B> - The proposed technique is reliable for tracking the rotor fault components over time-frequency domain. The quantitative analysis results based on this technique are the proof of its robustness.<B>Research limitations/implications</B> - The validity of the proposed diagnosis approach is not limitted to the analysis under steady-state operating conditions, but also for time-verying conditions where rotor fault components are spread in a wide frequency range.<B>Practical implications</B> - The developed approach is best suited for automotive or high power traction systems, in which safe-operating and availability are mandatory.<B>Originality/value</B> - The paper presents a diagnosis technique for rotor broken bar in double cage induction motor base on advanced use of Wavelet Transform which allows the extraction of the most relevant rotor fault component issued from axial vibration signal and clamping it in a single frequency bandwidth, avoiding confusions with other components and false interpretations. Article literatinetwork@emeraldinsight.com (Rosario Miceli, Yasser Gritli, Antonino Oscar Di Tommaso, Fiorenzo Filippetti, Claudio Rossi) Tue, 26 Aug 2014 00:00:00 +0100 FEA-based investigation of the generating capability of a novel hybrid excited claw pole alternator with improved cost-effectiveness http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115909&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper is devoted to an investigation of the generating capability of a novel hybrid excited brushless claw pole alternator (HEBCPA) with improved cost-effectiveness gained thanks to the substitution the rotor NdFeB-made PM with ferrite ones.<B>Design/methodology/approach</B> - The investigation of the magnetic features of the novel HEBCPA has been carried out using a 3D finite element analysis (FEA).<B>Findings</B> - It has been found that the machine generating capability is not affected by the substitution of the single rotor NdFeB-made PM by stator and rotor ferrite-made ones, which represents a crucial cost benefit.<B>Research limitations/implications</B> - An experimental validation of the features computed by FEA shall be considered as an outlook of the present work.<B>Practical implications</B> - The novel HEBCPA could be of great interest for automotive generating systems.<B>Originality/value</B> - The proposed HEBCPA with ferrite-made PMs is a novel concept. Article literatinetwork@emeraldinsight.com (Rabeb Rebhi, Amina Ibala, Ahmed Masmoudi) Tue, 26 Aug 2014 00:00:00 +0100 A coupled analytical-numerical approach for optimal sizing of power inductors http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115892&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - An optimal sizing methodology is presented in this paper. It is applied to a foil-coil powder core power inductor used in new generation inverters designed for hybrid and full-electric vehicles. The methodology includes a preliminary analytical calculation and a numerical optimization aimed at minimizing the component size.<B>Design/methodology/approach</B> - Unlike bulk magnetic alloys or ferrites, the magnetic non-linearity of powder materials cannot be neglected in the analytical calculation. This non linearity requires the use of an iterative calculation to search the set of parameters for which the target inductance value and the minimum volume are simultaneously reached. The numerical optimization process is based on 2D Finite Element analysis carried out with FEMM software tool and a simplex-type algorithm run in Scilab software. These two freewares are coupled using the scifemm.sci script which is included in the FEMM distribution.<B>Findings</B> - The association of analytical and FE approaches provides a relevent and quick sizing methodology. It was successfully applied to size a new power inductor.<B>Originality/value</B> - The strong non linearity of the powder material is correctly taken into account in the analytical model thanks to an iterative calculation process. Thus, the preliminary analytical solution is quite relevant. Consequently, a local FE based optimisation is enough to find the optimal solution close by the analytical one. No global optimisation is required. A local optimum is sufficient. Article literatinetwork@emeraldinsight.com (zaatar Makni, Richard Demersseman) Tue, 26 Aug 2014 00:00:00 +0100 Dual current control strategy to fulfill LVRT requirements in WECS http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115903&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper is devoted to the investigation of a control strategy to fulfill Low voltage Ride Through (LVRT) requirements in Wind Energy Conversion System (WECS). <B>Design/methodology/approach</B> - – This paper considers an active front-end converter of a grid connected WECS working under grid fault conditions. Two strategies based on symmetrical components are studied and proposed: the first one considers control only for positive sequence (PSC); the second one considered a dual controller for positive and negative sequence (PNSC). The performance of each strategy is studied on LVRT requirements fulfillment. <B>Findings</B> - This paper shows presents a control strategy based on symmetrical component to keep the operation of grid-connected WECS under unsymmetrical grid fault conditions. <B>Research limitations/implications</B> - This work is being applied to a 2 kVA laboratory prototype. The lab. prototype emulates a grid connected WECS. <B>Originality/value</B> - This paper validate the PNSC strategy to LVRT requirements fulfillment by experimental results obtained for a 2 kVA laboratory prototype. PNSC strategy allows constant active power delivery through grid-voltage dips. In addition, the proposed strategy is able to grid-voltage support by injection of reactive power. Additional features are incorporated to PNSC: sequence separation method using Delay Signal Cancelation and grid frequency identification using Phase Locked Loop. Article literatinetwork@emeraldinsight.com (Matías Díaz, Roberto Cardenas-Dobson) Tue, 26 Aug 2014 00:00:00 +0100 Challenges and lessons learned in the deployment of an offshore oscillating water column http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115867&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - To disseminate the lessons learned from the successful deployment of a Wave Energy Converter (WEC) and accelerate growth in the field of ocean energy.<B>Design/methodology/approach</B> - A thorough, well-structured, documented, industrial approach was taken to the deployment because of the depth and scale of the task required. This approach is shown throughout the paper, which reflects the importance of a comprehensive project plan in success as well as failure.<B>Findings</B> - The findings demonstrate the viability of the use of off shore WEC to generate electricity and that such a project can be completed on time and on budget.<B>Research limitations/implications</B> - The research implications of the paper include the importance of an enhanced, integrated supervisory system control in terms of efficiency, operation and maintenance, and long term viability of WECs. This paper can be used to help guide the direction of further research in similar areas.<B>Practical implications</B> - The practical implications include proof that WEC deployments can be carried out both on time and under budget. It highlights much of the practical data collected throughout the course of the project and presents it so that it might be used as a guide for future projects.<B>Originality/value</B> - At the time of this paper, successful deployment of off shore WECs has been a rare accomplishment. Because the project was publicly funded, the data collected during this project, both technical and practical, is freely available. Article literatinetwork@emeraldinsight.com (James Franics Kelly, Dara O'Sullivan, William M. D. Wright, Raymond Alcorn, Tony Lewis) Tue, 26 Aug 2014 00:00:00 +0100 Self-sustained all-electric wave energy converter system http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116137&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper describes the design and function of Fred. Olsens Wave Energy Converter system Lifesaver with special focus on the stand-alone electrical system that is implemented for operation without grid-connection.<B>Design/methodology/approach</B> - The paper focus on the detailed design of the DC-Link system that drives the industrial 400 VAC inverters and generators for the production system. The DC-Link is stabilized by an ultracapacitor bank and has no external source or grid-connection.<B>Findings</B> - The system has been tested through extensive sea trials since April 2012 and has proved its function. Some results from real sea testing are presented.<B>Practical implications</B> - This paper proves the viability of the specied design and may serve as a basis for the design if similar systems in the future.<B>Originality/value</B> - This paper presents a Wave Energy Converter system that has proven successful operation through practical tests, and is therefore regarded as a high value paper as there is limited experience on this subject. Article literatinetwork@emeraldinsight.com (Jonas Sjolte, Gaute Tjensvoll, Marta Molinas) Tue, 26 Aug 2014 00:00:00 +0100 DC-link voltage selection for a multi-MW wind turbine http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115906&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The purpose of this paper is to investigate how the dc-link voltage for the converter of a wind generator should be selected. i.e., to determine the losses in the generator and the converter when using various dc-link voltage levels.<B>Design/methodology/approach</B> - To presents the efficiency evaluation of 5 MW wind turbine generating systems, two 5 MW surface mounted permanent magnet synchronous generators with medium and low rated voltage is designed. A 2-level transistor converter is considered for ac/dc conversion. Three different dc-link voltage levels are used. By using these voltage levels the PMSG is utilised in slightly different ways.<B>Findings</B> - It is found that the system with the lower voltage machine has slightly higher annual energy efficiency compare to the higher voltage system. Furthermore, it is shown that the best choice for the dc-link voltage level is a voltage between the minimum voltage which gives the desired torque and the voltage which gives MTPA.<B>Originality/value</B> - A procedure as well as investigations with quantified results on how to find the highest complete drive system efficiency for a wind turbine application. Based on two given PMSG, the most energy-efficient dc-link voltage has been established. Article literatinetwork@emeraldinsight.com (Poopak Roshanfekr Fard, Torbjorn Thiringer, Sonja Lundmark, Mikael Alatalo) Tue, 26 Aug 2014 00:00:00 +0100 Stator voltage harmonics and unbalance compensation of the sensorless standalone doubly fed induction generator http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115936&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - Doubly fed induction generator DFIG is widely used in wind energy conversion systems and it can operate with other primary movers. The paper is focused on the standalone operation of DFIG which may expand the area of possible applications and increase capabilities of the generation system in term of power quality.<B>Design/methodology/approach</B> - Synthesis of the control method was preceded by analysis of mathematical model of the machine. The control method based on the negative sequence and high harmonics extraction has been developed and verified in the laboratory unit. Control of the fundamental frequency component use neither rotor speed nor position sensors.<B>Findings</B> - The original method allows to compensate negative sequence and high harmonics of the generated voltage. At the same time, due to the active filtering capability of the grid side converter, the stator phase current shape is close to sine wave. Thus, it is seen by the machine as a linear load, what eliminate the electromagnetic torque ripples.<B>Practical implications</B> - The system and control method can be applied in variable speed generation systems, e.g. wind turbines or diesel engines operating in the standalone mode.<B>Originality/value</B> - Although the selective compensation of negative sequence and harmonics are known in the literature, until now the methods have been verified for the system with a rotor position sensor. Moreover, the stator current feedforward improving the transient properties, as well as results of transient states caused by the load step change, have not been proposed in publications. Article literatinetwork@emeraldinsight.com (Grzegorz Iwanski, Piotr Pura, Tomasz Luszczyk, Mateusz Szypulski) Tue, 26 Aug 2014 00:00:00 +0100 Design, optimisation and application of a resonant DC link inverter for solar energy systems http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17115935&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper examines to diminish switching losses in a solar energy conversion system in order to utilize the full efficiency of a solar panel.<B>Design/methodology/approach</B> - – In this paper, a boost converter and a resonant DC link inverter are controlled by a microcontroller. The MPPT algorithm implemented for boost converter supplies to track maximum power point of solar panel. The Class D full-bridge resonant inverter that is considered to be supplied by boost converter is modeled and zero voltage switching operation is performed by controlling the inverter with sinusoidal pulse width modulation (SPWM) control scheme. The control algorithm is managed with a feedback detecting the current of the boost converter and the zero voltage levels of capacitor voltage in the resonant circuit. <B>Findings</B> - There are several control techniques have been proposed to reduce switching losses and harmonic contents in conventional or resonant DC link inverters (RI). Solar panels are used in low power applications among other renewable energy sources. By considering that the efficiency parameter of an actual solar panels is around 14~17%, the switching losses occurred in energy conversion systems causes the efficiency are reduced. <B>Originality/value</B> - The proposed approach has been decreased the switching power losses owing to resonant DC link inverter while the developed MPPT algorithm provides to generate maximum power. This paper introduces a novel soft switching technique in solar energy applications in order to maximize the possible efficiency. Article literatinetwork@emeraldinsight.com (Ilhami Colak, Mehmet Demirtas, Ersan KABALCI) Tue, 26 Aug 2014 00:00:00 +0100 A 2.5-D frequency-domain nonlinear computer model of coupled-cavity traveling wave tubes http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116023&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The paper aims to present a 2.5-dimensional (2.5-D) frequency-domain nonlinear computer model for the beam-wave interaction of coupled-cavity traveling wave tubes (CC-TWTs).<B>Design/methodology/approach</B> - MKK (proposed by Malykhin, Konnov, and Komarov) equivalent circuit model is used to describe the coupled-cavity slow-wave structure. And the losses are taken into account in the MKK equivalent circuit. Instead of one-dimensional (1-D) disk model, the electron beam is divided into a set of discrete rays and the electron dynamics are treated using the three-dimensional (3-D) Lorentz force equations.<B>Findings</B> - The simulated result obtained show that the computer model can give a good predict for coupled-cavity traveling wave tubes in V-band.<B>Practical implications</B> - The computer model is capable of treating nonlinear problems. Compared with particle-in-cell (PIC) simulation, the 2.5-D frequency-domain computer model spends less time. Besides, the 3-D electron trajectory can be used to design high-efficiency collectors for coupled-cavity traveling wave tubes.<B>Originality/value</B> - The computer model is able to simulate nonlinear problems of coupled-cavity TWT faster. Article literatinetwork@emeraldinsight.com (Chunjiang Bai, Yulu Hu, Jianqing Li) Tue, 26 Aug 2014 00:00:00 +0100 Calculation of inrush current using adopted parameters of the hysteresis loop http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116040&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The primary purpose of this paper is to propose an accurate model for simulation of inrush current in power transformers with taking into account the magnetic core structure and hysteresis phenomenon. Determination of the required model parameters and generalization of the obtained parameters to be used in different conditions with acceptable accuracy is the secondary purpose of this work.<B>Design/methodology/approach</B> - The duality transformation is used to construct the transformer model based on its topology. The inverse Jiles-Atherton (JA) hysteresis model is used to represent the magnetic core behavior. Measured inrush waveforms of a laboratory test power transformer are used to calculate a fitness function which is defined by comparing the measured and simulated currents. This fitness function is minimized by particle swarm optimization (PSO) algorithm which calculates the optimal model parameters. <B>Findings</B> - An analytical and simple approach is proposed to generalize the obtained parameters from one inrush current measurement for simulation of this phenomenon in different situations. The measurement results verify the accuracy of the proposed method. The developed model with the determined parameters can be used for accurate simulation of inrush current transient in power transformers. <B>Originality/value</B> - A general and flexible topology based model is developed in PSCAD/EMTDC software to represent the transformer behavior in inrush situation. The hysteresis model parameters which are obtained from one inrush current waveform are generalized using the structure parameters, switching angle, and residual flux for accurate simulation of this phenomenon in different conditions. Article literatinetwork@emeraldinsight.com (Ramezan Ali Naghizadeh, Behrooz Vahidi, Seyed Hossein Hosseinian) Tue, 26 Aug 2014 00:00:00 +0100 High-order fast integration for earth-return impedance between underground and overhead conductors in Matlab http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116057&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The earth-return mutual impedances between underground and overhead conductors can be expressed by Pollaczek integrals. Many efforts have been exerted to calculating this kind of integrals. However, most of numerical methods turn out to be time-consuming as integrands become highly oscillatory and strongly singular. Therefore, efficient algorithms should be devised.<B>Design/methodology/approach</B> - We separate the singularity from the whole integral and couple with the singularity and oscillation, respectively. A sinh transformation is applied for the finite part and complex integration method is used to calculate the tail.<B>Findings</B> - Numerical experiments show that the given method shares the property that the stronger the singularity and the higher the oscillation, the better the accuracy of the calculation<B>Originality/value</B> - The sinh transformation is first proposed to calculate Pollaczek integrals. This efficient algorithm can be used to evaluate mutual impedances between conductors. Also, it provides a new aspect of the research on fast calculation of Pollaczek integrals and Sommerfeld integrals. Article literatinetwork@emeraldinsight.com (Junjie Ma, Shuhuang Xiang) Tue, 26 Aug 2014 00:00:00 +0100 Application of local coordinates rectification in linearization of selected parameters of dynamic nonlinear systems http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116035&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - This paper aims to an application of element of the theory of differential geometry for building the state space transformation, linearizing nonlinear dynamic system into a linear form.<B>Design/methodology/approach</B> - It is assumed that the description of nonlinear electric circuits with concentrated parameters or electromechanical systems is given by nonlinear system of differential equations of first order (state equations). The goal is to find transformation which leads nonlinear state equation (written in one coordinate system) to the linear in the other – sought coordinate system.<B>Findings</B> - The necessary conditions fulfilled by nonlinear system undergoing linearization process are presented. Numerical solutions of the nonlinear equations of state together with linearized system obtained from direct transformation of the state space are included (transformation input - the state of the nonlinear system).<B>Originality/value</B> - Application of first order exact differential forms for determining the transformation linearizing the nonlinear state equation. Simple linear models obtained with the use of the linearizing transformation are very useful (mainly because of the known and well-mastered theory of linear systems) in solving of various practical technical problems. Article literatinetwork@emeraldinsight.com (Andrzej Zawadzki) Tue, 26 Aug 2014 00:00:00 +0100 A second order s-to-z transform and its implementation to IIR filter design http://www.emeraldinsight.com/journals.htm?issn=0332-1649&volume=33&issue=5&articleid=17116019&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - Development of a design tool for IIR digital filters obtained from analog prototypes, which preserves simultaneously the amplitude and the group delay response. <B>Design/methodology/approach</B> - A new s-to-z transform is developed based on a second order formula used for numerical integration of differential equations. Stability of the newly obtained transfer functions in the z- domain is proved to be preserved. Distortions introduced by the new transform into the original amplitude and group delay responses are studied.<B>Findings</B> - The new formula, when implemented to all-pole prototypes, exhibits lower selectivity than the original while reducing the pass-band group delay distortions. In the same time its structure is importantly simpler than the functions obtained by the well-known bilinear transform. When implemented to a prototype having "all kinds" of transmission zeros the resulting filter has almost ideally the same characteristic as the prototype.<B>Research limitations/implications</B> - The new transform may be used exclusively to synthesize even order filters. The new function is twice the order of the analog prototype. This kind of transformations are used to design IIR digital filters only. Low-pass transfer functions were studied being prototypes for all other cases.<B>Originality/value</B> - This is a new result never mentioned in the literature. Its effectiveness is confined to a niche problem when simultaneous sharp selectivity and low group delay distortions are sought. Article literatinetwork@emeraldinsight.com (Dejan Dragan Mirkovic, Predrag M Petkovic, Vanco B Litovski) Tue, 26 Aug 2014 00:00:00 +0100