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Purpose: The purpose of this study is to investigate a novel rotor design model to improve the technical performance of a superconducting synchronous generator. Design/methodology/approach: Superconducting synchronous generators with a modular rotating cryostat for a single coil of the superconducting winding instead of an old-style single cryostat in which all rotor components are cold are briefly discussed. Subsequently, a new method of cryostat arrangement in the magnetic system of a rotor is considered. Different options were compared for the cryostat placement. The advantages of the novel rotor design model are noted. Findings: In the novel rotor design model, the leakage coefficient of the excitation winding decreases, and the air gap magnetic flux increases, which will save on a superconductor material. Research limitations/implications: For the purposes of this investigation, a finite element study of flux distribution in the cross section of a superconducting synchronous generator with a 10 MW rating at 10 rpm was conducted, and the magnetic fluxes and air gap flux densities were obtained for different modes. For direct-drive superconducting synchronous generators with distributed winding and different pole numbers, the calculations of magnetic fluxes were carried out by calculating the magnetic conductivities. Originality/value: A new method of the cryostat arrangement in the magnetic system of a rotor has been classified as an invention and was protected by a patent. This paper is directly applicable to the field of superconducting synchronous generators. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the relationship between leakage flux coefficient and the coreless axial magnetic field permanent magnet synchronous generator (AFPMSG) size and obtain the expressions of leakage flux coefficient. Design/methodology/approach: In this paper, a magnetic circuit model of coreless AFPMSG is proposed. Four kinds of leakage permeances of permanent magnet (PM) are considered, and the expression of no-load leakage flux coefficient is obtained. Solving the integral region of leakage permeances by generator size, which improves the accuracy of the solution. Findings: Finite element method and magnetic circuit method are used to obtain the no-load leakage flux coefficient and its variation trend charts with the change of pole arc coefficient, air gap length and PM thickness. The average errors of the two methods are 2.835%, 0.84% and 1.347%, respectively. At the same time, the results of single-phase electromotive force obtained by magnetic circuit method, three dimensional finite element method and prototype experiments are 19.36 V, 18.82 V and 19.09 V, respectively. The results show that the magnetic circuit method is correct in calculating the no-load leakage flux coefficient. Originality/value: The special structure of the coreless AFPMSG is considered in the presented equivalent magnetic circuit and equations, and the equations in this paper can be applied for leakage flux evaluating purposes and initial parameter selection of the coreless AFPMSG. [ABSTRACT FROM AUTHOR]

Purpose: On-time fault diagnosis in electrical machines is a critical issue, as it can prevent the development of fault and also reduce the repairing time and cost. In brushless synchronous generators, the significance of the fault diagnosis is even more because they are widely used to generate electrical power all around the world. Therefore, this study aims to propose a fault detection approach for the brushless synchronous generator. In this approach, a novel extension of Relief feature selection method is developed. Design/methodology/approach: In this paper, by taking the advantages of the finite element method (FEM), a brushless synchronous machine is modeled to evaluate the machine performance under two conditions. These conditions include the normal condition of the machine and one diode open-circuit of the rotating rectifier. Therefore, the harmonic behavior of the terminal voltage of the machine is obtained under these situations. Then, the harmonic components are ranked by using the extension of Relief to extract the most appropriate components for fault detection. Therefore, a fault detection approach is proposed based on the ranked harmonic components and support vector machine classifier. Findings: The proposed diagnosis approach is verified by using an experimental test. Results show that by this approach open-circuit fault on the diode rectifier can effectively be detected by the accuracy of 98.5% and by using five harmonic components of the terminal voltage [1]. Originality/value: In this paper, a novel feature selection method is proposed to select the most effective FFT components based on an extension of Relief method, and besides, FEM modeling of a brushless synchronous generator for normal and one diode open-circuit fault. [ABSTRACT FROM AUTHOR]

Purpose: In a power system, the purpose of automatic voltage regulator (AVR) is the voltage control of synchronous generator. Power system stability and security depends on the AVR. Design/methodology/approach: The present work is concentrated on the precise terminal voltage control of AVR system and simultaneously maintaining the stability of the system. Therefore, an optimal proportional–integral–derivative (PID) controller is proposed. An optimization technique inspired from Mother Nature, i.e. water cycle algorithm (WCA) is used to evaluate the optimum parameter values of PID controller leading to WCA-tuned PID (WCA-PID). The performance of WCA-PID is compared with other controller reported in the literature. Findings: Simulation results show that WCA-PID regulates the terminal voltage more preciously and accurately in comparison to other controller. Further, it is more robust toward parametric uncertainty, set-point tracking and disturbance rejection in comparison to other controller reported in the literature. Originality/value: The work is not published anywhere else. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to obtain an accurate methodology for modelling and analysis of the permanent magnet synchronous generator connected to power electronic components. Design/methodology/approach: This paper presents the methodology of the co-simulation of a permanent magnet synchronous generator. It combines Simulink, Maxwell and Simplorer software to demonstrate the electrical machine behaviour connected with the power electronics' circuit. The finite element analysis performed on the designed machine exhibit a more accurate behaviour over simplified Simulink models. Results between both simulation and co-simulation are compared to measurements. Findings: The co-simulation approach offers a more accurate depiction of the machine behaviour and its interaction with the non-linear circuits. Research limitations/implications: This paper focuses on the interior permanent magnet type of PMSG and its interaction with a passive rectifier (nonlinear circuit). Practical implications: The advanced capabilities of the co-simulation method allow to analyse more variations (geometry, materials, etc.), and its interaction with non-linear circuits, than previous simulation techniques. Originality/value: The co-simulation as a tool for analysis and design of systems interconnected with unconventional and conventional electrical machines and prototypes, and the comparison of the obtained results with classical analysis and design methods, against measurements obtained from the prototype. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to clarify the relationship between stator tooth shape and DC voltage fluctuation of a double salient hybrid excitation generator (DSHEG). It analyzes the asymmetrical characteristics of the magnetic circuit and inductance between each phase. The study aims to reduce voltage fluctuation by using a stator shape optimization scheme, which helps reducing inductance difference. Design/methodology/approach: This paper opted for a method combined with theoretical analysis, simulation and experimental verification. The stator tooth optimization scheme is given based on theoretical asymmetrical analysis and Taguchi method. A series of two-dimensional finite element analysis simulation of different conditions are conducted. Two prototypes with different stator tooth shape are made and experiments are carried out. Findings: The paper provides empirical insights into how the stator tooth shape influences the asymmetry of inductance and DC voltage fluctuation. Compensation adjustments to the stator tooth shape can narrow the inductance differences of each phase. It suggests that "LTL" shaped DSHEG has lower voltage ripple than "III" shaped DSHEG without sacrificing output power. Research limitations/implications: Because of the chosen research approach, the gap between magnets and stator and end effect are not considered. Errors exist between simulation and experimental results. Practical implications: The paper includes implications for other "C" shaped tooth optimization. Study on phase asymmetry of the special machine can further improve quality testing and simplify control strategy. Originality/value: This paper analyzes the asymmetry of DSHEG and proposes an optimized stator tooth shape to reduce DC voltage fluctuation. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to propose a novel hybrid excitation permanent magnet synchronous generator (HEPMSG) utilizing tooth harmonic for excitation, the structural features and operation principle of which are also described. Design/methodology/approach – To obtain the operation performance quickly, this paper derives the mathematical model of the machine system represented by circuit, and analyzes the operation mode of rectifier circuit in the tooth harmonic excitation system, then the standard state equations for each operation mode are obtained. Combining the inductance parameter of this machine with the load resistance and inductance, the armature current waveform, the field current waveform and tooth harmonic winding current waveform are obtained by using the numerical method to solve the standard state equation. Findings – Comparing with the experimental results, the availability of the principle and the validity of the model of the machine system are verified. Practical implications – This HEPMSG is a new brushless self-excited and self-regulated generator, which is suitable for an independent power source. Originality/value – Unlike the existing hybrid excitation permanent magnet machine, this HEPMSG utilized the inherent tooth harmonic EMF of the rotor to adjust the air-gap magnetic field of the permanent magnet machine. [ABSTRACT FROM AUTHOR]

Purpose – Eddy current testing (ECT) is a nondestructive testing method for the detection of flaws that uses electromagnetic induction to find defects in conductive materials. In this method, eddy currents are generated in a conductive material by a changing magnetic field. A defect is detected when there is a disruption in the flow of the eddy current. The purpose of this paper is to develop a new noniterative inversion methodology for detecting degradation (defect characterization) such as cracking, corrosion and erosion from the measurement of the impedance variations. Design/methodology/approach – The methodology is based on multi-output support vector machines (SVM) combined with the adaptive database schema design method (SDM). The forward problem was solved numerically using finite element method (FEM), with its accuracy experimentally verified. The multi-output SVM is a statistical learning method that has good generalization capability and learning performance. FEM is used to create the adaptive database required to train the multi-output SVM and the genetic algorithm is used to tune the parameters of multi-output SVM model. Findings – The results show the applicability of multi-output SVM to solve eddy current inverse problems instead of using traditional iterative inversion methods which can be very time-consuming. With the experimental results the authors demonstrate the accuracy which can be provided by the multi-output SVM technique. Practical implications – The work allows extending the capability of the experimentation ECT defect characterization system developed at LGEP. Originality/value – A new inversion method is developed and applied to ECT defect characterization. This new concept introduces multi-output SVM in the context of ECT. The real data together with estimated one obtained by multi-output SVM model are compared in order to evaluate the effectiveness of the developed technique. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to quantify the impact of the constraints of the power take-off system (PTO) on the power extraction of a point absorber wave energy converter (WEC). Such constraints include power, torque and maximum stroke limitations. Two different concepts, unidirectional and bidirectional point absorbers, are analysed, which both are relevant for practical applications in the wave energy industry. Design/methodology/approach – The two different cases of unidirectional and bidirectional point absorbers are analysed and directly compared. Moreover, a simplified control strategy is considered for the point absorber, which is based on a constant torque reference. The WEC performance is first evaluated in selected sea states and then the analysis is extended to assess the impact of the different solutions on the expected yearly wave energy production of the point absorber, when deployed at a specific location. The European Marine Energy Center (EMEC) is selected as the target site for the analysis. Findings – The analysis was performed in selected sea states and then it was extended to all the sea conditions occurring at the EMEC test site. The comparison between unidirectional and bidirectional operated devices suggested a clear superiority of the latter, ensuring similar power extraction at the expense of a halved required torque by the PTO. Moreover, a selective control strategy was implemented, and the results showed an increase in yearly energy production for the bidirectional device. Research limitations/implications – The study proved the importance of including the actual PTO constraints in the preliminary power assessment in order to avoid unrealistic overestimation of the expected power performance. Originality/value – The paper quantifies the power performance obtained with the application of such control strategy considering both unidirectional and bidirectional point absorbers. This analysis and comparison is extremely relevant since both unidirectional and bidirectional devices are reaching the market. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to deal with the modeling of a claw pole alternator (CPA) by a 3D magnetic equivalent circuit (MEC) taking into account the saturation and magnetic armature reaction effects then its utilization for the prediction of the machine losses. Design/methodology/approach – Following the derivation of the proposed model, it is validated experimentally at no-load and load operations. Proposed MEC is applied to the investigation of a conventional CPA losses. Findings – The CPA efficiency is affected by different loss mechanisms. Indeed, the copper losses are dominant at lower speeds, while the iron and ventilation ones are more significant at high speeds. Research limitations/implications – An experimental validation of the losses computed by the MEC shall be treated in the future. Practical implications – The CPA is equipping most if not all embedded generating systems of road vehicles. The improvement of its efficiency is of great importance. Originality/value – The MEC-based prediction of the CPA losses represents the major contribution of the present work. [ABSTRACT FROM AUTHOR]

Purpose – Renewable generation is a main component of most hybrid generation systems. However, randomness on its generation is a characteristic to be considered due to its direct impact on reliability and performance of these systems. For this reason, renewable generation usually is accompanied with other generation elements to improve their general performance. The purpose of this paper is to analyze the power generation system, composed of solar, wind and diesel generation and power outsourcing option from the grid as means of reserve source. A multi-objective optimization for the design of hybrid generation system is proposed, particularly using the cost of energy, two different reliability indexes and the percentage of renewable energy as objectives. Further, the uncertainty of renewable sources and demand is modeled with a new technique that permits to evaluate the reliability quickly. Design/methodology/approach – The multi-state model of the generators and the load is modeled with the Universal Generating Function (UGF) to estimate the reliability indexes for the whole system. Then an evolutionary algorithm NSGA-II (Non-dominated Sorting Genetic Algorithm) is used to solve the multi-objective optimization model. Findings – The use of UGF methodology reduces the computation time, providing effective results. The validation of reliability assessment of hybrid generation systems using the UGF is carried out taking as a benchmark the results obtained with the Monte Carlo simulation. The proposed multi-objective algorithm gives as a result different generators combinations that outline hybrid systems, where some of them could be preferred over others depending on its results for each independent objective. Also it allows us to observe the changes produced on the resulting solutions due to the impact of the power fluctuation of the renewable generators. Originality/value – The main contributions of this paper are: an extended multi state model that includes different types of renewable energies, with emphasis on modeling of solar energy; demonstrate the performance improvement of UGF against SMC regarding the computational time required for this case; test the impact of different multi-states numbers for the representation of the elements; depict through multi-objective optimization, the impact of combining different energies on the cost and reliability of the resultant systems. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to propose a new nonlinear control algorithm to control a wind turbine based on permanent magnet synchronous generator (PMSG) connected to the grid via a back-to-back converter. The control algorithm is composed of a flatness-based method for the machine side convertor (MSC) and a voltage-oriented method for the grid side converter (GSC). Design/methodology/approach – For the MSC control, the output variable is chosen properly to prove that the system is flat at first. Then, the appropriate reference trajectories are planned on its components. The reference trajectories are such designed that the system operates in maximum power point tracking (MPPT) mode. Finally, state feedback regulators are used to force the system output to follow its reference. To control the GSC, a classical voltage-oriented control method is used. Findings – The simulation results obtained with a random wind speed are presented in order to prove the validity of the proposed control algorithm. These results show that the system is controlled successfully while it operates in the MPPT mode or in its maximum power limitation mode. Originality/value – In this paper, a new algorithm based on flatness property is presented to control a variable speed wind turbine based on a PMSG. The proposed control method allows the system to operate in optimal operating modes. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to propose a new converter topology for integrating PV plants constituted by many panels into the grid. The converter is capable of implementing MPPT algorithms on different subset of modules and can balance the different energy supplied by panels differently irradiated. The output voltage presents a very low ripple also if small filters are used for grid connection. Design/methodology/approach – In the paper, at first the converter configuration is presented. Then a control strategy for obtaining, at the same time the distributed MPPT and the power balancing on the three phases is proposed. Finally, by means of numerical simulations, the good performances of the proposed converter are shown. Findings – The proposed converter, lent from MMC configurations, is deeply studied and a suitable control strategy is well analyzed in the paper. Analytical model for voltage and current balancing are given. Research limitations/implications – The analysis presented in the paper complete some studies started in the last years and partially presented in previous scientific papers. It reaches a final point and gives all the specific for the realization of the converter and of its control. Practical implications – The paper gives all the instrument to design and realize a PV power plant integrated into building façade. Originality/value – The converter and the control for voltage and current balancing presented in this paper represent a significant original contribution of this work. [ABSTRACT FROM AUTHOR]

Purpose – To foster the grid integration of both electric vehicles (EV) and renewable generators, the purpose of this paper is to investigate the possible synergies between these players so as to jointly improve the production predictability while ensuring a green mobility. It is here achieved by the mean of a grid commitment over the overall power produced by a collaborative system which here gathers a photovoltaic (PV) plant with an EV fleet. The scope of the present contribution is to investigate the conditions to make the most of such an association, mainly regarding to the management strategies and optimal sizing, taking into account forecast errors on PV production. Design/methodology/approach – To evaluate the collaboration added value, several concerns are aggregated into a primary energy criterion: the commitment compliance, the power spillage, the vehicle charging, the user mobility and the battery aging. Variations of these costs are computed over a range of EV fleet size. Moreover, the influence of the charging strategy is specifically investigated throughout the comparison of three managements: a simple rule of thumb, a perfect knowledge deterministic case and a charging strategy computed by stochastic dynamic programming. The latter is based on an original modeling of the production forecast error. This methodology is carried out to assess the collaboration added value for two operators’ points of view: a virtual power plant (VPP) and a balance responsible party (BRP). Findings – From the perspective of a BRP, the added value of PV-EV collaboration for the energy system has been evidenced in any situation even when the charging strategy is very simple. On the other hand, for the case of a VPP operator, the coupling between the optimal sizing and the management strategy is highlighted. Originality/value – A co-optimization of the sizing and the management of a PV-EV collaborative system is introduced and the influence of the management strategy on the collaboration added value has been investigated. This gave rise to the presentation and implementation of an original modeling tool of the PV production forecast error. Finally, to widen the scope of application, two different business models have been tackled and compared. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to devote the optimal substitution of slip rings through an inductive power transfer system for field winding supply of generators or motors with a wound rotor. By a rotational pot-core transformer approach, the rotor-side energizing of the excitation windings can be provided isolated and free of wear. Design/methodology/approach – For design purpose, an analytical model of the inductive link and the compensation network elements is shown. Based on a pot-core transformer approach, possible types of compensation networks regarding motor-specific constraints were carried out and compared among themselves by parameter studies. The analytical parts of the model were subsequently validated with measured data of an appropriate core and accompanying FEM calculations. On the basis of an experimental prototype system, the approach has been tested both stationary and transient. Findings – The publication exemplifies how a brushless excitation system for generators and motors can be inexpensively designed and implemented. Originality/value – This paper systematically presents a comprehensive analytical approach for brushless excitation systems as well as a prototypical system. Compensation network elements regarding motor-specific constraints were carried out and compared among themselves by parameter studies. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to focus on various control strategies for permanent magnet synchronous generator (PMSG) systems, in order to stabilize the dc link output voltage over a wide operation speed range. Design/methodology/approach – Two control methods, namely, the flux regulation control (FRC) which adjusts the stator flux linkage and then indirectly stabilize the dc link voltage, and the direct voltage control (DVC) which directly stabilize the dc link voltage by regulating the power angle, are proposed in this paper. Both methods can be realized by either approach of the conventional space vector pulse width modulation (SVPWM) or the proposed single voltage vector modulation (SVVM). Findings – The FRC can optimize the field in the PMSG, however, the realization is complicated. The DVC need not estimate and regulate the stator flux linkage, hence is easy to implement. On the other hand, the SVPWM can provide smooth armature current and dc link voltage, while the SVVM applies only one voltage vector during each control cycle, hence, is simple to realize and requires the minimum switching on the PWM rectifier. All cross-combinations between the two control methods and the two realization approaches work well. Originality/value – The proposed FRC and DVC methods are simpler than the conventional field oriented control, while the proposed SVVM is a novel and efficient approach to generate the PWM status. Optimal cross-combination, either of SVPWM-FRC, SVVM-FRC, SVPWM-DVC and SVVM-DVC, can be chosen to satisfy the system characters and requirements. [ABSTRACT FROM AUTHOR]

Purpose – The starting hesitation of a switched reluctance motor (SRM) is an issue which must be considered in the early motor design. It is mostly handled as a control concern. The starting procedure of a SRM using a single Hall-effect position sensor is analysed in this paper. This low cost position measurement solution requires a specific control strategy. That has been developed for a three-phase 6/4 SRM. The paper aims to discuss these issues. Design/methodology/approach – The starting procedure begins with a rotor alignment step intending to bring the rotor to a known position. Afterward, only one phase is supplied on a periodic basis, to drive the rotor in the desired direction and accelerate up to a predefined speed threshold. Thus, the proposed procedure drastically simplifies the control strategy and permits a low cost sensor based control. 2D finite elements simulations are performed to analyse the starting performances in terms of response time and power efficiency. Both electrical and mechanical transients are considered in the simulation model thanks to simplifying assumption which consists in applying a time averaged voltages instead of instantaneous switching. Finally, the entire starting procedure with a one phase supply procedure is tested experimentally. Findings – A starting procedure of a three-phase SRM is implemented. The control effectiveness is validated by complementary FE calculations and measurements. Originality/value – The starting hesitation issue of a three-phase SRM is solved with an easy control strategy. During the acceleration phase, only one phase is self-controlled. [ABSTRACT FROM AUTHOR]

Purpose – Due to linear structure, linear switched flux permanent magnet machines (LSFPMMs) also may have odd pole primary, such as 9, 15, 21, etc., without unbalanced magnetic force in equivalent rotary machines. The paper aims to discuss these issues. Design/methodology/approach – In order to increase the thrust force density, the influence of some major design parameters, including split ratio, PM thickness, primary slot width and secondary pole width, are investigated by finite element analysis. For reducing the thrust force ripple under on-load condition, the end auxiliary teeth are adopted and their positions are also optimized. Findings – This novel 9/10 primary/secondary poles LSFPMM has high average thrust force and low thrust force ripple by optimization. The results demonstrate that the odd pole primary may be a good candidate for long-stroke linear direct drive application. Originality/value – A novel 9/10 primary/secondary poles linear switched flux permanent magnet machine is developed in this paper. The similar conclusions could be obtained for other LSFPMMs with odd pole primary. [ABSTRACT FROM AUTHOR]

Purpose – The use of power electronic equipment such as conventional AC-DC-AC converters cause several problems in electrical networks and its components. They generate harmonic currents and disturb the electrical power sources; so, it is necessary to research alternative topologies of power electronic converters based on advanced intelligent controllers, which reduce or even eliminate harmonics to achieve energy-saving and environmental protection. The use of matrix converter (MC) is, considered as an attractive solution to maintain pure sinusoidal input and output current waveforms. The paper aims to discuss this issue. Design/methodology/approach – The studied system is composed of a three phase matrix converter (TMC) feeding a linear R, L load and a trees phase rectifier considered as a non-linear load; the proposed control strategy is based on a fuzzy logic controller (FLC) associated to the (space vector modulation) SVM modulation technique, this choice is motivated by the advantages that represent the combination of FLC and SVM in term of power quality enhancement in both input and output sides of MC. Findings – The model is validated based on simulation results that illustrate the effectiveness of the proposed system in term of power quality amelioration. The high performance of the proposed FLC is illustrated in all study cases especially in the case of perturbed input voltage, it is not only able to keep the whole system stable, but also it reduces harmonic distortion THD to respect international standards recommendation. Originality/value – In this paper, an associated linear (RL), non-linear loads and TMC is studied. From the mathematical point of view, the MC is modeled and analyzed. From the technique point of view, the MC allows sinusoidal current absorbance from the network with good qualities in term of harmonic distortion compensation, and high reliability under various loads and disturbed input voltage. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is propose a novel integrative transverse-flux linear compressor (TFLC), which integrates compressor into a single-phase transverse-flux linear oscillating actuator with moving magnet. Its main merit is having similar lamination as rotate motor which is easy to be stacked. Design/methodology/approach – The simple lumped circuit model accounting for magnetic saturation, armature reaction and axial fringing effect is proposed. Based on this model, the magnetic field in air gap is calculated, and then the optimal PM height, PM length, split ratio and pole number are found. The predicted thrust force, stroke and system resonant frequency at no load are validated by prototype measurement. The relation of system resonant frequency and load are also measured. Findings – In this novel TFLC, the optimal split ratio is in area of 0.54∼0.56 and pole number is 6. For designed stroke 10 mm, suitable PM height and length are 3 mm and 63 mm, respectively. By measurement, the predicted thrust force, stroke and system resonant frequency at no load are validated. The measurement also shows that the system resonant frequency can be improved from 30 Hz of no load to 39 Hz at 0.7 Mpa air load. Originality/value – The novel TFLC has excellent driving performance and simple structure for maintenance. It can produce enough pressure to meet the requirement of refrigerator, so it is a strong candidate for refrigerating apparatus. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to deal with several approach to recover the torque production capability of a five phase double-layer fractional-slot PM machine under faulty operation. The considered fault is an open-circuit coil in a given phase. Design/methodology/approach – In a first step, the mean futures, such as the phase back-EMFs and the electromagnetic torque, are computed by finite element analysis under healthy operation, and are taken as references. Then, they are investigated, under a faulty coil, for different approaches to recover the torque production capability. Findings – A comparison of the potentialities of the torque recovery approaches has clearly highlight the superiority of the approach consisting in the re-adjustment of the current initial phases, in an attempt to equilibrate the resulting air gap MMF. Research limitations/implications – This work should be extended by an experimental validation of the predicted results regarding the back-EMFs and the electromagnetic torque. Practical implications – The investigation of the considered five phase fractional-slot PM machine under faulty operation should be extended to several faulty scenarios in order to fulfill the requirements of many applications such as the propulsion systems. Originality/value – The paper proposes different approaches to recover the torque production capability of a five phase fractional-slot PM machine under faulty operation. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to investigate the effects of different faulty scenarios on the induction motor (IM) operation with emphasis on the currents in the rotor bar and end rings. Design/methodology/approach – The modeling of the IM followed by a graphical representation-based analysis of the rotor steady-state currents under healthy operation is treated. Then, a case study is considered in order to investigate different faulty scenarios with a focus on the rotor cage currents. Findings – It has been found that the rotor faults greatly affect the currents in the bars and in the end rings both in amplitude and in harmonic content. These vary according to the relative positions with respect to the fault such that: the currents in the bars adjacent to the faulty one(s) have the highest amplitudes with the lowest harmonic content; and the ones in the ring portions adjacent to the faulty one have the lowest amplitudes with the highest harmonic content. Research limitations/implications – Although the simulated model has confirmed the well known IM behavior under healthy operation, it would be appreciated if the obtained results under faulty operation would be validated by finite element analysis. Practical implications – It is of great interest to investigate the effects of faulty scenarios on the rotor cage currents, in order to take appropriate actions starting from the design of the IM. Originality/value – A deep investigation (including the waveforms, the phasor diagrams and the harmonic content) of the effects of different faulty scenarios on the IM rotor cage currents represents the major contribution of this work. [ABSTRACT FROM AUTHOR]

Purpose – Oscillations and related stability problems of synchronous generators are harmful and can lead to power outage. Studies have shown that currently available commercial applications of power system stabilizers (PSSs) do not ensure damping of modern generators operating in contemporary power systems at peak performances. The purpose of this paper is to contribute to development of the new PSS, which would replace currently used linear stabilizers. Design/methodology/approach – A synthesis of theoretical research, numerical simulations and laboratory experiments was the basic framework. Findings – Within a problem analysis, it was empirically confirmed that the currently used PSSs are not up to the needs of the present power systems. Based on an analysis of the contemporary solutions, it was found out that the most appropriate solutions are adaptive control and robust control. In this paper, the robust sliding mode theory was implemented for the PSS design. Research limitations/implications – The most notable restriction of rapid transfer of scientific solutions into a practice represents limited testing of proposed solutions on synchronous generators in power plants. Practical implications – The new PSS which would replace currently used conventional stabilizers will have an exceptional value for all producers of the excitation systems. Originality/value – The originality of the paper represents the development of the new robust sliding mode PSS and qualitative assessment of the developed stabilizer with two competitive stabilizers, i.e. the conventional linear- and advanced direct adaptive-PSS. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to focus on the machine design and control strategy of the permanent magnet synchronous generator (PMSG) system, especially utilized in variable speed applications, in order to stabilize the output voltage on the dc link over a wide speed range. Design/methodology/approach - Different ac/dc power converter topologies are comparatively studied, each with an accordingly designed PMSG, so as to investigate the influence of the armature winding inductance as well as the relationship between the PMSG and power converter topologies. Findings - Pulse width modulation (PWM) rectifier is preferable for the said application due to its good performance and controllability. Moreover, by employing the PWM rectifier, relatively large inductance of the PMSG is considered for both short-circuit current reduction and field regulation. Originality/value - Field-regulating control is realized with a space vector PWM (SVPWM) rectifier, which can weaken the PMSG magnetic field during high-speed operation, while even properly enhance the field at low speed, ensuring a small change of the PMSG output voltage and a stable dc voltage. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to present a numerical approach for the computation of 3D magnetic fields in rotating electrical machines. The technique is suitable for the computation of flux densities and forces in the end windings of large synchronous turbo generators (TG). Design/methodology/approach – The magnetostatic FEM model of the generator end windings is carried out for different displacements of the rotor axis to the stator magnetomotive force (MMF) axis. The method is based on a parallel integral formulation allowing to substantially reduce the computational effort. Findings – The computational model requires only the discretization of magnetic materials and conductors and is fast enough for carrying out 3D analyses on a time scale fast enough for the needs of the designer. As far as the present application is concerned, the analysis of a synchronous generator in the class of 300-400 MVA has shown that the most stressed elements of the armature conductors are those closer to the stator ends. The study demonstrates that the maximum stress component on the end windings is axial and is achieved when the MMF is aligned to the direct axis. Originality/value – The present approach combining an efficient integral formulation, the sparsification of the relevant matrices and the parallel implementation of the related algorithms gives rise to an original computational tool that allows a more accurate description of the machine in comparison to other numerical simulations that can be found in the literature. [ABSTRACT FROM AUTHOR]

Purpose – The paper seeks to present a methodology of computer simulation of coupled magneto-thermo-mechanical processes in various electrical engineering devices. The methodology allows determining their parameters, characteristics and behaviour in various operation regimes. Design/methodology/approach – The mathematical model consisting of three equations describing magnetic field, temperature field and field of mechanical strains and stresses (or thermoelastic displacements) is solved numerically, partially in the hard-coupled formulation. Findings – The methodology seems to be sufficiently robust, reliable and applicable to a wide spectrum of devices. Research limitations/implications – At this stage of research, the hard-coupled formulation of thermo-mechanical (or thermoelastic) problems is still possible only in 2D. Practical implications – The methodology can successfully be used for design of numerous machines, apparatus and devices from the area of low-frequency electrical engineering ranging from small actuators to large synchronous generators. Originality/value – Complete numerical analysis of coupled magneto-thermo-mechanical phenomena in electrical devices. [ABSTRACT FROM AUTHOR]

Purpose - In order to research the law of the low-frequency power oscillation which often exists in the synchronous generator rectification system, the purpose of this paper is to study theoretical analysis and numerical calculation on the static stability of the system. Design/methodology/approach - Different from the common three-phase synchronous generator operating in large power networks, the stability of synchronous generator rectification systems is much more difficult to analyze because of its nonlinear loads. Some papers have analyzed the stability of the synchronous generator rectification system and presented different parameter conditions of system stability, but since factors that influence the system stability are complex, the essence of this kind of oscillation is not completely known yet. By considering rectification systems as an equivalent to DC circuits, the correct circuit model which is necessary to analyze the rectification systemic stability is set up, the changing law and relationship of various parameters under mini-disturbances is analyzed, a linear differential equation about the DC-side average current is derived, the stability of the synchronous generator rectification system is analyzed and deduced by using Hull criterion, all parameters influencing system stability are calculated and analyzed, and their ranges for a stable rectification system are given. Also, the reason why and how the parameters affect system stability is explained. Findings - The operational stability of synchronous generator rectification systems is completely and correctly recognized. Practical implications - The paper has a reference value for the design and safe operation of synchronous generator rectification systems. Originality/value - The paper puts forward system stability criterion and gives a rational physical explanation about system stability. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to develop a controller for damping of oscillations of a synchronous generator connected to the electric network. The goal is to determine the configuration of the controller and to set up the procedure for determination of the controller parameters. Design/methodology/approach - On the basis of the analytical and numerical analysis of the so-far proposed stabilizers, the new directions towards improved and efficient stabilizer have been established. The advantage of the proposed approach has been confirmed with simulations and experimental results. Findings - Three main contributions can be highlighted: on the basis of the synchronous generator analysis, it is shown that the conventional power system stabilizer is inappropriate for optimal oscillation damping through the entire operating range; the possibility of application of the model reference adaptive control theory for stabilizer design is confirmed; and the rules have been set up for selection of the stabilizer parameters. Research limitations/implications - The power system control is rather conservative and does not allow new approaches to the control concepts. Originality/value - The paper's originality lies in the fact that the proposed adaptive approach for realizing the control system for damping of oscillations is presented completely. The configuration of the controller is presented, as well as the method for determining the adaptation mechanism parameters. [ABSTRACT FROM AUTHOR]

Purpose - Operation of synchronous machines in the power range of several 10?MW with variable speed up to 7,000?rpm using a current converter is, thanks to the development of power switches, possible and economically reasonable today. However, current harmonics, produced by converter, generate additional losses, especially eddy current losses on the rotor surface are produced by the converter, which strongly depend on the rotor permeability. The purpose of this paper is to show that an accurate machine modeling is required, in order to consider the nonlinearity of electromagnetic processes inside. Design/methodology/approach - This paper concentrates on the determination of the rotor surface losses in a three-phase turbogenerator feeding a current converter. Saturation of rotor steel is taken into account using a transient finite element method model of the machine, coupled with a converter model. Findings - A detailed analysis of the damper currents and losses in a turbogenerator operating with a frequency converter is presented. The effectivenes of damper winding modifications, concerning the eddy current loss reduction in the rotor surface, is depicted. Practical implications - The introduced modelling technique presents an accurate electromagnetic modelling of an I-converter-fed synchronous generator with massiv poles, which is fed by a current converter and so has to sustain additional eddy current losses in the rotor surface. In this way, the amount and distribution of these losses are evaluated more accurately which allows a more efficient design of the damper winding as well as machine cooling system. Originality/value - Some researchers have made contributions to the analysis of current converter-fed synchronous machine, regarding terminal behaviour of the machine. This paper focuses on eddy current losses on the rotor surface, considering the time and space dependent saturation aspect in the machine, particularly in the rotor. [ABSTRACT FROM AUTHOR]

The article presents a study which discusses a theory of adjustable speed decoupled generation systems. It cites the drawbacks of conventional fixed speed generation based on a synchronous generator and proposes a hybrid adjustable speed generation system made from internal combustion (diesel) engine, three phase AC/AC converter, and axial flux permanent magnet generator. It states that the hybrid system delivers high quality of AC power independent of speed and grid connection operation.