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Most permanent magnet (PM) loss studies consider only eddy current loss and neglect hysteresis. In this article, the hysteresis behavior of two NdFeB PM grades with different magnetic properties is assessed when applied in a PMSM. Data from vibrating sample magnetometer measurements and hysteresis modeling are used as a base. In addition to the main magnetic phase, the samples contained magnetic phases with reduced coercivity. Such phases may contribute to hysteresis losses in a PM material. A new model is introduced to simulate the hysteresis of rare-earth magnets of any geometric shape in the second and first quadrants of the intrinsic BH -plane. The magnetic field strength distribution in the PM material of an electrical motor is analyzed by two-dimensional finite-element method. The results are used as the input data for an analytical hysteresis model. The results indicate that the hysteresis loss resulting from the structural imperfections and geometry of the magnet may introduce a considerable loss in NdFeB PMs applied in rotating electrical machines.

This study provides an insight in the analytical estimation of the electric field along the surface of a stress grading system (SGS) in the end-winding region of an electrical machine. An analytical approach is derived for the field grading materials (FGMs) having power-law electric-field-dependent conductivity. Despite some limitations, the introduced model can be used for the preliminary analysis of SGS with specific geometric and dielectric parameters, both during sinus and pulsed voltage condition. The analytical considerations are verified with finite element simulations for 15 markedly different nonlinear FGMs, which were previously reported in the applications related to the medium voltage rotating electrical machines. Post-print / Final draft

The impact of the current vector angle on the performance of a synchronous reluctance motor (SynRM) with an axially laminated anisotropic (ALA) rotor intended for high-speed applications is studied. The paper shows that the current vector angle not only impacts on the stator winding Joule losses and iron losses, but also strongly influences eddy current losses in the rotor (when the rated torque is produced). The rotor eddy current losses are determined by the flux density harmonics produced by the stator. The air gap flux is affected both by the magnitude and angle of the current vector. However, the rotor surface harmonics are not directly related to the overall flux level (which can be quite low at a high current angle) but depend more on the values of the individual slot current linkages. Considering the dependence of rotor losses on the current vector angle, the most efficient operating point is suggested to be close to 45° or slightly larger, up to 65°, where a compromise between increasing rotor eddy current losses and winding Joule losses and decreasing stator iron losses is found. The eddy current loss distribution between the layers of an ALA rotor is analyzed in detail. With a larger current vector angle, the eddy current losses increase most in the layers close to the d-axis. This is explained by the largest current linkage in the stator slots that are in front of the layers close to the d-axis. The dependence of torque ripple on the current vector angle is also observed. An analysis of rotor and stator high-order harmonics, which determine the torque ripple, is performed.

5-kW high-efficiency induction motor is analyzed using two-dimensional (2-D) open-source platform and the results are compared with commercial software and measurements. The importance of equivalent circuit parameters in 2-D analyses is highlighted. The noncommercial and commercial software give similar results. The motor is further analyzed in the 2.5-D domain and the results are compared with measured results. The losses obtained with 2-D, 2.5-D, and using the IEC segregation procedure of losses procedure are compared. The performance of an induction machine depends significantly on different parameters such as air gap and stator tooth tip height. Their impact on losses is studied with open-source finite-element analysis. The benefit of this open-source platform in the electrical motor analysis is the ability to use parallel-computing effectively and reduce the time required to solve the electromagnetic problem. Other benefits are the transparency of all features of the software and license-free usage. It is concluded that in 2-D analyses, the open-source software can be used on industrial-scale problems as it showed acceptable results for losses, and lower computational time when using appropriate mortar and conforming boundary conditions.

New global energy efficiency classification standard IEC 61800-9-2 for frequency converters and motor systems has been recently launched. It classifies the energy efficiency of the converters and motor-drive systems and introduces three different methods to determine voltage-source converter (VSC) losses for the classification. In here, experimental tests are carried out using the input–output method and the calorimetric method to determine the losses and efficiency of a 160-kW commercial VSC. The measurement results with these two independent methods are compared and the uncertainty of the methods is analyzed. The converter electric input and output power distributions are analyzed in the frequency domain and are used further to estimate the electric power measurement uncertainty. The measurement uncertainty related to losses obtained with the input–output method is compared with the loss difference between the two methods. This is the first research work to accurately evaluate the experimental methods for the determination of the power losses and examine the validity of the energy efficiency classes of the frequency converters according to new IEC61800-9-2. An urgent need to update the loss boundaries of the IE-classes has been found and the measurement uncertainty effect on the IE-classification is discussed.

A new method for computing convection heat transfer coefficients in axial flux permanent magnet synchronous machines (AF-PMSMs) is introduced. The method is based on a two-step finite element analysis (FEA). In the first step, a simple 2D model is introduced and fluid flow and temperature fields are studied using computational fluid dynamic (CFD) technique. Convective heat transfer coefficients for all heat transfer surfaces of the model are extracted from CFD analysis and are then used as inputs to a 3D thermal finite element model. Two case studies are considered to check the accuracy of the abovementioned two-step method. One of the case studies is an air-cooled AF-PMSM that has air inlet and outlet on its enclosure and the other case is a totally enclosed AF-PMSM. The correctness of the mentioned method is verified by practical measurements on the second case. In addition, an experimental set-up is conducted to measure the temperature of different parts of the second case. It is observed that the results of the two-step CFD-FEA model are in good agreement with the experimental data. In the other case, the effect of inlet air velocity on heat transfer coefficients, as well as the thermal behaviour of the machine are explored.

This paper studies a modular permanent magnet synchronous machine (MPMSM) converted from a traditional single-core 24-slot 20-pole tooth-coil winding permanent magnet synchronous machine (TCW PMSM). The performance of the TCW PMSM is compared with the performance of the MPMSM (rearranged from this TCW PMSM) by the finite element method (FEM). It is found that if an electrical machine with a modular structure is designed, the efficiency of the MPMSM may be degraded compared with the conventional structure, especially, if a solid rotor yoke is used. However, the advantages of the proposed MPMSM are related to an option to scale up the machine by applying a certain number of modules, or removing faulty modules (while keeping the healthy modules working). This makes this type of a motor design applicable in certain life-critical applications, or in applications where scaling of the motor power might be needed. As a prototype, a low-power, low-speed generator added to a hook block of a hoist to supply power to measurement electronics is studied.

The impact of the thickness of the magnetic and nonmagnetic layers in an axially laminated anisotropic (ALA) rotor in a synchronous reluctance motor (SynRM) aimed at high-speed applications was studied. Considering possible manufacturing issues, the layers are desired to be thick rather than thin. At the same time, the layer thickness is related to the electromagnetic capabilities of the ALASynRM. In the study, a 12 kW ALASynRM was considered. As a reference, a 12 kW IM with a smooth solid rotor with copper end rings was used for comparison with the designed ALASynRM. The manufacturing procedures of an ALA rotor with certain materials were verified in practice. Strength tests of the samples were implemented showing the suitability of the selected materials for application in the prototype. In the electromagnetic design, the thickness of the ALA rotor layers has shown to have a significant impact on the rotor eddy current losses. The stator iron losses and the winding Joule losses also depend on the rotor design. Torque ripple is considerably affected by the thickness of the rotor layers and their position in relation to the stator slots.

High-speed electric machines are special types of electric machines which aim for compact, direct-driven high-speed applications and highly efficient operation, especially, when gearbox can be avoided. Design of these types of machines is highly iterative combining multiphysics optimization and leads to custom types of machines which fulfill the application-specific requirements. Synchronous Reluctance Machines (Syn-RMs) might have an axially-laminated solid rotor structure, which combines magnetic and non-magnetic layers rigidly bonded to each other by vacuum brazing, hot isostatic pressing, soldering, explosion welding or even by additive manufacturing. In the study five non-magnetic materials and nine magnetic materials are cross compared and the results show clear differences in performance, efficiency and physical properties of the rotor when made of different material combinations, and thereby can suggest the best pairs when application-specific performance criteria are known. The study is carried out on a 12 kW machine with a maximum speed of 24000 rpm.

Brushless synchronous generators (BSG) are typically used to produce an island network whose voltage is close to the nominal voltage of the generator. Generators are often used also in test-field applications where also zero output voltage is needed. The exciter construction and magnetic remanence may lead to a situation where the non-loaded generator terminal voltage cannot be controlled close to zero but a significant voltage is always generated because the exciter remanence. A new brushless synchronous generator excitation and de-excitation converter topology for test applications is proposed. The purpose is to achieve full voltage control from zero to nominal level without modifications to the generator. Insulated-gate bipolar transistor (IGBT) and Field-Programmable Gate Array (FPGA) technology are used to achieve the required fast and accurate control. In the work, simulation models were first derived to characterize the control performance. The proposed converter topology was then verified with the simulation model and tested empirically with a 400 kVA brushless synchronous generator. The results indicate that the exciter remanence and self-excitation can be controlled through the exciter stationary field winding when the proposed converter topology controls the field winding current. Consequently, in highly dynamical situations, the system is unaffected by mechanical stresses and wear in the generator.

This paper presents a comparison of optimized tooth-coil-winding modular permanent-magnet synchronous machines (TCW-MPMSMs) with H-shape and U-shape stator segments for fault-tolerance applications. Four optimization objectives are studied by means of a Particle-Swarm-Optimization (PSO) based routine: maximum rated torque, minimum torque ripple, maximum efficiency, and minimum mutual inductance. Two 22-pole and 24-slot TCW-MPMSMs with H-shape and U-shape stator cores were evaluated and optimized aiming to optimize each objective. From the results, it was found that U-shape machines are suitable for high-torque and low-mutual-inductance requirements, crucial in fault-tolerant applications, whilst H-shape machines offer low ripple torque and slightly lower performance indices for fault-tolerance applications.

A high-speed squirrel-cage induction machine requires a totally different design compared to the traditional squirrel-cage industrial motor because of the mechanical limitations caused by the high speed. This results in a more complicated rotor construction and expensive material selection, and sets higher standards for the manufacturing precision. The objective of this paper is to demonstrate the design aspects, material selection, and manufacturing of a squirrel-cage rotor for high-speed applications. In this paper, the rotor dimensioning approach based on equations and data analysis is presented. Rotor material selection and construction topology influence on the electrical machine design are discussed. The results are illustrated with the design of a 6-kW, 120 000-r/min induction machine for a turbo circulator. The influence of rotor parameters on the electromagnetic performance of the designed machine is demonstrated. Mechanical stresses for different topologies are studied with finite-element method analysis. Several manufacturing methods for producing a high-precision rotor are described and compared. The presented rotor design approach, which enables high electromagnetic performance and robust construction, is verified by the testing of a prototype.

In this paper, a direct liquid cooling method is proposed for a radial-flux permanent-magnet motor. To demonstrate the feasibility of the cooling method, a test motor with a rated output of 205 kW was designed, constructed, and tested in an actual vehicle application, an electric city bus. The energy consumption tests were conducted by applying a heavy-duty chassis dynamometer capable of simulating the inertia, weight, and road loads that the buses are subjected to in the normal on-road operation. The electricity consumption on the real bus route of the Espoo line 11 in Finland was 0.61 kWh/km. The test results of the cooling solution show that the motor is capable of meeting the most challenging requirements of the load cycle even with a full payload. The highest winding temperature rise in the test driving cycles was only 26 °C, which proves the effectiveness of direct-liquid-cooled coils in a vehicle motor.

A permanent magnet traction motor integrated with a planetary gearbox is studied. A machine of this kind can be employed as a propulsion motor in off-road machines like agricultural tractors that have to produce either very high traction forces at low speeds or reach higher traveling speeds at lower torques. In principle, a constant power curve as a function of speed is desired, which means that the output torque of the drive system should be inversely proportional to the operating speed of the off-road machine. Such driving conditions are challenging as the electric motor has to be heavily overloaded at the lowest speeds. Therefore, it is essential to accurately evaluate not only the electromagnetic performance but also the thermal performance of the machine. This paper studies the integration principles of an electrical machine and a planetary gear. The integration poses some new challenges to the design. For example, also the lubrication and cooling can, and, in practice, must be integrated into the system. The thermal performance of the motor and cooling with the lubrication oil of the gear were analyzed. The long-term tests with the oil cooling system were carried out to verify the successful integration.

Off-road traction applications require extremely high torque, especially, at low speeds. Such a high torque can be reached by gearing up the torque of an electrical machine. A tooth-coil permanent magnet synchronous machine with an integrated planetary gear is proposed as a solution for heavy off- and on-road traction applications. The key benefits of tooth-coil permanent-magnet synchronous machine (PMSM) in the proposed drive system and its integration with a planetary gearbox are explained in detail. A multi-objective optimization is performed to determine the slot/pole combination of the PMSM and the design process of the proposed drive system is entirely clarified. The proposed tooth-coil PMSM is investigated by electromagnetic and structural finite element analysis to obtain the final design and highlight the machine performance. A prototype is built to validate the proposed system. The results show that the traction drive system works well in laboratory and offers means to serve as a traction system in heavy off- and on-road applications.

High-speed induction machines equipped with a solid steel rotor are capable of achieving a high-rotating speed than other types of machines, because of their simpler and more robust rotor structure. At the same time, however, the eddy-current losses in the solid rotor may be critical, because of the high conductivity of the rotor material, which makes it easy for axial eddy currents to travel in the solid rotor. To efficiently mitigate the rotor eddy-current losses, it is important to accurately determine the rotor eddy-current losses induced by a particular harmonic in advance. In this paper, an improved virtual permanent magnet harmonic machine (VPMHM) model equipped with a sinusoidally magnetized virtual magnet based on the finite element method (FEM) is proposed for determination of the rotor eddy-current harmonic losses. The 2-D fast Fourier transform was used to accurately analyze the time-spatial air-gap flux density harmonics. The VPMHM model was enhanced to ensure that it was able to exactly produce the required flux density harmonics in the air gap. Two algorithms for the improved VPMHM models with different hybrid excitations were proposed to determine the harmonic losses together with the other important harmonic behavior. The model was further investigated to separate the electromagnetic transients from different harmonics. Finally, the simulation time for the harmonic losses required by the enhanced VPMHM model was significantly reduced by separating the harmonic transients. All the results and conclusions presented in this paper are based on the FEM analysis.

Pulse-width-modulated (PWM) voltage source inverters (VSI) are a common way to drive induction motors in variable speed applications. As switching hardware improves, motors are driven with increasing switching frequencies, extending the frequency range of PWM harmonics. Discrete Fourier Transform (DFT) can be used to analyze the differences in the active power spectrum as switching frequency is changed. This paper covers the basic methodology on DFT-based analysis of input power measurements. Analysis on the input active power spectrum of a PWM VSI driven 5-kW induction motor is conducted at different switching frequencies.

Effective and educative induction motor (IM) Direct Torque Control (DTC) simulation with Simulink software is presented. Motor model is realized in stator reference frame and the inverter modulation is controlled with DTC principle. Inverter non-idealities are neglected and inductances and resistances of the motor are considered as constants. The DTC model is created with multiple subsystems which allows to break down the whole control system to smaller and easily understandable parts. This way the basics of the DTC can be comprehended easier, and the model used in the education of electrical drives. In addition, the Simulink model utilizes only the basic Simulink blocks, so no additional libraries are required.

This paper investigates the segregation of losses in a 5-kW IE3-rated induction machine. The stator and rotor copper, iron core, stray and mechanical losses are experimentally determined using the IEC segregation of losses-method. The loss components determined from the laboratory measurements are compared with simulated ones. Two alternative methods are used to calculate the losses using a finite element software. The first method is post-processing and the second method is to emulate the loss segregation measurement procedure. By emulating the measurements, FEM output values can be used to calculate variable and fixed losses. The results indicate that the measured losses show a good correspondence with both utilized methods.

The paper considers an idea of novel modular approach to a resolver design. The rotor of the resolver represents a simple piece of laminated steel with variable reluctance as in commercial resolvers. The stator part, however, is different. Each stator tooth is replaced with an H-core segment, which contains two windings: excitation and sensing. The design is unified in such a way that the same cores can be used in manufacturing resolvers of different sizes with different pole numbers. The size of the stator is significantly reduced because it can cover only about one saliency pitch of resolver. The solution is especially advantageous in electrical drives where the motor has a large number of poles. However, the side effect, which has a negative impact on the accuracy of a resolver with the proposed stator, should be considered during the design. The side effect is analyzed in the proposed resolver structure using the finite element method (FEM) and some approaches to reduce its negative effect are proposed.

Bearing currents are stressing industrial drives which include switching power supplies. Researchers frequently propose new countermeasures. One of the promising approaches is the reduction of parasitic capacitive couplings inside an electrical machine. Slot-opening-embedded electrostatic shields are considered a viable concept. In this work, a way to further increase the effectiveness of the approach is presented. The importance of taking the end windings into account is recalled, and a design of extended slot-opening-embedded electrostatic shields that cover also the winding overhangs is studied. The effect of the suggested extension is examined via modeling electric machines with different power ratings. In addition, the paper closes the knowledge gap of the scaling behavior of the previously introduced capacitive coupling elimination technique, based on the slot-opening-embedded grounded electrode.

A novel electrohydraulic energy converter for hybrid off-road machines is presented. The converter is utilized as a power source for hydraulic actuators enabling electrical energy recuperation. The authors have designed, built and tested a device which combines a 7 kW S3 70% electric motor, a planetary gear and a bent-axis hydraulic pump. The integration aims for a power dense small volume device, which can perform the load cycles e.g. of a log stacker. The load cycles are first simulated to define design boundaries for the motor design. The motor uses a moderate amount of oil inside motor chamber as heat transfer medium bringing the motor losses to the converter outer surfaces to be then dissipated in the ambient. The converter is attached to a log loader and real load-cycle performance is investigated. Real load cycles for a log loader are recorded, the converter performance and thermal behaviour are studied. Motor thermal behaviour and losses are studied with no oil or with a moderate amount of oil in the motor. The converter prototype cleared well the requirements in the load cycles tested.

This paper investigates the losses of a 5-kW converter-fed induction motor. The loss evaluation sensitivity in Finite Element Analysis using different calculation time steps is studied. The motor losses are studied experimentally using a sinusoidal or PWM voltage supply at different operation points. In the experiments, the recorded voltage sampling interval is $1\ \mu\mathrm{s}$ to include all the PWM – induced harmonic content in the data. However, $1\ \mu\mathrm{s}$ time step leads to a long calculation time in time stepping FEA, therefore the data is down sampled to 10 us, 50 and 100 us. The length of the FEA time step is analyzed against the calculation speed and accuracy of the results.

More and more commonly, the rotating field machine drives are equipped with a frequency converter. The frequency converters enable the control of the magnetization state, torque and speed of the machine according to the needs of applications and, in principle, save energy. In turn, the pulse-width-modulation (PWM) creates additional harmonic losses over the fundamental losses in the machine. The harmonic power induced by the PWM is examined here in a case of 75 kW high efficiency squirrel-cage induction motor. The examination is carried out using an experimental setup with three commercial frequency converters at 30 different operation points of the motor. In each of the measurement points, the three-phase voltage and current waveforms are recorded as well as the corresponding electric power, current and voltage values. In the analysis, the harmonic power is segregated from the total electric power and examined as a function of the frequency, load and switching frequency.

The paper presents a design and mechanical analysis of a 100-kW high-speed electric motor with a stator core made of amorphous magnetic material for the air conditioning system of more electric aircrafts. Evaluation of critical rotational speeds and rotor mechanical stresses are reported. Experimental research has been made at a rotational speed range of 10000-60000 rpm accompanied with the rotor vibration measurements. During the tests, special attention was paid on assessing the critical rotational speeds. The paper will be useful to researchers and engineers working in the field of aircraft electrical machines and high-speed electric machines.

Torque ripple and cogging torque are thoroughly studied phenomena that occur in permanent magnet synchronous machines (PMSM). They are highly unwanted because they cause extra vibrations and noise in the system. Therefore, special design methods of PMSMs are used to reduce the torque ripple and cogging torque. This paper introduces and discovers a new method for the reduction of the torque ripple and cogging torque by applying so called quasi-skew-asymmetric rotor structure. In the paper it is shown that this method achieves similar performance advantages as of the traditional stepped skewing method and can apply several quasi-skew steps without need to apply actual skewing. This helps to avoid extra complicity of the rotor structure and extra costs related to the skewing. Further, the proposed method is very robust in terms of appearing of unwanted torque ripple and cogging torque components if some motor parameters are changed (e.g. pole geometry, stator geometry or air gap flux density harmonics), compensating all the possible torque ripples and cogging torque in a similar manner as in a traditionally skewed machine.

The problem of bearing currents as a parasitic phenomenon in electrical machines is a problematic issue in the modern industry. Although the origins and generation mechanisms of the phenomenon have been actively studied a general solution has not been given. The study presented here offers one countermeasure proposal. Not only the lamination stack area of the electrical machine is responsible for the building up of parasitic capacitances between different parts of the machine, but also the end-windings area has a significant contribution. The current paper introduces several designs of specific electrostatic shields, intended to cover the end-windings. The rate of capacitive coupling reduction was evaluated by FEM-analysis, and the effectiveness of differently designed shields was compared.

The conductivity of carbon-nanotube-based yarns is developing gradually. Individual carbon nanotubes (CNTs) offer very high conductivity levels but yarns spun of them still are in their infancy and develop slowly. Currently, CNTs are typically grown with chemical vapour deposition from methane, methanol or other carbon-rich hydrocarbons. Theoretical ideas of using graphene as a basic material to create high-conductivity nanotubes have also been presented lately. However, already present-day CNT-based yarns demonstrate conductivity levels that are considered good in principle for certain applications. This paper studies the applicability of CNT-based winding materials in electrical machine design.

Increasing the specific torque and power of a propulsion permanent magnet synchronous machine (PMSM) is important for the improvement of the performance of electrical vehicles. Among all technologies, increasing the current density and at the same time increasing the cooling capacity accordingly might be the most promising one. In this paper, the specific power of an outer-rotor PMSM is investigated by using different winding impregnation techniques. Both stator water jacket and winding direct liquid cooling are utilized. The continuous power of the designed PMSM is estimated by 3D thermal finite element analysis (FEA). For the sake of simplicity of the 3D FEA, equivalent thermal conductivities in the whole conducting region with different materials are first estimated by more detailed 2D FEA. After that, the estimated equivalent thermal conductivities are applied in 3D thermal FEA. The continuous power of the PMSM is further estimated based on temperature constraints. It is found out that the winding impregnation technique has a significant impact on the equivalent liquid-cooled winding thermal conductivity and, as a result, on the continuous power of the PMSM.

The paper concentrates on the design challenges of a 1.5 kW, 50 Hz direct on-line synchronous reluctance motor with a rotor topology defined by natural-flux-line-curve approach. A direct rotor substitution of a squirrel cage induction motor by a rotor of synchronous reluctance motor equipped with a damper winding does not guarantee a sufficient starting capability. To design a direct on-line synchronous reluctance motor with stronger starting capabilities the natural-flux-line-curve approach was modified. The proposed approach was applied in optimisation of the direct on-line synchronous reluctance motor using a genetic algorithm. The optimisation results show a clear tendency in the rotor design when trying to achieve the reliable starting capability and to maximise the steady-state performance of the synchronous reluctance motor. Both the stator design and the rotor diameter of the optimised direct on-line synchronous reluctance motor are different from those of a corresponding squirrel cage induction motor.

Being much more rugged than a rotor made of traditional steel sheets, a solid rotor is frequently used in high-power high-speed induction machines (IMs). Furthermore, by a solid-rotor machine, a higher rotating speed can be achieved. However, the solid rotor also has certain disadvantages, the relatively high solid-rotor eddy-current losses being the most serious one. Basically, solid-rotor eddy-current losses are mainly induced by time–spatial air-gap flux density high-order harmonics. The suppression of the high-order harmonics is the key means to mitigate the rotor eddy-current losses. In this paper, a novel computational model is proposed for evaluating the rotor harmonic eddy-current losses of a 2 MW, 12 000 r/min IM. The model was built on a special machine referred to as a virtual permanent magnet harmonic machine (VPMHM). The model was constructed by applying the finite-element method (FEM), and it is based on the time–spatial harmonics produced by a rotating magnet with sinusoidal magnetization. The VPMHM model links the air-gap flux density harmonics directly to the specific rotor eddy-current losses. Furthermore, according to the proposed model, three options, namely, the use of air-gap permeance modifying notches on the stator teeth, semimagnetic wedges, and their combination, were investigated in detail for mitigating the rotor eddy-current losses in the motor nominal operating point. The results and conclusions in this paper are based on the FEM analysis.

The study analyzes a potential to improve the local waste and wastewater management in a Finnish community. The Lappeenranta wastewater treatment plant (WWTP) is used as a case study. Two different technological setups are considered for improving the wastewater treatment plant. These are used to construct four alternative wastewater reclamation scenarios. The mass and energy balances for the considered scenarios are developed and used as input for the profitability evaluation. The utilization of the sewage sludge from the WWTP and municipal solid waste fraction that cannot be recycled for the generation of heat and electricity at the CHP plant is investigated with the aim to improve the economic performance of the wastewater treatment facility. The studied scenarios are initially compared based on their investment and operational costs. The cost of water treatment increases significantly in the case of the investigated tertiary treatment systems: higher amounts of chemicals and electricity are needed to improve the water quality. At the same time, the study indicates that the profitability of a WWTP integrated with a CHP plant can be reasonably high in a wide range of likely price scenarios for alternative wastewater purification systems. The results of the analysis showed a significant potential for the investigated wastewater reclamation systems to improve the efficiency of solid waste and wastewater management in the community.

Disruptive innovations in electrical machine design optimization are observed in this paper, motivated by emerging trends. Improvements in mathematics and computer science enable more detailed optimization scenarios that cover evermore aspects of physics. In the past, electrical machine design was equivalent to investigating the electromagnetic performance. Nowadays, thermal, rotor dynamics, power electronics, and control aspects are included. The material and engineering science have introduced new dimensions on the optimization process and impact of manufacturing, and unavoidable tolerances should be considered. Consequently, multifaceted scenarios are analyzed and improvements in numerous fields take effect. This paper is a reference for both academics and practicing engineers regarding recent developments and future trends. It comprises the definition of optimization scenarios regarding geometry specification and goal setting. Moreover, a materials-based perspective and techniques for solving optimization problems are included. Finally, a collection of examples from the literature is presented and two particular scenarios are illustrated in detail.

Electromagnetic design of a moving magnet frictionless linear actuator with self-holding functionality for mechanical gear shifting in a transmission application is presented. The actuator consists of a tubular magnetic circuit with stationary armature and axially moving rotating permanent magnet assembly with radial magnetisation in the air gap. The armature contains a two-piece magnetic core with a space for a winding. The effects of armature slot opening and magnetic circuit materials on the self-holding force and the acting force are studied in the whole moving range. The designed moving magnet linear actuator improves the performance of the vehicle by enabling shift times below 50 ms with no energy consumption between the shifts.

High-power high-speed induction machines (IMs) are gaining ground in various industrial applications, especially in replacing traditional motors and gearboxes driving compressors or high-pressure pumps, etc. However, the high-speed technology presents extra challenges for the mechanical structure of the machine including bearing systems. Therefore, it is often reasonable to use active magnetic bearings (AMBs) instead of traditional bearings as they provide much smaller friction and allow a not perfectly centered orbit of the rotor without affecting the lifetime of the bearings. Using AMBs in a machine, the nonuniformity of the rotor leads to an inevitable rotor eccentricity; the level of which depends on the control tolerance and dynamic characteristics of the AMB and the maximum force generated by the AMB. This rotor eccentricity results in an unbalanced magnetic pull (UMP) of the rotor, which has to be compensated by the AMB. This paper analyzes the UMPs of a 2 MW, 12 000 r/min IM in the static eccentricity, dynamic eccentricity, and mixed eccentricity conditions. The AMB system was designed and optimized with the consideration of gravity and UMP effects. Furthermore, the required current compensation for the forces in the horizontal and vertical directions was studied during the operation and verified by the finite-element method.

This study proposes a methodology to predict power losses of traction motor having an integrated planetary gear set permanent magnet electric motor, including both load-dependent and load-independent power loss components. The methodology combines a planetary gear set loss model which accounts for sliding and rolling losses at the external and internal gear mesh contact interfaces, a bearing mechanical and drag loss model, a gear drag loss model, an external and internal gear mesh pocketing loss model, a permanent magnet synchronous machine iron, and copper loss model. Power loss measurements from a developed prototype traction motor having integrated planetary gear set permanent magnet electric motor is compared to model predictions to successfully demonstrate the accuracy of the proposed methodology.

Traditional industrial electrical machines are designed avoiding strong iron saturation in the magnetic circuit. Flux-switching permanent magnet synchronous machines (FSPMSMs), however, differ significantly by their construction and magnetic circuit from the traditional PMSMs. In PMSMs, local saturation in the stator at no load can be avoided by a proper stator tooth and yoke design, but in FSPMSMs, the flux accumulates in the teeth toward the air gap, and the armature steel often becomes heavily saturated in the region close to the air gap. Therefore, it is difficult to avoid local saturation in an FSPMSM, and proper design tools are required to take this saturation into account when the machine is designed. This paper demonstrates the importance of accurate knowledge of steel properties in regions with heavy magnetic saturation. It is shown that especially the design process of an FSPMSM should be supported by an accurate $B - H$ curve of the steel up to 2.2 T and beyond (or at the point where the steel is completely saturated), because it has a significant influence on the overall performance of the machine.

Interest in producing heat and power using municipal wastewater sewage sludge as a fuel is increasing worldwide. Since its water content is initially high, sludge must be dewatered and further dried if it is to serve as an effective fuel for combustion. However, to maximize net energy production, the drying processes must use as little energy as possible. The water content in sewage sludge comprises both unbound and bound water. Unbound water content is typically extracted using a number of mechanical dewatering techniques. In terms of total solids content (TS), dewatering processes can take sludge from an initial 3–5% to a more solid 25–45% TS with minimal energy expenditure. However, this level of dryness is not sufficient for effective combustion. To produce an effective fuel, TS levels must be increased. Achieving high level of dryness involves removing any remaining unbound water and substantial bound water content as well. Heat is normally applied to accomplish this by changing the phase of the water from liquid to vapor. Although dewatering is energy-efficient, thermal drying is not. The energy used to thermally dry sludge can be two orders of magnitude greater than the energy used for dewatering. Therefore, to expend as little energy as possible to achieve the needed dryness, conventional dewatering processes clearly must be improved. This paper describes work carried out to identify promising ways to efficiently enhance the dewatering and drying of sewage sludge. Available dewatering approaches were reviewed and experiments were carried out to examine the relative effects of temperature, atmospheric pressure, and high-power ultrasound. The high-power ultrasound approach seemed to be particularly effective. The mechanisms involved include atomization, microstructural effects, cavitation, and the sponge effect, which work to reduce both internal and external resistances. Applied in the right way, ultrasound could become a very effective way to enhance mechanical dewatering.

Hysteresis losses in ferrite permanent magnets (PMs) of a rotor-surface-magnet (RSM) PM synchronous machine (PMSM) were studied by means of vibrating sample magnetometer (VSM) measurements, updated static history dependent hysteresis model (HDHM) and finite element analysis (FEA). Open magnetic circuit VSM measurement results were applied to determine the magnet intrinsic properties. The HDHM developed originally for electrical steel hysteresis modeling is adopted for ferrite PM material. FEA-based results for magnetic field strength in PMs of a tooth coil winding RSM PMSM under ideal sinusoidal and frequency converter supplies were used as input data for the HDHM and the hysteresis losses were calculated in the machine's magnets. Differently from NdFeB and SmCo PMs ferrite PMs do not seem to demonstrate significant hysteresis behavior. It was found that the hysteresis loss could be neglected in ferrite PMs in most PMSM designs if the magnet is fully polarized.

Efficient cooling is needed, for example, in traction motors which face regularly high torque peaks and generate high stator Joule losses. This paper studies the feasibility of the direct liquid cooling in the thermal management of a low-power low-voltage permanent-magnet machine. A tooth-coil axial-flux permanent-magnet double-stator-single-rotor test machine was first equipped with indirect liquid cooling using water cooling jackets and then with direct winding cooling. The winding material used is a hybrid conductor comprising a stainless steel coolant conduit tightly wrapped with stranded Litz wire. The performance of the motor is examined at various power levels using oil or water as the cooling fluid. The results confirm that the proposed direct cooling method is practical also in small machines, and furthermore, it offers significant improvements in the machine thermal management, especially, in cases where stator Joule losses dominate.

Permanent-magnet synchronous machines (PMSM) are gaining a foothold in a growing number of applications. However, the high cost of these machines compared with the prices of induction motors, whose production process is mature and material costs are low, limits the use of PMSMs with rare-earth permanent magnets in many potential cases. A viable design solution for a PMSM cost reduction is to use low-cost ferrite magnets instead of rare-earth ones. Nevertheless, it is challenging to apply ferrite magnets to a high-power rotor surface magnet PMSM because of their weaker magnetic properties compared with the rare-earth magnets and the risk of irreversible demagnetization. This paper aims to investigate the boundaries and limiting factors for achieving the maximum tangential stress and linear current density at a certain air gap diameter by using rotor surface ferrite magnets. The computed results are validated by a prototype, which was designed within the described boundaries.

Carbon nanomaterial applications are expected for consumer use within next decade. Risk management methods are reviewed by National Institute for Occupational Safety and Health, Safe Work Australia, Health and Safety Executive, and additionally Dupont's and Environmental Defense Fund's Nano Risk Framework. A new risk management method for handling carbon nanoparticles is presented, directed especially to universities and to research institutes. Small scale operations are different than those conducted in enterprises. Typically work started from the scratch, and researchers with limited experience of working with hazardous materials are distinctions to enterprise work flows. The promoter in this study has also been the life-cycle perspective for handling hazardous materials already in early stages of the research. Two risk evaluation cases are introduced in the use of multiwalled carbon nanotubes. The method behind inference logics in risk evaluation is demonstrated, and it was successfully implemented in the real carbon nanotube research project. The straight-forward spreadsheet implementation is an additional advantage due to short set-up time, due to easy system maintenance and due to the easy use of different evaluation parameter weights.