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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.

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 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.

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.

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.

In permanent magnet synchronous machines (PMSM), depending on the machine application, different types of permanent magnets (PM) can be used. The most common PMs are ferrite magnets, neodymium iron boron magnets (NdFeB), and samarium cobalt magnets (SmCo). The selection of a suitable magnet for a particular machine design depends on the magnet properties: remanence, conductivity, mechanical rigidity, losses, and demagnetization characteristics. Usually, the possibility of hysteresis losses in PM materials is neglected. In this paper, however, it is demonstrated that possible hysteresis losses have to be evaluated in the machine design. It is shown by measurements and simulations that in some machine designs, hysteresis losses in NdFeB, SmCo, and ferrite magnets can be a source of significant additional ac losses that may lead to too high PM operating temperatures and a reduction in the machine efficiency.

A proper real-time system identification method is of great importance in order to acquire an analytical model that sufficiently represents the characteristics of the monitored system. While the use of different time-domain online identification techniques has been widely recognized as a powerful approach to system diagnostics, the frequency-domain identification techniques have primarily been considered for offline commissioning purposes. This paper addresses issues in the online frequency-domain identification of a mechanical system with varying dynamics; particular attention is paid to detect the changes in the system dynamics. A closed-loop online identification method is presented that is based on a sliding discrete Fourier transform at a selected set of frequencies. The method is experimentally validated by a closed-loop controlled servomechanism with a limited stroke and time-varying parameters.

Fast methods to estimate iron losses of the permanent magnet traction motor during the drive cycle of the electrical vehicle are compared. The methods use the iron loss information calculated by a finite-element analysis as a function of rotational speed both at no load and with a short-circuited stator to take into account the variable frequency and field weakening of the traction motor. The effect of iron losses on the optimal current components, providing the maximum efficiency, is studied. Several methods yield a good accuracy even based on the no-load iron loss only, but the accuracy can be improved especially in deep field weakening by including the short-circuit iron loss information in the analysis.

An electrical and mechanical design process for a traction motor in a hybrid bus application is studied. Usually, the design process of an electric machine calls for close cooperation between various engineering disciplines. Compromises may be required to satisfy the boundary conditions of electrical, thermal, and mechanical performances. From the mechanical point of view, the stress values and the safety factors should be at a reasonable level and the construction lifetime predicted by a fatigue analysis. In a vehicle application, the motor has to be capable of generating high torque when accelerating, and in normal operation, the losses of the machine should be low to be able to cool the machine. Minimization of the no-load iron losses becomes a very important electrical design requirement if the traction motor and the generator are mechanically connected with an internal combustion engine when it is operating as the only source of torque. The manufacturing costs of the motor are also taken into account in this paper.

High-speed permanent-magnet synchronous machines (HS PMSMs) are a popular topology among modern electrical machines. Suitable applications for such machines are low-power vacuum pumps, compressors, and chillers. This paper describes a systematic design methodology for an HS PMSM using two case studies. The design process for such high-speed (HS) machines is multidisciplinary and highly iterative due to the complex interaction of the many design variables involved. Consequently, no single optimum solution exists, and multiple possible solutions can meet the customer requirements. Practical solutions should be within acceptable thermal limits, should be energy-efficient, and should be rigid enough to withstand the forces exerted during operation. The proposed design flow is divided into steps that are presented in this paper in the form of a flowchart with emphasis on mechanical aspects. Each step represents a task for a thermal, mechanical, or electrical engineer. The features of each step and the prerequisites for moving to the next step are discussed. The described methodology was implemented in the design of two HS PMSMs. The output performance results of the design flow are compared with measured results of the prototypes. The design process described in this paper provides a straightforward procedure for the multidisciplinary design of HS permanent magnet electrical machines.

Thermal properties are a key issue in many applications associated with electrical machines. Because of its special configuration, an axial-flux electrical machine usually uses self-ventilation. However, this cooling method has a significant impact degrading the machine operating characteristics, and thus, an independent cooling system is desirable. The focus of this paper is on the steady-state thermal modeling and laboratory testing of an axial-flux permanent-magnet (AFPM) electrical machine intended for a traction application. The proposed hybrid cooling arrangement consists of a frame cooling circuit with a water flow inside, a set of copper bars inserted in the teeth, and a segment of potting material around the end windings. Computational fluid dynamics and finite-element analysis are applied for the preliminary design. This paper provides experimental verification of the simulation results on a 100-kW AFPM electrical machine.

Many control schemes rely on an analytical model of the servomechanism to be controlled, and hence, accurate knowledge about the position- and time-dependent parameter variability becomes crucial in many contexts, such as robust control methods. Although a properly designed robust controller can cope with a large parameter variation, real-time identification of the system parameter behavior could lead to several advantages by means of monitoring the varying dynamics, e.g., the predetermined uncertainty region around the nominal value. This paper addresses issues in online parameter estimation of a linear tooth belt drive with a limited stroke. Particular attention is paid to detecting the position-dependent changes in the system dynamics by using recursive least squares algorithm and exciting the system in different cart positions in order to identify the varying dynamics. The algorithm used is based on an indirect output-error identification scheme. The experimentally estimated parameters are compared with the corresponding two-mass model parameters. The results show an acceptable agreement and demonstrate the feasibility of the estimation method to estimate the parameters of a closed-loop controlled servomechanism with a limited stroke and time-varying parameters.

Analytical calculation methods for all the major components of the synchronous inductance of tooth-coil permanent-magnet synchronous machines are reevaluated in this paper. The inductance estimation is different in the tooth-coil machine compared with the one in the traditional rotating field winding machine. The accuracy of the analytical torque calculation highly depends on the estimated synchronous inductance. Despite powerful finite element method (FEM) tools, an accurate and fast analytical method is required at an early design stage to find an initial machine design structure with the desired performance. The results of the analytical inductance calculation are verified and assessed in terms of accuracy with the FEM simulation results and with the prototype measurement results.

Armature-reaction-compensated permanent-magnet synchronous generators are a particular type of hybrid excitation synchronous generators, where the main flux is created by the permanent magnets and the field winding is needed only to compensate the armature reaction. This paper studies the feasibility of an armature-reaction-compensated permanent magnet synchronous generator in island operation by comparison with a conventional electrically excited synchronous generator and permanent magnet synchronous generator. The aim of this paper is to demonstrate the performance of an armature-reaction-compensated permanent magnet synchronous generator and its operation principle in island operation. As part of the study, a 55 kW prototype was built and tested. The experimental results of the prototype are presented.

An accurate measurement of power or heat losses of high-efficiency electrical devices is difficult with input and output powers. In the calorimetric method, these losses are measured directly. In this paper, a functional heat loss measurement concept with adequate data processing methods is suggested for heat losses up to 2 kW. Such a heat loss range can be applied to present-day power electronic converters with the rated power of up to 110 kW and motors up to 37 kW. The measurement system does not require a complex mechanical structure or a large footprint area on the measurement site. The concept is scalable to different sizes. New features to the balance type calorimeter data processing are introduced. These include a mass flow correction, a technique to detect the thermal equilibrium, and a method to correct measured heat losses to improve the measurement repeatability and reduce the measurement uncertainty. The measurement uncertainty of the proposed calorimetric concept is 0.4%. Laboratory measurements are carried out both for a commercial frequency converter and an electric motor. These are measured at the same time with two calorimeters. The losses of these devices are measured both by the input-output and calorimetric methods.

The standard squirrel-cage induction machine has nearly reached its maximum efficiency. In order to further increase the energy efficiency of electrical machines, the use of permanent magnets in combination with the robust design and the line start capability of the induction machine is extensively investigated. Many experimental designs have been suggested in literature, but recently, these line-start permanent-magnet machines (LSPMMs) have become off-the-shelf products available in a power range up to 7.5 kW. The permanent magnet flux density is a function of the operating temperature. Consequently, the temperature will affect almost every electrical quantity of the machine, including current, torque, and efficiency. In this paper, the efficiency of an off-the-shelf 4-kW three-phase LSPMM is evaluated as a function of the temperature by both finite-element modeling and by practical measurements. In order to obtain stator, rotor, and permanent magnet temperatures, lumped thermal modeling is used. Pre-print

Traction motor design significantly differs from industrial machine design. The starting point is the load cycle instead of the steady-state rated operation point. The speed of the motor varies from zero to very high speeds. At low speeds, heavy overloading is used for starting, and the field-weakening region also plays an important role. Finding a suitable field-weakening point is one of the important design targets. At the lowest speeds, a high torque output is desired, and all current reserves of the supplying converter unit are used to achieve the torque. In this paper, a 110-kW 2.5-p.u. starting torque and a maximum 2.5-p.u. speed permanent-magnet traction motor will be studied. The field-weakening point is altered by varying the number of winding turns of machine. One design is selected for prototyping. Theoretical results are verified by measurements.

New types of heavy litz wires with noninsulated or insulated strands are offered for high-power low-voltage electrical machines, where skin and proximity effects can cause serious problems if traditional windings are used. This paper evaluates the ac resistance of a litz wire and its usability in megawatt-range low-voltage electrical machines. The evaluation is made by finite-element analysis and by resistance measurements with an experimental test setup. A simple amplifier configuration was used to minimize current and voltage phase shift errors, which are critical in this kind of low-impedance and low-frequency measurement. A simple measurement device based on the aforementioned configuration was prepared to ensure a precise measurement result. Tests were done in a frequency range of 50-200 Hz, to cover a wide range of practical high-power low-voltage electrical machines. It is found that the measured litz wire with originally noninsulated strands can be used in large electrical machines up to about 120 Hz if about 50% increase in ac resistance compared to the dc resistance is allowed. Impregnation of the originally noninsulated litz wire with vacuum pressure impregnation improved the ac resistance in one test case, and in the other case, it seemed to have no effect on the ac resistance.

Heat transfer is a limiting factor in the performance of electrical machines. Measuring the heat flux in an electrical machine is traditionally carried out indirectly with temperature measurements as there are only a few sensors for heat flux measurements. This paper describes a new experimental method to measure the local heat flux inside an electrical machine. The measurement was proven successful in the air gap of the permanent magnet machine, 37 kW 2400 min-1, under an influence of the air gap magnetic flux. The heat flux was measured by using sensors based on the transverse Seebeck effect. The test machine was an axial flux permanent magnet machine with two stator stacks and one internal, ironless rotor disc. A gradient heat flux sensor was installed in the air gap on the stator side. Local Nusselt and Reynolds numbers were calculated according to the measured heat flux results and compared with the results given by traditional methods to verify the new measurement method.

Hybrid and full electric technologies are fast emerging in vehicles and mobile working machines, where electric machines and internal combustion engines are used together to power the systems. Permanent magnet (PM) technology plays an important role here despite the high magnet prices. This paper theoretically and empirically studies the design principles of PM synchronous machines (PMSMs) for hybrid applications, where a high starting torque and a wide field weakening range are needed. Several embedded-magnet PMSM magnetic circuit topologies are considered as possible candidates. A 10-kW PMSM prototype was built and tested. Experimental results verify the theoretical considerations well.

The influence of slot-and-pole-number combinations on the leakage inductance of double-layer fractional-slot concentrated nonoverlapping winding (i.e., tooth-coil winding) permanent-magnet synchronous machines is studied. A Fourier-analysis-based method for calculating the harmonic air-gap leakage inductance applied to the current-linkage waveform (winding function) in the air gap is suggested. Different slot-and-pole combinations are considered, and their influence, in particular, on the air-gap leakage inductance is indicated. In tooth-coil machines, the air-gap harmonic leakage can have a surprisingly large impact on the machine performance.

This paper provides design guidelines for the passive LC filters. Based on these guidelines, a method to design a new type of a passive filter, called hybrid LC filter, is proposed. A filter design example accompanies the considerations; simulation and test results of the proposed filter in time and frequency domains are shown.

Permanent magnet synchronous machines (PMSM) are considered a viable option in various types of applications. However, particularly in consumer and low-power industrial applications, the price may be a factor that limits the use of PMSMs. In addition to a different technology, the main reason for the high price of PMSMs is the use of expensive neodymium or samarium-cobalt magnets. Their use is necessary only if a high motor torque T to linear current density A ratio (T/A) is required. Ferrite permanent magnets are low cost, abundant, and have negligible eddy current losses in low-frequency applications such as motor drives. They have a much lower energy product (BHmax) than the most modern magnets. Because of the high prices of rare earth magnets, many parties are seeking for opportunities to use ferrites instead. In the case of rotor surface ferrite magnets, the air gap flux density remains low. The air gap torque producing tangential Maxwell stress is proportional to the product of the air gap flux density Bδ[ Vs/m2] and the linear current density A [A/m]. If the flux density is low and A cannot be increased, the rotor has to be made larger than in machines having a high air gap flux density. In the case of multiple pole machines, the outer rotor approach, with its low rotor yoke height, offers an interesting alternative. The air gap diameter of these machines can be made larger than in conventional inner rotor type motors without increasing the machine outer dimensions. In this paper, an outer rotor PMSM with ferrite magnets is analyzed and tested. The machine characteristics in a fan drive are compared with an induction machine of the same power.

The energy efficiency of an electro-hydraulic forklift is significantly improved by using a permanent-magnet-synchronous-motor-servo-drive-based direct pump control to control the position of the fork without control valves. This paper provides a short evaluation of the hydraulic system and a more detailed analysis of the losses of the electric machine drive system. A theoretical approach is taken and the results are verified by practical measurements. Finally, possible improvements of the energy efficiency in the suggested system are discussed.

Energy efficient pulse-width modulation inverters are widely used to control electrical machines accurately for process needs. The pulse-width modulation, however, has also adverse effects and produces additional losses in the motor. These losses increase the motor temperature and result in derating of the machine power in converter use. A reliable and reasonably accurate loss model of an induction motor drive system is important for the performance prediction of a variable-speed drive. A two-level frequency converter main circuit model is coupled to a finite-element method motor model. The drive model is controlled by closed-loop direct torque control. The frequency converter losses are calculated analytically, and the finite-element method motor model provides an analysis of the motor losses. The simulation results are compared with measurement results.

This paper continues the design considerations of a novel type of passive filter called hybrid LC filter (HLCF). The filter is aimed at significant reduction in high-frequency differential mode (DM) and common mode (CM) currents in speed-controlled ac drives. A model of the HLCF is presented. Based on the model, a transfer function of the HLCF is found. The HLCF behavior is analyzed in frequency domain. A method for HLCF frequency-domain behavior estimation with asymptotes is proposed. A comparison of the measured, simulated, and calculated results in frequency domain is presented.

Mechanical interactions between a wind turbine and a direct-driven permanent-magnet synchronous generator (PMSG) are studied, and a model to analyze the system behavior is suggested. The proposed model can be applied to analyze the mechanical vibrations of direct-driven wind turbine installations both in steady state and in dynamic cases. The cogging torque and torque ripple of the PMSG are used as excitation sources in the mechanical model. Four different permanent-magnet rotor constructions are analyzed. It is shown that the maximum allowable value of the cogging torque of the direct-driven permanent-magnet wind generator in this case is 1.5%-2% of the rated torque even when the corresponding resonance frequency does not occur in the operational speed range of the wind turbine. Furthermore, it was noticed that the resonance caused by the excitation torque should occur at the lowest possible speed.

This paper introduces an alternative implementation of the traditional LC filter, called hybrid LC filter (HLCF). The construction described in this paper contains two foil windings that integrate inductance and capacitance into one unit. The main aspects of the HLCF design are considered. The experimental data show that the device proposed here can be used, instead of traditional LC filters, as an alternative solution for the mitigation of the adverse effects of the pulse-width modulation (PWM).

This paper investigates the suitability of solid-rotor induction-motor technology for a natural-gas-compression application with a high power output. To this end, a new solid-rotor design for an 8-MW 6.6-kV 12 000-min-1 motor without any copper parts in the rotor was developed, and the motor performance was tested. In this paper, solid-rotor material selection, rotor slitting, and the end effects of the purely solid rotor are discussed. A frequency-dependent end-effect correction factor is introduced, and a method for the rotor-end-leakage correction is presented. The performance of the proposed end-effect correction factor is verified by comparing the calculated torque and power factor with the measured values.

A lumped-parameter-based thermal analysis applicable to radial-flux electrical machines with a high power density is presented. The modeling strategies using T-equivalent lumped-parameter blocks as well as conventionally defined thermal resistances are discussed. Special attention is paid to the modeling of the convective heat transfer in the air gap of radial-flux electrical machines at different rotational speeds. A brief overview of the evaluation of different loss components is given. The performance of the developed thermal model was verified by comparing the calculated temperature values with the measurements in three different applications.

The basic direct torque control (DTC) principle is to rotate the flux linkage forward, if the torque must be increased, and reverse, if the torque must be decreased. The torque is, however, increased only up to a maximum torque of the machine, which corresponds to a load angle of about 90/spl deg/ in a synchronous machine. This paper presents a method to overcome the possible loss of synchronism when using DTC. This requires either that the rotor angle is measured or estimated. Both of these cases are considered. Simulation and laboratory results are presented to show the effectiveness of the presented method.

An improved integration method is presented for the estimation of the stator flux linkage for speed- and position-sensorless direct-torque-controlled AC machine drives. The method is based on monitoring the scalar product of the estimated stator flux linkage and the measured stator current. The AC part of the scalar product is extracted using filtering and the correction for the estimated stator flux linkage is formed from that part. Adequate performance is obtained by using simple low-pass filtering. By using adaptive filtering in the extraction, the performance of the drive is excellent. Both simulation and laboratory test results are presented, which show that the presented method works well both in steady state and in transients.

A novel rotor structure for a tooth-coil-winding (concentrated winding) open-slot axial-flux permanent-magnet (PM) machine that reduces the eddy currents and increases the main flux linkage is proposed in this paper. A composite-body-based rotor assembly and a steel-laminated layer inserted on top of the magnets are used to reduce eddy-current losses in the PMs. A prototype of an axial flux generator for a heavy-duty vehicle following this structure is optimized, analyzed and measured. The tooth coil windings produce high-amplitude harmonics in the air gap and the large slot openings reduce the rotor flux. Consequently, a rotor structure that decreases the amount of harmonics travelling through the magnets is required. Steel laminations covering the magnets have positive effects on both phenomena. Two-dimensional and three-dimensional finite-element analysis is used to verify and optimize the geometry of the laminations. Computations are verified by experimental measurements of a 100 kW test machine prototype.