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The number of auxiliary electric drives can exceed 100 for luxury cars. Due to their ever‐increasing prevalence, the electromagnetic emissions (EME) of these drives are becoming increasingly important. This work explores the influence of four different stator winding topologies on the electromagnetic emissions and the efficiency performance of fractional horsepower (FHP) brushless direct current (BLDC) drives. Two monofilar windings with a wire diameter of 0.15 and 0.27 mm, an untwisted bifilar winding, and a twisted bifilar winding are inspected. The parasitic stator to winding coupling capacitance is the motor's main source for common mode currents and thus, for radiated emissions. A three‐media capacitance model is introduced to allow estimating this coupling path in the design phase of the motor. Twisting the phases of a bifilar winding reduces the excitation of this path. Therefore, the radiated emissions are reduced by 5 dBμV/m ${\mathrm{B}}_{\mu \text{V/m}}$. The stator winding topology also affects the winding resistance and thus the efficiency. The monofilar winding with a wire diameter of 0.27 mm shows the lowest level of consumed power, followed by the monofilar winding with a wire diameter of 0.15 mm, the untwisted bifilar winding and the twisted bifilar winding. [ABSTRACT FROM AUTHOR]

This article investigates the additional opportunities and aspects in the design process of large hydro power wound-field salient-pole synchronous machines provided by full-size converter (FSC) operation. As a matter of fact, thus far, power converters for hydro power plants have been mainly selected to meet the demands of conventionally designed machines and retrofit applications. The new optimization possibilities in the motor-generator design given by the FSC operation have not yet found much attention in the literature. This article shows how FSC operated hydro power synchronous machines can be designed to have smaller volumes, lower material cost, and higher efficiencies than their conventional counterparts. A cost evaluation of various generator designs including costs for materials as well as costs for power loss during operation is performed. Furthermore, the power loss evaluation cost factors are varied to show their impact on the choice of the machine parameters for an optimum generator design. For the presented evaluation, the partial load operation of large pumped storage power plants in turbine and pumping modes is analyzed, as is the effect of the free choice of the design frequency, the power factor, as well as the synchronous reactance. Finally, a suggestion for the generator design for FSC operation is presented. [ABSTRACT FROM AUTHOR]

Electrical discharge machining bearing currents that may occur within electric machines of variable-speed-drive motor systems have been recognized for a long time. One key influential factor, the machine's capacitive voltage divider “bearing-voltage-ratio” (BVR) strongly depends on the rotor-to-frame and the stator winding-to-rotor capacitances; these are, in turn, affected by the design of the machine's stator slot. This paper presents an approach to improve the accuracy with which these capacitances can be estimated. It is based on the well-known plate capacitance equation which is then corrected by normalization functions. The functions are defined by extensive parameter studies using electrostatic finite element method (FEM) simulations. The final expressions not only allow for the prediction of the stator-winding-to-rotor and rotor-to-frame capacitances, they are also readily applicable. Thereby, they facilitate, for example, the clear-cut study of the sensitivity of the BVR towards changes in the different stator slot parameters. [ABSTRACT FROM AUTHOR]

Literature agrees that cutting may damage the electromagnetic properties of electrical steel sheets, notably along the cut edge. However, statements on the depth of the deterioration vary. An analysis of the various results presented would allow for a better consideration of the material degradation in the modeling of electromagnetic properties of the cut steel sheet in electric machines. To this aim, this paper analyzes and summarizes the deterioration depths presented in the literature. It not only provides an overview of the quantitative results, but discusses these in the context of the respective measurement method, since every technique used only provides an image of some of the aspects of the cut material affected by the cutting process. [ABSTRACT FROM AUTHOR]

Summary: This work investigates the effect of voltage unbalance on the starting and steady‐state performances of squirrel cage induction motors. Emphasis is placed on the rotor flux and slip. Both copper losses accumulated during the run up and at steady state are investigated. Five motor ratings of up to 4000 kVA operating at partial and at full load are studied. Because the same voltage unbalance factor may result in different behaviors, a voltage code is proposed to simplify referring to the individual per unit phase magnitudes. Full load operation at a voltage unbalance factor higher than 3.5% showed an increase of copper losses of more than 50%. Voltage unbalance cases that fail to pull up the motor to at least 50% of the rated speed show rotor fluxes too low to generate the required torque. [ABSTRACT FROM AUTHOR]

State-of-the-art design methods for electric machines use published correlations of either power or torque with electromagnetic and current loading, available for different cooling approaches. However, the applicability of these correlations for electric machines used within hybrid electric vehicles, with their different degrees of integration into the overall system, is limited. Using an integrated starter generator and an electric rear axle drive as example case applications, we study the influences of the thermal environment within the hybrid electric vehicle application, i.e., heat sinks and sources external to the machine on the thermal design of the machines. We quantify these influences by scaling factors for the air-gap shear stress of the machine. [ABSTRACT FROM PUBLISHER]

In this paper, the influence of three different cutting techniques, in particular mechanical cutting, solid-state laser cutting, and carbon dioxide laser cutting, on the quasi-static hysteresis curves of three different materials, commonly used with electric machines, is investigated. Furthermore, the additional effects of sample size and cutting direction are discussed. In contrast to the commonly used Epstein frame or ring sample tests, the examinations are carried out with a permeameter. A significantly different shape of the hysteresis curves of the small laser-cut in contrast to the mechanically cut samples is found. Furthermore, for some samples a point of intersection is observed above which the magnetic behavior of laser-cut samples is better than that of the mechanically cut samples. [ABSTRACT FROM PUBLISHER]

Various approaches for modeling the degrading effect of cutting on the magnetic properties of electrical steel sheets have been proposed. They differ significantly with respect to their underlying concept, applicability, and need for measurements for parameter adjustment. In this paper, we propose a classification of the different models, study their differences, and analyze the respective implementation efforts. We hereby aim to provide a tool that enables the selection of the most suitable modeling approach for a given design task, taking the influence of the cutting into consideration. [ABSTRACT FROM PUBLISHER]

Inverter-induced high-frequency bearing currents are a recognized cause of bearing failure in frequency converter-fed electric machines. Mechanical bearing faults are generally identified by vibration measurements. In this work, we submit bearings to electric discharge machining bearing currents, measure the electrical stress placed on the bearings, the resulting vibration signal and operating temperature, and apply time- and frequency-domain signal processing techniques for feature extraction. Experiments are run for 940 h of operation, so as to study the incipient bearing failure behavior. After the end of the test run, the bearing surfaces are inspected using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Bearing faults may significantly reduce the useful life of electric machines. With the advent of modern fast-switching frequency converters, electric currents induced by the high-frequency common-mode voltage of these converters have been recognized as additional, sometimes severe, contributors to bearing degradation. The degradation is understood to progress both by damaging the bearing surfaces and by altering the chemical composition of the lubrication greases, which can lead to ineffective lubrication and reduction in permissible mechanical bearing load. This paper studies the effect of grease degradation due to discharge currents on the grease dielectric strength and chemical composition of several greases typically used with electric drives. From this, conclusions on the grease selection for variable-speed drive applications are drawn. [ABSTRACT FROM AUTHOR]

This paper compares the designs of an induction and a synchronous reluctance machine-based actuator for use in an elevated-temperature environment application and compares their dynamic and loss performances: The dynamic requirements of the application must be met, while the low permissible overtemperature of the windings calls for minimum loss designs, all within a certain limited available volume. The comparison is done both theoretically, using semianalytic models, and experimentally, with realized prototype machines. The uncertainties introduced by the manufacturing process are also considered and their influences on the final products’ performances investigated. [ABSTRACT FROM PUBLISHER]

This paper discusses the design process of permanent-magnet-free ac machine-based actuators working in elevated-temperature environments for high-dynamic applications. Both demands given by the application with respect to maximum volume, torque-over-speed performance, and the thermal limits of the insulation materials, which limit the maximal loss that may occur, have to be considered. Starting from the geometry, semianalytic modeling approaches are used within an optimization algorithm to obtain a machine design suitable for this application. [ABSTRACT FROM AUTHOR]

The degrading influence of different cutting techniques on the magnetic behavior of electrical steel sheets has been well recognized. However, more research is needed to understand how the influences of different cutting techniques compare, notably with respect to laser versus mechanical cutting and for different materials. This paper addresses the influences of CO2 laser cutting, FKL laser cutting, and mechanical cutting on the magnetization characteristics and specific losses of electrical steel sheets determined by Epstein frame measurements on rectangular samples and by the measurements of stator lamination stacks. Experimental results based on three different materials commonly used with electric machines and investigated at different frequencies are provided. [ABSTRACT FROM PUBLISHER]

This paper describes a method for fast identification of the thermal behavior of vehicle integrated electric drives to propose a better understanding of electric machine design tailored to driving cycles. A simple, but satisfactorily accurate, calculation method for the estimation of machine losses, which is an input for the analytic thermal network, in the early design stage is introduced. The analytic models, which are verified using measurement data, are used for parameter and case studies for consideration of the thermal environment, with a focus on the gearbox. The first case study analyzes the influence of the gearbox on the thermal behavior of critical machine components. Aiming to use the gearbox lubricant for cooling the winding heads, an improvement of machine performance using an alternative cooling approach, which cools down the end windings, is shown in the second case study. [ABSTRACT FROM PUBLISHER]

Permanent magnet brushless dc (BLDC) machines are widely used due to various advantages such as high efficiency and high torque density, and therefore compactness as well as long expected lifetime. All of these benefits are of major interest when designing a drive for a small fan application of a few watts. This paper presents the design investigations of a small single-phase BLDC motor for such an application. Notably, it discusses different constraints which arise during the design process and which may be of special relevance due to the particular given power level and application. [ABSTRACT FROM PUBLISHER]

This paper introduces a detailed nonlinearity characterization technique for insulated-gate bipolar transistor inverters in a drive system which is able to measure device nonlinearities. Methods are derived from measurements of the voltage on the inverter phases. These measurements are obtained while applying a set of direct currents to an electrical machine. These methods are then applied to tests using alternating current. The study of inverter nonlinearities is useful in order to conduct condition monitoring. These methods fulfill the need to characterize each device in an inverter. In addition to characterizing every device using either ac or dc current, the method is resistant to noise; for these reasons, the method is applicable in the field. Simulations and experimental work demonstrate the benefits and applicability of the methods. [ABSTRACT FROM AUTHOR]

The possibility of bearing damage caused by inverter-induced bearing currents in modern variable-speed drive systems has been well recognized. However, the breakdown and current conduction mechanisms have still not been well understood today. We present results on the HF impedance properties of rolling element bearings at 300-kHz and 1.5-MHz signals—frequencies taken from the typical spectra of HF circulating bearing currents. Different motor speeds, bearing temperatures, voltages across the bearing, and two different motor sizes are investigated. Notably, we analyze the frequency of transitions between ohmic and capacitive behavior (or vice versa)—the “mode transitions”—as a function of these operating parameters: For some operating conditions, the bearing impedance alternates between capacitive and ohmic behavior without any modification of the macroscopic conditions it is subjected to. [ABSTRACT FROM PUBLISHER]

The possibility of bearing damage caused by inverter-induced bearing currents in modern variable-speed drive systems has been well recognized today. Further research is needed to develop appropriate nonintrusive methods for detection and monitoring of such currents. A radio-frequency-based nondestructive method has been applied to detect discharge bearing currents. The method is understood to work on the energy that is radiated in the electric field during the bearing discharge event. We show that the method is also applicable to high-frequency circulating bearing currents that have so far been associated with ohmic bearing characteristics and no discharges occurring. The analysis and understanding of the applicability of the method to detect such currents also contributes to further understanding of the electric characteristics of the bearing, notably the moment the current conduction begins. [ABSTRACT FROM AUTHOR]

Common-mode voltage (CMV) in voltage-source inverters (VSIs) has been well defined and is frequently referred to in the literature. While often referred to, there is no real consistency with respect to how the CMV properties of an individual modulation scheme are evaluated, lacking tools to assess the relative merits or disadvantages of a certain topology or modification of a control scheme. The way that it is analyzed is still mostly a matter of the different authors' foci. In this paper, we propose a metric for the analysis of the CMV, aiming to fill the aforementioned gap. Thereby, the CMV in VSIs is quantified by the number of possible levels and the step sizes between different levels, as well as the respective frequencies of occurrence. The first two are given by the number of levels and the number of phases of the inverter. Depending on the modulation (control) schemes, all possibly available levels or a few of these levels are present in the CMV. We illustrate the use of the tool by applying it to thoroughly study the CMV properties intrinsic to the topologies of multilevel multiphase single- as well as double-ended diode-clamped VSI drive systems. As part of this analysis, we uncover new relationships concerning the existence of zero CMV level. Furthermore, we exemplarily apply the developed tool to the assessment of the CMV properties of selected pulse width modulation (PWM) control schemes and translate the findings into an interpretation of the endangerment of a given drive to suffer damage from inverter-induced bearing currents. The theoretical findings are supported by measurements. This paper also reviews the literature on CMV in multilevel multiphase VSI systems. With the proposed metric in mind, the CMV being mostly discussed as an element of different foci becomes even clearer, confirming again the need for the development of such a tool. [ABSTRACT FROM AUTHOR]

A quick and simple test method for measuring the B– H curve and power loss in generator stators, both as loose laminations and finished core packs, has been developed. This provides a greater level of understanding about the characteristics of stator cores at various stages of the manufacturing process in order to prevent finished generators from being out of specification. The capabilities of the measurement rig have been explored both theoretically and experimentally. Experiments have been carried out on-site on industrially manufactured synchronous generators, and permeability and power loss in a batch sample of stators have been measured. Considerable degradation in the steel's magnetic properties has been found. The mean permeability at 1 T decreased by 23% after compression and welding. For specific power loss, the welding process caused an increase of 5% in the mean value and an increase of 36% in the standard deviation. The results allow conclusions to be drawn regarding manufacturing effects, variability, and generator performance. [ABSTRACT FROM AUTHOR]

Wave-propagation effects in machine windings are commonly simulated on the basis of a transmission-line model (TLM) where the parameters are extracted from cross-sectional electroquasistatic and magnetoquasistatic finite-element (FE) models of a stator slot. In this paper, three improvements are proposed. First, an additional radially-axially oriented FE model deals with the complicated return path of the common-mode current through the laminated core and leads to an additional impedance to be inserted into the TLM. Secondly, an additional TLM section is constructed using parameters extracted from an axisymmetric FE model of the winding overhang. Thereby, the impedance mismatches caused by the end-winding overhangs along the wave propagation direction are incorporated in the model. Thirdly, the capacitive and inductive inter-wire couplings are taken into account. The simulation results indicate the need of all three additions. [ABSTRACT FROM PUBLISHER]

A simplified design calculation for common-mode chokes for reducing motor ground currents provides insight on the effects of various parameters and allows easy design. Key simplifying assumptions are that the voltage rise time is short compared to the ring period and that the damping is small. Example designs for machines up to 450-mm frame size show how effective ground-current reduction is possible with small inexpensive single-turn chokes. [ABSTRACT FROM AUTHOR]

While the cause-and-effect chains of inverter-induced bearing currents have been well understood today, not much is known about the damage mechanism inside the bearings. Research has suggested that the bearing degradation is approximately proportional to the frequency of occurrence of the bearing currents. For bearing currents that occur statistically distributed—such as discharge bearing currents—this parameter has not been thoroughly researched yet. In this paper, we present an analysis of the influence of different motor operating parameters on the frequency of occurrence (“discharge activity”) of discharge bearing currents, using a non-intrusive detection method. When analyzed individually, the motor speed, motor shaft temperature, inverter switching frequency, and inverter dc-link voltage influence the discharge activity. However, the overall running time of the motor, the state—steady-state versus instantaneous—and the “operating history” on the time-scale of several days have the strongest effect on the frequency of the discharge bearing current occurrence. [ABSTRACT FROM AUTHOR]

Certain conditions can require a three-phase induction motor to be operated on a single-phase supply. The proper sizing of the required auxiliary capacitor to meet certain criteria has been discussed, both for constant and for electronics-based variable capacitors. Generally, constant motor parameters are assumed. However, as of a certain motor size, and hence, slot depth, the rotor impedance varies with slip because of skin effect. In this paper, we discuss the influence of this phenomenon on the motor performance, focusing on the peculiarities of single-phase operation. The analysis not only includes Y- and \Delta-connected motors but also a third type of connection that we refer to as “Y-segregated leg-connection” and that has not yet found much attention. [ABSTRACT FROM AUTHOR]

We present an alternative approach to analytic force computation in permanent-magnet machines, focusing on the tangential forces that generate the armature and the cogging torque. We extend previously presented methods using conformal mapping to overcome the limits imposed by the singularity of the magnetic flux density at the tooth tip that occurs during the transformation. Using our approach, the cogging and armature torques developed in lightly loaded electric machines can be computed without these limits and without introducing auxiliary parameters. We also revisit Maxwell's stress theory to compute the force on the interface of two materials with different permeabilities, in contrast to the common application to compute the force on a rigid body placed in an electromagnetic field. Using this technique, we then calculate the forces at the slot sides so that the influence of the machine design parameters on the result is directly available. [ABSTRACT FROM AUTHOR]

Linear and nonlinear Cauer-network models for nanocrystalline inductor cores are developed and used for circuit simulations of common-mode chokes for inverter-based drive systems of several hundred kW. Experimental measurements of the chokes' performance in a high-power test bed are compared to the model results. When the model is based on measured characteristics of the material used, the match to measured behavior is good. Damping inherent in the material characteristic is adequate, such that additional damping is not useful. The primary limitation to accurate prediction of loss in practice is the tolerance on specifications of core characteristics, particularly at high frequency where limits are not specified. [ABSTRACT FROM AUTHOR]

We report on a new type of inverter-induced bearing current (BC) that can occur with large inverter-based drive systems with one journal bearing. This current is a variation of the "high-frequency circulating" BC type that has been described by different authors over the last years. As with the first, the BC mirrors the common-mode (CM) current as a result of inductive coupling. However, the voltage across the bearing also mirrors the stator winding CM voltage and is not reduced to zero by the current flow. We show experimental results of measured currents and give physical explanations from which we then derive an effective mitigation technique, which is also illustrated through measurement results. [ABSTRACT FROM AUTHOR]

Ocean energy conversion systems have recently seen renewed interest, stimulated mostly by today's increasing energy discussions. In addition to ocean current energy converters, several commercial ocean wave energy projects have already been undertaken; however, no clear economic model exists for developers to follow. Therefore, this paper focuses on U.S. economic factors that affect the use of wave power for generation of electric energy. These are addressed with regard to economic and business incentives for renewables and wave energy. This paper also investigates incentive programs needed to promote wave energy conversion technology. [ABSTRACT FROM AUTHOR]

The additional high-frequency (HF) common-mode (CM) current of inverter-based drive systems can cause parasitic effects such as HF bearing currents. This HF CM current can be significantly reduced by purpose-designed CM chokes that are inserted in the drive at the inverter output. This paper discusses scaling issues related to the design of such CM chokes, of both wound and feed-through toroidal types. The requirements for the design of chokes for these applications can differ from those for CM chokes designed for use in the inverter input, such as those used for the purpose of electromagnetic interference filtering. This difference is notably due to the comparatively large magnitude of the currents involved. The developed correlations allow taking full advantage of the possibilities offered by such chokes to reduce the HF CM current and mitigate the resultant parasitic effects. The discussed relationships are derived analytically, and the results are supported by measurements. [ABSTRACT FROM AUTHOR]

Carbon brushes using electrically conductive carbon graphite have been used for shaft-grounding and current-conduction purposes for a long time. We present an alternative brush concept made from millions of conductive microfibers. If properly designed, such brushes can meet all the demands on carbon brushes but exclude the problems of excessive and hot-spotting/thermal wears commonly quoted with the first. These brushes have ultralow friction and negligible wear and are very robust toward contamination, when compared with conventional carbon-based brushes. In addition, they are particularly suitable for use with high-frequency currents and voltages, as they also allow current-conduction based on electric field emission. We develop the design criteria for such brushes, both for prevention of voltage buildup and current conduction of several tens of amperes with frequencies in the megahertz range. We support the theoretical results with measurement results taken at different rotor shaft speed. [ABSTRACT FROM AUTHOR]

In this survey paper, we show by straightforward mathematical scaling considerations that small inverter-fed ac motors of up to typical 20 kW at 1500/mm are likely to suffer from discharge (electric discharge machining) bearing currents, whereas larger motors are likely to be subjected to high-frequency (HF) circulating bearing currents. When comparing motors that operate at the same voltage level, the resulting bearing-current density is high for very small and very large motors. Smaller values occur in between these two extremes with medium size motors in the range of 10-100 kW. Therefore, electric bearing insulation is useful for larger motors to interrupt the HF circulating bearing-current path, whereas small motors need rotor shielding, common-mode voltage filters, or hybrid bearings. [ABSTRACT FROM AUTHOR]

Today, the physical cause-and-effect chains of inverter-induced high-frequency bearing currents have been well understood, but little has been known on not only theoretically possible, but also cost-effective mitigation techniques for a certain drive configuration. This paper focuses on the mitigation of discharge bearing currents, which occur predominantly with smaller motors of up to several kilowatts. We present a new mitigation technique where any voltage build-up across the bearing is discharged via static charge dissipation through a parallel path before an electric breakdown inside the bearing occurs. The technique is based on the field emission effect, has ultralow friction and negligible wear, and is very robust toward contamination, when compared with conventional carbon-based brushes. [ABSTRACT FROM AUTHOR]

Inverter-induced high-frequency bearing currents are a parasitic effect that can occur in variable-speed drive systems. While the physical cause-and-effect chains are understood, little has been known on appropriate quantitative assessment of the phenomena. This paper discusses reliable techniques for the measurement of different parameters of importance for the bearing damage assessment, including their effects on the phenomena and measured quantities. A good understanding of these correlations allows custom-design cost-effective handling of the matter. [ABSTRACT FROM AUTHOR]

The influence of different parameters of a variable-speed drive system on the phenomena of inverter-induced bearing currents has been studied under exactly the same conditions on inverter-operated alternating current motors from 1 to 500 kW. Detailed modeling may not always be applicable with practical applications in the field, where many parameters might be unknown. Therefore, the most important correlations are summarized in the form of a flowchart that is based on the physical cause-and-effect chains. This flowchart can serve as a tool for engineers to estimate the endangerment of a drive system due to inverter-induced bearing currents and select an appropriate mitigation technique if necessary, where detailed knowledge of the different design parameters is not available. [ABSTRACT FROM AUTHOR]

The occurrence of high-frequency discharge bearing currents (also called "electric discharge machining (EDM) currents") that can occur in machines of inverter-based drive systems depends strongly on the value of the capacitive voltage divider "bearing voltage ratio" (BVR) of the machine. This paper presents a straightforward approach to calculate the involved motor capacitances in order to predict the voltage across the bearing and, thereby, the likeliness of such EDM currents that are caused by this voltage to occur. The approach is based on the design parameters of the machine and does not involve additional measurements. It combines ease of application and satisfying accurateness, and allows prediction of the risk of endangerment of an inverter-based drive system due to discharge bearing currents. [ABSTRACT FROM AUTHOR]

The high-frequency circulating bearing current that may occur in machines of inverter-based drive systems can be described by an eddy-current model. The parameters of an equivalent circuit are derived from the model. The ratio between bearing current and common-mode current amplitudes for different machines is calculated. The theoretical maximum ratio is about 0.35. Copper loops applied for bearing current measurement may decrease the circulating bearing currents up to almost 40%. [ABSTRACT FROM AUTHOR]

The high-frequency (HF) circulating bearing current that may occur in the machines of the inverter-based drive systems can be reduced or even completely suppressed by the use of the electrically insulated bearings or the insulated inner bearing seats. This paper proposes a method to calculate the influence of the thickness of the insulating coat on the obtained current reduction as a function of the several machine-design parameters. The parameters of the equivalent circuit are derived from an eddy-current model. The calculation considers the transient nature of the current flow. For the standard fan-cooled motors with up to 500-kW rated power, a minimum thickness of the insulating coat of 250 μm is required to reduce the circulating bearing currents to values where the apparent bearing-current density is less than 0.1 A/mm², which is commonly taken as the threshold to the bearing failure. [ABSTRACT FROM AUTHOR]

This article introduces a unique three-phase induction machine with a large air gap and a copper-coated iron cylinder. The motor is built in an X-ray tube for medical applications where key performance indicators are the start-up time, generated rotor, and total energy during the run-up. The common equivalent circuit for induction motors is utilized to systematically analyze the effect of the rotor protrusion length variation on these key performance indicators by means of three-dimensional (3D)-FEA. However, due to the large air gap and dominating winding head standard evaluation tools, such as the no-load and locked-rotor tests do not provide accurate circuit parameters. Thus, a combined no-load and locked-rotor test evaluation is introduced. Furthermore, to avoid the time and computational effort of time-stepping 3D-FEA, time harmonic and static 3D-FEA is introduced. To validate these simplified 3D-FEA simulations, results are compared with the selected time-stepping 3D-FEA results. Experimental results verify the 3D-FEA results. After establishing a routine to identify accurate equivalent circuit parameters by means of 3D-FEA, the parameters for three different stator lengths each combined with six different rotor lengths are identified. V/f-controlled run-up simulations are then conducted to generate the results. Results quantify the tradeoff between start-up time, generated rotor, and total energy depending on the rotor protrusion, e.g., the start-up time is indirectly proportional to the rotor protrusion and directly proportional to the rotor frequency (the relative frequency between stator field and rotor speed). The effect of the rotor temperature, which can reach up to $\sim 390^\circ \,$ C, on the results is included. [ABSTRACT FROM AUTHOR]

Finite element models of electrical machines allow insights in electrothermal stresses which endanger the insulation system of the machine. This paper presents a thermal finite element model of a 3.7 kW squirrel-cage induction machine. The model resolves the conductors and the surrounding insulation materials in the stator slots. A set of transient thermal scenarios is defined and measured in the machine laboratory. These data are used to assess the finite element model. [ABSTRACT FROM AUTHOR]

Depending on the stator lamination manufacturing processes (e.g., punching, laser cutting, clamping, welding, interlocking, and bonding), the motor’s magnetic performance parameters, such as cogging torque, hysteresis torque, and iron losses, can vary significantly. In sub-fractional horsepower (SFHP) permanent magnet motors, the manufacturing influence is typically even more severe because, due to their small dimensions, practically, the whole stator material is likely to be affected. This article analyzes the magnetic performance parameters cogging torque, hysteresis torque, and iron losses of three different stator lamination stacks (i.e., M250-35A punched with interlocking, M250-35A laser cut with bonding, and NO10 laser cut with bonding) of an SFHP single-phase brushless permanent magnet motor often found in automotive fan applications. A rheometer is used for extremely accurate torque measurements in the sub-millinewton meter range, and electron backscatter diffraction measurements are performed to visualize changes in the grain morphology and crystal orientation. The findings reveal that the punched stator with interlocking is affected the most by the manufacturing process, showing the lowest cogging torque yet the highest average hysteresis torque and thus up to 40% higher iron losses. The results presented in this article allow for both making basic stator lamination design choices and translating the iron losses, as well as the hysteresis torque and cogging torque waveforms, of a laser cut and bonded prototype into those of its punched and interlocked mass-produced counterpart. [ABSTRACT FROM AUTHOR]

In recent years, electromagnetic compatibility (EMC) has become progressively important because of the rise in the number of electronic auxiliary devices in motor vehicles. This article presents an angle modulated switching strategy for fractional horsepower drives. It allows decreasing the size of the necessary EMC filter, for the example case drive used, down to less than 50%, from nine to four capacitors. Simultaneously, it reduces the radiated electromagnetic emissions over a wide frequency range by almost 10 $\,\text{dB}_{\mu \text{V/m}}$. The EMC measurements performed in a shielded chamber are compared with the results for two conventional switching strategies. Subsequently, the influence of the presented switching strategy on the efficiency and on the emitted airborne and structure-borne noise is investigated. [ABSTRACT FROM AUTHOR]

Cogging torque reduction measures are hardly applied to low-cost sub-fractional hp brushless direct current (BLDC) motors, because the additional fabrication operations involved typically increase both the manufacturing complexity and cost significantly. By proposing an innovative punching layout, this paper shows how to minimize the high cogging torque of the mass-produced single-phase outer-rotor BLDC claw-pole motor—opposed to conventional cogging torque reduction—with no increase to the manufacturing cost. Systematically, a way is presented in which the selected introduction of auxiliary slots can double the cogging torque fundamental frequency, making stator claw skewing much more effective in reducing the cogging torque; both measures can be included at the stage of punching the steel sheets and subsequent deep-drawing thereof, at no additional cost. A detailed analysis of the effects of the cogging torque reduction measures on the most important motor performance parameters is conducted. The findings show that, with the exception of a three percentage point reduction in the efficiency, the proposed design can reduce the peak-to-peak cogging torque by 70% in both the simulations and experiments. The reduction in the cogging torque translates into a reduction in the output torque ripple of 17%, ensuring smoother operation especially at low speeds. [ABSTRACT FROM AUTHOR]

As for mass-produced sub-fractional horsepower drives, non-optimal motor behavior (e.g., high cogging torque, output torque ripple, and noise) is often accepted when cost can be reduced, provided reliability is not compromised. This paper proposes an innovative claw-pole motor design for a low-cost single-phase brushless direct current fan drive, improving motor behavior with no increase to the manufacturing cost: 1) reducing cogging torque by proposing unconventional claw-pole skewing and 2) ensuring self-starting capability by implementing air-gap asymmetry. Both measures help reduce the total output torque ripple. The goal is to reduce fan drive noise, especially at low-speed operation, where cogging torque is often the dominating noise source. The design of stator claw skewing and air-gap asymmetry is presented; their effects on motor quantities are studied via simulations and experiments. With the exception of a small reduction of about 1.8% in the back electromotive force fundamental, skewing the stator claws by 30 $^{\circ }$ can reduce the cogging torque by 23% in the simulations and by 28% in the experiments. [ABSTRACT FROM AUTHOR]

Advancing the turn-off angle of the phase current of brushless direct current (BLDC) motors is a common control practice to improve the operating behavior and energy conversion efficiency of such drives by, e.g., reduction of current peaks, copper losses, and breaking torques. This paper investigates a refined switching strategy for a single-phase BLDC motor with bifilar winding to increase the energy conversion efficiency of the system. In addition to advancing the phase current turn-off angle, the turn-on angle is delayed to improve the drive's performance and increase the efficiency even further. This efficiency increase of up to 20.6% is verified experimentally for a speed range from 3000 to 8000 rpm, translating into a reduction of copper losses of up to 37.4% or a decrease of current peaks by 27.4%. The focus is on sub-fractional horsepower single-phase BLDC motors with bifilar winding which, concerning this matter, have not drawn much attention in the literature yet. The findings show that the improved switching strategy can reduce current peaks, breaking torques, copper losses, and therefore increase efficiency over the speed range of interest for fan applications. [ABSTRACT FROM AUTHOR]

While the use of foil windings in transformers and air core inductors is not uncommon, their use in electric machines is just emerging. Although prototype realizations have been reported in the literature, a definitive analysis of their thermal performance is necessary to evaluate their potential for broad applications. This paper is devoted to presenting a comprehensive model for evaluating their thermal performance including loss modeling and temperature rise prediction in realistic designs. An overview of foil windings in electric machines and their advantages in improved fill factor is presented, along with experimental results that compare the ac losses and temperature distribution under identical steady-state operating conditions with a prototype round conductor coil and foil conductor coil. A lumped parameter thermal model that predicts the heat transfer behavior of the foil conductor coil is presented along with supporting experimental results. [ABSTRACT FROM AUTHOR]

Single switch open-circuit faults in three-phase ac drives lead to undesired effects and potentially to a total failure of the drive. This paper proposes a postfault operation strategy for such faults with a focus on the limitation of losses after the reconfiguration and thereby an extension of the possible range of operation. Furthermore, a method for the reduction of alternating torque components during the postfault operation of a squirrel cage induction machine drive is proposed. The performance of the postfault operation strategy and the alternating torque reduction method are shown both via simulations and experiments. [ABSTRACT FROM PUBLISHER]

This paper presents a new method for measuring the specific losses and magnetostriction of grain-oriented electrical steel coils of up to 6000 kg. Since large power transformer (LPT) core manufacturers are mainly supplied with entire steel coils, a fast incoming goods inspection is desirable. The proposed method identifies the specific losses of the entire steel coil. In addition, we measured the magnetostriction of the coiled material, which in turn enabled us to classify the main property for LPT no-load noise. Furthermore, we show the structure and setup of the developed coil measurement system. We provide an explanation of the measurement technique and identify its requirements. Exemplary results of specific power losses and magnetostriction of steel coils are provided, and the reproducibility of the results is shown. [ABSTRACT FROM AUTHOR]

Open-switch faults in inverter-driven electric drives have recently gained increasing attention in the scientific community. Since these faults may lead to undesired effects, their fast and unambiguous detection is desirable. This paper proposes a detection algorithm for open-switch faults, which is based on the observation of the current control deviation and a subsequent test procedure. This algorithm detects the fault immediately after its occurrence within a few switching periods, even during transient operation. The proposed method is tested via simulations and experiments at different operating points of a surface permanent magnet drive. [ABSTRACT FROM PUBLISHER]