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This article presents the dynamic modeling and analysis of an electric motor with integrated magnetic spring (EMMS) when it is coupled to a weaving loom application. The EMMS can provide the majority part of the oscillating part of the load in a passive way by the magnetic spring. The electric motor provides the average torque and the remaining oscillating part in an active way. This reduces the energy consumption. To create an accurate dynamic model for the EMMS, lookup tables are generated from a finite-element model. Further, a 4-bar linkage mechanism is employed to emulate the behavior of the shedding mechanism of a real weaving loom application. Eventually, the whole system dynamic model was created in Matlab environment. Moreover, a complete experimental setup was constructed to validate the effectiveness of the proposed dynamic model and the EMMS behavior. It is shown that the proposed dynamic model effectively predicts the performance of the EMMS system. Besides, it is proved that the EMMS can effectively reduce the energy consumption of the weaving loom application. The amount of reduction in the energy consumption depends on the designed magnetic spring. For the considered application, it can reach 57%. [ABSTRACT FROM AUTHOR]

Thanks to the absence of rotor windings and permanent magnets, switched reluctance motors have a small weight construction. The integration of a modular power converter in a switched reluctance motor leads to a highly compact and fault-tolerant motor drive with small weight and high power density. In this article, a polygon-retrofitted integration topology is proposed for switched reluctance motors. Both the switched reluctance motor and the power converter are cooled with one shared cooling circuit. The power converter is designed and implemented using silicon carbide technology for its low losses and small thermal resistance. The proposed integration topology is extensively studied using multiphysics modeling and experimental measurements on a fully integrated rotating setup. A highly compact and power dense drive of 3.1 kW/L is obtained. [ABSTRACT FROM AUTHOR]

In this article, a circulating-current-excited switched reluctance generator system using a standard diode rectifier is proposed and examined. It features a dc power source connected in series with the ring-connected windings, which provides the dc-bias current as the excitation current in the windings. Using a series-connected dc power source, a dc-bias current is easily realized in the ac winding. Compared with the existing machine having dc-bias in the ac winding, the proposed generator can provide dc power with a standard diode rectifier. Less active legs and no rotor position sensor are needed for the control of the circulating current of the proposed generator, which increases the reliability of the generation system. The system configuration and the operation principle are introduced in detail. Then, the electromagnetic performance of the proposed generation system is analyzed at both open-circuit and load conditions. The asymmetric current distributions are deduced and verified by the simulations. At last, the prototype is tested under varied operation conditions and the experiments agree well with the analysis. [ABSTRACT FROM AUTHOR]

Multiphase machines with a prime number of phases (five and seven) have shown better torque density than machines with other phase numbers. Unfortunately, these machines require a special stator design. Hence, this article proposes general rewinding techniques to obtain a five-phase winding from the existing standard three-phase stator frames. The proposed rewinding techniques are applied to construct a five-phase star-connected synchronous reluctance machine (SynRM 1) and a novel combined star-pentagon winding (SynRM 2). Simple mathematical formulations are introduced to compute the equivalent winding factor. The performance of five-phase SynRMs is analyzed using two-dimensional Ansys Maxwell transient simulations under the same copper volume for both healthy and faulty cases. SynRM 1 and 2 provide 6.56% and 13.35% higher torque compared to the three-phase SynRM at rated current and at optimal current angle. The torque ripple is decreased by 17% and 30%, respectively. Moreover, SynRM 1 and 2 offer a better performance at the faulty case; e.g., at one phase opened, the average torque of SynRM 1 and 2 is 82% and 108% higher compared to the three-phase SynRM. In addition, the torque ripple is reduced by about 63% and 81%. Finally, experimental results are done to validate the proposed winding techniques. [ABSTRACT FROM AUTHOR]

In this paper, a circulating-current-excited switched reluctance generator system with the diode rectifier is comparatively studied with a field-current-separated switched reluctance generator. By using a DC power source connected in series with the winding to provide the circulating current, a controllable excitation field is established in the proposed generator. To highlight the influence of this DC voltage source, the injected field current of the field-current-separated generator is kept the same as the circulating current of the circulating-current-excited generator. Then, both advantages and disadvantages of the generators are summarized. The circulating-current-excited switched reluctance generator system inherits both the advantages of good reliability of the separated-winding generator by using the diode rectifier and low copper loss of the integrated-winding machine by combining the AC and DC current in one set of windings. Furthermore, two more practically conventional field-current-separated generators are also compared with the proposed generator in terms of the external characteristics. These two conventional generators have different winding configurations. At last, the analysis is verified by experiments. [ABSTRACT FROM AUTHOR]

This article compares the performance of an existing three-phase synchronous reluctance machine (SynRM) with an identical machine that is upgraded to a five-phase machine. Two different methods are possible to convert the existing three-phase machine to a five-phase one with minimum cost. In the first method, a five-phase SynRM (SynRM 1) is obtained by replacing the existing stator by another one that has an integer number of slots per pole, i.e., a multiple of five. In the second method, a five-phase SynRM (SynRM 2) is obtained by rewinding the existing stator with a special type of winding. This is because the slot number of the existing stators is not a multiple of five. The novelty of the article is that two five-phase SynRMs are compared with the original three phase reference machine in terms of torque and torque ripple, in healthy and fault conditions. At rated condition and optimal current angle, SynRM 1 performs better than SynRM 2 in terms of rated torque: SynRM 1 and 2 have 11.8% and 6.6% higher torque than the three-phase machine. But, SynRM 1 has 25% more torque ripple than the three-phase reference machine, while SynRM 2 has 17% lower torque ripple. At faulty case, SynRM 1 and 2 work at 74% and 79% of the healthy rated torque of the three-phase SynRM, while the three-phase SynRM works at only 43% with a very huge torque ripple. Finally, experimental measurements are obtained to validate the theoretical work. [ABSTRACT FROM AUTHOR]

Due to the significant advantages of cost savings, low temperature rises and high efficiency, synchronous reluctance machines (SynRMs) have attracted growing interest from academia to industrial applications. Numerous articles have been published to obtain a SynRM with improved performance (i.e., a high torque density and efficiency and a lower torque ripple) using different focusing points at healthy and faulty conditions such as rotor design, magnetic steel grade, stator winding, and fault tolerance control (FTC) strategy. Hence, this article reviews the scientific researches about SynRMs aiming to improve their performance. These scientific researches can be categorized into four sections: 1) optimal rotor design; 2) magnetic steel grade; 3) winding configurations; and 4) FTC strategies. [ABSTRACT FROM AUTHOR]

In this article, a fault tolerant deadbeat controller is proposed, which is able to compensate for both partial and uniform demagnetization faults in axial flux permanent-magnet synchronous machines with double rotor, even with asymmetric defects in both rotors. For this purpose, the system model used by the deadbeat controller is equipped with a look-up table of the back-emf, in function of the mechanical rotor position. This look-up table is generated by means of an analytical model based on the magnetic vector potential. With this information, the deadbeat controller can eliminate both the additional bias and ripple in the stator current components caused by demagnetization faults. The proposed control strategy is validated on a 4 kW test set-up of an axial flux permanent-magnet synchronous machine with yokeless and segmented armature topology fed by a three-phase two-level voltage source inverter, both by simulations and experiments. Key performance indicators concerning bias and ripple of the current components illustrate the superior performance of the proposed control strategy in comparison to a standard deadbeat controller without an up-to-date look-up table of the back-emf. [ABSTRACT FROM AUTHOR]

This paper proposes a method to design an electrical variable transmission (EVT) of which the stator and inner rotor contain a distributed three-phase winding, and the outer rotor is equipped with permanent magnets and a dc-field winding. The main problem with the design of EVTs is that the modeling relies on time-consuming finite-element (FE) calculations. Studying the effect of design changes is, therefore, a cumbersome task. To minimize the need for FE calculations, scaling laws are applied, which reduce the computational effort to a matter of milliseconds per design. Therefore, the losses of multiple scaled designs can be analyzed for a given load cycle while taking constraints into account such as maximum torque. By presenting this data in a performance map, the optimal design regarding the losses is easily deduced. To validate the presented methodology, FE calculations, measurements, and available literature are used. [ABSTRACT FROM AUTHOR]

This paper presents a simple and efficient magnetic equivalent circuit (MEC) model for surface axial flux permanent magnet synchronous machines. The MEC model is used to solve all the electromagnetic properties of the machine including the no load, full load voltages, cogging torque, torque ripple, and stator iron core losses. Moreover, this approach can be extended for all surface permanent magnet synchronous machines. The main novelty of this approach is the development of a static system, which accounts for the rotation. The model takes into account the rotor rotation via time-dependent permanent magnet magnetization sources. The static system matrix facilitates a very fast solving. In addition, to take into account the three-dimensional (3-D) effect, a multislicing of the machine in the radial direction is done. This boosts the simulation time to only 60 s for six slices and 50 time steps including the nonlinear behavior of the stator elements with a great accuracy. Additionally, the number of elements in the MEC can be adjusted to reduce the computational time. This model is verified by means of 3-D and two-dimensional (2-D) multislice finite-element models. In addition, experimental validations are also provided at the end. [ABSTRACT FROM AUTHOR]

A continuous demand for more efficient and more compact drives is pushing the popularity of high-speed permanent magnet synchronous machines (PMSMs). However, high rotational speeds and extreme power densities imply that an appropriate cooling of the rotor may be difficult. This is all the more important because of the risk of demagnetization when permanent magnets are operated at high temperatures. Therefore, it is paramount to reduce the losses in the rotor of high-speed machines as much as possible. One technique to reduce the eddy-current losses is introducing a shielding cylinder, i.e., a conductive sleeve that is wrapped around the magnets. However, when badly designed, such a shielding cylinder may increase, rather than decrease, the losses. Therefore, an in-depth study of the effect of the shielding cylinder on the eddy-current losses in high-speed PMSMs is required. By studying how the eddy-current losses are affected by the shielding cylinder’s thickness and its conductivity, this paper aims at providing more insight in how the eddy-current losses can be reduced. Moreover, the study of the eddy-current losses is repeated for different stator sources to evaluate the importance of accounting for the actual control strategy during the machine’s design. [ABSTRACT FROM AUTHOR]

Yokeless and segmented armature (YASA) axial flux permanent magnet synchronous machines may have asymmetrical demagnetisation defects in their two rotors. Condition monitoring, therefore, becomes more complicated than in conventional single rotor machines. To develop a real‐time condition monitoring algorithm for demagnetisation faults in YASA machines – which requires solving an inverse problem – a fast forward model is necessary. A frequency‐based analytical model is used to calculate the three‐phase terminal voltages based on the three‐phase current waveforms and the demagnetisation defects including asymmetrical defects in the two rotors. To reduce the computational time of the forward model, this study focuses on the sensitivity of different voltage harmonics on several demagnetisation faults. To this end, the Cramér–Rao lower bound technique is used to analyse the harmonics sensitivity to the demagnetisation faults. The goal of the sensitivity analysis is to select an appropriate set of harmonics that gives maximal information about the defects. It becomes much faster and useful for real‐time condition monitoring. The results of the analysis show that the subharmonics around and including the fundamental are the most sensitive harmonics to the demagnetisation defects. The analytical model is validated with experimental data and finite element simulations. [ABSTRACT FROM AUTHOR]

This paper describes how an electrical variable transmission (EVT) can be used as an alternative for mechanical continuously variable transmission (CVT) systems. An EVT is an electromagnetic power split device having two mechanical and two electrical ports. The speed ratio between both mechanical ports (rotors) can be varied in a continuously variable way, so that this machine can be used as an electromagnetic alternative for the mechanical push-belt and half-toroidal CVT. Its operating principle is based on splitting the power into an electromagnetic direct path and an electrical path involving two inverters connected back to back. Its potential use as a CVT is investigated by comparing experimental data against toroidal and belt CVT data from literature having comparable power ratings. To this end, measurements are performed on a prototype \text120-kW permanent magnet EVT. [ABSTRACT FROM AUTHOR]

An electrical variable transmission (EVT) is an electromagnetic power-split device with two mechanical and two electrical ports. It can be used in hybrid electric vehicles to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. Although crucial for the EVT design and evaluation, no papers are found to give a detailed overview of the different loss components in such a machine and how they can be calculated and measured. In contrast to conventional electrical machines, this machine has more degrees of freedom, which can be exploited to measure the different loss contributions separately. This paper proposes a methodology to identify and measure the different loss components in this kind of machines. The proposed method is able to identify the iron losses in stator and inner rotor, the copper losses, bearing losses, and slip ring friction losses separately. To this end, measurements of both torque and speed sensors in different operating points are combined. The methods are applied to identify the different loss contributions in a prototype permanent magnet assisted EVT, both in no-load operation as under load where its functionality as power-split device is evaluated. [ABSTRACT FROM PUBLISHER]

A time-harmonic analytical model is presented for a combined study of demagnetization and rotor eccentricity in single-stator double-rotor axial flux permanent magnet synchronous machines (AFPMSM). Demagnetization defects are modeled by scaling the magnetization “square wave” by magnetization factors for each individual magnet on both rotors. Static, dynamic, and mixed rotor eccentricities are modeled using a permeance function. The original contribution of the model is that asymmetrical defects in the two air gaps of the machine can be described with acceptable accuracy and limited additional calculation time. The model is validated with a finite element method and experiments in both healthy and defected operations. Because the model has a short computation time, it is useful for real-time condition monitoring of any AFPMSM with double air gap and either concentrated or distributed windings. [ABSTRACT FROM PUBLISHER]

The paper studies demagnetization detection in axial flux permanent magnet synchronous machines of the yokeless and segmented armature (YASA) type. In YASA machines, asymmetrical defects can occur: the demagnetization defects in the permanent magnets of both rotors differ from each other. Many techniques can indicate that there is a defect, even if it is an asymmetrical defect, but cannot detect which rotor has the defect, i.e., exactly locate the asymmetrical defect. In this paper, a method is proposed to detect and locate asymmetrical demagnetization defects in AFPMSMs. The method is useful for real-time condition monitoring of demagnetization defects, or as virtual temperature sensor for the magnets. A sensing coil is placed in each air gap. An analytical model is constructed, which uses the demagnetization defect and the three-phase current as input and calculates the sensing coil back-EMF. Sensing coils back-EMF data are combined with the data from the analytical model to solve an electromagnetic inverse problem. The results are the demagnetization amount and location of the demagnetization defect. The method is validated with the experimental data. [ABSTRACT FROM AUTHOR]

An electrical variable transmission (EVT) is an electrical machine consisting of a stator and two concentric rotors. It is a competitive alternative for power split devices used in current series–parallel hybrid electric vehicles (HEVs). Although tending to have high power densities, permanent magnet (PM) machines suffer from no-load iron losses. Since the torque interaction between stator and outer rotor is low during large time intervals, the EVT in this paper possesses a flux bridge with dc-field winding to modulate the stator field, while maintaining the inner rotor flux linkage. In this paper, a torque controller is proposed that optimally combines the stator, dc-field, and inner rotor currents in order to minimize the copper and iron losses in every operating point of torque and speed on both rotors. Also the electromagnetic coupling between both rotors is considered. It turns out that there are two optimal load angles for the stator currents, of which one of the two is dominant depending on speed and torque. The control is tested on a 120 kW prototype EVT, and measurement results are given to illustrate the optimal performance obtained with the proposed torque control. In addition, efficiencies are measured in order to support the statements made concerning the proposed method. [ABSTRACT FROM PUBLISHER]

In synchronous reluctance motors (SynRMs), the d- and q-axis inductances ( Ld and Lq) are nonlinear functions of d- and q-axis currents (id and iq) and rotor position ( \theta r). The main research question for dynamic studies of SynRMs in this paper is how accurate should the inductance model be to have a reliable computation of dynamic behavior and stability limits? The stability limits are important in the case of $V/ f$ control without position feedback. To answer the question, we consider three cases: 1) inductances are function of id , iq, and \theta r; 2) inductances are function of id and iq, averaged over the position \theta r; and 3) inductances are constant values, with properly chosen values. The cases 1 and 2 include saturation and cross saturation, while case 3 does not. It is found that averaging the rotor position \theta r is almost not jeopardizing accuracy of the SynRM model. However, including magnetic saturation is crucial: it is observed that using constants Ld and Lq to represent the SynRM modeling leads to a large deviation in the prediction of the torque capability compared to the practical motor. In addition, including the magnetic saturation effect in the closed-loop control of SynRMs is necessary. Then, maximum torque per ampere can be achieved. Finally, the proposed method of including the magnetic saturation and the rotor position effects in the SynRM modeling has been validated by experimental measurements. [ABSTRACT FROM AUTHOR]

An electrical variable transmission (EVT) can be used as a power splitting device in hybrid electrical vehicles. The EVT analyzed in this paper is a rotating field electrical machine having two concentric rotors. On the outer rotor, permanent magnets (PMs) are combined with a dc-field winding, being the first implementation of its kind. The magnetic field in the machine as well as the electromagnetic torque on both rotors are a function of the q- and d-axis currents of the stator and inner rotor, as well as the dc-field current. To describe and fully understand this multiple-input multiple-output machine, this paper gives an overview of the influence of the different current inputs on the flux linkage and torque on both rotors. Focus is given to the hybrid excitation in the d-axis by combining the dc-field current and the alternating currents. This has the advantage compared to other EVT topologies that unwanted stator torque can be avoided without stator d-axis current flux weakening. Results of the analysis are presented by means of the torque to current characteristics of a double rotor PM-assisted EVT, as well as the torque to current ratios. The machine characteristics are finally experimentally verified on a prototype machine. [ABSTRACT FROM PUBLISHER]

This paper analyzes and compares the synchronous reluctance motor (SynRM) performance for a conventional star winding and for a combined star-delta connected winding under healthy and faulty conditions. The finite element method is used to simulate the SynRM characteristics in case of normal star and in case of combined star-delta connected windings. For the healthy case, it was found that for the same current, the SynRM output power increased by about 5% for the star-delta connected windings compared with the conventional star connection. Moreover, the efficiency increased slightly by 0.20%. Probably the strongest advantage of the combined star-delta winding is observed when a phase fault occurs. When one phase is missing, for the same current, the star-delta connected motor keeps 80% of the rated torque in the healthy case, while the star connected motor only keeps 40%. Furthermore, the torque ripple of the star wound machine is extremely high in case of a missing phase, compared to the star-delta wound machine. Simulation results were validated by experimental results to show the effectiveness of the star-delta connected windings on the SynRM. [ABSTRACT FROM PUBLISHER]

The rotor design of Synchronous Reluctance Motors (SynRMs) has a large effect on their efficiency, torque density and torque ripple. In order to achieve a good compromise between these three goals, an optimized rotor geometry is necessary. A finite element method (FEM) is a good tool for the optimization. However, the computation time is an obstacle as there are many geometrical parameters to be optimized. The flux-barrier widths and angles are the two most crucial parameters for the SynRM output torque and torque ripple. This paper proposes an easy-to-use set of parametrized equations to select appropriate values for these two rotor parameters. With these equations, the reader can design a SynRM of distributed windings with a low torque ripple and with a better average torque. The methodology is valid for a wide range of SynRMs. To check the validity of the proposed equations, the sensitivity analysis for the variation of these two parameters on the SynRM torque and torque ripple is carried out. In addition, the analysis in this paper gives insight into the behavior of the machine as a function of these two parameters. Furthermore, the torque and torque ripple of SynRMs having a rotor with three, four and five flux-barriers are compared with three literature approaches. The comparison shows that the proposed equations are effective in choosing the flux-barrier angles and widths for low torque ripple and better average torque. Experimental results have been obtained to confirm the FEM results and to validate the methodology for choosing the rotor parameters. [ABSTRACT FROM AUTHOR]

An electrical variable transmission (EVT) is an electromagnetic device with dual mechanical and electrical ports. In hybrid electric vehicles (HEVs), it is used to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. The most important feature is that the power splitting is done in an electromagnetic way. This has the advantage over mechanical power splitting devices of reduced maintenance, high efficiency, and inherent overload protection. This paper gives a conceptual framework on how the torque on both rotors of the EVT can be simultaneously controlled by using a field-oriented control (FOC) scheme. It describes an induction-machine-based EVT model in which no permanent magnets are required, based on classical machine theory. By use of a predictive current controller to track the calculated current reference values, a fast and accurate torque control can be achieved. By selecting an appropriate value for the flux coupled with the squirrel-cage interrotor, the torque can be controlled in various operating points of power split, generation, and pure electric mode. The conclusions are supported by simulations and transient finite-element calculations. [ABSTRACT FROM PUBLISHER]

This paper investigates the influence of various electrical steel grades on the torque and efficiency of synchronous reluctance motors (SynRMs). Four different steel grades are studied for the same motor geometry. A finite-element method is combined with an experiment-based magnetic material model to study the effect of the four steel grades on the performance of the SynRM. On the one hand, there is a negligible effect on the torque ripple because this ripple depends mainly on the motor geometry. On the other hand, it was found that the material properties have an obvious effect on the SynRM efficiency and output power. Evidently, the low loss grades result in higher efficiency: 9% point higher for NO20 compared with M600-100A. One of the four considered grades is designed to have a higher flux density in the useful magnetic field range (a few hundreds to a few thousand amperes per meter). This grade has somewhat lower efficiency, but results in a higher saliency ratio and an 8% higher torque output compared with the worst grade. Some experimental validation results are shown. [ABSTRACT FROM AUTHOR]

The rotor discs in axial flux permanent magnet (PM) machines have similar properties as a radial fan, and therefore, the convective cooling may have a significant influence on the thermal design of these machines. To research the impact of convective cooling on the thermal properties of axial flux PM machines, a coupled electromagnetic and thermal model is introduced in this paper. This technique models a segment of the stator and the rotor only and links them together by analytical equations of the convective heat transfer at different boundaries of the machine model. This results in an accurate and time efficient multiphysics model. The coupled electromagnetic and thermal modeling technique is validated with measurements on a 4 kW axial flux PM machine having the yokeless and segmented armature topology. [ABSTRACT FROM AUTHOR]

This paper presents a complete analytical model for surface-mounted permanent magnet synchronous machines (PMSMs). A new simple and fast technique was developed to obtain accurate results in the calculation of machine parameters electromotive force (EMF), torque, and losses. This technique is based upon the combined solution of two models. The first model generates an exact solution of Maxwell’s equations in the air gap area applied to a very simple geometry. The second model gives an accurate solution in the detailed parts with complex geometry, based on a magnetic equivalent circuit (MEC) to obtain fast and accurate results in a simple way. The machine’s global quantities are then obtained and validated using the results of a finite element model (FEM) for different loading conditions and geometries. Compared with FEM, the proposed combined solution has the advantage of flexibility in the geometrical machine parameters, significantly less CPU time and an accuracy for the considered PMSM up to 4.85% in the EMF, 4.41% in the torque, and 4.44% in the iron losses. Finally, the relation between grid refinement in the MEC (coarse or fine grid of reluctances) and accuracy is pointed out, showing that the EMF can be accurately computed with a rather coarse grid, while accurate loss computation requires a fine grid. [ABSTRACT FROM AUTHOR]

This paper presents an analytical method for permanent magnet demagnetization detection in an axial flux permanent magnet synchronous machine. First, a forward model is built to calculate the three phase terminal voltages with inputs of three phase currents, the geometry of the machine, and the electromagnetic properties of the machine. To model the demagnetization fault, the scalar potential equation is solved. The magnetization waveform is a square wave corrected with magnetization factors that represent the individual magnetization of every magnet. Second, the forward model is inverted so that the magnetization factors are computed out of the three phase currents and the three phase terminal voltages. The forward model is validated with experimental data and finite element simulations. [ABSTRACT FROM AUTHOR]

The efficiency of permanent-magnet (PM) synchronous machines with outer rotor and concentrated windings is investigated as a function of the mass of magnets used, keeping the power, volume, and mechanical air-gap thickness constant. In order to be useful for electric vehicle motors and wind turbine generators, the efficiency is computed in wide speed and torque ranges, including overload. For a given type and amount of magnets, the geometry of the machine and the efficiency map are computed by analytical models and finite-element models, taken into account the iron loss, copper loss, magnet loss, and pulsewidth-modulation loss. The models are validated by experiments. Furthermore, the demagnetization risk and torque ripple are studied as functions of the mass of magnets in the machine. The effect of the mass of magnets is investigated for several soft magnetic materials, for several combinations of number of poles and number of stator slots, and for both rare earth (NdFeB) magnets and ferrite magnets. It is observed that the amount of PM material can vary in a wide range with a minor influence on the efficiency, torque density, and torque ripple and with a limited demagnetization risk. [ABSTRACT FROM PUBLISHER]

Due to their high efficiency and power density, permanent magnet synchronous machines (PMSMs) operating at high speed have recently gained a lot of attention. The development of high-speed PMSMs requires a good understanding of the physics related to the operation of such machines. Moreover, accurate modeling tools are needed when designing high-speed electrical machines. In this paper, the subdomain modeling technique is used to analytically compute the magnetic field of an electrical machine. The idea behind this technique is to divide the machine in a number of subdomains, in which the problem is simplified. The solutions in the different subdomains are then linked by imposing physical boundary conditions. The described model immediately considers the slotting effect and the eddy-current reaction field of a shielding cylinder (SC). The SC is a conductive sleeve, which is wrapped around the magnets. Its goal is to reduce the rotor losses at high-speed operation. This paper starts by introducing the applied modeling technique and the studied machine. Second, the basics of the model and its development are discussed. Finally, the results are compared with results of a finite-element (FE) model. A very good agreement between the proposed model and the FE model is observed. This implies that the developed model is indeed a powerful modeling tool for high-speed PMSMs. Moreover, it provides great insight in the machine’s physics as well. [ABSTRACT FROM PUBLISHER]

Similar to standard three phase direct on line induction motors are three phase line-start permanent-magnet machines (LSPMMs) susceptible to grid voltage distortion. Although straight forward adaptation of harmonic loss mechanisms for standard squirrel-cage induction motors to LSPMMs seems appropriate, this study will indicate that harmonic loss calculations of induction machines are unsuitable to give accurate or even reasonable estimations of the influence of supply voltage distortion on the energy efficiency of LSPMMs. This research will specifically address the interaction of rotor-induced harmonic currents. Finite-element modeling is used in order to address the effect of supply voltage distortion on the segregated losses of an LSPMM. Finite-element modeling (FEM) allocates the majority of the harmonic loss to the rotor and shows shifting the relative phase angle between identical magnitudes of superimposed supply distortion of fifth and seventh order can result in a 30% reduction of rotor loss and 0.5 percentage points in overall energy efficiency. The results obtained by FEM are validated by practical measurements. [ABSTRACT FROM PUBLISHER]

On the rotors of an axial-flux PM machine, NdFeB permanent magnets (PM) are very often placed because of their high energy density. As the NdFeB-magnets are good electric conductive, electric currents are induced in the magnets when they are exposed to a varying magnetic field. This varying magnetic field has two causes: variation of the airgap reluctance due to the effect of stator slots and armature reaction due to the stator currents. As axial-flux PM machines have an inherent 3-D-geometry, full 3-D-finite-element modeling seems necessary to calculate the eddy currents in the PM and to evaluate their corresponding losses. In this paper, however, the 1-D airgap magnetic fields of multiple multilayer 2-D finite-element simulations are combined to a 2-D airgap magnetic field using static simulations. In a subsequent step, this 2-D airgap magnetic field is imposed to a 2-D finite-element model of the PM to calculate the eddy currents and eddy current losses. The main benefit of this multilayer 2-D–2-D coupled model compared to 3-D finite-element modeling is the reduction in calculation time. Accuracy of the suggested multilayer 2-D–2-D coupled model is verified by simulations using a 3-D finite-element model. [ABSTRACT FROM AUTHOR]

This paper presents the efficiency study of a 6-pole and 2-pole induction motor (IM), converted into a 6-pole and 2-pole permanent magnet synchronous machine (PMSM). Firstly, the stator of the IM was kept unchanged and the rotor was converted into a permanent magnet (NdFeB magnets) rotor, resulting in higher average efficiency. Secondly, we investigated how much the efficiency can be increased by replacing the electrical steel in the stator by another material grade. The numerical approach is based on the finite element method (FEM), taking into account the rotor movement. Iron losses are computed according to the loss separation theory. From measurements and simulations, it is observed that the efficiency increases significantly compared to the original IM. The average efficiency of the original 1.5 kW IM converted into the 1.5 kW PMSM led to a 14% higher efficiency in a speed range 0.5\Omeganom-\Omeganom and torque range 0.5Tnom-Tnom. When the stator iron is replaced by M235-35A laminations with the same geometry, the average efficiency increases by an additional 2% for the 1.5 kW PMSM with modified stator. [ABSTRACT FROM PUBLISHER]

At low speed, the rotor-position estimation in sensorless control is often carried out based on the evaluation of the phase-current ripples resulting from the supply of high-frequency voltage test signals. However, the rotor-position estimation is affected by cross-saturation in the machine, resulting in less accurate position estimations at higher loads. As the importance of sensorless control of interior permanent-magnet synchronous machines (IPMSMs) increases, it is useful to design IPMSMs in such a way that they are optimized for accurate sensorless control. The goal of this paper is to determine design aspects in the rotor geometry of an IPMSM to minimize the position estimation error due to cross-saturation. Simulations of a sensorless drive are usually based on a state-space model with constant q- and d-axis inductances and no mutual inductances. In this paper, this technique is improved by calculating the inductance matrix from several finite-element models, which allows the study of the effect of variable q- and d-axis inductances and cross-saturation on the performance of the sensorless control. The rotor design is discussed, for both IPMSMs with and without flux barriers, in order to reduce the estimation error caused by cross-saturation. [ABSTRACT FROM PUBLISHER]

The performance of a variable speed wind turbine using a direct-drive permanent-magnet synchronous generator (PMSG) as well as a PMSG with single stage planetary gearbox is compared for two grades of electric steel applied for the generator stator core lamination. A ring type, radial flux PMSG is modeled. For a fixed mechanical power input, the geometry of the generator is optimized for each turbine systems and two materials to maximize the annual efficiency of the generator. The annual efficiency is calculated based on the power curve of the generator and the probability density function of the wind speed. This function is approximated by the Weibull distribution function for a site with average wind speed of 7 m/s. For both generator systems, the annual efficiency of two optimized generators using different steel grades differs around 1%. The difference depends on a mass of active material of the generator. [ABSTRACT FROM AUTHOR]

This paper studies the losses in the magnets of a permanent-magnet synchronous machine (PMSM) with surface magnets caused by square voltage pulse width modulation (PWM) waveforms. First, the conductivity of the magnets is determined. Second, the effect of segmentation on the losses is calculated by a 3-D time-harmonic finite element model for sinusoidal waveforms. More segmentation of the magnets in axial and circumferential direction results in much lower losses in the magnets, but more losses in the massive rotor yoke. In a third step the losses are simulated and measured on an experimental PMSM for square waveforms generated by PWM. Superposition of appropriate sinusoidal losses obtained by a time-harmonic FEM seems to be acceptable in order to predict losses in a PMSM for square voltage waveforms. [ABSTRACT FROM AUTHOR]

The torque density and efficiency of synchronous reluctance machines (SynRMs) are greatly affected by the geometry of the rotor. Hence, an optimal design of the SynRM rotor geometry is highly recommended to achieve optimal performance (i.e., torque density, efficiency, and power factor). This paper studies the impact of considering the current angle as a variable during the optimization process on the resulting optimal geometry of the SynRM rotor. Various cases are analyzed and compared for different ranges of current angles during the optimization process. The analysis is carried out using finite element magnetic simulation. The obtained optimal geometry is prototyped for validation purposes. It is observed that when considering the effect of the current angle during the optimization process, the output power of the optimal geometry is about 3.32% higher than that of a fixed current angle case. In addition, during the optimization process, the case which considers the current angle as a variable has reached the optimal rotor geometry faster than that of a fixed current angle case. Moreover, it is observed that for a fixed current angle case, the torque ripple is affected by the selected value of the current angle. The torque ripple is greatly decreased by about 34.20% with a current angle of 45° compared to a current angle of 56.50°, which was introduced in previous literature. [ABSTRACT FROM AUTHOR]