Search

A bridgeless rotor of a synchronous reluctance machine is proposed to enhance the performance of high-power and -speed synchronous reluctance machines (SynRMs). Unlike traditional transversally laminated designs that rely on radial and tangential ribs or bridges to provide mechanical integrity for the rotor, the suggested rotor incorporates separate flux guides attached to non-magnetic back plates to form SynRM rotor modules that are stacked on the shaft of the machine. This innovative structure eliminates the need for radial and tangential bridges which form a performance-deteriorating bottleneck in the design of high-power SynRMs. The paper presents a detailed analysis of the electromagnetic and mechanical aspects of the proposed bridgeless rotor synchronous reluctance machine (BLRSynRM). Furthermore, a comprehensive optimization method is implemented to demonstrate the capabilities of the proposed BLRSynRM along with comparison with conventional transversally laminated SynRM. The results show a significant increase in torque and power factor compared with conventional structure rotor. However, the proposed bridgeless structure introduces new electromagnetic and mechanical challenges to machine design and they are explained and overcome in this research.

Permanent magnet synchronous machines (PMSM), synchronous reluctance machines (SynRM), and electrically excited synchronous machines (EESM) are widely used in the industry and transportation sectors. Their rotors are often equipped with conducting parts like permanent magnets, thick rotor laminations, damper windings, or a conducting sleeve, or they even have a solid rotor core. Such conducting elements do not allow applying standard AC supply techniques for inductance measurements because of the alternating flux induced by eddy currents. We propose a new technique for inductance measurement at a standstill with a quasi-static voltage supply, which mitigates the eddy current phenomenon. The inductance is measured at several rotor positions over a complete electrical cycle, which allows to proceed with a harmonic spectrum analysis of the inductance variation. With this information, it is possible to estimate motor performance characteristics, such as optimum torque, voltage control, power factor, and torque ripple. The new technique is experimentally validated on a 12 kW axially laminated anisotropic solid-rotor high-speed SynRM. In principle, the method also suits PMSMs, EESMs, and other synchronous machines (not verified in this paper). Experimental validation with a solid-rotor SynRM shows a good correspondence with the simulation. Furthermore, the torque computed using the measured inductance is very similar to the experimental one confirming the effectiveness of the method.

The complication of the structure, topology and composition of the future electrical networks is characterized by difficult-to-recognize circuit-mode situations and requires modern methods for analyzing information parameters. The growing trend of digitizing signals in substations and the use of the IEC 61850 standard results in a huge amount of new data available at the nodes of the electrical network. The development and analysis of new methods for detecting and recognizing the modes of electrical networks (normal and emergency) are topical research issues. The article explores a new approach to recognizing a faulted section of an electrical network with branches by concurrently analyzing several information features and applying machine learning methods: decision tree, random forest, and gradient boosting. The application of this approach for decision-making by relay protection has not been previously implemented. Simulation modeling and the Monte Carlo method are at the heart of obtaining training samples. The results of testing the studied methods under review showed the required flexibility, the ability to use a large number of information parameters, as well as the best results of fault recognition in comparison with the distance protection relay.

A fully submersible permanent magnet synchronous machine (PMSM) is introduced in this paper. Underwater operation requires that the machine parts have to be resistant to corrosion, and the electrically conducting parts need to be properly insulated from water. The machine under study consists of a rotor-surface permanent magnet rotor, protected by a glass-fiber-reinforced plastic (GFRP) cover, and a fully stainless stator. The novelty of the machine is found in the design and special materials used in the manufacture. The stator core is made of ferritic stainless steel laminations, and the selected winding material is polyvinyl chloride (PVC) insulated copper wire. An extra low-speed, stainless-core submersible PMSM was constructed and tested. To simplify the machine construction, a tooth-coil single-layer winding was adopted. An asymmetric stator design was selected to enhance the machine performance. The performance of the 1.7 kW, 80 r/min machine was analyzed by finite element analysis (FEA) and validated by experimental tests, where despite a very low rotational speed, 74% efficiency was reached at the target load point. The PMSM was found to be fully functional for the application.

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

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

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

The performance capabilities of an axially laminated anisotropic rotor (ALA) in a high-speed synchronous reluctance motor (SynRM) were studied. A 12 kW ALASynRM was designed as an alternative to a high-speed induction motor (IM) with a solid rotor. The electromagnetic design was implemented taking into account possible issues related to the new manufacturing methods, which require thicker rotor layers than in a typical ALA. The ALASynRM shows a higher efficiency than the corresponding IM with a smooth or slitted solid rotor equipped with copper end rings. To verify the design method, a prototype IM with a smooth solid rotor was built and tested. In the analysis, it was found that, similar to IMs, in an ALASynRM a considerable part of losses takes place in the rotor despite the absence of slip-related losses in the SynRM. The distribution of eddy current losses in the ALA rotor is significantly uneven. The torque ripple in the ALASynRM is considerably larger than the corresponding ripple in IMs.

This paper presents an analysis of a permanent magnet synchronous machine (PMSM) with an unequal teeth width. The use of the concentrated nonoverlapping winding, also known as tooth-coil winding, has certain advantages. In addition, asymmetric features can be exploited by adopting this winding configuration to improve the machine performance. The procedure involves increasing the stator tooth width and, to the same extent, reducing the adjacent stator tooth width. In this paper, an analytical method was employed to predict and understand the back-EMF behavior, and a finite element analysis (FEA) was performed to verify the analytical method. Furthermore, a detailed study of the machine performance (electromagnetic torque, flux density, and losses) was carried out by the FEA. The machine was built and tested to validate the performance of the machine.

The phenomenon of third-order harmonics in synchronous reluctance motors (SynRMs) with an axially laminated anisotropic (ALA) rotor is studied. The paper shows that a specific rotor geometry can distort the air-gap flux density and induce third-order currents in the stator winding if it is delta connected. The third-order currents in different phases have the same phase shift angle and cannot, therefore, produce a rotating air-gap flux. Instead, they produce an air-gap flux that pulsates in time, and thus, causes eddy current losses in the rotor conducting parts. The phenomenon was described and proven with finite element simulation (FEM) of a 12 kW high-speed ALASynRM. The research underlines the importance of considering the third harmonic phenomenon in the design of a two-pole ALASynRM intended for high-speed applications, where a specific rotor geometry with a wide magnetically conducting middle layer is required.

The analysis of global epidemics, such as SARS, MERS, and COVID-19, suggests a hierarchical structure of the epidemic process. The pandemic wave starts locally and accelerates through human-to-human interactions, eventually spreading globally after achieving an efficient and sustained transmission. In this paper, we propose a hierarchical model for the virus spread that divides the spreading process into three levels: a city, a region, and a country. We define the virus spread at each level using a modified susceptible–exposed–infected–recovery–dead (SEIRD) model, which assumes migration between levels. Our proposed controlled hierarchical epidemic model incorporates quarantine and vaccination as complementary optimal control strategies. We analyze the balance between the cost of the active virus spread and the implementation of appropriate quarantine measures. Furthermore, we differentiate the levels of the hierarchy by their contribution to the cost of controlling the epidemic. Finally, we present a series of numerical experiments to support the theoretical results obtained.

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

High-torque-density electrical machines applied to traction operate at a varying torque and speed, and therefore, when minimizing the torque ripple, a wide variety of possible loads must be considered. Different loads need different current vectors, which affect the magnetic state of the machine. Thus, the torque ripple must be analyzed by using appropriate current vectors as it is proposed and described in this paper. The torque ripple values were estimated also for a skewed machine using a new method of torque ripple estimation of a skewed machine. The method is computationally less heavy and allows computing the torque ripple at all possible load points. Using the proposed method in the analysis of the machine parameters, the rotor pole geometry was adjusted to minimize the torque ripple without degradation of the other properties of the machine. Finally, the best machine performance was compared with the measured results.

Finite-element analysis (FEA) is one of the most significant tools in the designing and analyzing of electrical machines, which mainly includes the transient-magnetic (TM), magnet-static (MS) and time-harmonic (TH) solutions. The transient-magnetic (TM) solution in FEA is capable of considering both the harmonic effects and eddy-current effects accurately, which makes it suitable for the induction machine (IM) simulation. However, the drawback of the TM FEA for the IM modelling is that it takes some time before reaching the steady state because of the longer numerical transient, which is affected by the inherent electromagnetic time constants of the IM directly. In this paper, a new approach is proposed to reduce the duration of the numerical transient of the IM in the time-stepping FEA so that the steady state can be achieved in a short time. The proposed approach is capable of creating an initial condition close to the final steady state for the simulation by eliminating or reducing the stator and rotor electromagnetic time constants separately. The stator electromagnetic time constant is eliminated by an initial current excitation (obtained by the TH solution or the analytical method) and the rotor electromagnetic time constant is reduced by a locked rotor model at the beginning of the simulation. Then the initial current excitation is switched to a voltage excitation and the locked rotor is turned to the rotating state at proper time. Finally, the proposed approach is tested and proved efficient to reduce the transients by two typical cases (a solid-rotor IM and a squirrel-cage IM) with 2D FEA.

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

High-speed solid-rotor induction machines (IMs) suffer from higher rotor eddy-current losses (as a result of the air-gap flux density harmonics) more than any other type of high-speed machines because of the solid-rotor steel. A double-layer short-pitch asymmetric winding arrangement with prefabricated coils is proposed in this paper to mitigate the solid-rotor losses and enable easier assembly. However, the asymmetric winding also brings some current unbalance because of three-phase asymmetric stator inductances, especially the winding leakage inductances. Current unbalance can cause harmful effects for both the machine and supply, e.g., torque ripples, unbalanced magnetic pulls, and unbalanced thermal loads of the supply network and supply power electronics. Additionally, a three-phase unbalanced current can cause an extra source of electromagnetic emission to the environment, which can be harmful to surrounding electronics and can cause extra eddy-current losses in surrounding solid surfaces (e.g., a metal terminal box). To mitigate the current unbalance, two methods are compared in this paper. The first method is a slight increase of the stator slot height and placing of the coil sides at the top or bottom within the slot height for different phases. The stator slot height is optimized based on the 2-D finite-element method (FEM) to achieve the best solution for mitigation of the current unbalance. The other method is based on the results of the first method, and the coil side position for a specific phase is further adjusted. Unlike conventional methods of mitigating the current unbalance by power electronics, the proposed method suppresses the current unbalance solely by adjusting the machine design, which avoids extra investments for power electronics devices. In addition, the machine control strategy remains unchanged compared with the traditional one.

In the current study, we define a hierarchical epidemic model that helps to describe the propagation of a pathogen in a clustered human population. The estimation of a novel coronavirus spreading worldwide leads to the idea of the hierarchical structure of the epidemic process. Thus, the propagation process is divided into three possible levels: a city, a country, and a worldwide. On each level, the pathogen propagation process is based on the susceptible-exposed-infected-recovered (SEIR) model. We thus formulate a modified transmission model of infected individuals between levels. The control of the pathogen’s spread can be seen as an optimal control problem. A trade-off exists between the cost of active virus propagation and the design of appropriate quarantine measures. Each level of the hierarchy is defined by its network. A series of numerical experiments was conducted to corroborate the obtained results.