Optimal Design of Special High Torque Density Electric Machines based on Electromagnetic FEA

Electric machines with high torque density are essential for many low-speed direct-drive systems, such as wind turbines, electric vehicles, and industrial automation. Permanent magnet (PM) machines that incorporate a magnetic gearing effect are particularly useful for these applications due to their potential for achieving extremely high torque density. However, when the number of rotor polarities is increased, there is a corresponding need to increase the number of stator slots and coils proportionally. This can result in manufacturing challenges. A new topology of an axial-flux vernier-type machine of MAGNUS type has been presented to address the mentioned limitation. These machines can attain high electrical frequency using only a few stator coils and teeth, which can simplify construction and manufacturing under certain conditions. Additionally, the inclusion of auxiliary small teeth within the stator main teeth can generate a noteworthy increase in output torque, making it a unique characteristic of this motor. By analyzing the operating principle of the proposed VTFM PM machine, possible pole-slot combinations have been derived. The process of designing an electric machine is complicated and involves several variables and factors that must be balanced by the designer, such as efficiency, cost, and performance requirements. To achieve a successful design, it is crucial to employ multi-objective optimization. Using a 3D FEA model can consider the impact of magnetic saturation, leakage flux, and end effects, which are not accounted for in 2D. Optimization using a 3D parametric model can offer a more precise analysis. Validating the machine\u27s performance requires prototyping a model and testing it under different operating conditions, such as speed and load, which is a crucial step. This approach provides valuable insights into the machine\u27s behavior, allowing the identification of any areas for improvement or weaknesses. A large-scale multi-objective optimization study has been conducted for an axial-flux vernier-type PM machine with a 3-dimensional (3D) finite element analysis (FEA) to minimize the material cost and maximize the electromagnetic efficiency. A detailed study for torque contribution has indicated that auxiliary teeth on each stator main teeth amplify net torque production. A prototype of optimal design has been built and tested

Axial flux permanent magnet machines for direct drive applications

This thesis explores aspects of the design, analysis, and experimental test of permanent magnet axial flux machines for use in diesel engine generator sets, vertical axis wind turbines, and wheel motors for solar cars. The characteristic geometry of axial flux machines is naturally more suitable than that of conventional topologies in certain applications. However, convenient and accurate methods of electromagnetic design and analysis are less well established for such machines. The purpose of the research described herein is to benchmark a range of methods of analysis which can be extended to novel designs. There is a particular focus on the use of Finite Element Analysis to facilitate greater understanding of these machines through the illustration and quantification of the electromagnetic aspects of their operation, and the verification of a selection of analytical approaches. Prototype TORUS machines are first considered; the various analyses are then extended to iron-cored axial flux machines having slotted conductors and finally to a selection of novel machines having concentrated coils and an ironless stator. The analyses are successfully extended to a range of machines, and the particular suitability of axial flux permanent magnet machines in certain direct drive applications is demonstrated

SRM drives for electric traction

"GAECE" -- PortadaDescripció del recurs: 11 maig 2020GAECE (Grup d’accionaments elèctrics amb commutació electrònica). The group of electronically commutated electrical drives is a research team of Universitat Politècnica de Catalunya (UPC BARCELONATECH), which conducts investigation in four areas: electrical drives, power electronics, mechanics and energy and sustainability. Regarding electrical drives, research focuses on the development of new reluctance, permanent magnet and hybrid electrical drives. The main goal of those electrical drives is the integration of the power converter/controller and the mechanical transmission, being specially intended for the traction of light electric vehicles. That research is carried out by using the analysis of finite elements, taking into account eco-design criteria, considering new materials and new control strategies.First editio

Optimum Design of Axial Flux PM Machines based on Electromagnetic 3D FEA

Axial flux permanent magnet (AFPM) machines have recently attracted significant attention due to several reasons, such as their specific form factor, potentially higher torque density and lower losses, feasibility of increasing the number of poles, and facilitating innovative machine structures for emerging applications. One such machine design, which has promising, high efficiency particularly at higher speeds, is of the coreless AFPM type and has been studied in the dissertation together with more conventional AFPM topologies that employ a ferromagnetic core. A challenge in designing coreless AFPM machines is estimating the eddy current losses. This work proposes a new hybrid analytical and numerical finite element (FE) based method for calculating ac eddy current losses in windings and demonstrates its applicability for axial flux electric machines. The method takes into account 3D field effects in order to achieve accurate results and yet greatly reduce computational efforts. It is also shown that hybrid methods based on 2D FE models, which require semi-empirical correction factors, may over-estimate the eddy current losses. The new 3D FE-based method is advantageous as it employs minimum simplifications and considers the end turns in the eddy current path, the magnetic flux density variation along the effective length of coils, and the field fringing and leakage, which ultimately increases the accuracy of simulations. After exemplifying the practice and benefits of employing a combined design of experiments and response surface methodology for the comparative design of coreless and conventional AFPM machines with cores, an innovative approach is proposed for integrated design, prototyping, and testing efforts. It is shown that extensive sensitivity analysis can be utilized to systematically study the manufacturing tolerances and identify whether the causes for out of specification performance are detectable. The electromagnetic flux path in AFPM machines is substantially 3D and cannot be satisfactorily analyzed through simplified 2D simulations, requiring laborious 3D models for performance prediction. The use of computationally expensive 3D models becomes even more challenging for optimal design studies, in which case, thousands of candidate design evaluations are required, making the conventional approaches impractical. In this dissertation a new two-level surrogate assisted differential evolution multi-objective optimization algorithm (SAMODE) is developed in order to optimally and accurately design the electric machine with a minimum number of expensive 3D design evaluations. The developed surrogate assisted optimization algorithm is used to comparatively and systematically design several AFPM machines. The studies include exploring the effects of pole count on the machine performance and cost limits, and the systematic comparison of optimally designed single-sided and double-sided AFPM machines. For the case studies, the new optimization algorithm reduced the required number of FEA design evaluations from thousands to less than two hundred. The new methods, developed and presented in the dissertation, maybe directly applicable or extended to a wide class of electrical machines and in particular to those of the PM-excited synchronous type. The benefits of the new eddy current loss calculation and of the optimization method are mostly relevant and significant for electrical machines with a rather complicated magnetic flux path, such is the case of axial flux and of transvers flux topologies, which are a main subject of current research in the field worldwide

An Equivalent Circuit Model for Predicting the Core Loss in a Claw-Pole Permanent Magnet Motor with Soft Magnetic Composite Core

© 1965-2012 IEEE. Soft magnetic composite (SMC) materials and SMC electromagnetic devices have attracted strong research interest in the past decades. However, SMC devices have large core loss that needs to be put into consideration even at the design stage. Effective and accurate prediction of the core loss becomes crucial for the design and optimization of high-performance motors with these materials. Equivalent circuit model is a widely used method for machine analysis, due to the advantages in the fast calculation with a clear physical mechanism. This paper presents an equivalent circuit model to predict the core loss of a claw-pole permanent magnet motor with SMC stator core. All the parameters including the equivalent core-loss resistance in the equivalent circuit model are identified based on the finite-element method to achieve high accuracy, and the effectiveness of the parameters identification methods is experimentally verified. The proposed equivalent circuit model can predict the core loss and motor's performance efficiently both under no-load and loading conditions

Thermal Modelling of the Ventilation and Cooling inside Axial Flux Permanent Magnet Generators

Axial flux permanent magnet generators are of particular interest for power generation in harsh and confined conditions. Due to their compactness and high power density, the ventilation and cooling inside axial flux permanent magnet generators have becoming increasingly important for further performance improvement. This thesis describes the developments of a lumped parameter, thermal modelling technique for axial flux permanent magnet generators. The main aim of this research is to develop a fast and accurate thermal modelling tool which can be used for rapid machine design and ultimately, to replace complex and time consuming CFD analyses in the machine design process. The thesis illustrates the construction of a generic thermal equivalent circuit, which comprises of conductive and convective sub-circuits, to model the conduction and convection heat transfers and temperature distributions in the radial and axial directions, within these machines. The conduction heat transfer between the solid components of these electrical machines is modelled by an annulus conductive thermal circuit derived from previous researchers; whereas, for convection heat transfer between the working fluid (air) and solids, the author has developed two convective thermal circuits, which are demonstrated as the Temperature Passing Method (TPM) and Heat Pick-up method in (HPM) in the thesis. Several case studies were designed to investigate the validity and accuracy of these thermal sub-circuits with both steady and transient boundary conditions. Since all the thermal impedances and capacitances used in the thermal circuits are in dimensionless form, the developed generic thermal equivalent circuit is capable of performing thermal simulations for axial flux generators of different sizes and topologies. Furthermore, special correction factors were introduced into the developed generic thermal equivalent circuit, to take into account the heat transfer in the circumferential direction in axial flux machines. The thesis also demonstrates how the heat transfer in the stator windings is modelled in the generic thermal equivalent circuit. Two analytical models, which are the Simple Concentric Model (SCM) and Concentric-annulus Layer Model (CLM) were developed, for the evaluation of the thermal resistances of the stator windings. The results evaluated from these analytical models were validated by several numerical models and experimental results of two-phase materials published by previous researchers. Lastly, experimental validation of the lumped parameter thermal equivalent circuit model and CFD simulations was conducted. Heat transfer coefficient measurements were carried out on two separate test rigs, which were a simplified single-sided axial flux machine test rig and a large-scale low speed axial flux machine. The experimental results were compared with the numerical results obtained from both the lumped parameter and CFD models. Good agreement between the experimental, lumped parameter model and CFD results were found. These indicate that the developed generic thermal circuit is potentially capable of replacing CFD analyses in the axial flux machines design process

Thermal modeling of hollow conductors for direct cooling of electrical machines

A direct cooling design using hollow conductors with the coolant flowing inside can significantly improve the heat dissipation in an electrical machine. To predict the thermal performances of an electrical machine with such cooling configuration, this paper proposes a computationally efficient thermal model of hollow conductors with direct cooling features. The hollow conductor is modeled using four equivalent solid cuboidal elements with a three-dimensional thermal network and internal heat generation. The heat transfer coefficient between the coolant and conductors is determined by an empirical model considering fluid dynamics behaviors. Axial discretization is performed to take into account the nonuniform temperature distribution along the axial direction. Experimental validation is performed with a U-shaped hollow conductor test rig. Compared to computational fluid dynamics analysis, the proposed thermal model is much more computationally efficient, and thus can be incorporated into design optimization process and electrothermal simulations of the electrical machine over a driving cycle

Theoretical and Experimental Investigations of a Permanent Magnet Excited Transverse Flux Machine with a Segmented Stator for In-Wheel Motor Applications

A three-phase transverse flux permanent magnet (PM) motor with flux concentrating (FC-) topology that has a segmented stator is studied in this dissertation. The phases of the stator have been placed around the rotational axis of the machine instead of placing them in a classical way over each other along the axial direction. Through this phase arrangement, the electrical and mechanical shifts between the phases are considered to ensure proper operation of the transverse flux machine (TFM) without the need of extra components such as a start-up capacitor or a special designed power supply. The segmented stator construction has required that the conventional ring coils to be replaced by a type of concentric winding that take a saddle shape enabling parallel magnetic circuits to take place. This has initiated studying the effect of the distances located between the phases on all over the performances of the machine. In order to select an initial construction for the stator, a preliminary assessment study of some conventional PM-TFMs having ring coils are carried out, through which they are re-designed as outer rotor motors and compared based on the level of electromagnetic torque and the inductance profile. As the main application of the design is to achieve a compact construction for an outer rotor, low noise and speed too for possible future in-wheel applications, the most interesting issue in this study is how to bring all the phases of the machine around the shaft in one layer without losing the torque productivity as when the phases are placed under each other in the conventional way. Therefore, the designed machine is set in further theoretical evaluation studies via finite element method (FEM) with the conventional layered TFM, and it shows that the TFM with segmented windings has a better torque density as its correspondence in the conventional layered structure. This result is in favor to the segmented structure, in particular, about 31% of the PMs number in the segmented structure (i.e., total number of PMs located between the phases) will not have an active role in the torque production. A detailed mathematical theory has been analytically developed and investigated to show the validity and limitation of the design. The study has incorporated how the segmentation of each phase and placement of the two parts opposite to each other can improve the mechanical balance of the TFM and hence quite rotation. The approach has been shown for two- and three-phase PM-TFMs. Moreover, illustration for applying the same principle of segmented stator to surface PM topology of TFMs is analytical verified and shown via FEM. Possible constructions with segmented stators are developed in a periodical table format to give the machine designer a shortcut for a possible construction with the selected number of magnets, number of segments per phase and the desired space between the phases. Since the noise is a well-known problem of TFMs, due to the ripple in the electromagnetic torque waveform and the natural magnetic normal forces, the normal and axial forces in PM-TFM with segmented stator have been investigated too, where introducing more segments per phase will reduce their effects. In order to validate the theoretical investigation, a low-scaled test machine is designed, constructed and a complete test bench has been built to experimentally test the machine. The experimental investigations have included generator and motor operation modes as well as measuring the ratings, performances of the machine and the starting methods. The test machine has reached via the conducted tests an average torque of about 2.1 Nm with an efficiency of 53% and it has a great development potential to be improved via shaping of stator poles, the room available for the windings, fill factor and more optimization possibilities. Based on the theoretical and experimental investigations, the operation of the segmented winding design of PM-TFM proves itself to work and to have a future for compact motors in industrial operation, or as in-wheel outer rotor motor for mobile platforms. For higher power applications, a machine with such type of stator should be designed with big diameters that will allow the utility of more PMs as well as more segments per phase, where both are involved in the torque production, i.e., more torque density for the segmented TFM

Design of low speed axial flux permanent magnet generators for marine current application

The aim of this research work is to design, built and test low speed multi-pole permanent magnet generators for ocean energy conversion systems. Vertical axis drag/lift type ocean current turbines have low speed due to water speed of less than 1m/s. A low speed permanent magnet generator can be utilized to deliver low power that can be used to power- rated sea pods. The study focuses on the design of a permanent magnet generator, which is suitable for under water application and can generate electric power from the low speed marine currents (typically below 100rpm). This thesis explores different low speed permanent magnet generators and focuses on multi-pole direct driven axial flux permanent magnet Generator (AFPMG). AFPMG is suitable for direct coupled systems. Two types of AFPMG are designed and tested for several performance criterions. The prototyped AFPMGs are tested and the results are presented and discussed in this thesis. The first design produced 5.2V, 3.5W and the second design produced about 5.5V, 2W at 70 rpm. Both designs are simple in construction, economically viable and suitable for low electric power generation from ocean currents

Advances in the Field of Electrical Machines and Drives

Electrical machines and drives dominate our everyday lives. This is due to their numerous applications in industry, power production, home appliances, and transportation systems such as electric and hybrid electric vehicles, ships, and aircrafts. Their development follows rapid advances in science, engineering, and technology. Researchers around the world are extensively investigating electrical machines and drives because of their reliability, efficiency, performance, and fault-tolerant structure. In particular, there is a focus on the importance of utilizing these new trends in technology for energy saving and reducing greenhouse gas emissions. This Special Issue will provide the platform for researchers to present their recent work on advances in the field of electrical machines and drives, including special machines and their applications; new materials, including the insulation of electrical machines; new trends in diagnostics and condition monitoring; power electronics, control schemes, and algorithms for electrical drives; new topologies; and innovative applications