Dovetail rotor poles in synchronous permanent magnet and reluctance machines

Robust synchronous permanent magnet and reluctance machine designs are developed. In the designs, the rotor structure is simple and strong and the leakage flux is relatively small. For the new design solution, a dovetail form-blocked rotor structure, specific analyzing principles are also developed. The dovetail designs are shown to be good solutions with their lower leakage flux and at least the same strength against centrifugal forces as the conventional rotor solutions. The compared conventional solutions considered have inseparable rotor sheets in which the parts of the rotor are kept still by using bridges between them. In the dovetail rotor, the forms of the rotor parts keep them together and no bridges between them are needed for support. The simplicity of the dovetail solution has also been kept the same or better. In addition, the manufacturing method is the same for both solutions. The dovetail design can also be used for saving the magnetic material of permanent magnet synchronous machines because it has a smaller leakage flux than the conventional V-shaped designs with supporting bridges. The problem of how to compare the dovetail designs to the conventional ones is considered in depth. The strength of the dovetail structure has to be defined in a different way than in the conventional design with supporting bridges. In bridge-fixed design, the strength of the bridges is critical for rotor durability but in the dovetail design wider areas of the rotor affect the strength of the rotor. However, the basic electrical properties could be defined with the same method. Additional methods for defining the electrical properties of dovetail designs are also considered. One method is that the load angle can be defined only from the forms of phase currents in delta-connected synchronous machines and phase voltage and current in star-connected synchronous machines. The load angles defined are successfully used to find a good model for the test results. The other method is to view the normalized local torque density in the air gap as a function of time. In this work, several dovetail synchronous reluctance and permanent magnet machines are designed, manufactured, tested, and analyzed. The design, manufacturing, testing, and analysis methods are defined and developed especially for dovetail designs

Modeling demagnetization of sintered NdFeB magnet material in time-discretized finite element analysis

The aim of this work was to develop a tool able to simulate the behavior of a permanent magnet machine after demagnetization. The tool would include a demagnetization model, an eddy current model, and a thermal model. The eddy current calculation accuracy in two-dimensional geometries will also be improved. The other goals were to study how the demagnetization should be modeled in different situations and to evaluate a mixed-grade pole idea, where there can be several magnet grades in a pole of a machine. A demagnetization model based on an exponential function was developed. The new model can be defined by using only four parameters. The new model can take into account the squareness of the hysteresis curve. The new model also takes into account the demagnetizing field perpendicular to the orientation direction, which is often ignored. The demagnetization model was implemented in an existing finite element method model. The demagnetization model was evaluated by modeling a locked-rotor situation of a permanent magnet machine. The simulation results were compared with the demagnetization of the magnets of a real motor after the same situation. It was discovered that the demagnetization model can accurately predict the demagnetization of the magnets in a permanent magnet machine. The resistivity of NdFeB permanent magnet material was measured as a function of temperature. The resistivity of rare earth magnet materials was found to be anisotropic. It was shown that the resistivity can be treated as an isotropic scalar property, as long as the resistivity value perpendicular to the magnetization direction of the magnets is used. An eddy current model was developed. The eddy current model modifies the resistivity of the magnet material as a function of temperature and as a function of the shape of the magnet. The modification as a function of the shape was shown to improve the accuracy of the eddy current calculation in two-dimensional modeling. The modeling of the demagnetization was studied with simulations using an overheated motor loaded with a constant torque as an example. It was shown that it is important to include a thermal model in the demagnetization calculations. The mixed-grade pole machine was used as a calculation example in the simulations. It was shown that a slight improvement in the performance of the machine can be achieved with a simultaneous potential for cost savings by using a mixed-grade pole

Evaluation of a High-Pole Number Reluctance Synchronous Wind Generator Technology

Electrical and Electronic Engineerin

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

A Novel Flywheel and Operation Approach for Energy Recovery and Storage

Flywheel has intrinsic advantages over other energy storage forms such as hydraulic storage, batteries and compressed airs. These advantages include higher robustness, longer life cycle, great energy density, higher efficiency, lower loss, better discharge depth and relatively easier recycling, etc. In this dissertation a novel shaftless flywheel was developed. The most important feature of our novel design is the integration of the motor generator and the magnetic suspension into the flywheel disk, which removes the need for a support shaft and enables our solid disk design. This design was shown to have big advantages than traditional designs using annular discs press-fitted on shafts. This was illustrated by a comparison between annular and solid 4340 discs in stress levels, SN lives and fatigue lives with cracks. Due to the scale of the system, our rotating speed is relatively lower than traditional designs. This makes possible the usage of unlaminated magnetic bearings to reduce the system cost at partial expense of the system performance. A 4340 steel sample was tested to retrieve its magnetic behavior. The novel magnetic levitation was then designed using ANSYS static analysis based on the measured data. The position stiffness and current stiffness were retrieved with the analysis. The eddy losses of the magnetic bearings were retrieved through FEM motor software CARMENTM by Vector FieldTM. The total bearing loss was calculated based on the simulated eddy loss and measured hysteresis loss on 4340. The system equilibrium temperature was simulated with ANSYSTM. The Frequency weakening effect of the magnetic bearing was analyzed with ANSYSTM harmonic analysis. The closed-loop control stability of the system was investigated based on the results. A motor design concept was proposed with the variable motor/generator gain capability. This capability was a key feature in optimizing the charge/discharge performances of the flywheel in both grid level and hybrid locomotive applications. Based on EPA average data, the benefits of our hybrid locomotives on fuel and NOx savings were simulated on various train operations. The optimization for regenerative braking was also discussed. The dissertation concludes with the discussion of the flywheel system isolation from train operation induced vibrations

Investigation of novel multi-layer spoke-type ferrite interior permanent magnet machines

The permanent magnet synchronous machines have been attracting more and more attention due to the advantages of high torque density, outstanding efficiency and maturing technologies. Under the urges of mandatory energy efficiency requirements, they are considered as the most potential candidates to replace the comparatively low-efficient induction machines which dominate the industrial market. However, most of the high performance permanent magnet machines are based on high cost rare-earth materials. Thus, there will be huge demands for low-cost high-performance permanent magnet machines. Ferrite magnet is inexpensive and abundant in supply, and is considered as the most promising alternative to achieve the goal of low cost and high performance. In consideration of the low magnetic energy, this thesis explored the recent developments and possible ideas of ferrite machines, and proposed a novel multi-layer spoke-type interior permanent magnet configuration combining the advantages of flux focusing technique and multi-layer structure. With comparable material cost to induction machines, the proposed ferrite magnet design could deliver 27% higher power with 2-4% higher efficiency with exactly the same frame size. Based on the data base of International Energy Agency (IEA), electricity consumed by electric machines reached 7.1PWh in 2006 [1]. Considering that induction machines take up 90% of the overall industrial installation, the potential energy savings is enormous. This thesis contributes in five key aspects towards the investigation and design of low-cost high-performance ferrite permanent magnet machines. Firstly, accurate analytical models for the multi-layer configurations were developed with the consideration of spatial harmonics, and provided effective yet simple way for preliminary design. Secondly, the influence of key design parameters on performance of the multi-layer ferrite machines were comprehensively investigated, and optimal design could be carried out based on the insightful knowledge revealed. Thirdly, systematic investigation of the demagnetization mechanism was carried out, focusing on the three key factors: armature MMF, intrinsic coercivity and working temperature. Anti-demagnetization designs were presented accordingly to reduce the risk of performance degradation and guarantee the safe operation under various loading conditions. Then, comparative study was carried out with a commercial induction machine for verification of the superior performance of the proposed ferrite machine. Without loss of generality, the two machines had identical stator cores, same rotor diameter and stacking length. Under the operating condition of same stator copper loss, the results confirmed the superior performance of the ferrite machine in terms of torque density, power factor and efficiency. Lastly, mechanical design was discussed to reduce the cost of mass production, and the experimental effort on the prototype machine validates the advantageous performance as well as the analytical and FEA predictions

In-wheel motors for electric vehicles

PhD ThesisThe in-wheel motor technology as the source of traction for electric vehicles has been researched recently because it is compact and ease-to-integrate. The motor is housed in the wheel. Since the room for the motor is tightly defined by the size of the wheel and there is no gearing system, the motor must have a high torque density to drive the vehicle directly and a high efficiency to keep cool. The existing motor uses a surface-mounted magnet topology. To make it more cost-competitive, the magnet material needs to be reduced while maintaining the torque performance at the rated operating condition. It is the motive of this Ph.D. research. The thesis starts with a brief introduction on the background of the electric vehicle. Then the major challenges of the in-wheel motor technology are summarised. With the derived specifications, an induction machine and a switched reluctance machine are then simulated and analysed. Still, the permanent magnet synchronous machine is proved to have the highest torque density. Change from surface-mounted to interior topology, six new magnet topologies are investigated. The V-shaped interior magnet topology shows superior torque-to-magnet-mass ratio and is easy-to-manufacture. It gives 96% torque while using 56% of the magnet mass compared to the existing motor due to the assist from the additional reluctance torque and the lower magnetic circuit reluctance. The key to use less magnet mass while avoiding the demagnetisation is the front iron shielding effect. The analytical explanation on the better resistance to demagnetisation in the V-shaped motor is provided. The magnet loss mechanism is discussed for proper segmentation. Detailed design adjustments are made to compromise between the torque-to-magnet-mass ratio and the manufactural practicality. Issues regarding to lower mechanical rigidity occurred in initial assembly of the prototype and solutions are proposed. Followed by successful assembly, experimental tests were conducted and results show good agreement with the simulation. A specific form of torque ripple is found in the V-shaped motor and occurs generally in all fractional-slot concentrated-winding machines with saliency. It is explained by an analytical model. This model is also extended to explain the generally lower reluctance torque in vi fractional-slot concentrated-winding machines. Potential design improvements are suggested and simulated for future versions.Protean Electri

Structures performance, benefit, cost-study

New technology concepts and structural analysis development needs which could lead to improved life cycle cost for future high-bypass turbofans were studied. The NASA-GE energy efficient engine technology is used as a base to assess the concept benefits. Recommended programs are identified for attaining these generic structural and other beneficial technologies

High Frequency Permanent Magnet Generator for Pulse Density Modulating Converters

This thesis describes an investigation of high frequency permanent magnet generators for use in a novel power generation system for aerospace applications. The system consists of a high frequency generator (in the 10s of kHz range) which feeds a full-wave rectifier to produce to a high frequency pulse train as input to a pulse-density modulated soft-switched converter. Various topologies of flux-switching, flux-reversal and Vernier machines are investigated using electric-circuit coupled finite element analysis. Having demonstrated the limitations of these topologies, a comprehensive design study into a single-phase, surface mounted permanent magnet machine based on a single turn serpentine winding is described. This study covers both internal and external rotor machines with pole numbers of 192 and 96 which correspond to generator fundamental frequencies of 32kHz and 16kHz at the rated speed of 20,000rpm. Several aspects of the machine design are optimised through extensive use of finite element modelling, including mechanical analysis of the rotor containment. This study includes a detailed consideration of iron loss, including consideration of iron powder based cores. This study has resulted in a down-selected design based on a low permeability but high resistivity powdered iron core. The manufacture of a demonstrator is described including the need to re-design the machine to employ ultra-thin Nickel Iron laminations because of the difficulties encountered in the machining of a powdered iron core. The performance of this Nickel Iron variant is investigated and a final design established. The numerous challenges involved in manufacturing this novel machine are described

Magnetically levitated hysteresis motor driven linear stage for in-vacuum transportation tasks

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 241-246).This thesis presents a new in-vacuum reticle transportation mechanism for extreme ultraviolet (EUV) photolithography machines. In the photolithography process, the reticle is a quartz plate that contains a pattern of the integrated circuit, which needs to be transported between a storage position and the exposure stage. In next-generation EUV lithography machines, the reticle handling system must satisfy the following requirements: (1) transport the reticle through a distance of 2 meters, (2) the height of the mechanism needs to be within 100 mm, (3) operate in vacuum, and (4) satisfy ultra-tight contamination requirements. To fulfill these requirements, a conventional robotic reticle handler is inadequate. In this work, we designed, built, and tested a magnetically-levitated linear stage prototype, targeting at the reticle transportation application. Compared with robot manipulators, linear stages typically require less volume for long-distance transportation tasks.Magnetic suspension is used to eliminate mechanical contact and thereby avoid particle generation that can contaminate the reticle. The stage's linear motion is driven by linear hysteresis motors, which allows using solid-steel motor secondaries on the moving stage. This is desirable for in-vacuum operation, since permanent magnets can out-gas in high vacuum when not encapsulated. The magnetic suspension of the stage is achieved using a novel linear bearingless slice motor design, where the stage's magnetic suspension in three degrees of freedom, including vertical, pitch, and roll, are achieved passively. This compact design effectively reduces the number of sensors and actuators being used. The prototype system has successfully levitated the moving stage. The resonance frequency of the passively levitated degrees of freedom is approximately 10 Hz, and the suspension bandwidth of the actively-controlled degrees of freedom is about 60 Hz.The stage's maximum thrust force is 5.8 N under a 2.5 A current amplitude, which corresponds to a stage acceleration of 1200 M/s². This is able to satisfy the acceleration requirement for reticle transportation task. The stage was tested to track a reticle handling reference trajectory, where the maximum position tracking error of our linear stage is 50 [mu]m. The stage's lateral displacements during motion is below 50 [mu]m, which is well below making mechanical contact to the side walls. To our knowledge, this work represents the first study of linear hysteresis motors, and the first linear bearingless slice motor design. Hysteresis motors are a type of electric machine that operates using the magnetic hysteresis effect of the secondary material. Since the magnetization in the rotor lags behind the external field, a thrust force/torque can be generated.In prior usage, hysteresis motors have been operated in open-loop, which makes them unsuitable for applications where dynamic performance is critical. As a part of this thesis work, we also studied the modeling and closed-loop torque and position control for hysteresis motors. The proposed control method was tested with three rotary hysteresis motors, including two custom-made motors of different rotor materials and one off-the-shelf hysteresis motor. Experimental results show that position control for all three motors can reach a bandwidth of 130 Hz. To our best knowledge, this is the first work that enabled high-bandwidth torque and position control for hysteresis motors, which allows this motor to be used for servo applications.Sponsored by ASMLby Lei Zhou.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineerin