PM Rotor Research Articles

Development of Flux Concentrated type Self-Bearing Motor

Self-bearing motor has combined function of AC motor and magnetic bearing. Usually levitation force is produced by Maxwell force while the motor torque is produced by Lorentz force. The authors have proposed Lorentz type self-bearing motor where strong magnetic flux is the key technology for good characteristics. In this paper three types of rotors are designed and compared: a flux concentrated PM rotor, Halbach rotors with iron back yoke and aluminum back yoke. The high density flat coils are designed and used for the stator. The experimental setup is fabricated and tested. The results obtained are compared and discussed in details.

Design Improvement of a Single-Phase Brushless Permanent Magnet Motor for Small Fan Appliances

In this paper, an adaptation of a shaded pole motor operating as a single-phase brushless PM motor is studied. After properly designing the rotor PM ring to avoid demagnetization problems, a nonlinear mathematical model for performance assessment and design improvement is proposed. The calculation of the model parameters is carried out by 2-D FEM analyses suitably corrected to also take into account 3-D effects, mainly due to different stator and rotor lengths. The procedure implemented in a numerical code makes it possible to investigate significant design aspects and determine the mechanical characteristic related to motor configurations adopted for small fan appliances.

Induction versus permanent magnet motors

It is clear that a premium will continue to be placed on energy efficiency in motors. The circumstances around global warming and the availability of future oil supplies only increase the focus on electric motors as key elements in the efficient utilization of energy resources. PMs offer an important tool in the quest for cost-effective ways to further increase motor efficiencies. The characteristics of PM motors are sufficiently distinct from that of induction motors that users need to understand their operation to ensure successful applications. The nonsalient PM rotor construction provides high efficiency and high-torque density, whereas the salient pole construction offers some distinct advantages, especially with regard to system issues. Full flexibility to use other than 50 or 60 Hz base frequencies to further optimize performance obviously requires application with an inverter. Once the decision is made to use an inverter, the variable-frequency degree of freedom, with regard to pole selection, works in favor of the PM motor design. The improving performance to cost relationship of PM materials is getting to the point where the increased power density of the PM motor can be large enough to offset the cost of the magnets. While the authors would not suggest that PM motors are going to replace the widespread usage of induction motors, the PM motors provide an interesting alternative, especially in the case where an inverter is to be used in the application. It is for those inverter-fed applications that the first usage is expected in the pulp and paper industry.

Performance Comparision of Internal and External Rotor Structured Wind Generators Mounted from Same Permanent Magnets on Same Geometry

In this study, internal and external rotor radial-flux machine constructions built with surface mounted by applying the same NdFeB were compared according to torque density, vigorous material weight, outer radius, total length and volume, generated power and efficiency. Induced phase voltages and winding currents under load, airgap flux density, output power versus speed and material consumption for internal and external rotor PM generators have been obtained as the results of comparison. It was inferred that external rotor PM machines have a smaller volume, lower output power and efficiency, higher armature thermal load and current density than internal rotor PM machines by applying the same PM geometry and features for a given power rating. Therefore it was seen that the external rotor construction was more suitable to be applied in wind power systems because of external rotor structured PM machines have lower total weight and cost. Ill. 12, bibl. 12 (in English; summaries in English, Russian and Lithuanian).

Design and Experimental Evaluation of Synchronous Machine Without Iron Loss Using Double-Sided Halbach Magnetized PM Rotor in High Power FESS

The rotational loss is one of the most important problems in high-power flywheel energy storage system (FESS) which supplies the electrical energy from the mechanical rotation energy. In our FESS with PM synchronous motor/generator (PMSM/G) and non-contacting system, the rotational loss is mainly generated in the laminated iron stator when PM rotor mounted on the flywheel is rotated. Therefore, this paper presents design and evaluation of a PMSM/G model composed of double-sided Halbach magnetized PM rotor and ironless 3-phase winding stator to minimize speed reduction of the flywheel. For one such motor structure we give analytical formulae for its magnetic field and back-electromotive force in a uniform way via the magnetic vector potential. As a result of experiment, dynamic performance of a manufactured double-sided PMSM/G is evaluated by comparison with those of the slotless PMSM/G in the idling mode. The result shows that the presented PMSM/G can be applicable to the high-power FESS.

Design of a Magnetic-Geared Outer-Rotor Permanent-Magnet Brushless Motor for Electric Vehicles

This paper proposes a novel in-wheel motor, which artfully integrates a magnetic gear into a permanent-magnet brushless (PMBL) DC motor so that they can share a common PM rotor, hence offering both high efficiency and high power density. Moreover, the low-speed requirement for direct driving and the high-speed requirement for compact motor design can be achieved simultaneously. A 2-kW 600/4400-rpm magnetic-geared outer-rotor PMBL DC motor is designed and analyzed, which is particularly suitable for battery-powered electric motorcycles

Flywheel Challenge: HTS Magnetic Bearing

A 200 mm cylindrical engineering prototype high temperature superconducting (HTS) was designed and fabricated. Measurements show that the 17 kg PM rotor can suspend safely 1000 kg in axial direction and 470 kg radially. The rationale for the bearing performance is to stabilize a 400 kg rotor of a new compact 5 kWh/280 kW flywheel energy storage system (COM - FESS). Measurements of the magnetic bearing force, stiffness and drag-torque are presented indicated the successful targeting a milestone in the HTS bearing technology. The influence of the PM configuration and the YBCO temperature on the bearing performance was experimentally studied, providing high-force or high-stiffness behaviour. The axial stiffness 5 kN/mm at 0.5 mm displacement is the highest value of a HTS bearing we know.

Rotation speed degradation of superconducting magnetic bearing made of unsymmetrical shaped YBCO bulks

The radial-type superconducting magnetic bearing (SMB) system consists of the superconducting stator (SC stator) and the permanent magnet rotor (PM rotor). The rotation speed degradation of the PM rotor is one of the most significant problems for the practical use of SMB to the energy storage flywheel system. This phenomenon is caused mainly by the eddy current in the PM rotor induced by the inhomogeneous magnetic field which is weakened at the joints between the YBCO bulks. In this research, the rotation speed degradation and the rotation energy loss were simulated, and their suppression effect was evaluated by the 3-dimensional superconducting current simulation code based on the current vector potential method (T-method) and the vector potential method ( A– ϕ method) [K. Demachi, R. Numata, R. Shimizu, K. Miya, H. Higasa, J. Mater. Process Technol. 108 (2001) 141].

Improving the Dynamics of Two Types of Flywheel Energy Storage Systems With SMBs

This paper describes two types of energy storage systems (I and II) with a flywheel rotor supported by superconducting magnetic bearings (SMBs). Both systems I and II are composed of a rotor and superconducting magnetic bearings (SMBs) at both ends of the rotor. The rotors of systems I and II are driven by using an air turbine and a brushless motor, respectively. The superconductors of the systems I and II are field-cooled by using liquid nitrogen and a cryogenic refrigerator, respectively. In this paper, a new method for improving the dynamics of the passive type SMBs for two types of flywheel energy storage systems is discussed. The method is performed by changing relative displacements between the SMBs and the rotor PMs after field-cooling process.

Numerical evaluation of rotation speed degradation of SMB in the 100 kW h superconducting flywheel

The radial-type superconducting magnetic bearing (SMB) consists of the superconducting stator (SC stator) and the permanent magnet rotor (PM rotor). The rotation speed degradation of the PM rotor is one of the most significant problems for the practical use of SMB to the energy storage flywheel system. This phenomenon is thought to be caused by the eddy current in the PM rotor induced by the magnetic field of the SC stator which is inhomogeneous because the SC stator does not consist of a single superconductor bulk. In this research, the rotation speed degradation of 100 kW h flywheel was simulated by the 3-dimensional superconducting current simulation code.

Numerical and experimental evaluation of rotation speed degradation of superconducting magnetic bearing

The radial-type Superconducting Magnetic Bearing (SMB) system consists of the SuperConducting stator (SC stator) and the Permanent Magnet rotor (PM rotor). The rotation speed degradation of the PM rotor is one of the most significant problems for the practical use of SMB to the energy storage flywheel system. This phenomenon is caused mainly by the eddy current in the PM rotor induced by the inhomogeneous magnetic field of the weakened at the joints between the YBCO bulks. In this research, the rotation speed degradation and the rotation energy loss were measured using our SMB equipment, and they agreed very well with the numerical results by the 3-dimensional superconducting current simulation code based on the current vector potential method ( T-method) and the vector potential method ( A– φ method) [J. Mater. Process. Tech. 108 (2001) 141].

Wear characterisation of small PM rotors and oil pump bearings

The mechanical, micro and physical properties exhibited by PM rotors and journal bearing employed in oil pumps of automobiles, decides life of the pump. In this work, the factors that markedly characterise wear are featured. Tip clearance between the driving and driven gears influences the volumetric efficiency of the pump. When the tip clearance exceeds 0.20 mm (0.007 in.), and the face clearance exceeds 0.1 mm (0.004 in.) the discharge drops below the desired volumetric efficiency of 70%. Relationships between microstructure, micro-hardness, surface roughness, tip clearance of fresh and worn out parts are investigated. PM bearing bushings are finding increasing use in automobiles and consumer durable products owing to favorable size to weight ratio and cost advantages. Superior life and torque characteristics of PM bearings are related to density, size and geometry. Bushings at 6.8 g/cc with a 0.8 μm bearing clearance were determined to give improved life. Apart from the conventional wear test practices in industries, the concept of accelerated wear test (AWT) is employed to simulate equivalent wear on rotors and bearings; the results obtained are compared with the actual field samples. An empirical data on wear behavior is arrived from experimental studies, which can be used for simulated endurance test of these parts. Possible remedies applicable to achieve optimum life are identified. By optimising the material properties, higher wear resistant PM rotors and bearings could be manufactured economically.

Magnet topology optimization to reduce harmonics in high-speed axial flux generators

Despite the wide-ranging application potentials high-speed permanent magnet generators can offer the literature reveals a scarcity of design studies on these machines. This paper, we concerns with the configuration of PM on the quality of induced voltage in an ironless high-speed Axial Flux PM generator (AFPMG). The generator is a 240V eight-pole disc type machine with rated output of 18kVA at 50,000 rpm. It comprises of two rotor discs, each with eight embedded PM poles, and an ironless stator winding positioned between the rotors. A semi-circular shape is chosen for PM rotor poles, due to the ease of machining and assembly over other possible alternatives, and also their ability to produce near sinusoidal waveforms with various stator-winding shapes relatively easily. The investigation focuses on the effects on the harmonic content of the induced voltage due to varying distance between adjacent magnets. An efficient 3D finite element model (FE) that exploits the symmetry of machine is constructed for the proposed generator. The model then generates the predicted induced back emf over a range of distance between adjacent magnets, while maintaining the volume of the magnets constant. A prototype with the semi-circular magnets was constructed to provide experimental validation to the FE model. The validated model forms the basis for further formulation of design rules, and in particular, on the study of harmonics minimization.

Numerical simulation of coupled problem of electromagnetic field and heat conduction in superconducting magnetic bearing

Abstract The superconducting magnetic bearing (SMB) system consists of the HTSC stator and the PM rotor, and is a no-contact bearing system using the levitation force between them. The SMB was expected to be applied to the electric power storage flywheel system because no friction causes the rotation speed degradation and decreases the energy storage capability. However, it was found that the electromagnetic friction of the SMB was not zero, due to electromagnetic forces; (1) the magnetic force interaction between the inhomogeneous magnetic field of the PM rotor and the eddy current it induces in the cryostat, (2) the magnetic force between the inhomogeneous magnetic field of the PM rotor and the shielding current it induces in the superconductor, (3) the magnetic force between the magnetic field of superconductors yielding the levitation force and the eddy current induced in the PM rotor. The magnetic field of superconductor is inhomogeneous too, because the superconductors consist of several HTSC bulks. We improved the PM rotor and succeed in suppressing the rotation speed degradation by inhomogeneous magnetic field of HTSC bulks by preventing the eddy current with many insulator thin films in the PM rotor [Trans. Supercond. (in press)]. On the other hand, the rotation speed degradation by inhomogeneous magnetic field of the PM rotor have not been able to be removed. The induced eddy currents generate temperature rise with Joule heat in HTSC bulks. Therefore we are able to estimate the rotation speed degradation by evaluating the temperature rise. Furthermore temperature rise can cause inhomogeneous magnetic field because physical properties is varied by it. The purpose of this research is to develop the electromagnetic field analysis method coupled with thermal analysis.

Performance Evaluation of a Permanent-Magnet Induction Generator

A permanent-magnet induction generator (PMIG) is a special induction machine self-excited from the inside of the squirrel-cage rotor by a permanent-magnet rotor (PM rotor). In order to evaluate the practical value of the PMIG, its steady-state performance is analyzed theoretically and experimentally. As a result, it was found that the PMIG exhibits good power factor and efficiency compared to a general-purpose induction generator (GPIG) of the same size.

High levitation pressures with cage-cooled superconductors

We present an analysis of and experimental results from a levitational system comprising a stationary, bulk high-temperature superconductor (HTS) and a levitated component (rotor) that consists of a cylindrical permanent magnet surrounded by an annular HTS. The rotor is cooled below the critical temperature of the HTS while surrounded by a ferromagnetic cage. When the ferromagnetic cage is removed, the flux from the permanent magnet is essentially excluded from the interior of the HTS. When brought into proximity with the HTS stator, the cage-cooled rotor experiences a levitational force. The levitational force may be calculated by applying magnetic circuit theory. Such calculations indicate that for a sufficiently high critical current density, the levitational pressure may exceed that between the permanent magnet and its mirror image. We constructed a rotor from an NdFeB permanent magnet and YBCO bulk HTS with a critical current density of ≈5 kA cm−2. A soft ferromagnetic steel cage was constructed in segments. The critical current density of the stator HTS was also ≈5 kA cm−2. Experimental results obtained with the cage-cooled rotor and stationary HTS show a significant increase in force over that of an equivalent PM rotor and stationary HTS.

Design and analysis of high speed slotless PM machine with Halbach array

Slotless machines have been applied for a very high rotational speed and/or the ripple-free torque. In this paper, slotless machines equipped with external 4-pole field Halbach and radially magnetized PM array for electro-mechanical battery. This paper describes the comparison of the design guidelines, magnetic field characteristics, required magnet volume and optimal thickness of windings for two types of PM rotors.

Dimensional control in production of thin walled PM rotors : K.Karthikeyan, S.Srinivasan. (Sundram Fasteners Ltd, Hosur, India.)

Dimensional control in production of thin walled PM rotors : K.Karthikeyan, S.Srinivasan. (Sundram Fasteners Ltd, Hosur, India.)

Open-circuit field distribution in a brushless motor with diametrically magnetised PM rotor, accounting for slotting and eddy current effects

An analytical model has been developed for calculating the open-circuit time-varying magnetic field distribution in the airgap/magnet/retaining sleeve region of a brushless permanent magnet motor equipped with diametrically magnetised magnets. It accounts for the stator slotting and curvature, as well as for parasitic eddy currents induced in the retaining sleeve and magnets. The analytically predicted time-varying field distribution in the different regions is compared with corresponding finite element predictions.

Pole Number Analysis of a Levtated Synchronous-Type Rotating Motor.

Magnetic bearings are being increasingly used because of their noncontact support capability. For some applications, a power motor should be installed between the radial magnetic bearings. In the previous paper, a new method of levitation control of a synchronous-type motor as introduced, that is, the radial position as well as the rotation of a PM rotor can be controlled. For analysis the rotor was assumed to have a sinusoidally distributed magnetic flux, while the stator had an arbitrarily distributed flux. In the experiment, the stator was approximated by 12 concentrated windings. This paper introduces the analysis of the least number of stator poles. The stator flux is assumed to be produced by the concentrated windings which produce the spatial higher harmonics. The rotor is assumed to have the sinusoidal distributed flux which can be produced by a permanent magnet. A simple experiment is conducted to confirm the validity of the analysis.