Stator Permanent Magnet Research Articles

Modeling and Analysis of a Linear Stator Permanent-Magnet Vernier HTS Machine

The superconducting machines are more and more attractive due to the advantages of high power density and high efficiency, in which the superconductor is adopted to be excitation windings, armature windings, and flux leakage shielding bulks, respectively. In this paper, a new linear stator permanent-magnet (PM) vernier high-temperature superconductor (LSPMV-HTS) machine is developed for the direct drive system. A double-sided design and inner-translator arrangement are adopted in the LSPMV-HTS machine in which both PMs and armature windings are placed on the stator, whereas the translator is designed as an iron core with salient teeth on the two sides and the HTS bulks are inset between every two adjacent salient teeth. Due to the flux leakage shielding of the HTS bulks, the power density of the machine can be improved effectively. The mathematical model of the LSPMV-HTS machine is derived based on the finite-element method results. Based on using the FEM, the theoretical analysis results are verified.

Power Mapping Characteristic of Double Stator Permanent Magnet Generator for Electrical Harvesting Machine

Power Mapping Characteristic of Double Stator Permanent Magnet Generator for Electrical Harvesting Machine

A New Dual-Stator Bidirectional-Modulated PM Machine and Its Optimization

A novel dual-stator bidirectional-flux modulated permanent magnet (PM) machine is presented in this paper. The key of the design is to locate consequent PM poles in both stator and rotor sides and the merit is that the magnetic flux produced by either the rotating or stationary PMs and dual-stator windings can be modulated by the stator teeth and rotor iron segments. It is shown that with this flux modulation effect and improved reluctance torque effect, the torque density of the machine can be increased. The bidirectional flux modulation theory and operation principle of the machine are explained and analyzed using time-stepping finite element method.

Core Loss Analysis and Calculation of Stator Permanent-Magnet Machine Considering DC-Biased Magnetic Induction

In this paper, core loss characteristics of stator permanent-magnet (PM) machines are analyzed and calculated, in which the unique dc-biased magnetic induction is taken into account. The flux density variation patterns in some key points in a doubly salient PM (DSPM) machine are analyzed by the two-dimensional time-stepping finite-element method. To calculate the core loss of stator and other minor hysteresis loops under dc magnetic bias, core loss characteristics of silicon steel sheet under dc-biased induction condition are first tested by a simple test system based on traditional Epstein frame and a functional relationship between the change of dc-biased induction and hysteresis loss is proposed. Two core loss calculation methods considering rotational magnetization based on flux density waveform are improved to take the influence of dc-biased magnetic induction into consideration. The calculation results are verified by experiments on a prototype DSPM machine. The conclusions are also applicable to other kinds of stator PM machines.

Modeling the magnetic disturbance of pulsatile blood flow in a static magnetic field.

Non-invasive continuous monitoring of blood flow may be particularly valuable for early detection of different anomalies such as hypovolemia and internal bleeding. Recent studies have demonstrated the potential clinical benefits of photo-plethysmography in detecting hypovolemia before the onset of cardiovascular decompensation. The magnetic sensing method bears advantages of size, weight, and cost along with less stringent body placement rules. In this work, a detailed three-dimensional mathematical model for the acquisition of the ventricular response using the disturbance created by magnetized blood undergoing a stationary permanent magnet is presented. The proposed model accounts for the different magnetic properties of the blood such as the relaxation time and the magnetic saturation. The blood flow is simulated by means of Navier-Stocks equations with pulsatile inlet pressure. The blood is assumed to be in the deoxygenated state and has a diamagnetic properties. Moreover, a moving mesh technique is implemented in the Finite-Element model to represent the idle and the moving states of the blood which provides the capability to model the magnetized blood as a moving magnet. The simulated magnetic field at different sensor locations is found to be in good agreement with experimental observations from the literature. The presented model can provide basis for understanding the magnetic modulated blood signal as well as the practical constraints that might be encountered in the design of such devices.

Analytical calculation of magnetic field and electromagnetic performance of flux reversal machines

A subdomain model is developed for the computation of the no-load and load magnetic field distribution in flux reversal machines. In the proposed model, the Laplace's and Poisson's equations are built in the subdomains, including semi-closed stator slot, rotor slot, air gap and permanent magnets. Based on the general solutions and the boundary conditions between the adjacent subdomains, the magnetic field in all subdomains can be obtained. According to the field solution, the electromagnetic performance, such as the flux linkage, back-EMF, cogging torque and electromagnetic torque are calculated. The calculated results by finite element analysis and experiment results are given to verify the analytical model.

A Novel Stator and Rotor Dual PM Vernier Motor With Space Vector Pulse Width Modulation

In this paper, an electric machine with dual permanent magnet (PM) structures in both stator and rotor is proposed. Multi-pole PMs are buried both in stator and rotor slots of the proposed machine and the magnetic field is modulated through the stator and rotor teeth. This machine with dual magnetic flux modulation can be categorized as one special case of flux-modulating machines. A time-stepping finite-element method combined with space vector pulse width modulation-based vector control method is used to analyze the steady-state and transient performance of the machine and its control system.

Polarity of the Stator Permanent Magnets of the Magnetic-Geared Motor

Polarity of the Stator Permanent Magnets of the Magnetic-Geared Motor

A Design Study of Dual-Stator Permanent Magnet Brushless DC Motor

Dual - stator permanent magnet brushless DC Motor (DSBLDC) feature s high efficiency and torque - densit y . As DSBLDC could operate in various states according to different winding connection modes , it is fully qualified for electric vehicle (EV) drive. Unfortunately, due to the particular dual - stator structure, th is kind of motor is difficult to be design ed by available design methods. However, this paper demonstrates that a DSBLDC with series magnetic circuit structure can be regarded as being consisted of two independent BLDCs , an inner-rotor BLDC and an outer-rotor BLDC. Thus, the DSBLDC can be divided into two single-stator BLDCs. Based on this demonstration, the design method is verified by finite element analysis (FEA) , and the basic design steps are given. Furthermore , experimental result s of the prototype motor have verif ied the correction of the method, which also indicates that the motor with superior performance is adapted to EV drive.

Design, Analysis, and Optimization of Ironless Stator Permanent Magnet Machines

This paper presents a methodology for the design, analysis, and graphical optimization of ironless brushless permanent magnet machines primarily for generator applications. Magnetic flux in this class of electromagnetic machine tends to be 3-D due to the lack of conventional iron structures and the absence of a constrained magnetic flux path. The proposed methodology includes comprehensive geometric, magnetic and electrical dimensioning followed by detailed 3-D finite element (FE) modeling of a base machine for which parameters are determined. These parameters are then graphically optimized within sensible volumetric and electromagnetic constraints to arrive at improved design solutions. This paper considers an ironless machine design to validate the 3-D FE model to optimize power conversion for the case of a low-speed, ironless stator generator. The machine configuration investigated in this paper has concentric arrangement of the rotor and the stator, solenoid-shaped coils, and a simple mechanical design considered for ease of manufacture and maintenance. Using performance and material effectiveness as the overriding optimization criteria, this paper suggests optimal designs configurations featuring two different winding arrangements, i.e., radial and circumferentially mounted. Performance and material effectiveness of the studied ironless stator designs are compared to published ironless machine configurations.

The Lorentz transformations of the vectors E, B, P, M and the external electric fields from a stationary superconducting wire with a steady current and from a stationary permanent magnet

In the first part of this paper we review the fundamental difference between the usual transformations of the three-dimensional (3D) vectors of the electric field E, the magnetic field B, the polarization P, the magnetization M and the Lorentz transformations of the 4D geometric quantities, vectors E, B, P, M, with many additional explanations and several new results. In the second part, we have discussed the existence of the electric field vector E outside a stationary superconducting wire with a steady current and also different experiments for the detection of such electric fields. Furthermore, a fundamental prediction of the existence of the external electric field vector E from a stationary permanent magnet is considered. These electric fields are used for the resolution of the "charge-magnet paradox" with 4D geometric quantities for a qualitative explanation of the Aharonov-Bohm effect in terms of fields and not, as usual, in terms of the vector potential and for a qualitative explanation that the particle interference is not a test of a Lorentz-violating model of electrodynamics according to which a magnetic solenoid generates not only a static magnetic field but also a static electric field.

Influence of Stator Slotting on the Performance of Permanent-Magnet Machines With Concentrated Windings

The use of slotted stator permanent-magnet machines with concentrated windings is increasing in industry. In this paper, the effect of the slot opening on flux linkage, internal voltage, mean torque, rotor eddy current loss, and stator iron losses is evaluated. This gives new insight into the influence of slotting on the performance of machines with a small slot opening. In addition, the slot opening can be chosen to maximize the internal voltage and the mean torque while minimizing the total iron loss. The limitations of the traditional analytical design model with small slot openings for permanent magnet machines are reported. Carter factor expressions found in literature are evaluated by comparing them with finite-element computations. The finite-element computations in turn are validated using measurements on two machines with semi-open slots and one machine with fully open slots. The measured and simulated values for amplitude and waveform of the flux linkage and internal voltages are in good agreement.

Novel motor design for rotating anode x-ray tubes operating in the fringe field of a magnetic resonance imaging system

Using hybrid x-ray∕MR (XMR) systems for image guidance during interventional procedures could enhance the diagnosis and treatment of neurologic, oncologic, cardiovascular, and other disorders. The authors propose a close proximity hybrid system design in which a C-arm fluoroscopy unit is placed immediately adjacent to the solenoid magnet of a MR system with a minimum distance of 1.2 m between the x-ray and MR imaging fields of view. Existing rotating anode x-ray tube designs fail within MR fringe field environments because the magnetic fields alter the electron trajectories in the x-ray tube and act as a brake on the induction motor, reducing the rotation speed of the anode. In this study the authors propose a novel motor design that avoids the anode rotation speed reduction. The proposed design replaces the permanent magnet stator found in brushed dc motors with the radial component of the MR fringe field. The x-ray tube is oriented such that the radial component of the MR fringe field is orthogonal to the cathode-anode axis. Using a feedback position sensor and the support bearings as electrical slip rings, the authors use electrical commutation to eliminate the need for mechanical brushes and commutators. A vacuum compatible prototype of the proposed motor design was assembled, and its performance was evaluated at various operating conditions. The prototype consisted of a 3.1 in. diameter anode rated at 300 kHU with a ceramic rotor that was 5.6 in. in length and had a 2.9 in. diameter. The material chosen for all ceramic components was MACOR, a machineable glass ceramic developed by Corning Inc. The approximate weight of the entire assembly was 1750 g. The maximum rotation speed, angular acceleration, and acceleration time of the motor design were investigated, as well as the dependence of these parameters on rotor angular offset, magnetic field strength, and field orientation. The resonance properties of the authors' assembly were also evaluated to determine its stability during acceleration, and a pulse width modulation algorithm was implemented to control the rotation speed of the motor. At a magnetic flux density of 41 mT orthogonal to the axis of rotation (on the lower end of the expected flux density in the MR suite) the maximum speed of the motor was found to be 5150 revolutions per minute (rpm). The acceleration time necessary to reach 3000 rpm was found to be approximately 10 s at 59 mT. The resonance frequency of the assembly with the anode attached was 1310 rpm (21.8 Hz) which is far below the desired operating speeds. Pulse width modulation provides an effective method to control the speed of the motor with a resolution of 100 rpm. The proposed design can serve as a direct replacement to the conventional induction motor used in rotating anode x-ray tubes. It does not suffer from a reduced rotation speed when operating in a MR environment. The presence of chromic steel bearings in the prototype prevented testing at the higher field strengths, and future iterations of the design could eliminate this shortcoming. The prototype assembly demonstrates proof of concept of the authors' design and overcomes one of the major obstacles for a MR compatible rotating anode x-ray tube.

Centrifugal gas-phase transition magnetophoresis (GTM) – a generic method for automation of magnetic bead based assays on the centrifugal microfluidic platform and application to DNA purification

Transportation of magnetic beads between different reagents plays a crucial role in many biological assays e.g. for purification of biomolecules or cells where the beads act as a mobile solid support. Therefore, usually a complex set-up either for fluidic processing or for manipulation of magnetic beads is required. To circumvent these drawbacks, we present a facile and automated method for the transportation of magnetic beads between multiple microfluidic chambers on a centrifugal microfluidic cartridge "LabDisk". The method excels by requiring only one stack of stationary permanent magnets, a specific microfluidic layout without actively controlled valves and a predefined frequency protocol for rotation of the LabDisk. Magnetic beads were transported through three fluidically separated chambers with a yield of 82.6% ± 3.6%. Bead based DNA purification from a dilution series of a Listeria innocua lysate and from a lambda phage DNA standard was demonstrated where the three chambers were used for binding, washing and elution of DNA. Recovery of L. innocua DNA was up to 68% ± 24% and for lambda phage DNA 43% ± 10% compared to manual reference purification in test tubes. Complete purification was conducted automatically within 12.5 min. Since all reagents can be preloaded onto the LabDisk prior to purification, no further hands-on steps are required during processing. Due to its modular and generic character, the presented method could also be adapted to other magnetic bead based assays e.g. to immunoassays or protein affinity purification, solely requiring the adjustment of number and volumes of the fluidic chambers.

Hybrid Excitation Topologies and Control Strategies of Stator Permanent Magnet Machines for DC Power System

The stator permanent magnet (PM) machines have simple and robust rotor structure as well as high torque density. The hybrid excitation topology can realize flux regulation and wide constant power operating capability of the stator PM machines when used in dc power systems. This paper compares and analyzes the electromagnetic performance of different hybrid excitation stator PM machines according to different combination modes of PMs, excitation winding, and iron flux bridge. Then, the control strategies for voltage regulation of dc power systems are discussed based on different critical control variables including the excitation current, the armature current, and the electromagnetic torque. Furthermore, an improved direct torque control (DTC) strategy is investigated to improve system performance. A parallel hybrid excitation flux-switching generator employing the improved DTC which shows excellent dynamic and steady-state performance has been achieved experimentally.

Design and Analysis of a New Fault-Tolerant Permanent-Magnet Vernier Machine for Electric Vehicles

This paper proposes a new outer-rotor fault-tolerant permanent-magnet vernier machine for electric vehicles. It can offer the advantages of high torque density, low-speed high-torque operation and inherently negligible coupling between phases, namely fault-tolerant characteristic. The key of the proposed machine is to newly introduce the flux-modulation poles which can effectively modulate the high-speed rotating field of the armature windings and the low-speed rotating field of the permanent-magnet (PM) outer rotor. In addition, single-layer and multi-phase fractional slot concentrated windings are adopted to improve fault tolerance. For the proposed machine, the relationship among the numbers of the stator slots, winding poles and PM pole pairs are analyzed and discussed. By using the time-stepping finite element method, the electromagnetic performances and the efficiency of the proposed machine are analyzed, verifying the effectiveness of the theoretical analysis.

Electromagnetic Performance Analysis of Double-Rotor Stator Permanent Magnet Motor for Hybrid Electric Vehicle

In this paper, a new double-rotor stator permanent-magnet (DR-SPM) motor is proposed for hybrid electric vehicles, which consists of both armature windings and PMs in the stator and inner rotor while no PM in the middle rotor. This motor not only inherits the merits of simple rotor structure, high reliability and high power density, but also can avoid the middle rotor's cooling problem effectively. The motor topology and operation principle are presented and by using a finite element method (FEM), the electromagnetic performance of the DR-SPM motor is investigated. To verify the FEM results, a 2 kW prototype motor is newly designed and manufactured. Finally, some experiments are conducted to evaluate performance of the motor.

Quantitative Comparison of Flux-Switching Permanent-Magnet Motors With Interior Permanent Magnet Motor for EV, HEV, and PHEV Applications

Permanent-magnet (PM) motors with both magnets and armature windings on the stator (stator PM motors) have attracted considerable attention due to their simple structure, robust configuration, high power density, easy heat dissipation, and suitability for high-speed operations. However, current PM motors in industrial, residential, and automotive applications are still dominated by interior permanent-magnet motors (IPM) because the claimed advantages of stator PM motors have not been fully investigated and validated. Hence, this paper will perform a comparative study between a stator-PM motor, namely, a flux switching PM motor (FSPM), and an IPM which has been used in the 2004 Prius hybrid electric vehicle (HEV). For a fair comparison, the two motors are designed at the same phase current, current density, and dimensions including the stator outer diameter and stack length. First, the Prius-IPM is investigated by means of finite-element method (FEM). The FEM results are then verified by experimental results to confirm the validity of the methods used in this study. Second, the FSPM design is optimized and investigated based on the same method used for the Prius-IPM. Third, the electromagnetic performance and the material mass of the two motors are compared. It is concluded that FSPM has more sinusoidal back-EMF hence is more suitable for BLAC control. It also offers the advantage of smaller torque ripple and better mechanical integrity for safer and smoother operations. But the FSPM has disadvantages such as low magnet utilization ratio and high cost. It may not be able to compete with IPM in automotive and other applications where cost constraints are tight.

A Linear Stator Permanent Magnet Vernier HTS Machine for Wave Energy Conversion

In this paper, a new linear stator permanent magnet (PM) vernier high-temperature superconductor (HTS) machine is proposed for wave energy conversion. The machine adopts a double-sided design and inner-translator arrangement where the stator consists of two plane iron cores with salient teeth wound with 3-phase armature windings and PMs mounted on the surface of the stator teeth. While the translator is designed as an iron core with salient teeth on the two sides, the HTS bulks are inset between every two adjacent salient teeth to shield the flux leakage, thus improving the power density of the machine. Based on using the finite element analysis, the characteristics and performances of the proposed machine are assessed. Also, the proposed machine is quantitatively compared with the existing linear stator PM vernier machine. Hence, it validates that its performance, especially the power density, can be improved significantly.

A Generalized Magnetic Circuit Modeling Approach for Design of Surface Permanent-Magnet Machines

This paper proposes a generalized equivalent magnetic circuit model for the design of permanent-magnet (PM) electric machines. Conventional approaches have been applied to PM machine design but may be insufficiently accurate or generalized without taking pole-slot counts into consideration. This would result in reduction of dimensioning accuracy at the initial design stage. Also, magnetic saturation is often ignored or compensated by correction factors in simplified models since it is difficult to determine the flux in individual stator teeth. In this paper, the flux produced by stator winding currents and PMs can be calculated accurately and rapidly using the developed model, taking saturation into account. A new modeling technique for PM poles is proposed so that the magnetic circuit is applicable to any pole-slot combinations. This aids machine dimensioning without the need for computationally expensive finite-element analysis (FEA). A 540-kW PM machine is first designed using the proposed method and then verified with FEA. Another 350-W machine is subsequently designed, manufactured, and validated by both FEA and experiments. The comparisons demonstrate the effectiveness of the proposed model.