Pole Pitch Research Articles

Electrical Design Study of 10-MW Salient-Pole Wind Turbine HTS Synchronous Generators

A conceptual structure of a 10-MW salient-pole wind turbine generator with race-track-shaped high-temperature superconductor (HTS) field coils is proposed, and a novel electrical design method for the salient-pole wind turbine HTS synchronous generators (WTHGs) is developed. In addition, the novel electrical design method derivation is introduced in detail according to the design process. In addition, the influence of some main machine parameters, e.g., pole pitch, stator outer diameter, magnetic flux density in the stator teeth, and electric loading, on HTS generator performance is clarified, and the optimal parameters are obtained thereby. Moreover, the optimized performance parameters of a 10-MW WTHG are compared with the conventional wind turbine generators with copper field windings. Finally, it is indicated that large-scale WTHGs have a higher power density, lighter weight, and higher efficiency than the conventional counterparts.

영구자석형 동기전동기의 고저/선회 제어용 드라이버 설계 모델링

The purpose of this paper is to control of the low-speed, high-precision PMSM 2- axes pitch/turning. In this paper, apply the PAM-PWM inverter for it. However, The PAM-PWM inverter, control algorithms and hardware is complex. But it is possible to improve the performance in the low-speed operation can reduce the effect of the PWM ripple and Dead Time of inverter by applying suitable DC-bus voltage control. The direct driver PMSM(Permanent Magnet Synchronous Motor) configured to vector control part, PAM control part and the other controller. The vector control part includes PI current, speed control, additional space vector modulation. PAM control part has to have PI voltage controller and P current controller for DC-bus voltage control. Besides, the motor position estimator , the speed estimator and the counter electromotive force and Dead Time Compensation are added. With this arrangement, PMSM was driven with a low pole pitch / turning by performing the current control to the current command or torque command is the paper. As a result, it was possible to minimize the disturbance component that appears in the drive in proportion to the DC voltage magnitude. The use of a hydraulic drive method for a two-axis bubble column is a typical tank. When using the PWM PAM inverter driver is in the turret can be driven by high-precision, low vibration, low noise compared to the hydraulic drive may contribute to the computerization of the turret.

Optimization Design of the Planar Switched Reluctance Motor on Electromagnetic Force Ripple Minimization

In planar switched reluctance motors (PSRMs), the electromagnetic force ripple minimization is important to reduce the noise and vibration for high-precision motions. In this paper, an improved PSRM by optimization design for minimization of the electromagnetic force ripple is proposed. The structure, principle, and mathematical model of the PSRM are clarified. Based on Ansoft Maxwell, optimization design of the PSRM is performed by improved structure with smaller pole pitch and incremental number of mover poles. Experiments of the improved PSRM are implemented based on dSPACE. The experimental results verify that the improved PSRM effectively reduces electromagnetic force ripple with planar trajectory tracking.

Influence of Stator and Rotor Pole Arcs on Electromagnetic Torque of Variable Flux Reluctance Machines

The influence of stator and rotor pole arcs on electromagnetic torque of variable flux reluctance machines (VFRMs) having different stator and rotor pole combinations is investigated. Different from 6/4 stator/rotor pole switched reluctance machines, which usually employ equal stator pole arc and stator slot opening, unequal stator pole arc and slot opening can boost the torque density of the VFRM. Moreover, the optimal rotor pole arc to rotor pole pitch ratio in VFRMs is \(\sim ~1/3\) and the optimal stator pole arc is equal to or slightly smaller than the optimum rotor pole arc. For a 6-pole stator, the 4-, 5-, 7-, and 8-pole rotor VFRMs with the optimal stator and rotor pole arcs can increase the average torque by 1%, 4%, 30.7%, and 72.9% compared with those having equal stator pole arc and stator slot opening. In addition, the 6/7 stator/rotor pole VFRM exhibits the largest torque density. Prototype machines with optimal stator and rotor pole arcs are manufactured and measured to validate the analysis.

Effect of the size of GdBCO-Ag secondary magnet on the static forces performance of linear synchronous motors

Bulk high temperature superconductor magnets (HTSMs) have a higher flux-generating capability compared to conventional permanent magnets (PMs). These materials potentially can be used in high temperature superconducting (HTS) linear synchronous motors (LSMs) as superconducting secondary magnets, what will result in a reduced volume and weight as well as in higher force density and efficiency of these devices when compared to conventional PMs. The focus of this paper is on the effect of size of the secondary HTSM on the static performance (thrust force and normal force) of a LSM. In order to obtain high-field HTSM as the secondary, single grain bulk GdBCO-Ag superconductors of diameter 20 mm, 30 mm and 40 mm, which have higher Jc and trapped fields than YBCO superconductors, were used in this device for the first time following application by the same optimized magnetization condition. It was found that both thrust and normal forces increase and saturate with the increasing size of the HTSM secondary at the small size range, and then potentially distort when the physical size of the HTSM secondary approaches the pole pitch of the linear three-phase primary windings of the LSM. Furthermore, more experiments of a larger-sized multi-seeded HTSM secondary, confirmed that the relationship between the HTSM secondary size and the pole pitch of the primary is an important factor for achieving higher thrust and normal forces. It is suggested that the multi-pole HTSM secondary will be more beneficial to future HTS LSM designs since the single-pole HTSM secondary size should be equal to or smaller than the stator pole pitch in the paper.

Optimization of the Thrust Ripple of a Tubular Flux-Switching Permanent Magnet Linear Motor

The effective optimization methods are needed to reduce the thrust ripple for the tubular flux-switching permanent magnet linear motor (TFSPMLM), which is significant for reducing the vibration, and improving the reliability. The auxiliary teeth and core bridge are set and analyzed for the bipolar and single-polar winding structures. On this basis, this paper focused on a new method of the secondary pole pitch fine-tuning which can overcomes the disadvantages of increasing the volume, decreasing the average thrust, adding the cost, and so on. The influences of tuning the secondary pole pitch on the average thrust and the thrust ripple for the different winding structure motors are calculated and analyzed. The conclusion can provide reference for the application of the method of tuning secondary pole pitch to the TFSPMLM for different background demands.

The design and fabrication of a small MHD pump for liquid sodium circulation

The linear annular magnetohydrodynamic (MHD) pump was designed for the purpose of transporting the electrically conducting liquid sodium that is used as a coolant in a Sodium cooled Fast Reactor (SFR) operating at high temperatures (over 550°C). The MHD pump was designed by using an equivalent circuit method which is commonly employed to the design of the induction machines. The mathematical equations on the developing pressure and efficiency was found out by using Laithewaite’s standard design formula. The main geometrical parameters for the design were the pump core length, the diameter of the pump and the annular gap size. The dominant electromagnetic variables were the input frequency, magnetic pole pitch and number, and coil turns. Especially, it was shown that the developing pressure and efficiency were maximized at the range of frequencies below the commercial value of 60Hz. Also, the size of an annular gap was suitably selected considering the hydraulic frictional loss at the narrow annular channel. The P–Q characteristic was theoretically predicted according to the change of the input current, voltage and power. The functional and structural components of the pump consisted of the material compatible with the high temperature and chemical reactivity of the liquid sodium. The designed pump was predicted to have the nominal flowrate of 10L/min and the developing pressure of 4bar.

Design and Operation of Very Slow Speed Generators for a Bristol Cylinder Sea Wave Generating Device

This paper describes the operation of a direct-drive brushless generator for a Bristol Cylinder ocean wave device. This is a very low-speed device; thus, the pole number and diameter are very large. Although the machine may be large, its pole pitch and axial length is low. The application is described and simulated using analytical and finite-element analysis techniques. A 248-pole design with surface rotor magnets is developed with both surface and slotted windings. An analysis of the control is put forward.

Multi-pole fine magnetic scale for high-resolution magnetic encoders evidenced by a simplified method

Magnetic encoders are widely used in linear and rotary positioning applications, specifically under harsh environments. The finer the magnetic pole-pitches of the magnetic scale in magnetic encoders the higher the resolution of the encoder. Conventional non-structured magnetic scales can be achieved with ease by dedicate magnetizing fixture at a pole pitch larger than 1 mm. It becomes extremely difficult to magnetize the poles with pitch much <1 mm, say, 0.1 mm. We propose a simple magnetic grating structure to alleviate this difficulty and verify its feasibility. The magnetic grating was first designed according to the demagnetization curve of a permanent magnet with proper dimensions to attain high magnetic flux density. Simulation results showed that periodical signal of sinusoidal nature can be obtained from such a magnetic grating being magnetized by merely a single magnetizing the grating as a whole. The periodicity conforms to the 1:1 ratio of pole-width and groove-width. Magnetic flux density in z direction increases enormously with decreasing detection gap. These results are significant for signal processing. Experimental results by using a simplified verification method confirm the simulated results. Instead of by magnetizing, the precision of such a magnetic encoder is governed solely by the precision of machining the pole-groove structure. The proposed method can thus be easily achieved by various high precision machining methods such as wire-EDM, laser-beam machining, or photo-lithography, and etc.

Proposal of C-core Type Transverse Flux Motor for Ship Propulsion – Increasing Torque Density by Dense Stator Configuration –

Electric ship propulsion system has been drawing attention as a solution for savings in energy and maintenance costs. The system is mainly composed of motor, converter and gearbox and required for high torque at low speed. In this situation, transverse flux motors (TFMs) have been proposed to fulfill the low-speed high-torque characteristic due to suitable for short pole pitch and large number of poles to increase torque output. In this trend, we have proposed C-core type motors taking advantage of TFMs’ structure. In this manuscript, a simple design method based on the magnetic-circuit theory and simple modeling of the motor is proposed to search a design parameter for maximizing torque as a pre-process of numerical study. The method takes into consideration the effects of magnetic leakage flux, magnetic saturation and pole-core combination in accordance with the systematic theory. The simple modeling is conducted based on a dense armature structure in previous axial flux motors (AFMs) applied to the new motor design. The validity of the method is verified by 3-D finite element analysis (FEA) and relative error is at most 20%. The minimalist design is shown to be advantageous for effective use in 3-D FEA. As a detailed design by the FEA, high torque density and low cogging to output ratio can be achieved simultaneously in the proposed machine.

High-aspect-ratio nanoimprinted structures for a multi-pole magnetic scale

Conventional non-structured magnetic scales can only achieve a pole pitch of around 1 mm by dedicate magnetization process; a smaller magnetic pole pitch yields a higher resolution. This study describes a practical approach to obtain high resolution multi-pole magnetic scales using high-aspect-ratio nanoimprinted structures. The dimensions of structure were designed according to demagnetization curve of a magnet, which indicates that a high-aspect-ratio structure is required. Simulation results show that the high-aspect-ratio grating has a larger magnetic strength, steeper variation, and greater tolerance of detection gap than those of low-aspect-ratio gratings. Magnetic flux density in the z direction increases significantly with a decrease of the detection gap. High magnetic strength and flux density contrast benefit signal detection and processing. Nanoimprint technology has shown its potential to fabricate a multi-pole magnetic scale with a pole-pitch of down to 72 nm. To further implement we need to optimize magnetic materials and magnetic sensors such as those widely used in T-bit hard disks, CoCrPt media and giant magneto-resistance sensors.

Reducing Cogging Force of a Permanent Magnet Transverse Flux Linear Synchronous Motor

This paper presents means to minimize the cogging force of a new type of permanent magnet excited transverse flux linear synchronous motor (PMTFLSM). The translator of this linear motor consists of cross-shaped core sets. Varying the parameters of air gap length, magnet dimensions, pole pitch and tooth width of the translator, the cogging force of the PMTFLSM will be analyzed. Taguchi's parameter method including 2D finite element analysis (FEM) is employed to minimize the cogging force. Analytical and simulation results indicate the usefulness of our approach in practice

Investigation and General Design Principle of a New Series of Complementary and Modular Linear FSPM Motors

The conventional linear flux-switching permanent-magnet (FSPM) motors directly split from a rotary FSPM motor suffer from drawbacks such as unbalanced magnetic circuit of end coil, bigger cogging force, and force ripple. In this paper, to reduce cogging force and thrust force ripple, some complementary and modular linear FSPM (LFSPM) (MLFSPM) motors with mover/stator pole pitch ratio τm/τs of about one, namely, τm/τs = 10/12, 11/12, 12/12, 13/12, 14/12, 15/12, will be investigated using finite-element method (FEM) and experimental method at first. Then, another new LFSPM motor with τm/τs = 3 is analyzed. Based on τm/τs = 3, some new MLFSPM motors are designed, investigated, and compared using FEM. To fully investigate these motors, the optimal MLFSPM motor with τm/τs = 3 is quantitatively compared with the two optimal motors with τm/τs ≈ 1 . Finally, the general design principle for this series of MLFSPM motors with different τm/τs values is concluded.

Analysis of a Tubular Linear Permanent Magnet Motor for Reciprocating Compressor Applications

This paper describes a design optimization to achieve optimal performance of a two novel single-phase short-stroke tubular linear permanent magnet motors (TLPMMs) with rectangular and trapezoidal permanent magnets (PMs) structures. The motors equipped with a quasi-Halbach magnetized moving-magnet armature and slotted stator with a single-slot carrying a single coil. The motors have been developed for reciprocating compressor applications such as household refrigerators. It is observed that the TLPMM efficiency can be optimized with respect to the leading design parameters (dimensional ratios). Furthermore, the influence of mover back iron is investigated and the loss of the motor is computed. Finite element analysis (FEA) is employed for the optimization, and the optimal values of the ratio of the axial length of the radially magnetized magnets to the pole pitch as well as the ratio of the PMs outer radius-to-stator outer radius (split ratio), are identified.

A New Linear Double Salient Permanent Magnet Motor with Complementary Winding

In this paper, two novel structures of linear double salient permanent magnet (LDSPM) motor having magnets and armature windings in primary are proposed and compared. Firstly, the design principles of both motors are presented. Then, for a fair comparison, two motors are designed based on the same primary dimensions including the slot area, teeth number, pole pitch, permanent magnet volumes and coils number per phase, while the stator pole pitch and the primary structure are different. Finally, the configurations and static characteristics of both motors are critically compared based on finite element (FE) analysis. The results indicate that the proposed topology can avoid the asymmetry of back-EMF waveforms and reduce cogging force and thrust force ripple. Also, the proposed primary permanent magnet linear motors are suitable for the longer stator application such as urban rail transit (URT).

The use of Quadrature Axis Flux Barriers in Linear Synchronous Machines

The paper explores the use of quadrature axis flux barriers in planar linear synchronous motors. It is shown that the use of the barriers produces a decrease in the flux driven by the armature windings. This leads to a reduction in the tendency for de-magnetisation of the magnets and improved power factor with only a minor reduction in the force. A simple analysis is developed to enable broad assessments of the flux barrier effects and this is validated by the use of 2D finite element analysis in a time stepping routine. The simple analysis is used to consider machines of three different pole pitches with a range of quadrature axis gap dimensions. The braking force produced in short circuit conditions is important in some applications and it is shown that the use of flux barriers gives enhanced forces.

Analytical 2-D Calculations of Torque, Inductance, and Back-EMF for Brushless Slotless Machines With Surface Inset Magnets

In this paper, the electromagnetic torque, reluctance torque, inductance, and back-EMF are analytically calculated for brushless slotless machines with surface inset magnets. The calculations are based on the 2-D analytical magnetic field distributions. Although the expressions can be used for any magnetization patterns, the effects of three different magnetization patterns, i.e., radial, parallel, and Halbach, on the developed torque, back-EMF and inductances are examined. Besides, the influences of three types of armature current waveforms (sinusoidal, ideal rectangular, and six-step rectangular) on the mentioned quantities are investigated. The effects of pole arc per pole pitch ratio on the performance of slotless brushless machines are also studied. To evaluate the proposed 2-D analytical expressions, the analytical results are compared with those obtained by finite element analyses.

Cogging Torque Optimization of Flux-Switching Transverse Flux Permanent Magnet Machine

In this paper, cogging torque characteristics in both single-phase and three-phase flux switching transverse flux permanent magnet machines (FS-TFPMM) are analyzed by 3-D finite element method (FEM). It is found that the cogging torque of the FS-TFPMM is significantly influenced by the ratios of stator and rotor core circumferential widths to pole pitch, $k_{s}$ and $k_{r}$ . When $k_{r}>1-k_{s}$ , the cogging torque waveform has additional two zero-crossing points, whilst its amplitude is significantly reduced. The optimal ratios of $k_{s}$ and $k_{r}$ are selected to reduce the cogging torque and to maximize the permanent magnet flux linkage. A 380 W three-phase prototype is designed, manufactured, and tested to verify the optimization.

Comparison of Complementary and Modular Linear Flux-Switching Motors With Different Mover and Stator Pole Pitch

Linear flux-switching permanent magnet (LFSPM) motors with both permanent magnets and armature windings on the short primary mover have attracted considerable attention due to their simple and cheap stator which only consists of iron. Hence, this kind of liner motor is very suitable for long stator applications such as in urban rail transportations. However, the conventional LFSPM motors directly split from rotary FSPM motor suffer from drawbacks such as unbalanced magnetic circuit of end coil, heavy mover, and bigger cogging force and force ripple. Modular LFSPM (MLFSPM) motors can mitigate the problem of unbalanced magnetic circuit of end coil. But some MLFSPM motors with different stator/mover pole pitch τs/τm=12/14, 12/10 don't have complementary phase armature windings, which will lead to asymmetrical and non-sinusoidal back-electromotive force, bigger cogging force and thrust force ripple. The key of this paper is to propose, investigate, and compare four complementary and modular structures for the LFSPM motors with different τs/τm . The electromagnetic performance and dimensions of the proposed complementary MLFSPM motors with different τs/τm are investigated, compared and confirmed by the means of finite element analysis and experimental results. Based on the analysis results, two complementary MLFSPM motors with τs/τm=12/13 are chosen to be the two best motors, which can offer the biggest thrust force, relatively smaller cogging force and thrust force ripple, and shorter mover length.

Optimal design of ironless permanent magnet planar motors for minimisation of force ripples

This study concerns the analysis and minimisation of the force ripples existing in ironless permanent magnet planar motors. The force ripples is one of the key factors for moving accuracy of the planar motors. One of the main sources of the force ripples, the neglected higher harmonics of the magnetic flux density distribution, is analysed for synthesis of real-time control model in this study. An analytical model of the planar motor is firstly developed, which illustrates that the force ripples part caused by some higher harmonics can cancel each other when the length of the coil is an even multiple of the pole pitch of the magnet array. As a result, the force ripples caused by the higher harmonics can be basically eliminated with a selected coil. Finally, the analysis results are both validated by comparative simulation and experiment of two partial motors.