Pole Pitch Research Articles

Investigation of scaling effect on power factor of permanent magnet Vernier machines for wind power application

This study investigates the scaling effect on power factor of surface mounted permanent magnet Vernier (SPM-V) machines with power ratings ranging from 3 kW, 500 kW, 3 MW to 10 MW. For each power rating, different slot/pole number combinations have been considered to study the influence of key parameters including inter-pole magnet leakage and stator slot leakage on power factor. A detailed analytical modelling, incorporating these key parameters, is presented and validated with two-dimensional finite-element analysis for different power ratings and slot/pole number combinations. The study has revealed that with scaling (increasing power level), significant increase in electrical loading combined with the increased leakage fluxes, i.e. (i) magnet leakage flux due to large coil pitch to rotor pole pitch ratio, (ii) magnet inter-pole leakage flux and (iii) stator slot leakage flux, reduces the ratio of armature flux linkage to permanent magnet flux linkage and thereby has a detrimental effect on the power factor. Therefore, unlike conventional SPM machines, the power factor of SPM-V machines is found to be significantly reduced at high power ratings.

New Applications for Linear Induction Drives used for Silent Propulsion Systems in Nuclear Submarines and Supercarriers

A 2-dimensional analytical and numerical theory for linear induction drives (LIDs) using hot seawater from coolant systems of nuclear reactors as a driving medium has been presented. This work suggests its use in nuclear submarines as it could be considered an important application on how to utilize the coolant output from nuclear reactors in nuclear submarines to generate energy that can be used in nuclear submarine and supercarriers as silent propulsion systems. In this paper, the stepped distribution of the 3-phase winding of the LID has been presented by Fourier integrals. The boundary value problem of the LID has been solved using Fourier transform techniques. The force and seawater input power expressions of the LID have been given in Fourier integral forms, which permit studying the effect of the design parameters of the LID to get the optimum performance. The effect of changing the conductivity of seawater due to the change in seawater temperature has been studied, showing the necessity of injecting hot water from the coolant system of the nuclear submarines or supercarriers, into the LID to improve their performance. The paper shows that the duct size, the conductivity, and the frequency are crucial factors for controlling the silent speed of these machines. For the same length of the machine, the paper shows that decreasing the number of poles and increasing the pole pitch improves the performance than increasing the number of poles and decreasing the pole pitch.

An Effective Method to Improve the Accuracy of a Vernier-Type Absolute Magnetic Encoder

This article proposes a method to improve the accuracy of a vernier absolute magnetic encoder. The encoder consists of a master and a nonius multipolar magnetic track. Sinusoidal signals from the master and nonius tracks are used to infer the absolute information. Unfortunately, these signals are contaminated by nonideal factors such as different amplitudes, dc-offsets, phase shifts, and random noise. Moreover, harmonics existing in the encoder signals distort the vernier principle and significantly affect the accuracy of the encoder. To address these problems, the present article proposes an efficient method with three main parts. The first is an observer phase-locked loop (OPLL), which is used to estimate the phase and eliminate the nonideal factors. The second is nonlinear phase compensation, which is used to correct the vernier principle that deviated due to the existing harmonics. Finally, a pole pitch compensation method is introduced to modulate the master phase angle from the OPLL to eliminate the harmonic distortion. The proposed method can eliminate the nonideal factors, harmonic distortion and improve the accuracy of the encoder. All the proposed methods were implemented on an ARM STM32F407ZG. The experimental results confirm the validity of the proposed method for practical applications.

Development, Design, and Analysis of a Dual-Consequent-Pole Transverse Flux Linear Machine for Direct-Drive Applications

Transverse flux machines can achieve high force density by reducing the pole pitch because of the decoupling of electric and magnetic loadings. But the main flux linkage interlinking with the armature coils will decrease as the pole pitch reduces, resulting in motor performance degradation. Unlike the approaches adopted by many literatures to suppress the leakage flux, this article proposes a novel dual-consequent-pole transverse flux linear machine by adopting dual-PM structure. Without increasing the occupied volume, the coil flux linkage is enhanced and the force density can be further improved. At first, the basic configuration and operation principle are introduced at first. Then the leading parameter influence on the force density is investigated. The electromagnetic performance of the proposed machine is investigated by three-dimensional finite element analysis and is compared with its counterparts. The field distribution, winding flux linkage, back electromotive force, detent force, and thrust force are emphasized as well as the efficiency and power factor. Finally, a prototype machine is constructed and tested to validate the theoretical analysis.

Scaling Effect on Electromagnetic Performance of Surface-Mounted Permanent-Magnet Vernier Machine

This article investigates the impact of scaling on the electromagnetic performance of surface-mounted permanent-magnet Vernier (SPM-V) machines with a main focus on open-circuit induced Electro Motive Force (EMF). Three different power ratings, i.e., 3 kW, 500 kW, and 3 MW, have been chosen for this article. For each power rating, the SPM-V machines are analyzed for different slot/pole number combinations to compare their optimal performance with a conventional SPM machine. Step-by-step development of an analytical equation is presented for the prediction of induced EMF taking into account the interpole leakage of rotor permanent-magnets. 2-D finite-element analysis (FEA) has been used to validate the analytical equation across different power ratings. The analytical equation is thereafter utilized to study the influence of different geometric parameters on the performance of the SPM-V machines. It reveals that the back EMF and torque of SPM-V machines, for a given normalized pole pitch (rotor pole pitch to magnetic airgap length), are unaffected by the increase in airgap length due to scaling. However, the power factor of SPM-V, unlike the conventional SPM, reduces significantly with the increase in electrical loading due to the scaling effect. The analytical model for induced EMF and the 2-D FEA predicted results are validated by experiments using conventional SPM and SPM-V machine prototypes.

Analysis of a model for longitudinal electromagnetic stirring in the continuous casting of steel

A recent three-dimensional (3D) model that revisited earlier theoretical work for longitudinal electromagnetic stirring in the continuous casting of steel blooms is analyzed further to explore how the bloom width interacts with the pole pitch of the stirrer to affect the magnetic flux density. Whereas the first work indicated the presence of a boundary layer in the steel near the interface with the stirrer, with all three components of the magnetic flux density vector being coupled to each other, in the analysis presented here we find that the component along the direction of the travelling wave decouples from those in the other two directions and can even be determined analytically in the form of a series solution. Moreover, it is found that the remaining two components can be found via a two-dimensional computation, but that it is not possible in general to determine these components without taking into account the surrounding air. The validity of the asymptotically reduced model solution is confirmed by comparing it with the results of 3D numerical computations. Moreover, the asymptotic approach provides a way to compute the time-averaged Lorentz force components that requires two orders of magnitude less computational time than the fully 3D approach.

Design of dual rotor axial flux permanent magnet generators with ferrite and rare-earth magnets

This article addresses dual rotor axial flux Ferrite permanent magnet (PM) generator, as an alternative to a surface mounted and spoke types Nd-Fe-B generator which have concentrated windings. The performance parameters of all generators, particularly the efficiency, are identical. The design objective function is the generators mass minimization using a population-based algorithm. To predict the performance of the generators a finite element (FE) technique is applied. Besides, the aims of the design include minimizing cogging torque, examining different rotor pole topologies and different pole arc to pole pitch ratios. Three-dimensional FE technique is employed. It is shown that the surface mounted Ferrite generator topology cannot develop the rated torque and also has high torque ripple. In addition, it is heavier than the spoke type generator. Furthermore, it is indicated that the spoke type Ferrite PM generator has favorable performance and could be an alternative to rare-earth PM generators, particularly in wind energy applications. Finally, the performance of the designed generators is experimentally verified.

Design and analysis of a high-performance surface inset permanent magnet motor with asymmetrical rotor

This paper presents a novel design strategy for surface inset permanent magnet (SIPM) motors to suppress torque pulsations and maintain the high output torque by integrating the magnet skewing and asymmetrical rotor configurations. The magnet skewing is implemented within one magnet pole pitch to reduce cogging torque by avoiding excessive torque degradation, and the asymmetrical rotor is designed to improve the utilization of the torque components, thus to compensate the decreased torque due to the magnet skewing. To highlight the advantages of the proposed motor, a conventional SIPM motor is adopted for performance comparison with the aid of the finite element method. As a result, the proposed SIPM motor highly reduced the cogging torque (−79.7%) and torque ripple (−54.7%) while maintaining a high average torque when compared to the conventional SIPM motor.

Frequency Domain Solver를 이용한 양측식 평판형 선형유도전동기의 성능해석에 관한 연구

In this study, the thrust force of the flat type linear induction motor (LIM) was calculated by using the finite element analysis (FEA) of the frequency domain solver(FDS) method using the assumption that all physical quantities are the sinusoidal functions of the same frequency. For the analysis model of a simple linear induction motor adopting the concept of current sheet, a FEA using a time domain solver method(TDS), which can include the movement of objects and various frequency components, is performed. Through this, it was confirmed that the analysis error of the FDS is caused by the spatial harmonics component included in the moving magnetic field of the air gap. Finally, the thrust force of a flat type LIM of a specific specification was calculated using a FDS and a TDS, respectively. And the analysis result and analysis time between two analysis methods were compared. In addition, the analysis error and analysis time between the two methods were compared quantitatively while changing key design parameters such as air gap length and pole pitch. Through this, the feasibility study of the design of the flat type LIM using the FDS method is examined.

Research and Analysis of Electromagnetic Thrust of Variable Pole Distance Linear Induction Motor

According to the actual acceleration index requirements, a high-speed large-thrust linear induction motor for accelerating the system was designed. Due to the variable pole pitch design, the variation of the pole pitch plays a key role in the design, and the influence of the variation of the pole pitch on the output of the electromagnetic thrust is analyzed. The variable pole distance double-sided linear induction motor is used as the acceleration drive. It does not need to detect the speed and displacement. The primary winding current frequency is constant. As the speed increases, it will not be limited by the inverter frequency, and will not increase the motor loss. The frequency is constant and the control is optimized and simpler.

Sensorless Control of Planar Switched Reluctance Motors Based on Voltage Injection Combined With Core-Loss Calculation

In this article, a position estimation method is proposed to realize sensorless control of planar switched reluctance motor (PSRM) with core loss. First, a square-wave voltage generated through bipolar pulsewidth modulation (PWM) is injected into the idle phase of a PSRM, thereby generating core loss. The corresponding core-loss average power (CLAP), which contains position information, is calculated in real time. Then, depending on the six-phase CLAP, the initial position can be estimated for the PSRM startup. To stabilize the position estimation in different regions of pole pitches, position data measured in a long stroke are utilized to determine a function mapping from the CLAP with respect to position. Furthermore, a sensorless control system and commutation strategy are designed. Finally, the capability of different methods for position estimation and sensorless control of a PSRM system are experimentally investigated. The feasibility and effectiveness of the proposed method are verified through the experimental results.

A Novel Dual-Stator HTS Linear Vernier Generator for Direct Drive Marine Wave Energy Conversion

Marine wave energy is characterized by high power density and worldwide distribution, thus being an important renewable energy source. To better utilize the power, a novel dual-stator high-temperature-superconducting linear vernier generator (DS-HTS-LVG) is proposed in this paper. A special excitation winding arrangement with different pole pitches is presented in this paper to increase the thrust density and power factor. The configuration and operation principle of the presented machine are demonstrated. Some key parameters of the machine are optimized to achieve better electro-magnetic performance. Moreover, by using the finite-element method, the performance of the proposed DS-HTS-LVG is compared with a conventional DS-HTS-LVG. The results show that the proposed generator has ~36% higher power density and increases the power factor from 0.38 to 0.57, verifying the superiority of the proposed machine and the effectiveness of the novel winding arrangement.

Embedded position estimation using tunnel magnetoresistance sensors for permanent magnet linear synchronous motor systems

This paper presents an embedded position detection method for permanent magnet linear synchronous motor (PMLSM) using magnetic sensor. Tunnel magnetoresistance (TMR) sensors with the single axis sensitive direction are chosen as the sensing element to show the practicality. Differing from the common magnetic displacement sensor packaged with a magnetic grid, the proposed scheme takes the magnet of the PMLSM as a part of the sensor. With the motion of the PMLSM, TMR sensors separated by half of the pole pitch and excited with alternating voltages are utilized to pick up the changing magnetic field. The phase shift of output signals is proportional to the displacement of the PMLSM. High frequency time pulses are served as a measurement standard to realize the phase detection and the position is measured by counting the time pulses. From the industrial perspective, the proposed method is advantageous since it is high resolution, non-contact, and miniaturization.

How Choosing Precisely the Secondary Length of an Electromagnetic Catapult Could Prevent Vibrations

Dealing with electromagnetic catapults, using a simplified numerical approach discretizing the secondary into small parallelepipeds, we demonstrate that short secondary linear induction motors usually produce superimposed periodic force modulations (large ripple). The paper begins with analyzing force modulations in the simple case of an aluminum sheet moving at constant speed inside a stationary sinusoidal magnetic field. The second part extends the analysis to the motor case when both the magnetic field and the sheet are moving at different speeds with an algorithm controlling accelerations through the motor slip. The third part presents an application of the calculation method simulating vibrations of a suspended mass elastically linked to a launching aircraft. The paper concludes that the linear motor thrust is modulated at a variable frequency which depends upon the motor control strategy. The frequency of this modulation is the ratio of the speed difference, between the field velocity minus the motor velocity, divided by the motor pole pitch. The thrust modulation could induce strong vibrations on heavy parts, such as fuel tanks, suspended onto aircraft wings, when meeting their resonance frequency. It is demonstrated how this modulation is avoided completely when the secondary motor length is an exact multiple of the stator pole pitch.

Development and Analysis of Novel Flux-Switching Transverse-Flux Permanent Magnet Linear Machine

The flux-switching transverse-flux permanent magnet linear machine (FSTFPMLM) is proposed in this paper, combining the advantages of the transverse-flux linear machine and the flux-switching linear machine. First, the structure and operating principle of the FSTFPMLM is presented. Second, the magnetic field of a simplified FSTFPMLM is numerically computed by the three-dimensional (3-D) finite-element method (FEM). Third, the thrust characteristics of the machine, including the thrust force, cogging force, and force ripple, are numerically analyzed. The influence of structure parameters on the thrust characteristics has been analyzed by the 3-D FEM. The law of thrust, cogging force, and force ripple as the pole pitch ratio between primary and secondary, and the ratio between the tooth width and pole pitch of the secondary variable provides the guidance to design FSTFPMLM, which aims to achieve a larger thrust, smaller cogging and force ripple using less permanent magnet materials. The thrust force capabilities of FSTFPMLM are compared with other topologies of linear machines. Finally, the prototype and experimental setup have been developed, and the calculated results and the measured results are in good agreement.

Torque Analysis of Concentric Magnetic Gear With Interconnected Flux Modulators

In a concentric magnetic gear, the space harmonic fields at inner/outer air gap have equal number of poles and rotate synchronously with the inner/outer permanent magnets, thanks to the flux modulators. The shape of flux modulators is one of the key factors that affect the harmonic fields, and hence the torque capability and ripples. Conventionally, the flux modulators are assembled by stacking small separated pieces of steel laminations; however, it is not easy to hold those small laminations firmly together. In order to make the flux modulators less complicated and more reliable, interconnected flux modulators made from full laminations have been implemented in the previous work. This paper investigates the torque performances of magnetic gear with different configurations of the modulating ring that are characterized by the shape of modulator, the position of interconnecting bridge, and the ratio of pole arc to pole pitch.

Further study of linear PMSM driven ropeless lifts with consideration of imperfections by simulation

To provide a satisfactory lift service to super high-rise buildings (while maintaining a small footprint for the lift hoistways), ropeless multi-car per hoistway system may be the trend. In our previous paper, a simplified machine model and two primitive controllers were adopted and various features of such a ropeless lift car driven by a linear permanent magnet synchronous motor were illustrated by simulation. In this paper, imperfections including pole saliency, various types of friction such as Coulomb, viscous and Stribeck friction, cogging force and end-effect, etc. were considered. The controllers, control interval and simulation interval were improved in both quantity and quality to arrive at a controllably stable operation. For safety during a genuine power failure, the free-falling terminal speed was estimated both by analytical calculation and computer simulation with consideration of such imperfections. It was confirmed that a desirable operation could be achieved by having smaller and practical winding resistance and inductances, larger and practical permanent magnet magnetic flux, and an optimal pole pitch. This paper could be considered an enhanced version of the pervious paper in that the illustration is more realistic when imperfections are considered. It is hoped that experimenters would further verify the findings in this paper so that such technology could become popularly employed in the future lift industry. Practical application: Multi-dimensional multi-car in a hoistway configuration involving linear permanent magnet synchronous machines would become popular in the near future. This paper introduces a more comprehensive mathematical framework by taking into account of the imperfections in the design and evaluation of controllers as well as the drive performance for a multi-car lift system. The results may give lift designers and researchers a hint on how to design the machines and the controllers with the consideration of imperfections in terms of winding design with variation in resistance, inductance, magnetic field strength, pole pitch, saliency and different types of friction. The paper is aimed at providing lift designers and researchers with a more realistic picture to welcome the new age of multi-car multi-dimensional lift technology.

Development and Analysis of a Novel Transverse Flux Permanent Magnet Linear Motor With the Concentrated Flux Mover

The magnetic field computation and performance characteristics analysis for a novel transverse flux permanent-magnet linear motor with the concentrated flux mover have been discussed. The following issues have been emphasized as: the construction of the transverse flux linear motor, magnetic flux distribution, winding flux linkage, and thrust force characteristic. The force ripple coefficient is theoretically derived from the mechanism of production of a force ripple, i.e., improving the waveform of back-EMF. The influence of structure parameters on the thrust force and cogging force characteristics is analyzed in detail. A special attention is paid to the pole pitch ratio between stator and mover, the ratio between slot width and pole pitch of stator. Finally, a prototype of transverse flux permanent magnet linear motor has been developed.

Study on DC flashover characteristics of plastic sheds in small scale

The statistics of tripping data of transmission lines show that external damage has become the main cause of transmission lines tripping. The foreign object cutting-out, which accounted for 61.8% of the total, was the most common external damage in transmission line. This paper focuses on the DC flashover characteristics of small-scale plastic sheds of greenhouses with distances of 1m and 2m. The results of the study showed that the surface of plastic sheds was less dirty and the average surface conductivity was lower. In the dry condition, it can be regarded as an insulator, and in the case of moisture, however, its insulation resistance is reduced to a megohm level. Under the electric field of 70 kV/m, no flashover occurred in both the wrinkled and the tiled plastic sheds. The flashover voltage per unit length of the wrinkled is about 15%-21% lower than that of the tiled, and wrinkled plastic sheds flash over more easily. As the pole pitch increases, the flashover voltage per unit length decreases, and the flashover voltage per unit length of both the wrinkled and the tiled is reduced by about 30%.

Optimal Matching Design of Length and Width of Rectangular Ironless Coils for Magnetically Levitated Planar Motors

This paper proposes an approach to design the length, width, and bundlewidth dimensions of rectangular ironless coils for magnetically levitated planar motors. Firstly, a model for the propulsion and levitation forces generated from a single coil in Halbach permanent magnetic field by using Lorenz force volume integral method is developed. Then, a dimensionless factor named coil width dependent factor, $K_{\mathrm {c}}$ , which can define the amplitudes of propulsion and levitation forces, is formulated. In order to maximize the value of $K_{\mathrm {c}}$ , the optimal coils number, $n$ , of a square forcer is derived to be $m/2+1$ , where $m$ is the multiples of coil length $L_{\mathrm {c}}$ to magnetic pole pitch $\tau $ . Thereafter, the coil width $W_{\mathrm {c}}$ and bundlewidth $B_{\mathrm {c}}$ are determined considering the given magnetic pole pitch $\tau $ . The comparison between the proposed approach and other formulations verifies that if such designed coils is utilized in a forcer, the average amplitude and the quadratic sum of all coil currents are both minimal when the forcer is desired to generate the identical driving forces. The proposed approach can be used to design the dimensions of a single coil and also to configure the high power density forcers or coil arrays for magnetically levitated planar motors.