Pole Pair Combinations Research Articles

Analysis of Stator-Slot and Pole-Pair Combinations in a Two-Degree-of-Freedom Split-Stator Induction Machine Based on Motion Coupling Model

2-degree-of-freedom split-stator induction machine (2DoFSSIM) exhibits high integration and material utilization for 2DoF motions, but the attractive topologies are difficult to determine due to exciting two different magnetic fields and two-directional motions. This paper investigates the helical motion coupling effect of rotary and linear motion parts, then the influence of stator-slot and pole-pair combinations on three motion characteristics is analyzed. Based on the proposed motion coupling model, the resistant torque and force production mechanism is revealed. It can be concluded that the output torque, force, and helical motion coupling effect are dominantly determined by the magnetic loading and pole-pair number of two motion parts. However, there is a tradeoff in choosing the pole-pair number to get the 2DoFSSIMs with high output performances and low helical motion coupling effect. Then, the stator-slot and pole-pair combinations selection method is proposed, and the topologies with attractive performances are chosen at different geometric diameters. Finally, the finite element analysis and experimental results are given to validate the proposed technique. <list list-type="simple" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <list-item> 2-degree-of-freedom split-stator induction machine, motion coupling model, helical motion. </list-item> </list>

Design of a Wound Rotor Brushless Doubly-Fed Machine With 1/5 Pole-Pair Combination

The brushless doubly-fed machine (BDFM) can be used in the variable speed constant frequency field. For BDFM, the choice of the pole-pair combination and the design of the rotor are significant. The output factor of the BDFM with 1/5 pole-pair combination is higher than that of the 2/4 pole-pair counterpart. However, the rotor of the BDFM with 1/5 pole-pair combination is hard to design for its wide pole-pair ratio. This paper presents a 1/5 pole-pair combination BDFM used in hydro power with a three-phase symmetrical wound rotor to solve the design challenge. First, the magnetic field modulation theory of the BDFM and the optimal output power in terms of different pole-pair combinations are introduced. Then, the slot-number phase diagram and the ampere-conductor wave method are applied to design windings of a BDFM with 1/5 pole-pair combination. Finally, the finite element (FE) models of the 1/5 and the 2/4 pole-pair combination BDFMs are established for comparison. A prototype of the 1/5 pole-pair combination is manufactured based on the proposed design scheme. Simulated and experimental results verified the feasibility of the design scheme.

Birkaç kutup çifti kombinasyonunda CMG ve RPMG'nin dişli faktörünün araştırılması

The design on magnetic gear (MG) involves determining the gear ratio specific to its application. The gear ratio can be determined by the pole number of the inner rotor, outer rotor and the pole piece. In this research, the cogging torque of several pole pair combinations in concentric magnetic gear (CMG) and rotating pole piece magnetic gear (RPMG) were investigated. The gear ratio equations were initially derived for both CMG and RPMG. Based on these equations, four sets of pole pair combinations were determined. The cogging factor was calculated in each combination. To determine the cogging factor significance towards the cogging torque, the magnetic gears were simulated in 2D finite element software. The result revealed that the lower pole pair combination generates lower cogging torque than the higher pole pair combination. The simulation result also shows that the rate of increase in cogging factor did not correlate directly to the cogging torque in the simulation. It is concluded that the cogging factor is not a suitable tool to access the cogging torque level in CMG and RPMG.

A Non-Permanent Magnet DC-Biased Vernier Reluctance Linear Machine with Non-Uniform Air Gap Structure for Ripple Reduction

Thrust ripple and density greatly impact the performance of the linear machine and other linear actuators, causing positioning control precision, dynamic performance, and efficiency issues. Generalized pole-pair combinations are difficult to satisfy both the thrust and ripple for double salient reluctance linear machines. In this paper, a DC-Biased vernier reluctance linear machine (DCB-VRLM) is proposed to solve the abovementioned issues. The key to the proposed design is to reduce the ripple and enhance the thrust density with non-uniform teeth by utilizing and optimizing the modulated flux in the air gap. To effectively verify the proposed design, the DCB-VRLMs with different winding pole pairs and secondary poles are compared. The 12-slot/10-pole combination is chosen to adopt a non-uniform air gap structure. Moreover, the energy distribution of AC/DC winding is studied and optimized to further enhance the performance of the proposed DCB-VRLM. The results indicate that the DCB-VRLM with the non-uniform air gap has a lower thrust ripple, better overload capability, and higher thrust density, which confirms its superiority in long-stroke linear rail transit and vertical elevator applications.

Optimization of Rotor Salient Pole Reluctance for Typical Field Modulated Electric Machines

The objective of this article is to investigate the possibility to improve the torque characters of electric machines featuring rotor salient pole reluctance from the perspective of the general airgap field modulation theory. The torque production mechanisms of two typical field modulated machines, namely, the magnetically geared machine (MGM) and the flux-reversal permanent magnet (FRPM) machine, are discussed based on the Maxwell stress tensor (MST) method, where the mono-harmonic mechanism of rotor PM machine like the MGM is revealed. Several common theoretical salient rotor pole configurations, like the upright/inverted trapezoidal configuration, are introduced in detail, based on which general and modified rotor configuration advices for the two electric machines are proposed to provide initial design and future optimization guidance. It is proven that there is a possible opportunity to make the torque characters better via reasonable selection of rotor configuration and topological parameters. Electromagnetic performances validation based on 2-D finite-element analysis, such as improved airgap magnetic field harmonic distributions, load flux linkage/electromotive force (EMF), and general torque performances of two field modulated machines is provided to demonstrate the effectiveness of theoretical analysis. It is also verified by experimental measurements on the FRPM machines with different pole pair combination.

Influence of Pole-Pair Combinations on the Characteristics of the Brushless Doubly Fed Induction Generator

The brushless doubly fed induction generator (BDFIG) is an alternative to the doubly fed induction generator (DFIG), widely used in wind turbines which avoids the need for brush gear and slip rings. The choice of pole numbers for the two stator windings present in the BDFIG sets the operating speed, typically in the medium speed range to eliminate a gearbox stage. This paper focuses on how both the total number of poles and the assignment of poles between the windings affect machine performance. Analytical expressions have been developed for parameters including pull-out torque, magnetizing current and back-iron depth. The results show that the pole count can be increased without unduly compromising pull-out torque and that in cases where more than one combination of pole number is acceptable only the back iron depth is significantly affected. In addition an output factor has been introduced to enable a direct comparison to be made with conventional DFIGs. The torque density of a brushless DFIG is compromised to a degree relative to a comparable DFIG as a consequence of the presence of two magnetic fields and finite element analysis is needed to achieve an optimized design. Finally, predictions of the performance of multi-MW machines are made based on data from an existing 250 kW machine which show that suitable efficiencies can be obtained and excessive control winding excitation can be avoided.

A Dual-Modulator Magnetic-Geared Machine for Tidal-Power Generation

In this article, a new dual-modulator magnetic-geared machine (DM-MGM) is proposed for tidal-power generation with the virtue of high-torque output at low speed. First, the requirement of the DM-MGM for tidal-power generation is derived. Then, the flux-modulation principle and flux-enhancing effect of the extra modulator of the proposed DM-MGM are elaborated. After that, a finite-element analysis and multi-objective genetic algorithm (FEA-GA) combined method is used to solve a multi-objective optimization problem for the DM-MGM design. The electromagnetic performances of the optimized DM-MGM with different pole-pair combinations are quantitatively compared by FEA. The results show the effectiveness of the proposed machine, which is suitable to be applied in the tidal-power-generation scenario.

Design and Multi-Mode Operation of Double-Stator Toroidal-Winding PM Vernier Machine for Wind-Photovoltaic Hybrid Generation System

This paper proposes the design and multi-mode operation of a new double-stator toroidal-winding permanent-magnet vernier (DSTW-PMV) machine, which is for the wind-photovoltaic (W-PV) hybrid generation system. In the W-PV system, the wind and PV power are complementary with each other for power variation reduction. Through the multi-mode operation, the output voltage of the machine can be stabilized with high continuity under different rotational speeds to solve the inherently indeterminate wind speed problem and further improve the power smoothness of the whole W-PV system. First, the machine optimization is carried out to obtain the optimal pole-pair combination and geometrical topology for the proposed machine. Second, based on the optimal topology, the multi-mode operation principle of the output voltage adjustment is illustrated. By utilizing the diversities of the toroidal winding configurations and terminal connection strategies, the proposed machine accommodates 54 operating modes with different output voltages under rated speed. Accordingly, under the rated output voltage, the machine speed can be extended to three rated speed with high continuity. Furthermore, some modes generate the rated output voltage with identical speed, which contributes to the high redundancy and high operating efficiency. Hence, with the multi-mode operation and the auxiliary of the PV power, the whole power generation system accommodates the higher flexibility, stability, reliability, and efficiency.

Design and Analysis of a Magnetic-Field Modulated Brushless Double-Rotor Machine—Part II: Winding Configuration

The analysis of Part I shows that the integer-slot winding of the magnetic-field modulated brushless double-rotor machine (MFM-BDRM) can obtain very sinusoidal no-load and load back electromotive force (EMF) and quite small torque ripple under an optimal pole-pair combination of stator, permanent magnet (PM) rotor, and magnetic blocks. In practical applications, however, the integer-slot winding is usually replaced by the fractional-slot concentrated winding (FSCW), which can reduce end windings and easily realize automatic winding. This paper focuses on the influence of the FSCW on the electromagnetic performance of the MFM-BDRM and the application feasibility of the FSCW in the MFM-BDRM. First, the formation mechanism of the harmonic back EMF of FSCW is investigated. Then the pole-pair combination law of stator, PM rotor, and magnetic block for the FSCW of the MFM-BDRM is further investigated. Second, the specific FSCW of the MFM-BDRM with $Q = 2{p_s} \pm 1$ and $Q = 2{p_s} \pm 2$ and the integer-slot MFM-BDRM are comparatively investigated. It shows that the integer-slot winding of the MFM-BDRM is superior to the FSCW of the MFM-BDRM in no-load and load back EMF, torque ripple, maximum torque outputting capability, and power factor. Finally, the optimal winding configuration of the MFM-BDRM is determined. A prototype of the MFM-BDRM with the optimal winding configuration and pole-pair combination is designed and manufactured. The theoretical and finite-element analysis is verified by experiments.

Design and Analysis of a Magnetic-Field Modulated Brushless Double-Rotor Machine—Part I: Pole Pair Combination of Stator, PM Rotor and Magnetic Blocks

The magnetic-field modulated brushless double-rotor machine (MFM-BDRM) is a promising candidate for the power splitting device in hybrid electric vehicles. Due to its special operating principle, the magnetic field modulation principle, various harmonic magnetic fields are produced in the MFM-BDRM. Therefore, it is crucial for the design of MFM-BDRM to reduce the influence of nonworking harmonic magnetic fields on the electromagnetic performance of MFM-BDRM, like back electromotive force (EMF) and torque ripple. In this paper, first, the distribution law of permanent-magnet (PM) and armature modulated magnetic fields is analyzed. Second, since the analysis and calculation method of harmonic back EMF in a traditional PM machine is not suitable for the MFM-BDRM, the formation mechanism of harmonic back EMF in the MFM-BDRM is further investigated. Third, combined with the characteristic of modulated magnetic field and formed harmonic back EMF in the MFM-BDRM, the optimal pole pair combination of stator, PM rotor, and magnetic blocks is investigated. Finally, analysis and calculation of a specific MFM-BDRM by analytical and finite- element method shows the MFM-BDRM with the optimal combination can obtain very sinusoidal no-load and load back EMF and quite low torque ripple.

Stator/Rotor Slot and Winding Pole Pair Combinations of DC-Biased Current Vernier Reluctance Machines

The recent novel dc-biased sinusoidal current reluctance machines (dc-biased VRMs) adopt a doubly salient structure and concentrated windings, which is similar to that of switched reluctance machines (SRMs). The special point is that the phase current is in the form of an ac component superimposed with a dc component. Some literary works show that these machines would have better performance than the existing SRMs and variable flux reluctance machines. In this paper, the slot/pole combinations and winding configurations of the dc-biased VRMs are deeply investigated. First, relationships among slots/poles are given based on the operation principles. Then, several feasible slot combinations are obtained, and the electromagnetic performances including magnetizing inductance, virtual back electromotive force, torque quality, and losses are compared by the finite element analysis. Finally, the correctness of the proposed analysis is validated by the experiment on two 12/10 prototypes.

Modeling and Optimization of Brushless Doubly-Fed Induction Machines Using Computationally Efficient Finite-Element Analysis

The air-gap magnetic fields of brushless doubly fed induction machines (DFIMs) are complicated because of the cross-coupling between two stator fields via a special nested-loop rotor. Compared with classical analytical models, transient finite-element (FE) modeling is easier to evaluate the machine performance taking saturation into account. However, it is not efficient to evaluate lots of candidates in a large design space using transient FE models considering the time cost. In the transient simulation, the induced rotor currents are calculated by solving several time differential equations using the backward differentiation formula. This paper presents a computationally efficient FE analysis for brushless DFIMs. The induced rotor currents can be calculated using a single magnetostatic FE simulation. The average torque, losses, and efficiency can also be predicted using one magnetostatic solution. One candidate design can be evaluated within 1 or 2 min on a personal workstation. The efficient analysis is validated by the transient FE results. The presented model is applied to the optimization of a prototype. The influence of two construction variables, namely, pole-pair combinations and the number of loops per nest, is studied. One pole-pair combination is selected for manufacturing a prototype.

Design and Analysis of a Brushless Doubly-Fed Induction Machine With Dual-Stator Structure

This paper explores the feasibility of an intuitive solution for torque density improvement of conventional brushless doubly-fed induction machine by introducing dual-stator structure. A general purpose torque density equation for dual-stator topologies is developed to initialize the key dimensions and, more importantly, evaluate the torque capability of specific designs. The topological requirements for enhancing torque capability are derived. The relationship between torque capability and key design parameters, such as pole pair combination, split ratio, and turn ratio between outer and inner rotor windings, is revealed. A design example with detailed design procedure is presented to provide the designer a practical way to make initial calculation of machine dimensions and parameters. Moreover, finite element analysis is carried out to deduce the characteristics of the machine. Experimental results of a 7.5-kW prototype machine are given to verify the design and analysis.

General pole number model of the brushless doubly-fed machine

The brushless doubly-fed machine is receiving attention as a contender for several niche applications. In some cases, the speed ranges of these applications appear to be more readily met by judicious selection of the pole-pair numbers of the stator phase windings. In order to compare different proposed pole-pair configurations and to help in the development of specific designs, a general analytical model, in both dynamic and steady state forms, is presented. This model supersedes previous analyses which are restricted to the 3/1 pole-pair combination of early laboratory machines. The new model is also completely valid for both positive and negative control voltage sequences. The increased modeling flexibility enables sound estimations of the drive power converter ratings, the reduction of which is the key to the economic advantage of these machines. An example of the correlation of the performance predictions and test results encourages use of this new model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>