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Article

Jian-Xin Shen, Shun Cai, Jian Yuan, Shuai Cao and Cen-Wei Shi

The purpose of this paper is to evaluate the cogging torque in a surface-mounted permanent magnet (SPM) machine with both uniformly and non-uniformly segmented stator…

Abstract

Purpose

The purpose of this paper is to evaluate the cogging torque in a surface-mounted permanent magnet (SPM) machine with both uniformly and non-uniformly segmented stator cores and to find out the optimal solution of stator core segmenting.

Design/methodology/approach

The cogging torque with segmented stators is synthesized from a single slot model, and analytical prediction is given to analyze the cogging torque with both uniformly and non-uniformly segmented stators. Finite element method (FEM) is used to figure out the electromagnetic field and validate the analytical prediction. Moreover, models with various shapes and positions of connecting tongues between the stator core segments are explored to achieve the optimal design.

Findings

The cogging torque is found to be greatly related to the number of segments and the electrical angle between adjacent additional air gaps caused by the tolerance of stator segments. Different shapes of the connecting tongues are tested and proved to be of great importance to the flux density, both radial and tangential, and therefore affect the cogging torque. Finally, position of the connecting tongues is perceived to have little influence on the performance of machine.

Practical/implications

By utilizing analytical prediction and FEM calculation, the optimal solution is discussed to minimize the cogging torque in the SPM machine from the perspective of the stator core segmentation.

Originality/value

This paper establishes formula of cogging torque with segmented stators and predicts the variation of cogging torque with analytical method. Besides, different combinations of segments are compared and measures to reduce the cogging torque produced by the segmentation are proposed.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 35 no. 2
Type: Research Article
ISSN: 0332-1649

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Article

Lovrenc Gašparin, Andrej Černigoj, Stojan Markič and Rastko Fišer

The purpose of this study is to estimate the sensitivity of cogging torque in permanent magnet (PM) motor designs due to PM assembly tolerance and/or PM imperfections and…

Abstract

Purpose

The purpose of this study is to estimate the sensitivity of cogging torque in permanent magnet (PM) motor designs due to PM assembly tolerance and/or PM imperfections and to evaluate how such faults can be reliably detected in simulated and measured cogging torque signals.

Design/methodology/approach

PM motors exhibit inherent cogging torque, which creates torque ripple and prevents smooth rotation of the rotor, resulting in undesirable vibration and noise. While cogging torque minimization is necessary to improve PM motor performance, several FEM models have been developed to study and present data demonstrating the sensitivity of cogging torque to PM assemblies and/or PM imperfections. Some procedures that would predict and evaluate cogging torque components relative to measured PM positions on assembled PM motors were proposed.

Findings

On the basis of numerous performed simulations using different FEM models and experimental results on rotors from mass‐production, it was found and proved that PM assembly tolerance and/or PM imperfections cause the phenomenon of additional cogging torque harmonic components. Considering the presented theoretical aspects motor designers can predict which additional harmonic components will comprise the cogging torque, as a result of which the appropriate technique for minimizing native and additional harmonic components can be applied.

Research limitations/implications

The presented research of cogging torque sensitivity in different PM motor designs to assembly tolerance and/or PM imperfections should in future also consider stator irregularities and different methods of lamination stacking such as notches, welding, and interlocking.

Practical implications

By utilizing the presented method and considering recommendations, advanced motor designers have a reliable tool for predicting the order and level of additional harmonic components in total cogging torque. Thus, adequate critical manufacturing tolerances can be defined in order to achieve minimal waste in produced PM motors.

Originality/value

The originality of the paper is explained by the theoretical aspects and analytical equations of additional harmonic components in cogging torque of PM motors. Also original are the expressions for amplitude calculation of additional harmonic components influenced by manufacturing tolerances.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 27 no. 4
Type: Research Article
ISSN: 0332-1649

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Article

Lovrenc Gašparin, Andrej Černigoj and Rastko Fišer

The purpose of this paper is to estimate and evaluate how cogging torque in permanent magnet (PM) motor designs is sensitive to the number of applied interlocks in stator…

Abstract

Purpose

The purpose of this paper is to estimate and evaluate how cogging torque in permanent magnet (PM) motor designs is sensitive to the number of applied interlocks in stator back‐iron, which is a standard method for stator lamination stacking.

Design/methodology/approach

The PM motors exhibit inherent cogging torque, which creates torque ripple and prevents smooth rotation of the rotor resulting in undesirable vibration and noise. While cogging torque minimization is necessary to improve PM motor performance, several FEM models have been developed to study and present data demonstrating sensitivity of the cogging torque to the applied interlocks. A procedure that would predict and evaluate cogging torque components relative to chosen number and positions of interlocks was proposed.

Findings

On the basis of theoretical considerations, which were verified by numerous performed simulations using different FEM models, it was found out and proved that interlocks in the stator back‐iron cause the phenomenon of additional cogging torque harmonic components (AHC). Taking into account presented theoretical aspects motor designers can predict, which AHC will comprise the cogging torque. Each motor design has its own optimal value of interlocks, therefore a precise study should be performed during the design process.

Practical implications

By utilizing presented method and considering recommendations, advanced designers of PM motors will have a reliable tool for predicting the order and the level of AHC in total cogging torque due to the stator lamination stacking methods.

Originality/value

The paper presents theoretical aspects and analytical equations of AHC of PM motors. So far, the authors dealing with the cogging torque of the PM motors did not take into account the influence of the stator lamination stacking method on the level of torque oscillations. The new contribution is also the study of the sensitivity of different motor designs to the number and position of interlocks, which enables the minimization of the AHC in order to fulfil stringent market demands for low‐cogging torque level.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 3
Type: Research Article
ISSN: 0332-1649

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Book part

Martín Alessandro and Mariano Lafuente

This chapter analyzes the concept of the Center of Government (CoG) and its relevance for the public administration agenda in Latin America. It identifies five key…

Abstract

This chapter analyzes the concept of the Center of Government (CoG) and its relevance for the public administration agenda in Latin America. It identifies five key functions of the CoG: strategic management, policy coordination, performance monitoring and improvement, political management, and communications and accountability, and it assesses the region's performance for each of them, citing concrete experiences. The CoG is still an emerging topic for scholars and practitioners in Latin America. Despite the fact that CoGs in Latin America formally recognize most if not all of its five key functions, the region shows a relatively weak performance in practice. Nonetheless, recent innovative experiences show an increased interest in governments to strengthen the CoG and suggest paths that may lead to improved performance.

The CoG may be a relatively new topic in public administration research, but it is not a new phenomenon. It refers to functions that have been performed, and to structures that have existed, for several decades in many countries, including Latin American ones. However, a number of factors have led to an increased relevance of CoG institutions in recent years. The first section of this chapter will attempt to define the concept of “Center of Government”; to enumerate the CoG's main political and technical functions; to describe the typical structures that perform these functions; and to indicate why these institutions play a critical role in current times. Then, Section 2 will discuss how CoG institutions in Latin American countries have been performing their core functions, identifying regional trends and country-level configurations. The political economy of CoG strengthening will also be covered. Section 3 concludes.

Details

The Emerald Handbook of Public Administration in Latin America
Type: Book
ISBN: 978-1-83982-677-1

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Article

Lidija Petkovska, Paul Lefley and Goga Vladimir Cvetkovski

This paper presents the design techniques applied to a novel fractional-slot 6/4 pole permanent magnet brushless direct current (PMBLDC) motor, for cogging torque…

Abstract

Purpose

This paper presents the design techniques applied to a novel fractional-slot 6/4 pole permanent magnet brushless direct current (PMBLDC) motor, for cogging torque reduction. The notable feature of this motor is the simplicity of the design and low production cost. The purpose of this paper is to reduce the peak cogging torque of the motor. The focus is put on the stator topology tuning, and a new design for the stator poles is proposed. By determining the optimum stator pole arc length and the best pole shoe thickness, the cogging torque is significantly reduced. This new optimised motor design has been analysed in detail. The validation of the results is documented with respective figures and charts.

Design/methodology/approach

At the beginning, the design data for the 6/4 pole PMBLDC motor with concentrated three phase windings and asymmetric stator pole arcs is presented. In the study, this motor is taken as a reference model (A0, T0). A full performance finite element analysis of the reference motor has been carried out, and the weak points in the motor design have been identified. By simple design techniques, tuning the stator pole geometry, a two-stage design optimisation for cogging torque minimisation has been performed and the solution array has been derived. The optimised model is selected and proposed (Aopt, Topt). The comparative analysis of the reference and optimised motors show the advantages of the proposed novel design and prove the methodology.

Findings

The results of the work demonstrate how simple design techniques can minimise the peak of the cogging torque profile, while maintaining the specified electromagnetic torque value. The sensitivity of the cogging torque profile because of changes of the stator pole design inside the prescribed constraints is apparent. The stator poles of the reference motor have an arc length of 85° and pole shoe thickness of 6 mm. The newly shaped stator poles have an arc length of 78.5° and pole shoe thickness 4.8 mm. The peak-cogging torque has been reduced from 0.158 Nm to a respectable value of 0.066 Nm. However, to reduce electromagnetic torque ripple and pulsations, further investigations are required.

Originality/value

The paper presents an approach to cogging torque reduction for a 6/4 PMBLDC motor. A two-step original design procedure is introduced and an optimised stator pole geometry is defined. The minimised cogging torque has been demonstrated with improved usage of the active materials. This work could serve as a good basis for further optimisation of the motor design.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 39 no. 5
Type: Research Article
ISSN: 0332-1649

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Article

Shinichi Yamaguchi, Akihiro Daikoku and Norio Takahashi

This paper describes the cogging torque of the permanent magnet synchronous (PM) motors due to the magnetic anisotropy of motor core. The cogging torque due to the…

Abstract

This paper describes the cogging torque of the permanent magnet synchronous (PM) motors due to the magnetic anisotropy of motor core. The cogging torque due to the magnetic anisotropy is calculated by the finite element method using two kinds of modeling methods: one is the 2D magnetization property method, and the other is the conventional method. As a result, the PM motors with parallel laminated core show different cogging torque waveform from the PM motors with the rotational laminated core due to the influence of the magnetic anisotropy. The amplitudes of the cogging torque are different depending on the modeling methods in the region of high flux density.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 23 no. 3
Type: Research Article
ISSN: 0332-1649

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Article

Hongbin Zhao, Yu Cao, Chang Liu and Xiang Qi

The purpose of this paper is to investigate the performance of coke oven gas (COG)-combined cooling, heating and power (CCHP) system and to mainly focus on studying the…

Abstract

Purpose

The purpose of this paper is to investigate the performance of coke oven gas (COG)-combined cooling, heating and power (CCHP) system and to mainly focus on studying the influence of the environmental conditions, operating conditions and gas conditions on the performance of the system and on quantifying the distribution of useful energy loss and the saving potential of the integrated system changing with different parameters.

Design/methodology/approach

The working process of COG-CCHP was simulated through the establishment of system flow and thermal analysis mathematical model. Using exergy analysis method, the COG-CCHP system’s energy consumption status and the performance changing rules were analyzed.

Findings

The results showed that the combustion chamber has the largest exergy loss among the thermal equipments. Reducing the environmental temperature and pressure can improve the entire system’s reasonable degree of energy. Higher temperature and pressure improved the system’s perfection degree of energy use. Relatively high level of hydrogen and low content of water in COG and an optimal range of CH4 volume fraction between 35 per cent and 46 per cent are required to ensure high exergy efficiency of this integration system.

Originality/value

This paper proposed a CCHP system with the utilization of coke oven gas (COG) and quantified the distribution of useful energy loss and the saving potential of the integrated system under different environmental, operating and gas conditions. The weak links of energy consumption within the system were analyzed, and the characteristics of COG in this way of using were illustrated. This study can provide certain guiding basis for further research and development of the CCHP system performance.

Details

World Journal of Engineering, vol. 15 no. 6
Type: Research Article
ISSN: 1708-5284

Keywords

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Article

Lidija Petkovska, Goga Cvetkovski and Paul Lefley

The purpose of this paper is to investigate the impact of the stator core design for a surface permanent magnet motor (SPMM) on the cogging torque profile. The objective…

Abstract

Purpose

The purpose of this paper is to investigate the impact of the stator core design for a surface permanent magnet motor (SPMM) on the cogging torque profile. The objective is to show how the cogging torque of this type of motor can be significantly reduced by implementing an original compound technique by skewing stator slots and inserting wedges in the slot openings.

Design/methodology/approach

At the beginning generic model of a SPMM is studied. By using FEA, for this idealised assembly, characteristics of cogging and electromagnetic torque are simulated and determined for one period of their change. Afterwards, actual stator design of the original SPMM is described. It is thoroughly investigated and the torque characteristics are compared with the generic ones. While the static torque is slightly decreased, the peak cogging torque is almost doubled and the curve exhibits an uneven profile. The first method for cogging torque reduction is skewing the stator stack. The second technique is to insert wedges of SMC in the slot openings. By using 2D and 2 1/2D numerical experiment cogging curves are calculated and compared. The best results are achieved by combining the two techniques. The comparative analyses of the motor models show the advantages of the proposed novel stator topology.

Findings

It is presented how the peak cogging torque can be substantially decreased due to changes in the stator topology. The constraint is to keep the same stator lamination. By skewing stator stack for one slot pitch 10° the peak cogging torque is threefold reduced. The SMC wedges in slot opening decrease the peak cogging almost four times. The novel stator topology, a combination of the former ones, leads to peak cogging of respectable 0.182 Nm, which is reduced for 7.45 times.

Originality/value

The paper presents an original compound technique for cogging torque reduction, by combining the stator stack skewing and inserting SMC wedges in the slot openings.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 34 no. 2
Type: Research Article
ISSN: 0332-1649

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Article

Cristina Fróes de Borja Reis, André Barroso de Souza, Eliane Cristina Araujo and Knut Blind

This paper aims to investigate if the world top manufacturing corporations' cost structures are moving from tangible to intangible activities and their impact on profitability.

Abstract

Purpose

This paper aims to investigate if the world top manufacturing corporations' cost structures are moving from tangible to intangible activities and their impact on profitability.

Design/methodology/approach

The theoretical approach is interdisciplinary, combining global value chains, international manufacturing networks, cost management literatures. The empirical approach has a sample out of financial statements' data from 220 multinational corporations between 2006 and 2017, grouping them by technological intensity. It is created the “COGS-share” indicator – the ratio between the costs of goods sold and overall costs and expenses – as a proxy for the firms' expenses of tangible and intangible value chain activities. It is tested as an explanatory variable for the companies' profits through dynamic panel data econometric models.

Findings

The results show that the cost structure still is very concentrated in tangibles. Though costs of both tangible and intangible activities negatively impact profits, they affect value generation differently: the higher the share of intangible in comparison to tangible activities in overall cost and expenses, the greater the profits in most manufacturing groups, regardless of their technological intensity.

Research limitations/implications

The empirical analysis simplifies the composition of value chains per activity because financial statements data are aggregates, preventing detailed analysis by markets, business units or products. Stocks' levels are assumed to be at the desired level during the time series. The dataset does not allow value curves to be drawn because direct wages' data and more precise information on cost (especially deferred assets and wages) are missing.

Practical implications

The presented approach, particularly the COGS-share indicator, contribute to assess value generation from activities for improving corporate strategies and public policies on operations and cost management of global value chains.

Social implications

Supporting upgrading decisions that impact value production, allocation and distribution between workers, firms and countries.

Originality/value

Interdisciplinary theoretical and empirical assessment of the manufacturing companies' cost structures and profits based on financial statements data for the better understanding of value generation from tangible and intangible activities.

Details

Journal of Manufacturing Technology Management, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1741-038X

Keywords

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Article

Noboru Niguchi and Katsuhiro Hirata

The purpose of this paper is to propose a magnetic‐geared motor with permanent magnets only on the high‐speed rotor as a solution to the problems of magnetic gears…

Abstract

Purpose

The purpose of this paper is to propose a magnetic‐geared motor with permanent magnets only on the high‐speed rotor as a solution to the problems of magnetic gears. Magnetic gears have some advantages such as no mechanical loss and maintenance‐free operation that are not observed in conventional mechanical gears. Furthermore, they have inherent overload protection. A novel structure which the magnetic gear is integrated with the brushless motor (magnetic‐geared motor) was proposed by Atallah et al. This magnetic‐geared motor is based on the magnetic gear which consists of a high‐ and low‐speed rotor, and a stator. Although this magnetic‐geared motor has a high‐torque density, problems with manufacturing and cost exist because multi‐pole permanent magnets are mounted on the high‐speed rotor and stator.

Design/methodology/approach

A magnetic‐geared motor with permanent magnets only on the high‐speed rotor was proposed and its operational principle was described. The cogging torque characteristics were mathematically formulated and the authors ascertained that the cogging torque contains components of multiples of 60th order. In order to verify the order of the cogging torque, the 3‐D finite element method analysis was conducted and measurements on a prototype were carried out.

Findings

The 60th component and its multiples were observed in the computed and measured cogging torque waveform. However, the cogging torque characteristics, especially the order of the cogging torque on the low‐speed rotor, have not been clarified.

Originality/value

In the near future, cogging torque reduction methods will be proposed, and verified by conducting 3‐D FEM analyses and carrying out measurements on a prototype. Furthermore, the torque characteristics when an electrical current is applied to the coils and the eddy‐current loss characteristics will be verified.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 31 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

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