Jingsong Li, Lixiang Wang, Qingxin Yang, Shanming Wang, Yongjian Li, Changgeng Zhang and Baojun Qu
Due to existence of skin effect under rotational excitation, especially to high-frequency motors and power transformers run at the frequency of hundreds or even thousands of…
Abstract
Purpose
Due to existence of skin effect under rotational excitation, especially to high-frequency motors and power transformers run at the frequency of hundreds or even thousands of hertz, core losses will increase significantly, which may cause local overheating damage, and the efficiency and longevity will be decreased. The purpose of this paper is to accurately calculate the rotational anomalous loss in electrical steel sheets.
Design/methodology/approach
The influence of skin effect to rotational anomalous loss coefficient is described in detail. Based on the rotational core losses calculation approach, the transformed coefficient and parameters of rotational anomalous loss are determined in accordance with experimental data obtained by using 3D magnetic properties testing system. Then, a variable loss coefficient calculation model of rotational anomalous loss is built. Meanwhile, a separation of the total 2D elliptical rotation experimental core losses is worked out.
Findings
The two methods are analysed and compared qualitatively. It should be noted that the novel calculation model can be more effectively presented anomalous loss features. Moreover, quantitative comparisons between 2D elliptical rotation and alternating core losses have achieved beneficial conclusions.
Originality/value
Transformed rotational anomalous loss coefficient and parameters of electrical steel sheets considering skin effect are determined. Based on that, a novel calculation model evaluating 2D elliptical rotation anomalous loss is presented and verified based on the experimental measurement and the separation of the total 2D elliptical rotation core losses. The 2D elliptical rotation core losses separation method and quantitative comparison with alternating excitation are helpful to engineering application.
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Shanming Wang, Yonghong Xia, Shaogang Huang, Arui Qiu and Xiangheng Wang
In order to keep the advantages of PM generators and eliminate its disadvantage – difficulty in regulating the magnetic field, hybrid excitation is an effective way. The purpose…
Abstract
Purpose
In order to keep the advantages of PM generators and eliminate its disadvantage – difficulty in regulating the magnetic field, hybrid excitation is an effective way. The purpose of this paper is to propose a novel way to achieve hybrid excitation by use of tooth harmonic field.
Design/methodology/approach
Unlike weakening the tooth harmonics field and EMF in traditional machines, in this paper the tooth harmonics field is proposed to form a novel hybrid excitation permanent magnet synchronous generator (HEPMSG).
Findings
The generation mechanism of tooth harmonic electromotive force (EMF) of rotor winding is introduced, and its influencing factors are discussed in detail. The matching design of tooth harmonic winding and field winding for maximum output field current of tooth harmonic excitation system is analyzed.
Practical implications
This machine can achieve not only effective adjustment of the air-gap magnetic field, but also elimination of the brushes and slip rings.
Originality/value
Unlike weakening the tooth harmonics field and EMF in traditional machines, in this paper the tooth harmonics filed is proposed to form a novel hybrid excitation PM synchronous generator. This machine can achieve not only effective adjustment of the air-gap magnetic field, but also elimination of the brushes and slip rings.
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Mohamed Arbi Khlifi and Habib Rehaoulia
When magnetic saturation in ac machines is evolved, the theory of main flux saturation in d-q axes remains the best. Because of its simplicity, it is the most used in either…
Abstract
Purpose
When magnetic saturation in ac machines is evolved, the theory of main flux saturation in d-q axes remains the best. Because of its simplicity, it is the most used in either motoring or generating mode for synchronous or asynchronous machines. Although, it is considered as a global way of introducing the iron saturation, compared to other methods, today, its fidelity has no contest in predicting complex ac machine operations. For this purpose, the aims of this paper consists of modeling these machines whatever the state-space variables values are taking into account the magnetic saturation. Two unified procedures are proposed. The first one deals with a common approach to establishing a complete and detailed model synthesis in d-q axes. The second also presents a unified approach to introducing magnetic saturation of the iron core in the characteristic equations. The analysis takes the salient pole synchronous machine as a general case of study. Then the approaches are extended to undamped and smooth air gap synchronous machines as well as induction machines. The paper aims to discuss these issues.
Design/methodology/approach
The present paper, which is a first part of a work under study dealing with a unified method to derive multiple models of saturated ac machines, is intended to the description of an alternative method and its application for induction and synchronous machines. It mainly consists of the following parts: first, after writing the stator and rotor space vector d-q equations, the number of possible models is immediately discussed. By considering the currents and fluxes as state-space variables, 14 models are obtained for AC induction machine (IM and SM). They are classified into three families, current (three), flux (three) and mixed models (eight). Second, in order to easily introduce the magnetic saturation in the 14 developed models, a method is presented. It consists of just elaborating the model with the winding currents as state variables, then deriving all the other models from it. Third, to emphasize the influence of the presence of magnetic saturation, in each model, each inductance along the d and q axes is written with a fundamental expression which exists with or without saturation and an additional one due purely to saturation. Hence the additional terms can be studied and quantified in an easy way or simply removed when linear case is assumed. Fourth, adopting such strategy to write the different coefficients of the models had led to the definition of common saturation factors. In turn, the definition of common saturation factors had allowed the definition of different groups of models within each family. Fifth, an alternative to evaluate the static and dynamic saturation coefficients is also proposed. It is shown that by proper fitting of the experimental magnetizing curve, all saturation coefficients can be written only in terms of which is simply the magnitudes ratio of the magnetizing flux and current. Sixth, although the theory of the main flux saturation is now admitted, an investigation was carried out on a self-excited induction generator and the build-up of voltage and current phases of a standalone alternator, to prove the equivalence between the all developed models.
Findings
The number of models based on the state-space variables choice, of a saturated ac machine, is reviewed. A simple method consisting of elaborating just the winding currents model, with magnetic saturation and deriving all the other models from it, is presented. In this study special interest was particularly focussed on either novel models or existing models cited in the literature but cannot be obtained by other approaches. In all cases, if the differential equations of the machine are formulated in terms of a set of variables other than the winding currents, a noticeable reduction in the size of equations may be obtained and consequently less time computing. The approach seems to be able to derive any possible model whatever the state-space variables and the type of the ac machine and hence can be classified as a general approach.
Practical implications
The experiments of synchronous and induction machine transients prove the validity of the method.
Originality/value
By suitable choice of state-space characteristic vectors among the fluxes and the currents, a synthesis of AC machine models in d-q axes is established. To introduce magnetic saturation in each model, an approach-based uniquely on the elaboration of the winding currents model is exposed and applied. In addition, the analysis gives a detailed classification of all found models taking into account the state variables nature as well as the cross-coupling coefficient considered as a saturation factor. The study is completed with a simple alternative to evaluate all saturation factors by just calculating the static magnetizing inductance.
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Chang Li, Philip Chang, Shanming Li and Xinxiang Shi
Cross-border M & A is one of the most important ways of international capital flows, and scholars have paid a lot of attention to this area, but a general explaining model…
Abstract
Purpose
Cross-border M & A is one of the most important ways of international capital flows, and scholars have paid a lot of attention to this area, but a general explaining model has still not been generated. The purpose of this paper, based on Lambrecht (2004) and Bolton et al. (2013), is to build a general explaining model in this area and use the new model to explain some real world issues.
Design/methodology/approach
The model work in this paper is based on Lambrecht’s (2004) real option model, which is the classical modeling method in this area, and take the economic crisis method of Bolton et al. (2013) into consideration; the authors also use the relative market condition to illustrate the motivation and market timing of cross-border M & A in this paper to connected the bidders’ markets and targets’ markets together to build the general explaining model for cross-border M & A.
Findings
By analyzing the new model the authors build in this paper, the authors get three conclusions. Conclusion 1: when the bidders’ technologies are more advanced than the targets’, the bidders prefer market-seeking cross-border M & A, and the relatively higher the bidders’ technologies are, the stronger the preference is; when the bidders’ technologies are less advanced than the targets’, the bidders prefer technology-seeking cross-border M & A, and there exists an optimal relative technology ratio at which the bidders have the strongest motivation to exercise the technology-seeking type cross-border M & A. Conclusion 2: host country’s high economic growth helps attracting market-seeking cross-border M & A, conversely host country’s low economic growth helps attracting technology-seeking cross-border M & A. Conclusion 3: the bidders prefer to exercise the technology-seeking cross-border M & A when the home markets are stable or when economic crises happen in targets markets; and the bidders prefer not to exercise the market-seeking cross-border M & A when economic crises happen in home markets; and the relationship between the motivation for bidders to exercise market-seeking cross-border M & A and the possibility of the happening of economic crisis in home countries presents an inverse N-shape curve.
Originality/value
In this paper the authors first use the relative market condition to illustrate the motivation and market timing in the cross-border M & A research area and build a general model based on current literatures.
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Kunhong Hu, Yan Miao and Ziyan Lu
This paper aims to explore the preparation and tribological performance of MoS2 nanoparticles supported on fly ash (FA) microparticles.
Abstract
Purpose
This paper aims to explore the preparation and tribological performance of MoS2 nanoparticles supported on fly ash (FA) microparticles.
Design/methodology/approach
FA was activated by NaOH, oleic acid and HCl to obtain three modified FA samples. Nano-MoS2 was deposited on them to form MoS2/FA additives for poly-α-olefin (PAO) modification. Tribological tests were conducted on a reciprocating rig through the ball-on-disk friction manner. Using X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, Raman spectrometer and element analyzers, the products and their lubrication mechanisms were characterized.
Findings
At 1.5 Wt.%, nano-MoS2 and MoS2/FA could remarkably improve the tribological properties of PAO. The nano-MoS2 deposited on the HCl-activated FA presented better lubrication performance than nano-MoS2. It could reduce friction and wear by approximately 27% and approximately 66%, respectively. The lubrication of MoS2/FA can be attributed to the formation of MoS2 and carbon containing lubricating film.
Originality/value
FA was applied as a supporter to prepare MoS2/FA lubricants. The reuse of FA, a solid waste, is important for environmental protection. Moreover, MoS2/FA is more economical than nano-MoS2 as a lubricant, because it contains approximately 71% of low-cost FA.