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Special Issue "Electric Machines and Drives for Renewable Energy Harvesting 2017"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 December 2017)

Special Issue Editor

Guest Editor
Prof. Dr. K.T. Chau

Department of Electrical & Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong
Website | E-Mail
Interests: electric and hybrid vehicles; machines and drives; renewable and clean energies; power electronics

Special Issue Information

Dear Colleagues,

Renewable energy (RE) has been globally identified to be the key to combating air pollution and global warming. Over the years, there have been significant advancements in RE harvesting, especially in the areas of electric machines and drives.

This Special Issue, entitled “Electric Machines and Drives for Renewable Energy Harvesting”, invites articles that address state-of-the-art technologies and new developments of electric machines and drives for RE harvesting, including, but not limited to, power generation and energy storage. Articles that deal with the latest hot topics in RE machines and drives are particularly encouraged, such as permanent-magnet (PM) brushless machines, stator-PM machines, magnetless machines, magnetic-geared machines, Vernier machines, transverse-flux machines and high-temperature superconducting (HTS) machines, as well as their drive systems for direct torque control, efficiency optimization, and maximum power point tracking. In addition, articles that discuss direct-drive machines for micro-hydro, wind and wave power generation, as well as special machines for flywheel energy storage would be of particular interest. The discussion on the relationship between electric machines for different RE harvesting systems, such as hydro versus tidal or solar-thermal versus geothermal is most welcome.

Prof. Dr. K.T. Chau
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • renewable energy harvesting

  • PM brushless machine

  • magnetless machine

  • special machine

  • direct-drive machine

  • micro-hydro generator

  • wind generator

  • wave energy converter

  • power generation control

  • flywheel energy storage

Published Papers (7 papers)

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Research

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Open AccessArticle Electromagnetic Design and Losses Analysis of a High-Speed Permanent Magnet Synchronous Motor with Toroidal Windings for Pulsed Alternator
Energies 2018, 11(3), 562; https://doi.org/10.3390/en11030562
Received: 31 December 2017 / Revised: 28 February 2018 / Accepted: 2 March 2018 / Published: 6 March 2018
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Abstract
The configuration of conventional high-speed Permanent Magnet Synchronous Motors (PMSMs) is usually long and thin, with overlong axial end winding lengths, which is not suitable for those applications that place severe restrictions on the axial length, such as pulsed alternators. This paper first
[...] Read more.
The configuration of conventional high-speed Permanent Magnet Synchronous Motors (PMSMs) is usually long and thin, with overlong axial end winding lengths, which is not suitable for those applications that place severe restrictions on the axial length, such as pulsed alternators. This paper first studied the key design aspects of a flat-structure high-speed PMSM. The toroidal-windings, low-conductivity material of the retaining sleeve, large airgap and segmentation of magnets were studied to reduce the axial length of the motor. The division of the stator and the employment of a non-magnetic outer stator were used to improve overall performance. Then the losses of the prototype were calculated and the factors having an influence on the losses were also investigated, after which, their effects on the total loss were evaluated. The total loss could be effectively reduced by the decrease of strand number of conductors and the division of stator, while only being slightly reduced by epoxy resin pole fillers. Metal-stack pole fillers have the same effect on the reduction of rotor loss as epoxy resin, while maintaining the good thermal-conductivity of metal. In addition, the influence of the carrier frequency of the inverter on the losses was analyzed, and it was found that high carrier frequency was helpful to reduce rotor losses. Finally, a small-scale prototype was manufactured and the experimental results were provided. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)
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Open AccessArticle Optimal Pole Number and Winding Designs for Low Speed–High Torque Synchronous Reluctance Machines
Energies 2018, 11(1), 128; https://doi.org/10.3390/en11010128
Received: 16 November 2017 / Revised: 28 December 2017 / Accepted: 31 December 2017 / Published: 5 January 2018
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Abstract
This paper studies the feasibility of using synchronous reluctance machines (SynRM) for low speed–high torque applications. The challenge lies in obtaining low torque ripple values, high power factor, and, especially, high torque density values, comparable to those of permanent magnet synchronous machines (PMSMs),
[...] Read more.
This paper studies the feasibility of using synchronous reluctance machines (SynRM) for low speed–high torque applications. The challenge lies in obtaining low torque ripple values, high power factor, and, especially, high torque density values, comparable to those of permanent magnet synchronous machines (PMSMs), but without resorting to use permanent magnets. A design and calculation procedure based on multistatic finite element analysis is developed and experimentally validated via a 200 Nm, 160 rpm prototype SynRM. After that, machine designs with different rotor pole and stator slot number combinations are studied, together with different winding types: integral-slot distributed-windings (ISDW), fractional-slot distributed-windings (FSDW) and fractional-slot concentrated-windings (FSCW). Some design criteria for low-speed SynRM are drawn from the results of the study. Finally, a performance comparison between a PMSM and a SynRM is performed for the same application and the conclusions of the study are summarized. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)
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Open AccessArticle Study of an Altered Magnetic Circuit of a Permanent Magnet Linear Generator for Wave Power
Energies 2018, 11(1), 84; https://doi.org/10.3390/en11010084
Received: 15 November 2017 / Revised: 23 December 2017 / Accepted: 26 December 2017 / Published: 31 December 2017
Cited by 1 | PDF Full-text (3865 KB) | HTML Full-text | XML Full-text
Abstract
The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd2Fe
[...] Read more.
The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd2Fe14B-magnets to ferrites. In this paper, the magnetic circuit of the linear generator is further studied. Ferrite magnets of two different types (Y30 and Y40) are studied along with different shapes of pole shoes for the system. The finite element method (FEM) simulations in a program called Ace are performed. The results show that a linear generator including both Y30 and Y40 magnets and shortened T-shaped pole shoes can generate a similar magnetic energy in the airgap as a linear generator only containing Y40 magnets and rectangular pole shoes. This shows that the magnetic circuit can be altered, opening up sizes and strengths of magnets for different retailers, and thereby possibly lowering magnet cost and transportation. This work was previously presented as a conference at the European Wave and Tidal Energy Conference (EWTEC) 2017 in Cork, Ireland; this manuscript has been carefully revised and some discussions, on magnet costs for example, have been added to this paper. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)
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Open AccessArticle Investigation of Permanent Magnet Demagnetization in Synchronous Machines during Multiple Short-Circuit Fault Conditions
Energies 2017, 10(10), 1638; https://doi.org/10.3390/en10101638
Received: 14 September 2017 / Revised: 29 September 2017 / Accepted: 13 October 2017 / Published: 18 October 2017
Cited by 1 | PDF Full-text (1256 KB) | HTML Full-text | XML Full-text
Abstract
Faults in electrical machines can vary in severity and affect different parts of the machine. This study focuses on various kinds of short-circuits on the terminal side of a generic 20 kW surface mounted permanent magnet synchronous generator and how successive faults affect
[...] Read more.
Faults in electrical machines can vary in severity and affect different parts of the machine. This study focuses on various kinds of short-circuits on the terminal side of a generic 20 kW surface mounted permanent magnet synchronous generator and how successive faults affect the performance of the machine. The study was conducted with the commercially available finite element method software COMSOL Multiphysics ® , and two time-dependent models for demagnetization of permanent magnets were compared, one using only internal models and the other using a proprietary external function. The study is simulation based and the two models were compared to a previously experimentally verified stationary model. Results showed that the power output decreased by more than 30% after five successive faults. In addition, the no-load voltage had become unsymmetrical, which was explained by the uneven demagnetization of the permanent magnets. The permanent magnet with the lowest reduction in average remanence was decreased by 0.8%, while the highest average reduction was 23.8% in another permanent magnet. The internal simulation model was about four times faster than the external model, but slightly overestimated the demagnetization. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)
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Open AccessArticle Performance Comparison of Conventional Synchronous Reluctance Machines and PM-Assisted Types with Combined Star–Delta Winding
Energies 2017, 10(10), 1500; https://doi.org/10.3390/en10101500
Received: 23 August 2017 / Revised: 18 September 2017 / Accepted: 20 September 2017 / Published: 27 September 2017
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Abstract
This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star–delta winding. In addition, two rotors
[...] Read more.
This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star–delta winding. In addition, two rotors are considered: a conventional rotor without magnets and a rotor with ferrite magnets. The performance of the four SynRMs is evaluated using a two-dimensional (2D) Finite Element Model (FEM). For the same copper volume and current, the combined star–delta-connected stator with Permanent Magnets (PMs) in the rotor corresponds to an approximately 22% increase in the output torque at rated current and speed compared to the conventional machine. This improvement is mainly thanks to adding ferrite PMs in the rotor as well as to the improved winding factor of the combined star–delta winding. The torque gain increases up to 150% for low current. Moreover, the rated efficiency is 93.60% compared to 92.10% for the conventional machine. On the other hand, the impact on the power factor and losses of SynRM when using the star–delta windings instead of the star windings is merely negligible. The theoretical results are experimentally validated using four identical prototype machines with identical lamination stacks but different rotors and winding layouts. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)
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Open AccessArticle Sensorless Control for the EVT-Based New Dual Power Flow Wind Energy Conversion System
Energies 2017, 10(7), 888; https://doi.org/10.3390/en10070888
Received: 15 May 2017 / Revised: 6 June 2017 / Accepted: 20 June 2017 / Published: 30 June 2017
Cited by 1 | PDF Full-text (5467 KB) | HTML Full-text | XML Full-text | Correction
Abstract
The dual power flow wind energy conversion system (DPF-WECS) is a novel system which is based on the electrical variable transmission (EVT) machine. The proposed sensorless control for the DPF-WECS is based on the model reference adaptive system (MRAS) observer by combining the
[...] Read more.
The dual power flow wind energy conversion system (DPF-WECS) is a novel system which is based on the electrical variable transmission (EVT) machine. The proposed sensorless control for the DPF-WECS is based on the model reference adaptive system (MRAS) observer by combining the sliding mode (SM) theory. The SM-MRAS observer is on account of the calculations without the requirement of the proportional-integral (PI) loop which exists in the classical MRAS observer. Firstly, the sensorless algorithm is applied in the maximum power point tracking (MPPT) control considering the torque loss for the outer rotor of the EVT. Secondly, the sensorless control is adopted for the inner rotor control of the EVT machine. The proposed sensorless control method based on the SM-MRAS for the DPF-WECS is verified by the simulation and experimental results. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)
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Review

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Open AccessReview State of the Art and Trends in the Monitoring, Detection and Diagnosis of Failures in Electric Induction Motors
Energies 2017, 10(7), 1056; https://doi.org/10.3390/en10071056
Received: 17 June 2017 / Revised: 3 July 2017 / Accepted: 3 July 2017 / Published: 21 July 2017
Cited by 6 | PDF Full-text (1461 KB) | HTML Full-text | XML Full-text
Abstract
Despite the complex mathematical models and physical phenomena on which it is based, the simplicity of its construction, its affordability, the versatility of its applications and the relative ease of its control have made the electric induction motor an essential element in a
[...] Read more.
Despite the complex mathematical models and physical phenomena on which it is based, the simplicity of its construction, its affordability, the versatility of its applications and the relative ease of its control have made the electric induction motor an essential element in a considerable number of processes at the industrial and domestic levels, in which it converts electrical energy into mechanical energy. The importance of this type of machine for the continuity of operation, mainly in industry, is such that, in addition to being an important part of the study programs of careers related to this branch of electrical engineering, a large number of investigations into monitoring, detecting and quickly diagnosing its incipient faults due to a variety of factors have been conducted. This bibliographic research aims to analyze the conceptual aspects of the first discoveries that served as the basis for the invention of the induction motor, ranging from the development of the Fourier series, the Fourier transform mathematical formula in its different forms and the measurement, treatment and analysis of signals to techniques based on artificial intelligence and soft computing. This research also includes topics of interest such as fault types and their classification according to the engine, software and hardware parts used and modern approaches or maintenance strategies. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)
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