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

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

Deadline for manuscript submissions: closed (31 January 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 combat air pollution and global warming. Over the years, there have been significant advancements in RE harvesting, especially in the area 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 which 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 which 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 (11 papers)

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Research

Open AccessArticle Rapid Reserve Generation from a Francis Turbine for System Frequency Control
Energies 2017, 10(4), 496; https://doi.org/10.3390/en10040496
Received: 24 February 2017 / Revised: 27 March 2017 / Accepted: 31 March 2017 / Published: 7 April 2017
Cited by 1 | PDF Full-text (8853 KB) | HTML Full-text | XML Full-text
Abstract
The increase in contributions from non base load renewables, such as wind and solar, can have adverse effects on the stability of an electrical grid. In this study, the possibility of rapidly loading a Francis turbine from a tail water depression (TWD) mode
[...] Read more.
The increase in contributions from non base load renewables, such as wind and solar, can have adverse effects on the stability of an electrical grid. In this study, the possibility of rapidly loading a Francis turbine from a tail water depression (TWD) mode for providing additional system frequency control is investigated. Based on the analysis of full-scale TWD test results and key findings from the transient testing of a micro-hydro scale turbine unit, a detailed description of the TWD transition process is given. The formulation of an improved turbine model for use in one-dimensional hydro-electric plant models is presented with simulation results compared to full-scale data. The analytical model, which calculates output power according to the conservation of angular momentum and identified sources of loss, is used in parallel with full-scale and model scale test observations to elucidate the events and mechanisms occurring during this proposed transition. The output response, in terms of active power, was found to be highly dependent on guide vane opening rate in both full-scale and model tests. For an approximate doubling in opening rate, the duration of the reverse power flow was reduced by 38% and 21%, for full-scale and model units, while the low pressure transient increased by 16% and 8%, respectively. The analytical model was shown to capture the general response characteristic in all cases tested; however, output power response was over predicted due to two identified model assumptions made, while, for the more rapid opening, the penstock pressure was under predicted by approximately 15%. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Reluctance Machine for a Hollow Cylinder Flywheel
Energies 2017, 10(3), 316; https://doi.org/10.3390/en10030316
Received: 28 October 2016 / Revised: 20 February 2017 / Accepted: 28 February 2017 / Published: 7 March 2017
PDF Full-text (7983 KB) | HTML Full-text | XML Full-text
Abstract
A hollow cylinder flywheel rotor with a novel outer rotor switched reluctance machine (SRM) mounted on the interior rim is presented, with measurements, numerical analysis and analytical models. Practical experiences from the construction process are also discussed. The flywheel rotor does not have
[...] Read more.
A hollow cylinder flywheel rotor with a novel outer rotor switched reluctance machine (SRM) mounted on the interior rim is presented, with measurements, numerical analysis and analytical models. Practical experiences from the construction process are also discussed. The flywheel rotor does not have a shaft and spokes and is predicted to store 181 Wh / kg at ultimate tensile strength (UTS) according to simulations. The novel SRM is an axial flux machine, chosen due to its robustness and tolerance for high strain. The computed maximum tip speed of the motor at UTS is 1050 m / s . A small-scale proof-of-concept electric machine prototype has been constructed, and the machine inductance has been estimated from measurements of voltage and current and compared against results from analytical models and finite element analysis (FEA). The prototype measurements were used to simulate operation during maximal speed for a comparison towards other high-speed electric machines, in terms of tip speed and power. The mechanical design of the flywheel was performed with an analytical formulation assuming planar stress in concentric shells of orthotropic (unidirectionally circumferentially wound) carbon composites. The analytical approach was verified with 3D FEA in terms of stress and strain. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Performance Study on a Single-Screw Expander for a Small-Scale Pressure Recovery System
Energies 2017, 10(1), 6; https://doi.org/10.3390/en10010006
Received: 30 September 2016 / Revised: 1 December 2016 / Accepted: 2 December 2016 / Published: 22 December 2016
Cited by 8 | PDF Full-text (4486 KB) | HTML Full-text | XML Full-text
Abstract
A single-screw expander with 195 mm diameter is developed to recover pressure energy in letdown stations. An experiment system is established using compressed air as a working fluid instead of natural gas. Experiments are conducted via measurements for important parameters, such as inlet
[...] Read more.
A single-screw expander with 195 mm diameter is developed to recover pressure energy in letdown stations. An experiment system is established using compressed air as a working fluid instead of natural gas. Experiments are conducted via measurements for important parameters, such as inlet and outlet temperature and pressure, volume flow rate and power output. The influence of inlet pressure and rotational speed on the performance are also analyzed. Results indicate that the single-screw expander achieved good output characteristics, in which 2800 rpm is considered the best working speed. The maximum volumetric efficiency, isentropic efficiency, overall efficiency, and the lowest air-consumption are 51.1 kW, 83.5%, 66.4%, 62.2%, and 44.1 kg/(kW·h), respectively. If a single-screw expander is adopted in a pressure energy recovery system applied in a certain domestic natural gas letdown station, the isentropic efficiency of the single-screw expander and overall efficiency of the system are found to be 66.4% and 62.2%, respectively. Then the system performances are predicted, in which the lowest methane consumption is 27.3 kg/(kW·h). The installed capacity is estimated as 204.7 kW, and the annual power generation is 43.3 MWh. In the next stage, a pressure energy recovery demonstration project that recycles natural gas will be established within China, with the single-screw expander serving as the power machine. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Modeling of a Field-Modulated Permanent-Magnet Machine
Energies 2016, 9(12), 1078; https://doi.org/10.3390/en9121078
Received: 4 August 2016 / Revised: 3 December 2016 / Accepted: 12 December 2016 / Published: 19 December 2016
Cited by 2 | PDF Full-text (6944 KB) | HTML Full-text | XML Full-text
Abstract
In this work, an effective field-modulated permanent-magnet (FMPM) machine was investigated, in which the spoke-magnet outer rotor and open-slot stator were employed. The objective of this paper is to provide the mathematical modeling analysis that was performed for the purpose of control research
[...] Read more.
In this work, an effective field-modulated permanent-magnet (FMPM) machine was investigated, in which the spoke-magnet outer rotor and open-slot stator were employed. The objective of this paper is to provide the mathematical modeling analysis that was performed for the purpose of control research on this type of FMPM machine. The simulation results by means of finite element analysis (FEA) are given to verify the theoretical analysis and the validity of mathematical model. A prototype machine was also fabricated for experimentation. Both the analytical model and the FEA results are validated by experimental tests on the prototype machine. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Fault-Ride through Strategy for Permanent-Magnet Synchronous Generators in Variable-Speed Wind Turbines
Energies 2016, 9(12), 1066; https://doi.org/10.3390/en9121066
Received: 14 August 2016 / Revised: 28 November 2016 / Accepted: 6 December 2016 / Published: 15 December 2016
Cited by 10 | PDF Full-text (2226 KB) | HTML Full-text | XML Full-text
Abstract
Currently, the electric power production by wind energy conversion systems (WECSs) has increased significantly. Consequently, wind turbine (WT) generators are requested to fulfill the grid code (GC) requirements stated by network operators. In case of grid faults/voltage dips, a mismatch between the generated
[...] Read more.
Currently, the electric power production by wind energy conversion systems (WECSs) has increased significantly. Consequently, wind turbine (WT) generators are requested to fulfill the grid code (GC) requirements stated by network operators. In case of grid faults/voltage dips, a mismatch between the generated active power from the wind generator and the active power delivered to the grid is produced. The conventional approach is using a braking chopper (BC) in the DC-link to dissipate this active power. This paper proposes a fault-ride through (FRT) strategy for variable-speed WECSs based on permanent magnet synchronous generators (PMSGs). The proposed strategy exploits the rotor inertia of the WECS (inertia of the WT and PMSG) to store the surplus active power during the grid faults/voltage dips. Thus, no additional hardware components are requested. Furthermore, a direct model predictive control (DMPC) scheme for the PMSG is proposed in order to enhance the dynamic behavior of the WECS. The behavior of the proposed FRT strategy is verified and compared with the conventional BC approach for all the operation conditions by simulation results. Finally, the simulation results confirm the feasibility of the proposed FRT strategy. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Simple Design Approach for Low Torque Ripple and High Output Torque Synchronous Reluctance Motors
Energies 2016, 9(11), 942; https://doi.org/10.3390/en9110942
Received: 11 September 2016 / Revised: 27 October 2016 / Accepted: 7 November 2016 / Published: 11 November 2016
Cited by 2 | PDF Full-text (4786 KB) | HTML Full-text | XML Full-text
Abstract
The rotor design of Synchronous Reluctance Motors (SynRMs) has a large effect on their efficiency, torque density and torque ripple. In order to achieve a good compromise between these three goals, an optimized rotor geometry is necessary. A finite element method (FEM) is
[...] Read more.
The rotor design of Synchronous Reluctance Motors (SynRMs) has a large effect on their efficiency, torque density and torque ripple. In order to achieve a good compromise between these three goals, an optimized rotor geometry is necessary. A finite element method (FEM) is a good tool for the optimization. However, the computation time is an obstacle as there are many geometrical parameters to be optimized. The flux-barrier widths and angles are the two most crucial parameters for the SynRM output torque and torque ripple. This paper proposes an easy-to-use set of parametrized equations to select appropriate values for these two rotor parameters. With these equations, the reader can design a SynRM of distributed windings with a low torque ripple and with a better average torque. The methodology is valid for a wide range of SynRMs. To check the validity of the proposed equations, the sensitivity analysis for the variation of these two parameters on the SynRM torque and torque ripple is carried out. In addition, the analysis in this paper gives insight into the behavior of the machine as a function of these two parameters. Furthermore, the torque and torque ripple of SynRMs having a rotor with three, four and five flux-barriers are compared with three literature approaches. The comparison shows that the proposed equations are effective in choosing the flux-barrier angles and widths for low torque ripple and better average torque. Experimental results have been obtained to confirm the FEM results and to validate the methodology for choosing the rotor parameters. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Minimization of Cogging Force in Fractional-Slot Permanent Magnet Linear Motors with Double-Layer Concentrated Windings
Energies 2016, 9(11), 918; https://doi.org/10.3390/en9110918
Received: 27 July 2016 / Revised: 25 October 2016 / Accepted: 3 November 2016 / Published: 5 November 2016
Cited by 1 | PDF Full-text (2640 KB) | HTML Full-text | XML Full-text
Abstract
Permanent magnet linear motors (PMLMs) with double-layer concentrated windings generally show significant cogging forces due to the introduction of auxiliary teeth for eliminating the end-effect induced phase unbalance, even when the fractional-slot technology is applied. This paper presents a novel approach to reduce
[...] Read more.
Permanent magnet linear motors (PMLMs) with double-layer concentrated windings generally show significant cogging forces due to the introduction of auxiliary teeth for eliminating the end-effect induced phase unbalance, even when the fractional-slot technology is applied. This paper presents a novel approach to reduce the cogging force by adjusting the armature core dimensions in fractional-slot PMLMs with double-layer concentrated windings, together with magnet skewing. It is shown that the proposed technique is capable of reducing the cogging force of the motor in an effective way, with the peak value minimized to less than 0.4% of the rated thrust force in the case study. Such a technique can also be applicable to other linear motors with appropriate changes. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle A Novel Flux Focusing Magnetically Geared Machine with Reduced Eddy Current Loss
Energies 2016, 9(11), 904; https://doi.org/10.3390/en9110904
Received: 18 July 2016 / Revised: 26 October 2016 / Accepted: 27 October 2016 / Published: 2 November 2016
Cited by 1 | PDF Full-text (9751 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a novel flux focusing magnetically geared (MG) machine for wind power generation, considering the permanent magnets (PMs) eddy current loss and the balance between the pull-out torque of MG machine and the back-electromotive force (EMF)of the PM brushless machine. The
[...] Read more.
This paper proposes a novel flux focusing magnetically geared (MG) machine for wind power generation, considering the permanent magnets (PMs) eddy current loss and the balance between the pull-out torque of MG machine and the back-electromotive force (EMF)of the PM brushless machine. The PM eddy current loss in the two rotors of the conventional surface-mounted MG machine is calculated and analyzed by using finite-element method. By adopting serial-spoke structure in the inner rotor, a novel rotor structure for a MG machine is proposed to reduce the PM eddy current loss. Moreover, in order to balance the pull-out torque and the back-EMF, several serial-spoke structures and the main design parameters are investigated. Then, a quantitative comparison between the proposed topology and the conventional surface-mounted MG machine is performed. The analysis results indicate that the PM eddy current loss of the proposed MG machine can be significantly reduced and its pull-out torque and back-EMF can be balanced well. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle A Phase Current Reconstruction Approach for Three-Phase Permanent-Magnet Synchronous Motor Drive
Energies 2016, 9(10), 853; https://doi.org/10.3390/en9100853
Received: 10 July 2016 / Revised: 23 September 2016 / Accepted: 14 October 2016 / Published: 21 October 2016
Cited by 6 | PDF Full-text (20173 KB) | HTML Full-text | XML Full-text
Abstract
Three-phase permanent-magnet synchronous motors (PMSMs) are widely used in renewable energy applications such as wind power generation, tidal energy and electric vehicles owing to their merits such as high efficiency, high precision and high reliability. To reduce the cost and volume of the
[...] Read more.
Three-phase permanent-magnet synchronous motors (PMSMs) are widely used in renewable energy applications such as wind power generation, tidal energy and electric vehicles owing to their merits such as high efficiency, high precision and high reliability. To reduce the cost and volume of the drive system, techniques of reconstructing three-phase current using a single current sensor have been reported for three-phase alternating current (AC) control system using the power converts. In existing studies, the reconstruction precision is largely influenced by reconstructing dead zones on the Space Vector Pulse Width Modulation (SVPWM) plane, which requires other algorithms to compensate either by modifying PWM modulation or by phase-shifting of the PWM signal. In this paper, a novel extended phase current reconstruction approach for PMSM drive is proposed. Six novel installation positions are obtained by analyzing the sampling results of the current paths between each two power switches. By arranging the single current sensor at these positions, the single current sensor is sampled during zero voltage vectors (ZVV) without modifying the PWM signals. This proposed method can reconstruct the three-phase currents without any complex algorithms and is available in the sector boundary region and low modulation region. Finally, this method is validated by experiments. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Analytical Calculation of D- and Q-axis Inductance for Interior Permanent Magnet Motors Based on Winding Function Theory
Energies 2016, 9(8), 580; https://doi.org/10.3390/en9080580
Received: 30 April 2016 / Revised: 3 July 2016 / Accepted: 21 July 2016 / Published: 25 July 2016
Cited by 7 | PDF Full-text (5214 KB) | HTML Full-text | XML Full-text
Abstract
Interior permanent magnet (IPM) motors are widely used in electric vehicles (EVs), benefiting from the excellent advantages of a more rational use of energy. For further improvement of energy utilization, this paper presents an analytical method of d- and q-axis inductance
[...] Read more.
Interior permanent magnet (IPM) motors are widely used in electric vehicles (EVs), benefiting from the excellent advantages of a more rational use of energy. For further improvement of energy utilization, this paper presents an analytical method of d- and q-axis inductance calculation for IPM motors with V-shaped rotor in no-load condition. A lumped parameter magnetic circuit model (LPMCM) is adopted to investigate the saturation and nonlinearity of the bridge. Taking into account the influence of magnetic field distribution on inductance, the winding function theory (WFT) is employed to accurately calculate the armature reaction airgap magnetic field and d- and q-axis inductances. The validity of the analytical technique is verified by the finite element method (FEM). Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Control of a Dual-Stator Flux-Modulated Motor for Electric Vehicles
Energies 2016, 9(7), 517; https://doi.org/10.3390/en9070517
Received: 29 April 2016 / Revised: 23 June 2016 / Accepted: 28 June 2016 / Published: 2 July 2016
Cited by 3 | PDF Full-text (8555 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the control strategies for a novel dual-stator flux-modulated (DSFM) motor for application in electric vehicles (EVs). The DSFM motor can be applied to EVs because of its simple winding structure, high reliability, and its use of two stators and rotating
[...] Read more.
This paper presents the control strategies for a novel dual-stator flux-modulated (DSFM) motor for application in electric vehicles (EVs). The DSFM motor can be applied to EVs because of its simple winding structure, high reliability, and its use of two stators and rotating modulation steels in the air gap. Moreover, it outperforms conventional brushless doubly-fed machines in terms of control performance. Two stator-current-oriented vector controls with different excitation in the primary winding, direct and alternating current excitation, are designed, simulated, and evaluated on a custom-made DSFM prototype allowing the decoupled control of torque. The stable speed response and available current characteristics strongly validate the feasibility of the two control methods. Furthermore, the proposed control methods can be employed in other applications of flux-modulated motors. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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