Analysis of VRPM (Transverse-Flux) machines for renewable energy applications
Analysis of VRPM (Transverse-Flux) machines for renewable energy applications
Rotor speeds of tidal and wind energy conversion systems (10/150 rpm) are lower than in traditional power plants such as gas or steam turbines (1500/3000 rpm). The low speed of the rotor makes it necessary to install a gearbox when conventional electric generators are used, which can reduce reliability and increase maintenance cost. Since transverse flux machines (TFMs) have a high specific torque, they are attractive as direct-drive generators for wind and tidal turbines. However, TFMs have complex three-dimensional geometries and structures, which complicates the task of modelling. Therefore, the aim of this Thesis is to develop intuitive fundamental theory particularly tailored for the modelling of permanent magnet transverse flux machines.
The Thesis makes several novel contributions in the field of electromagnetic modelling of TFMs. Firstly, it develops a complex permeance framework for the case of TFMs using a scalar potential formulation. The complex permeance function is used to obtain the homopolar magnetic field distribution in the air-gap taking into account curvature and slotting. Furthermore, an algorithm to quickly obtain the coefficients of the complex permeance function is presented.
The complex permeance function is then used to formulate a torque equation. A generalisation of Harris et al.'s torque equation for TFMs is derived for any mmf waveform and phase advance angle. The torque equation is based on Lorentz's BiL principle, where i is the equivalent current of the magnets and B is the magnetic field produced by the stator winding. The result is a fairly simple equation that relates torque to the electric and magnetic loadings of the machine and a flux factor that depends on the machine's geometrical parameters.
In addition, a virtual mutual inductance (VMI) approach to calculate the flux linkage in TFMs is proposed. The VMI between the stator windings and the magnets' equivalent currents is obtained by integrating the flux produced by the stator windings over the surface of the magnets. Based on the reciprocity theorem (M12 = M21) it can be used to obtain the flux linkage in the stator windings. This methodology has been validated using experimental data and three-dimensional finite element analysis showing a reasonable level of accuracy. Key design parameters such as back emf and power factor are then readily calculated using the proposed methodology.
The well-known current sheet model has been adapted for the calculation of eddy current power losses, produced by asynchronous harmonics in the air-gap, in the outer rotor geometry of TFMs. Furthermore, the problem is formulated using transfer matrices, which reduces the complexity of the problem significantly. The transfer matrices are used to express the boundary conditions sequentially; this simplifies the solution because instead of inverting a large matrix, as commonly done in the literature, it is only necessary to invert a matrix of order two.
These analytical techniques are applied to optimise the design of a tidal generator. The optimisation philosophy developed in this Thesis emphasises the fact that torque and power factor are closely interlinked. Furthermore, it is shown that the low power factor of TFMs is not produced by the leakage flux in the classical way but due to the ineffective use of the magnetic flux. Understanding the relationship between torque and power factor is a key step to unlock the full potential of TFMs.
Finally, all through this Thesis a particular single-sided TFM design case study is used. However, the background theory developed is completely general and it can be applied to any kind of permanent magnet machine. The proposed future work includes the application of the methodologies developed for the analysis and design of radial permanent magnet machines, magnetic gears, magnetic actuators and more complex flux-concentrating TFMs.
University of Southampton
Renedo Anglada, Jaime
4ba2df6e-f91f-4ffc-8169-068852e59e90
22 February 2018
Renedo Anglada, Jaime
4ba2df6e-f91f-4ffc-8169-068852e59e90
Sharkh, Suleiman
c8445516-dafe-41c2-b7e8-c21e295e56b9
Renedo Anglada, Jaime
(2018)
Analysis of VRPM (Transverse-Flux) machines for renewable energy applications.
University of Southampton, Doctoral Thesis, 222pp.
Record type:
Thesis
(Doctoral)
Abstract
Rotor speeds of tidal and wind energy conversion systems (10/150 rpm) are lower than in traditional power plants such as gas or steam turbines (1500/3000 rpm). The low speed of the rotor makes it necessary to install a gearbox when conventional electric generators are used, which can reduce reliability and increase maintenance cost. Since transverse flux machines (TFMs) have a high specific torque, they are attractive as direct-drive generators for wind and tidal turbines. However, TFMs have complex three-dimensional geometries and structures, which complicates the task of modelling. Therefore, the aim of this Thesis is to develop intuitive fundamental theory particularly tailored for the modelling of permanent magnet transverse flux machines.
The Thesis makes several novel contributions in the field of electromagnetic modelling of TFMs. Firstly, it develops a complex permeance framework for the case of TFMs using a scalar potential formulation. The complex permeance function is used to obtain the homopolar magnetic field distribution in the air-gap taking into account curvature and slotting. Furthermore, an algorithm to quickly obtain the coefficients of the complex permeance function is presented.
The complex permeance function is then used to formulate a torque equation. A generalisation of Harris et al.'s torque equation for TFMs is derived for any mmf waveform and phase advance angle. The torque equation is based on Lorentz's BiL principle, where i is the equivalent current of the magnets and B is the magnetic field produced by the stator winding. The result is a fairly simple equation that relates torque to the electric and magnetic loadings of the machine and a flux factor that depends on the machine's geometrical parameters.
In addition, a virtual mutual inductance (VMI) approach to calculate the flux linkage in TFMs is proposed. The VMI between the stator windings and the magnets' equivalent currents is obtained by integrating the flux produced by the stator windings over the surface of the magnets. Based on the reciprocity theorem (M12 = M21) it can be used to obtain the flux linkage in the stator windings. This methodology has been validated using experimental data and three-dimensional finite element analysis showing a reasonable level of accuracy. Key design parameters such as back emf and power factor are then readily calculated using the proposed methodology.
The well-known current sheet model has been adapted for the calculation of eddy current power losses, produced by asynchronous harmonics in the air-gap, in the outer rotor geometry of TFMs. Furthermore, the problem is formulated using transfer matrices, which reduces the complexity of the problem significantly. The transfer matrices are used to express the boundary conditions sequentially; this simplifies the solution because instead of inverting a large matrix, as commonly done in the literature, it is only necessary to invert a matrix of order two.
These analytical techniques are applied to optimise the design of a tidal generator. The optimisation philosophy developed in this Thesis emphasises the fact that torque and power factor are closely interlinked. Furthermore, it is shown that the low power factor of TFMs is not produced by the leakage flux in the classical way but due to the ineffective use of the magnetic flux. Understanding the relationship between torque and power factor is a key step to unlock the full potential of TFMs.
Finally, all through this Thesis a particular single-sided TFM design case study is used. However, the background theory developed is completely general and it can be applied to any kind of permanent magnet machine. The proposed future work includes the application of the methodologies developed for the analysis and design of radial permanent magnet machines, magnetic gears, magnetic actuators and more complex flux-concentrating TFMs.
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Submitted date: 1 November 2017
Published date: 22 February 2018
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Local EPrints ID: 481128
URI: http://eprints.soton.ac.uk/id/eprint/481128
PURE UUID: 99096fc8-4aab-4987-a81c-d8eb27183b6f
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Date deposited: 16 Aug 2023 16:36
Last modified: 16 Mar 2024 07:52
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