N. J. Baker

Current and Novel Electrical Generator Technology for Wave Energy Converters

Wave energy is currently an untapped resource, but has the potential to make a significant contribution to the energy mix. In order to use conventional electrical generators mechanical interfaces are used, such as hydraulic systems and air-turbines. With the electrical generator these interfaces are known as the electrical power take-off and the type used depends upon the wave energy device. A brief description of the different power take offs is provided to show how conventional rotary generators are used in wave devices. Both advantages and disadvantages are highlighted in the paper. Direct drive systems can overcome some of the disadvantages, but there are additional engineering challenges to overcome, in particular physical size and mass. Current and more novel direct machine topologies are discussed in the context of these challenges.

Direct drive electrical power take-off for offshore marine energy converters

Abstract This paper investigates the issues associated with converting the energy produced by marine renewable energy converters, namely wave and tidal stream devices, into electricity using direct drive electrical power take-off, without use of complex pneumatic, hydraulic or other mechanical linkages. In order to demonstrate the issues, two alternative topologies of linear electrical machines are investigated: the linear vernier hybrid permanent magnet machine and the air-cored tubular permanent magnet machine. The electrical characteristics of these machines are described and compared in the context of mechanical integration. Potential solutions to the issues of sealing, corrosion and lubrication are discussed taking into account the electrical properties of the two topologies.

Three-Phase Modulated Pole Machine Topologies Utilizing Mutual Flux Paths

This paper discusses three-phase topologies for modulated pole machines (MPMs). The authors introduce a new three-phase topology, which takes advantage of mutual flux paths; this is analyzed using 3-D finite-element methods and compared to a three-phase topology using three single-phase units stacked axially. The results show that the new “combined-phase MPM” exhibits a greater torque density, while offering a reduction in the number of components. The results obtained from two prototypes are also presented to verify the concept; the results show that the “combined-phase” machine could provide both performance and constructional benefits over prior MPM topologies.

Design and Validation of a Synchronous Reluctance Motor With Single Tooth Windings

This paper presents for the first time the analysis and experimental validation of a six-slot four-pole synchronous reluctance motor with nonoverlapping fractional slot-concentrated windings. The machine exhibits high torque density and efficiency due to its high fill factor coils with very short end windings, facilitated by a segmented stator and bobbin winding of the coils. These advantages are coupled with its inherent robustness and low cost. The topology is presented as a logical step forward in advancing synchronous reluctance machines that have been universally wound with a sinusoidally distributed winding. The paper presents the motor design, performance evaluation through finite element studies and validation of the electromagnetic model, and thermal specification through empirical testing. It is shown that high performance synchronous reluctance motors can be constructed with single tooth wound coils, but considerations must be given regarding torque quality and the d-q axis inductances.

Reduction of Cogging Torque and EMF Harmonics in Modulated Pole Machines

This paper discusses a method for reducing cogging torque and harmonic content of back-electromotive force (EMF) waveforms in modulated pole machines (MPMs). Tooth pitching is applied to a separate phase MPM in order to reduce the most prominent harmonics present in a three-phase MPMs cogging torque. Experimental results show that the application of tooth pitching to these machines can reduce the cogging torque and back-EMF harmonics significantly. This comes without a significant impact to the useful output of the machine, which is confirmed by the comparison of measured results for two prototypes. Such a technique can be easily applied to existing machine designs without the need for extra components and for the same production cost.

Development of a linear test rig for electrical power take off from waves

This paper describes the design build and test of a linear test rig for demonstrating novel topology linear machines. The work is aimed at aiding the developments of power take off for wave and tidal energy converters. The rig consists of three parts: prime mover, test machine and converter. Experience and method for the design manufacture and initial testing of each of these components is detailed.

Design and build of a mass critical, air-cooled transverse flux machine for aerospace

Electric motors are becoming increasingly utilized in aircraft, replacing traditionally mechanical or hydraulic auxiliary systems to realize improvements in mass, control and efficiency. Aerospace motor design has the unique characteristic that mass and, therefore, torque density is of critical importance. For low maintenance, non-safety critical components, which are only used for short durations of the flight cycle, efficiency also becomes less important, whilst eliminating an external cooling circuit and gearbox will further benefit mass constraints. This paper considers the design of a high torque density machine in order to meet a specification for an aerospace application with a stringent mass target. As mass is reduced, thermal capability becomes critical and detailed thermal models, along with simulation results, are presented for operational characteristics.

Three-Dimensional Modelling of Demagnetization and Utilization of Poorer Magnet Materials for EV/HEV Applications

High performance electric motor designs with ferrite magnets have recently gained interest due to the high and volatile price of rare earth magnets. However, due to the relatively poor coercivity of ferrite magnets, these designs are highly susceptible to demagnetization, as a result of which accurate modelling and better understanding of this phenomenon is particularly important. In this paper, the impact of the motor stack length and level of magnetic saturation on the demagnetization risk are studied based on 3-dimensional finite element simulations and a proposed lumped circuit model. It is shown that reducing the stack length can significantly enhance the demagnetization resistance with the effect being more pronounced for designs with a higher level of magnetic saturation. To benchmark the practicality of the concept, a previously presented high-performance ferrite-based design is modified by using a 30% weaker grade of ferrite magnet whilst shortening the stack length. It is shown that the demagnetization withstand capability of the design was significantly enhanced and exceeded the short circuit requirement with a good safety margin. The theoretical findings have been supported by prototype testing.

Cost reduction of a permanent magnet in-wheel electric vehicle traction motor

This paper describes a motor for use within the wheel of an electric vehicle. It demonstrates the influence of various rotor parameters on an outer rotor permanent magnet motor (ORPM) with Surface-mounted magnets (SM). The aim of this paper is to reduce the magnet volume, while maintaining the torque performance through the complete operating range. Six different magnet topologies are investigated firstly. Then, Semi Surface-mounted Permanent Magnet (SSPM), I shape tangential PM (IPM) and V shape interior PM (VPM) designs are compared in terms of torque capability at certain magnet volume. The VPM gives highest torque performance. The iron shielding concept in VPM can protect the magnets from the opposing armature flux, thus providing increased resistance to demagnetisation, and hence permitting thinner magnets. Furthermore, a new slot/pole combination with higher torque capability has been studied. However, due to the increased inductance, motor with V shape design needs to work at a poorer power factor and consequently a reduced speed range for a given inverter. Lastly, Cost effective and simple manufacture method of the VPM rotor is also addressed with consideration of mechanical feasibility.

Flux Switching Modulated Pole Machine topologies which offer greater mechanical simplicity

This paper will present two new Flux Switching Modulated Pole Machine (FS-MPM) topologies which have a similar structure to a Modulated Pole Machine. It aims to address the complexity of the rotor, by introducing a FS-MPM design in which the magnets are removed from the rotor and placed on the stator. Furthermore the number of magnets in the FS-MPMs is greatly reduced when compared to a standard MPM; reduction in component count and simplification of the rotor will offer a significant benefit in terms of cost and ease of production.