Investigation of a low speed tubular linear generator with inter-modular permanent magnets

Farahani, EF; Baker, NJ

doi:10.1049/icp.2024.2167

Investigation of a low speed tubular linear generator with inter-modular permanent magnets

Lookup NU author(s): Dr Ehsan Farahani ORCiD, Professor Nick Baker ORCiD

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Abstract

© The Institution of Engineering & Technology 2024. Wave energy is a source of renewable energy which has demanding and unique requirements on the electrical drive. This paper presents a tubular linear inter-modular permanent magnet generator designed for integration into a wave energy converter. The proposed topology is specifically designed for a low operating speed of 0.5m/s and a magnetic gap of 3mm, characteristics not well-suited for conventional electric machines. The large gap is being driven by a desire to integrate the machine within the wave energy converter to accommodate sealing and encapsulation requirements. It is common for generators intended for wave energy to rely on magnetic gearing, provided by flux switching machines with small pole width magnets on the stator interacting directly with translator teeth. Unfortunately, most topologies of this nature rely on a small magnetic gap, and so are not suitable for a fully integrated design. Bias flux machines, however, have a larger pole width consisting of permanent magnets and the flux modulation is via a toothed stator and toothed translator. The resultant larger stator pole means they are potentially more appropriate for applications with a large magnetic gap. In the structure investigated here, the permanent magnets are embedded between the stator modules, providing cooling vents for efficient PM cooling, better resilience to a large gap and potential savings in the assembly process. Comparisons are made between the proposed generator and two other competing topologies of the same class. The optimized dimensions of the presented linear generators are achieved through a genetic algorithm, targeting an increase in average thrust force and a decrease in force ripple. Utilizing 2D axisymmetric finite element analysis, the generators are simulated under both no-load and full-load conditions, and a comprehensive comparison of the results is provided. Finally, the demagnetization state of the PMs within the proposed topology is discussed.