Design and performance investigation of a low-cost flux reversal machine for a direct-drive wind generator.
Kundanji, Kalengo
Kundanji, Kalengo
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Abstract
Wind turbine technologies have evolved from fixed-speed to variable-speed rotor operation, from geared to direct-drive and induction generator use to synchronous generators. The transition has been for the sole purpose of attaining more efficiency, power density, advancement in grid integration and drivetrain technology, as well as large turbine scaling. In the quest to attain large MW capacity, that is, a target of 20 MW of a single wind turbine particularly for offshore applications in the near future, many technological advances have been made, and the variable-speed direct-drive permanent magnet synchronous generator (PMSG) has emerged to be superior. The main problem with PMSGs is the high prices of rare-earth elements used for PMs and their monopolized supply by China. This is a concern to the world because if a repetition of the 2010 hike in prices and disruptions in PM supply happens, it would be a huge drawback to the fastrising large wind turbines. Therefore, a non-PM non-conventional direct-drive brushless machine such as the novel DC-excited flux reversal machine (DCFRM) is being proposed in this study. This direct-drive DCFRM will offer a low-cost and robust wind generator option. However, the potential for the proposed wind generator application remains to be seen in terms of torque density and efficiency, among others. The study addressed three sub-problems: evaluating the state of the art, determining the appropriate topology and sizing, and validating the initial concept through finite element analysis (FEA). The hypotheses guided the research, focusing on the necessity of DCFRM, the preferred topology, and the cost-effectiveness of the design. The performance of the DCFRM was compared with a PMFSM counterpart using 2D FEA, considering aspects such as flux
density, flux linkages, induced voltages, cogging torque, electromagnetic torque, output power, and voltage regulation. The study confirmed the feasibility of the DCFRM design, which exhibited satisfactory performance characteristics and cost advantages over the permanent magnet flux reversal machine (PMFRM), making it a promising alternative for small-scale direct-drive wind turbine generators. Further research is recommended to optimize the design, explore scalability, assess reliability, and consider advanced control strategies and power electronics integration.
Description
Submitted in partial fulfillment of the requirements for the degree, Master of Engineering in the Department of Electrical Engineering, Faculty of Engineering and Built Environment
at the Tshwane University of Technology.
Date
2023-12-01
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Tshwane University of Technology
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Keywords
Flux reversal machine, Direct drive, Wind generator, Wind turbine