Browsing by Author "Akuru, Udochukwu Bola"

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    Contemporary wind generators
    (Energy Research Centre, 2015) Akuru, Udochukwu Bola; Kamper, Maarten J.
    It is believed that wind energy is growing at a very rapid rate, especially in the last few years. When compared with other sources of renewable energy in the energy portfolio, it becomes evident that the bulk is wind energy-based. However, there are some backlogs to full manifestation of this technology ranging from initial high cost to performance and reliability issues, among others. But in spite of these bottlenecks, new research trends have been assertive in seeking out a sustainable solution for harnessing wind energy for power generation -especially in the design and construction of wind generators. In order to motivate and prime a sustainable energy mix among stakeholders, this paper is a shot at appraising the theory of these innovative wind generators towards ecological sustainability, economy, efficiency, and employment creation.
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    Design optimisation and performance evaluation of flux switching machines for geared medium-speed wind generator drives
    (Stellenbosch : Stellenbosch University, 2017-12) Akuru, Udochukwu Bola; Kamper, M. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: As wind turbines become large, the cost of energy increases because of the employed drivetrain (geared or direct–drive). Consequently, non–conventional geared medium–speed (MS) generators are gaining relevance, potentially due to better compromise to both the generator and gearbox costs. The study proposes a novel approach for the multi–objective design optimisation (MDO) of two variants of geared MS flux switching machines (FSMs) in their simple radial–flux structures––the 12–stator slots/10–rotor poles (12/10) and 12/14 machines, with major emphasis on rare–earth–free designs for industrial–scale applications. Based on finite element analyses (FEA), whereby torque density, torque ripple and power factor are prioritised, multiple design options are provided in different Pareto maps for the designer to make informed selections. From an initial optimal design comparison of the 12/10 machines based on rare–earth permanent magnets (PMs) in different wind generator drivetrains at 10 kW, the MS design yielded the best solution in terms of average torque densities per generator costs. Consequently, the focus on MS drivetrains was intensified to further evaluate the 12/10 and 12/14 rare–earth PM–FSMs as their power level shifts from 10 kW to 3 MW. As an indication of potentially adopting rare–earth–free designs, an improvement in terms of increased torque densities and reduced torque ripple values is obtained for the rare–earth designs at 3 MW due to a number of factors such as variations in their PM volumes and relative differences in their saliency ratios. Moreover, due to the optimal behaviour of key design parameters in the MDO environment, the superior performance of the 12/14 machines at 10 kW are reversed at 3 MW. Disappointingly, based on the same design requirements, the nominated rare–earth–free designs such as ferrite PMs and wound–field (WF) coils do not produce better torque ripple effects compared to rare–earth PMs, as should be expected for such flux–focusing machines. However, an inherent tradeoff was found between their aspect ratios and armature current densities which influence the active mass, especially for industrial– scale designs. Consequently, to ensure the feasibility of the optimal design, it may be needful to appropriately restrict the boundaries of the aspect and split ratios before engaging them in any MDO procedure. In another instance, it is found that it may be better to pursue MDO problems e.g., of WF– FSMs, by concentrating more on the performance (torque ripple and power factor) than on the cost of the machines. Interestingly, it was also found that the cheapest MS generator, even when compared with similar conventional wind generators at 3 MW, is the WF–FSM. Eventually, to validate the series of FEA prediction made during the study, a 10 kW WF–FSM generator prototype is selected, manufactured and tested, with certain novel implementations. Based on measured no–load, short– circuit, thermal, uncontrolled–normal and overload resistance, as well as current–controlled tests, the design feasibility as well as the conceptualisation of the proposed wind generator drivetrains has been proven beyond reasonable doubt. In agreement with Chen et al (2011) [44], there is, indeed, a bright future for FSMs. The study is concluded with a general conclusion and recommendations for the future.