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Design and control of a direct drive slotless permanent magnet alternating current generator for low speed Bristol cylinder wave device

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  • Tk Electrical Engineering. Electronics Nuclear Engineering
  • Design
  • Ecology
  • Mathematics


Global demand for renewable energy is at an all-time high. Renewable energy can be extracted from naturally available resources such solar, wind, tides, geothermal heat, sea waves and the others. The percentage of renewable energy in the energy resources is increasing at an ever increasing rate. While much renewable energy is large scale, it is also suitable for rural and remote areas. The challenges facing today’s renewable energy supply industry are many, especially in the wave energy field which is still underdeveloped. The number of commercialised wave energy devices is very limited and the concepts implemented for harnessing wave energy are very different between the different devices and often struggle to be effective or survive ocean-going conditions. Thus, major research is required to find new and effective methods for harnessing wave energy which are able to supply power to the grid with high conversion rate and good reliability. The proposed Bristol cylinder device, in theory, should be able to harness sea wave energy and to convert it into useful electricity, and this device is studied in detail here. This device is still new in terms of practical application in ocean conditions. It needs power electronics and effective controllers for high-efficiency power extraction and to be successfully integrated into the power grid. When the device was first investigated in the 1970s, power electronics and variable-speed brushless permanent-magnet machinery was simply not developed to the level it is today, hence the revisiting of this device several decades later. A successful Bristol cylinder wave device which can extract renewable energy may well impact on the renewable energy sector. The wave characteristics were studied and simulated using Airy Linear Wave Theory and Stoke’s Second Order Theory. The dynamic characteristics of the Bristol cylinder are investigated when interacting with waves, together with the control necessary to make it a functioning device. A lab scale wave tank suitable to test the Bristol cylinder is designed. A surface magnet permanent magnet synchronous generator (PMSG) design is considered in this research project. This generator configuration shows its suitability in producing high conversion-rate power when working in a low speed environment. The sizing exercise is performed to determine the size of the lab scale PMSG. Analytical analysis and finite element analysis is performed to study the performance of the designed PMSG. A study of the effect of the armature length with the corresponding incident wave is done. Field oriented control (FOC) is applied to control the speed of the generator. FOC is shown to be suitable for stable control of the generator speed. Simulations using MATLAB are utilized and Simulink is used to construct the model and evaluate the potential performance of the control system design. In this thesis, theoretical analyses and simulations of the generator performances are carried out for several generator topologies and sizes. The grid side converter controller technique is also simulated in MATLAB/Simulink and the performance evaluated.

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