Design of a modular, axial-flux direct drive permanent magnet generator for wind turbines

Başkaya, Aydın
Wind energy technology is becoming more important issue in terms of renewable energy applications. Theoretical maximum of wind energy utilization is known (which is predetermined by Betz as 59%) and generally imperfections in blade manufacture reduce the actual energy yield of the turbine less than the useable energy. Therefore, maximum energy yield from generator topology is desired. According to fault statistics of wind turbines, most of the cases are related to gearbox failures. Mechanical losses and heat losses are again result from these gear-box drive train systems. In this thesis, axial flux permanent magnet direct drive (AFPM DD) topology is investigated because of its high energy yield, lower maintenance periods due to its modular direct-drive concept and axial length advantages. Proposed generator has an electrical output power of 5 MW at 12 rpm. Outer stator axial flux concept will be used in the air-cored generator. Genetic Algorithm (GA) Optimization is used in determining analytical parameters of the design. In this thesis, cost based optimization procedure is carried under 9 different wind speed conditions in order to get a more realistic design. Wind speed data are taken from vi real field based measurement values of a sample wind power plant (WPP) located in Çanakkale, Turkey. The algorithm calculated the design parameters of the proposed AFPM generator based on a power generation reference of a commercial 5 MW Permanent Magnet Synchronous Generator (PMSG) wind turbine under aforementioned wind conditions. In addition, the algorithm also considers the wind speed time probabilistic and related generation incomes.In order to verify the validity of analytical design method, first a sample 50 kW AFPM design is simulated by using FEA (Finite Element Analysis) and then critical parameters such as air gap flux density, and induced emf values are compared with the analytical results. Comparison of the results of the designed generator supported the proposed analytical design method. Detailed electromagnetic and mechanical aspects of the designed 5MW/12 rpm modular generator and its simulation results are presented and verified by using FEA comparison. It is observed that in the proposed design, PMs contribute most in the total cost while PM mass is the least dominant component in total mass. Proposed generator has axial length advantage over other MW level generator counterparts although it suffers from a large diameter due to the selected direct-drive concept. Installation costs, crane costs for maintenance and installation, transportation costs and downtime costs can be reduced with modular design concept. When increasing importance of “reliability”, “modularity” and “fault-tolerance” taken into account, it is expected that the proposed modular AFPM generator system will contribute significantly in the MW level wind energy harvesting technologies both in onshore and offshore.


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Citation Formats
A. Başkaya, “Design of a modular, axial-flux direct drive permanent magnet generator for wind turbines,” M.S. - Master of Science, Middle East Technical University, 2018.