Characterization of a novel dual-stator electric generator using finite element analysis

Abstract

In a study published by the US National Renewable Energy Laboratory (NREL), it was shown that “Renewable energy sources, accessed with commercially available technologies, could adequately supply 80% of total U.S. electricity generation in 2050”. Therefore, a very rapid increase in renewable energy penetration in electric power systems is expected. The renewable energy harvesting process (except solar energy) involves technologies that utilize electric generators for energy conversion. Thus, the performance of generation units used in the renewable energy harvesting process is becoming more critical in electric power system stability, energy efficiency, and power cost. This project presents a characterization process performed on a novel dual stator permanent-magnet generator by using finite element analysis (FEM). The novel design is patented by the U.S. Patent and Trademark Office. The machine is built by using a state-of-the-art industryscale electromagnetic simulation tool available at the Department of Electrical and Computer Engineering at the University of Alaska Fairbanks. The patented design incorporates two types of generators; single-phase and three-phase types. This project is based on a three-phase design. The machine’s electrical and mechanical specifications which are detailed in the patent document were implemented, except the exciter design. It was decided to replace the proposed electromagnetic coils with permanent magnets. This selection was made to eliminate the copper loss in the field circuit (rotor) to maximize the machine’s efficiency. This also eliminated the use of slip rings and brushes which are considered a disadvantage due to the frequent maintenance requirement. However, it has the advantage of providing better control on the generated power at a wide range of speeds. NdFeB magnet is selected as it provides better flux density in low-speed operation. This was concluded via a comparison process conducted on magnet types available in the simulation tool. Based on the patented design, the generator was simulated with 12 rotor poles and 24 stator teeth. A reference speed of 600 rpm is used to ensure 60 Hz frequency operation. Due to the amount and type of steel used to build the apparatus, the machine demonstrates a quality reduction in the steel saturation under full-load operation especially at the critical parts of the machine (armature teeth). More importantly, the machine shows a high level of full-load efficiency. It is important to mention that this project is not a complete research work. Further characterization and optimization processes are still to be performed for the novel design to manifest its highest performance. This may be a research work to pursue in the future. This project was one step in this direction.