Electrical System for a Variable Speed Vertical Axis Wind Turbine

Abstract: The wind has been used as a source of energy for a long time. Wind power in power production has had a upswing in the last decade due to its renewable and clean nature. This thesis contributes to the wind power research done at the division of Electricity at Uppsala University. The research is aimed towards increasing the understanding of vertical axis wind turbines. The thesis focuses on vertical axis wind turbines of the H-rotor type with a directly driven permanent magnet synchronous generator. In this thesis a full-scale variable speed electrical grid connection system is developed and evaluated for a 12 kW prototype turbine. The proposed electrical system consists of a diode rectifier, IGBT inverter, LCL-filter and tap transformer. The full variable speed operation is achieved by adjusting transformer taps and adjusting the modulation of the inverter. The system has been assembled in a lab environment where efficiency and harmonic content have been evaluated for the operational scheme and site specifics of the 12 kW turbine. The work also looks into transformer magnetization losses, permanent magnet generator air cooling and control system design for a similar system. The results from simulations and experiments show that the tap transformer system has a high efficiency at nominal power and that the system efficiency at nominal power is increased by going up in tap. The study also shows that the total demand distortion for the system is well below 5% for full operating range of the 12 kW turbine.Keywords: VAWT, H-rotor, tap transformer, stall control, renewable energy, variable speed operation, transformer magnetization losses