Blade force measurements and electrical torque ripple of a vertical axis wind turbine

Abstract: Wind power has become an attractive alternative for clean energy production. Horizontal axis turbines are increasing in power rating and are maturing as products. The cost of maintenance, noise levels and durability are possible concerns of the modern horizontal axis wind turbines. The vertical axis wind turbine project at Uppsala University addresses these issues among others. The concept removes the need for any yaw or pitch mechanism. Even the gearbox is excluded with the use of a directly driven multi-pole permanent magnet generator. Additionally, the generator and power electronics is placed at ground level. The project has resulted in several open site prototypes of which a 12kW and 200 kW turbine are still subject to active research.One major disadvantage of vertical axis wind turbines are the oscillating forces acting on the turbine. The first part of this work presents a measurement system developed to capture the forces acting on a blade during operation of the 12 kW prototype. The systems performance and data output is presented and thorough error estimations has been performed.In modern turbines it is common to have the generator power rectified into a DC-voltage, feeding an inverter connected to the grid. The rectifier is usually also an inverter allowing full control of the generator and the DC-link voltage. In the concept used on the 12 kW prototype, the electric power of the generator is instead passively rectified using diodes to produce the DC-voltage. Diodes are considered a cheap and robust solution for producing the DC-voltage. However, one drawback is the high current ripples produced. The current ripples lead to an electric torque ripple. This work studies how this electric torque ripple translates into a mechanical torque ripple on the turbine. A simulation model is developed and the results are compared with the force measurements on the 12 kW prototype.