On the design and power output response of hydraulic wind turbines

Abstract

Standard horizontal axis wind turbines typically use gearboxes for large-scale applications and direct coupling for small-scale designs to connect the rotor to the generator. However, gearboxes pose challenges due to their weight, cost, and exposure to dynamic loads and vibrations within the nacelle. A promising alternative is replacing mechanical transmission with a hydrostatic counterpart, offering advantages such as reduced nacelle mass, generator placement at the tower base, and elimination of the gearbox. It can potentially lead to cost savings of up to 20% in the levelized cost of electricity for offshore wind turbines. This study compares regulated hydrostatic transmission with unregulated transmission and damping components under different wind conditions, including atmospheric boundary layer and low-level jet inputs. Dynamic simulations of a horizontal axis wind turbine incorporating a hydrostatic transmission are conducted to evaluate its response to wind fluctuations caused by prevailing wind velocity profiles, atmospheric boundary layer, and low-level jet velocity profiles. Addressing torque fluctuations and power impact on power quality and mechanical components is crucial in wind turbine operation. The proposed hydrostatic transmission includes primary and secondary proportional controllers for adaptability to varying wind speeds, along with integrated accumulators in the high and low-pressure lines. The main findings indicate that the regulated hydrostatic transmission achieves an efficiency range of 69%–75% across various wind velocity profiles, surpassing the unregulated counterpart. It reduces torque fluctuation amplitude by 35% and improves efficiency by nearly 20% compared to the basic transmission. Torque and power fluctuations are also reduced by 35% and 40%. These improvements are attributed to the damping capabilities of the hydrostatic transmission and the actions of the proportional controller. Implementing the regulated hydrostatic transmission offers several technical and economic advantages, including relocating the generator to ground level and achieving continuous hydraulic variable transmissions without the need for a gearbox. The methodology is applicable to a range of wind turbine sizes.