An offshore hydraulic wind turbine generator with variable-diameter rotor: Design,modeling and experiment

Offshore wind power is more abundant and stronger than the onshore, and more and more research enthusiasms have been raised in recent years. However, there are still many issues in the utilization of the offshore wind power such as the cost of installations and maintenance and the ability to resist extreme weather conditions. In this article, an offshore hydraulic wind turbine generator with variable-diameter rotor is presented. The diameter of the rotor can be regulated according to the wind speeds to achieve the maximum power coefficient. The hydraulic energy working as the transmission medium can improve the output power quality. The high-speed gearbox is removed, and the generator is installed on the platform, which facilitates the installations and maintenance. Here, the power conversion principle of the wind turbine generator was introduced first. Then, the dynamics and performance of the wind turbine generator was obtained. The relationship between the diameter of the rotor and the wind speed was established according to the dynamics and the optimum tip-speed ratio. Relying on the specific parameters, the dynamic response was calculated in Simulink. The results show that the instantaneous output of the wind turbine generator is relatively stable. Based on the power recovery method, the test platform was built, and the efficiency of the energy conversion device was tested. The experimental results demonstrate that the efficiency of the energy conversion device can be 88%. Finally, the total efficiency of the offshore hydraulic wind turbine generator was predicted to be 33.7%.