Transient Response of a Straight-Bladed Vertical Axis Wind Turbine to Step Wind (At Constant Rotational Speed or Constant Torque)

Abstract

In order to know the transient response of a straight-bladed vertical axis wind turbine to change of wind velocity, the response has been analyzed under the condition of either constant rotational speed or constant load torque. Wind that instantaneously increased like a step was generated as the input power. The rotational speed of a wind turbine was controlled by an induction motor in the former condition. On the other hand, the load torque was kept by a powder brake in the latter condition. Experiments under the condition of a constant rotational speed revealed the flow around a rotor followed the wind velocity change of the main flow very quickly. In the case of constant load torque condition, effective torque of the wind turbine abruptly increased up to the value on the torque curve of the final wind velocity, with turbine rotational speed kept almost constant. After that, the effective torque decreased along the torque curve of final wind level to reach the final stage.