|M.Sc Student||Eshel Ben|
|Subject||Closed-loop control of a plasma-enhanced vertical axis wind|
|Department||Department of Energy||Supervisor||Professor David Greenblatt|
|Full Thesis text|
Vertical axis wind turbine (VAWT) blades can experience large positive and large negative angles-of-attack that result in dynamic stall over their pitching blades. As a result, the VAWT blades experience a dramatic loss in lift and thus a reduction in turbine efficiency. Furthermore large unsteady loads are imposed on the bearings and drive train. Dielectric barrier discharge (DBD) plasma actuators can control dynamic stall and hence diminish those undesired effects. DBD plasma actuators were installed on a high solidity, double-bladed NACA0015, H-Rotor vertical axis wind turbine. The turbine was installed in a low speed blow-down wind tunnel and tested at typical atmospheric wind speeds (5m/s and 7m/s). Pulsed perturbations, at frequencies corresponding to flow instabilities, were introduced on the upstream half of the turbine azimuth. Simulated unsteady atmospheric conditions were achieved in the wind tunnel by means of a louver system mounted downstream of the turbine. The objectives of this research were to maximize the net turbine output power output and to regulate the power generation by means of closed-loop control.
Closed loop control schemes were developed on the basis of the integral rotational speed of the turbine. The control structure incorporated a feed-forward mechanism within the turbine azimuth, where initiation and termination of plasma pulses could be adjusted continuously. Closed loop control schemes of increasing complexity were implemented. The simplest was hysteresis control based on a turbine power threshold and the most complex was so-called Model Predictive Control (MPC) scheme. For the latter, a dynamic model of the turbine was developed and linearized. The model was then validated against experimental data and implemented in the MPC scheme. All of the control schemes produced positive net results in terms of net energy output. The control schemes are now sufficiently mature to be implemented on a full-scale test turbine. A major accomplishment of this work was a net turbine energy increase of about 4.6% and power fluctuation reduction of about 44% under simulated atmospheric conditions. Significantly larger net gains can be obtained with more powerful actuators or different actuator geometries. For example, serrated-edged electrodes produced greater net power output than straight-edged electrodes.