Analysis and Simulation of Dynamics and Control of a Hydrostatic Wind Turbine

Kω² control, also called torque control, is a popular tool for maximizing wind turbine power in region 2. For hydrostatic wind turbines, the Kω² law relates pressure and rotor speed. This work considers implementing the Kω² law as pressure-regulation or rotor speed-regulation. Dimensionless, linearized models of these two approaches are used to investigate dynamics and control. Analysis shows that the mechanical rotor dynamics are much slower than the hydraulic transmission dynamics and that frictional and leakage losses have a negligible effect on system dynamics. Root locus analysis shows how systems responses change with variation of PID controller gains. Both control approaches require derivative controller action to sufficiently damp their responses; both are also fundamentally limited in their speed of response by a slow stable pole regardless of their controller loop gains. Nonlinear system simulation shows that both control approaches track the maximum power point with nearly identical transient behavior and experience nearly identical power losses when using suboptimal values of the control law gain K.