Control model for X-ROTOR
The X-Rotor concept consists of a large vertical axis primary rotor with smaller secondary horizontal axis rotors mounted on the primary rotor to extract power. Both the pitch angle of the primary rotor blades and the thrust of the secondary rotors can be adjusted to control the turbine.
Based on the work being undertake in Tasks 3.1 and 3.4, it is clear, that the inputs to the X-rotor full envelop controller are the primary rotor speed and secondary rotor speeds or equivalently the frequencies of the power connections to the generators. The outputs are pitch angle demand for the upper primary rotor blades and a parameter that is equivalent to a tip speed ratio demand. It is, also clear that a separate controller incorporated into each power take-off unit, consisting of a secondary rotor, generator and converter, is required. These additional controllers are tasked with ensuring that the secondary rotor speed and aerodynamic torque maintain the relationship required to achieve the required tip speed ratio.
A nonlinear dynamic model of the power take-off unit and its associated linearised model, suitable for design of the power take-off controller are described. In addition, a nonlinear dynamic model of the X-rotor turbine and its associated linearised model, suitable for design of the full envelop controller, are described. A MATLAB script to determine the linear models for a given X-rotor operational strategy is developed and some illustrative examples provided.