Robust pitch controller for output power levelling of variable-speed variable-pitch wind turbine generator systems

A robust pitch (RP) controller for variable-speed variable-pitch wind turbine generator systems (VSVP-WTGS) is presented. The controller can not only level the wind energy conversion but also be applicable in a wide wind speed region even subject to large parametric or non-parametric disturbances. VSVP-WTGS consists of multi-subsystems with different time scales. The dominant 'slow' dynamics are non-affine and high nonlinear. By considering 'fast' subsystems as perturbations to the 'slow' one, the dynamics of VSVP-WTGS can be represented by a nominal model and an error one. The RP controller is composed of a nominal inverse-system controller and a robust compensator. With the nominal inverse-system controller, the nominal closed-loop system can track its reference dynamics. With the robust compensator, turbine parameter uncertainties and non-parametric perturbations are tolerated. The performance of the RP controller is confirmed through theoretical analyses and computer simulations. Results show that RP controller can operate in a wider wind speed region robustly compared with a proportional-integral-derivative controller. Compared with other nonlinear controllers, the RP controller is simpler and can be more easily extended to other kinds of WTGS.