Unitary power control strategy for low-power wind energy conversion system using active speed stall control for full-load regime

This study deals with the control of a low-power off-grid wind energy conversion system. As rotor blades are not pitchable, control is ensured by variable-speed operation in order to limit harvested power in high winds and to maximise it at low winds. Turbine power regulation is achieved through active speed stall control, which supposes operation at low rotational speed values. In this way, operation within admissible limits of rotational speed and torque is also ensured. A unique power controller is designed, with classical proportional-integral (PI) structure and switched parameters and references. An original solution for switching controller parameters so as to avoid local instability and preserve smooth transition between partial-load and full-load operating regimes is proposed. Switching is performed in an operating point where power controller output is sufficiently deep in saturation and the antiwindup structure is active. Guidelines for choosing this switching point are provided. This control structure does not require estimation of either wind speed or wind torque, or use of gain scheduling structures. The proposed approach is validated through experiments on a dedicated real-time simulator.