Performance Improvements of Switching Control for Wind Turbines

Modern variable speed wind turbines operate within a large range of wind speeds. Control of such a turbine is partitioned in two modes: a low wind speed mode and a high wind speed mode. Depending on the prevailing wind speed, a turbine is controlled to switch between these two modes. During mode switching, critical dynamics of the turbine such as the output power and mechanical loads can experience steep, large changes even though the switching action is Lyapunov as well as input-output stable. In this work, a new control technique is presented to attenuate the steep and large volatile dynamics during turbine switching while preserving the original system structure so that the established system stability still holds. An algorithm that modifies the generator torque control law in the low wind speed mode is developed to reduce the steep change of turbine power and torque. A Proportional-integral (PI) control of blade pitch angle in the high wind speed mode is proposed to optimize the system power variation and power generation. Simulations conducted under various wind speed classes demonstrate the effectiveness of the proposed control design.