LPV active power control and robust analysis for wind turbines

Active power control (APC) refers to a mode of operation where the wind turbine tracks a desired power reference command. It enables wind farms to perform frequency regulation and to provide ancillary services in the energy markets. This paper presents a linear parameter varying (LPV) approach for APC. The multiple-input, multiple-output controller builds upon a previous gain-scheduled design. An LPV controller is designed to coordinate the blade pitch angle and generator torque, which are standard inputs to a utility scale turbine. The objective is to track a given power reference command while also minimizing the structural loads. The controller has parameter dependence on the wind speed and the power output. The LPV approach, in contrast to the previous ad-hoc gain scheduled design, provides (in theory) guarantees on closed-loop stability and performance. This allows the turbine to be operated smoothly anywhere within the power /wind speed envelope. The performance of this LPV design is evaluated using high fidelity simulations. The robustness of the LPV system is analyzed using the theory of integral quadratic constraints (IQCs).