Power regulation and control of wind turbines: LMI-based output feedback approach

This paper addresses the problem of power regulation and control of wind turbines using an output feedback scheme formulated as a well-defined linear matrix inequality (LMI) problem. To this aim, first, a piecewise linear (PWL) model is constructed for the wind turbine system with the wind speed as a parameter. Then, using the achieved PWL model a set of output feedback controllers are formulated and solved as an LMI problem. To implement the designed controller in practice, 2 different approaches are proposed, ie, online and off-line approaches. In the first approach (online), an exact optimal control law is obtained by online evaluation of the PWL model and then solving the associated LMI problem which leads to a relatively high computational complexity. To deal with this computational complexity, an alternative approximate approach is proposed which puts parts of online computations to off-line precalculation with the cost of sub-optimality. In this approach, the controller is predesigned for some predefined operating points and then the sub-optimal controller is achieved by introducing a convex combination of precalculated controllers while guaranteeing the constraints satisfaction. Finally, the performance and characteristics of the proposed approaches are verified using simulation results.