Comparative study of maximum power strategy in wind turbines

Power characteristics of wind turbines are nonlinear. It is particularly true for Savonius vertical axis systems whose the provided power is very sensitive to the load. Thus, controlling its operating is essential to optimise the energetic behaviour. Several control strategies (maximum power point tracking) can be used for energy conversion. If the wind turbine characteristic (Cp(λ)) is supposed to be a priori known, it can be used for an optimal control of the torque, speed or of the output current. On the contrary, if this characteristic is unknown, an operational seeking algorithm such as fuzzy logic has to be implemented. Several structures are also possible following the AC-DC converter which can be a PWM converter or a simple diode bridge. A comparative study of these control strategies and architectures is proposed in this paper. The analysis is based on simulations and on some experiments.