Constant-Bandwidth Maximum Power Point Tracking Strategy for Variable-Speed Wind Turbines and Its Design Details

Implementation of maximum power point tracking (MPPT) control to variable-speed wind turbines below the rated wind velocity helps the turbine improve its efficiency, thereby increasing its annual energy yield. However, for the most commonly used optimum power (OP) MPPT method, it is proved to have the drawback of low tracking speed. Moreover, what is worse, the tracking bandwidth will get narrower when the turbine is operating under low wind velocities, which results in the reduction of annual energy yield. To overcome this drawback, an improved MPPT method, which is improved from the conventional OP control method, is designed in this paper to broaden the MPPT bandwidth. The design details on how to realize the improved MPPT method and the principle of choosing a proper system dynamics are both pointed out after analyzing the system dynamics in frequency domain. The theoretic analysis is verified by simulation and experimental results performed by a 1.2-kW variable-speed wind turbine.