Stability analysis of maximum power point tracking (MPPT) method in wind power systems

Variable-speed wind power systems are able to vary the rotor speed according to wind speed variation. The maximum power point tracking (MPPT) is the key to notably improve efficiency of such energy extraction systems. The characteristic power curve MPPT method is one of the popular MPPT methods. It does not need real-time wind speed measurement and by using the relationship between power and current, the reference current can be obtained easily. This paper presents the steady state and dynamic analyses of this MPPT method and proposes a single pole transfer function to describe the effect of variation of wind speed on the rotor speed. This is conducted by applying the small signal analysis on the turbine-rotor mechanical system. To verify the performances of wind turbine system, both simulation and experimental systems are implemented based on MPPT power control. By concentrating on step wind speed variation, all results - proposed theory, simulation and experiments - present good consistency.