Frequency regulation strategy for wind-storage systems based on improved torque limit control

Abstract

With a high proportion of wind power connected to the power grid, the decline of system inertia leads to the increasingly prominent problem of frequency stability. Because of the limited kinetic energy of the rotor, wind turbines are prone to causing secondary frequency drop when participating in frequency regulation, which threatens the safety of the power grid. This paper proposes a frequency regulation strategy for wind-storage systems based on an improved torque limit control. Firstly, the smooth power transition function is designed to improve the traditional torque limit control and prevent secondary frequency drop. Secondly, the speed recovery time mechanism related to wind speed is established to dynamically optimize the kinetic energy release process and accelerate the speed recovery.On this basis, an adaptive control strategy based on energy storage state of charge is designed to coordinate the power distribution between the wind turbine and the energy storage. The simulation results show that the proposed method can effectively raise the lowest frequency, restrain the secondary frequency drop, recover rotor speed smoothly and enhance the reliability of system operation.