Research on frequency control method for micro-grid with a hybrid approach of FFR-OPPT and pitch angle of wind turbine

Abstract

Micro-grid is the main application scenario of the renewable energy. When wind power serves as the dominant source of the micro-grid, the uncertainty of the wind energy caused by the climate makes the maintenance of the frequency stability of the micro-grid more complicated. Provided in this paper is a novel method to control the electrical output of WTG to maintain the frequency of the micro-grid close to its target. Firstly, a fast frequency response optimized power point tracking method (FFR-OPPT) is designed. The double excitation from the first-order and second-order derivative of the grid frequency can improve the speed of kinetic energy extraction of the wind turbine due to the increase of the virtual inertia time constant. Secondly, in order to enhance the service life of wind turbine, a hybrid control strategy of FFR-OPPT and pitch angle is proposed based on boundary analysis of the wind turbine. The control strategy can reduce the adjustment frequency and range of the pitch angle of wind turbine significantly. The proposed method is tested in a micro-grid combining by wind turbines and small thermal generations. The load frequency control in micro-grid is dominated by wind turbine and is assisted by thermal generation. The simulation results illustrate that the control strategy can control the frequency of micro-grid close to its schedule value effectively, accompanied by decrease of the frequency and range of pitch angle adjustment during control process.