Abstract
In order to solve the problems of large capacity and frequent charging and discharging of energy storage unit during low voltage traversal of energy storage assisted direct-driven wind turbine, a coordinated control method of wind turbine side, grid side and energy storage side is proposed. Firstly, the mechanism of dc voltage spike caused by voltage sag is analyzed, and the relationship between dc power and ac voltage under fault is deduced, and the coordinated control mechanism is established. Secondly, with the goal of effectively reducing the capacity of flywheel energy storage unit and the frequency of charge and discharge action, three kinds of faults are divided into mild, moderate and severe faults according to the voltage drop degree of power grid. The control modes of wind turbine side, grid side and energy storage side under different faults are analyzed, and a coordinated control strategy among the three is established. Under the premise of low flywheel energy storage capacity, low voltage ride through with different voltage drop depths can be realized, and the charge and discharge times of flywheel energy storage unit can be effectively reduced according to the voltage drop degree of the power grid. The system simulation model is established by using PSCAD/EMTDC, and the simulation results prove that the proposed coordination control strategy is correct and effective.