Research On Low Voltage Ride Through Capability Of Energy Storage Type Wind Farm

With the rapid development of wind power industry, the proportion of wind power in the power system is increasing year by year, large-scale wind power has an impact on the stability of power grid and the power sector has put forward higher requirements on low voltage ride-through capability of wind turbines. Therefore, the research on low voltage operation capacity of the wind turbine is very necessary and meaningful. Meanwhile, in recent years, in one way, with the rapid development of power electronic technology, various performance indexes for an energy storage device such as the response speed, the capacity have made great progress, resulting the properties of energy storage device gets significant improvements. In another way, the development of intelligent control theory makes the control of energy storage device easier and more flexible and the application field of energy storage device becomes more widely. At present, as the finite technology of wind turbine, applying energy storage system to improve the LVRT character of grid-connected wind farm will on study in this paper with both the theoretical and simulation method.Firstly, the development condition of wind power and the low voltage ride through capability of wind turbines on domestic and overseas are stated, meanwhile, the prospective of wind power generation and the problem of wind energy generation in our country is also introduced. Besides, the availability of applying energy storage system to wind turbines is also analyzed.Secondly, the basic working theory of doubly-fed induction generator(DFIG) is analyzed. The mathematic model mainly contains wind turbine, generator, etc and the dynamic response characteristics of stator, rotor current is introduced when grid voltage sags. The control strategy of reactive power is also explained in this section.Besides, the feedback control system of battery energy storage system which is based on the phase current is established. For the mathematical model of the battery energy storage system has complex nonlinear, time-varying parameters, the common PI control method being difficult to achieve high precision, fuzzy theory is introduced and it can be used to adjust its main control parameters Kp, Ki online. At the same time, the design of the control system is proposed.In the end, the low voltage ride through capability of energy storage type wind farm is tested and three kinds of grid voltage drop sag were analyzed by digital simulation in the environment of MATLAB/SIMULINK, the simulation result proves that the battery energy storage system which is based on the Fuzzy- PI control strategy can make a good compensation for the grid voltage sag, provide support for the grid, improve low voltage ride through capability of wind farm, ensure a safe and stable operation for grid.