The Research On Low Voltage Ride Through Control Strategies Of Double Fed Induction Wind Generators

Energy is an important material foundation of human society’s survival and development, especially renewable energy: wind power. The global wind farm located in remote area intensively, and power grid is easy to fault. When serious grid voltage happens, that will lead to further paralysis of the grid, leading to make large scale wind generator trip. In order to guarantee the stability of power grid safe operation, foreign and Chinese wind power grid code clearly shows that grid-connected wind generator must have Low Voltage Ride Through ability. So currently the LVRT research on large-scale grid connected DFIG has important theoretical and practical significance.Firstly paper summarizes the global energy and environmental crisis, and the necessity of development of wind power, and introduces the research status of LVRT at home and abroad and introduces the research status and the control strategy of the low pressure through problems, analyzed the superiority and inferiority from existing various kinds of control strategies.Secondly introduces the common wind power fault briefly, and obtained transient fault response of DFIG by theoretical analysis and formula deduction under various wind power failure, then concludes that the optimization control goal of DFIG in the power grid failure, that provides theory basis for the research and design of following chapters.Thirdly build model of DFIG system, including wind turbines and doubly-fed induction generator, with analysis of mathematical model and traditional control strategy of DFIG system. Then obtained transient fault response by theoretical analysis and formula deduction under symmetric and asymmetric grid failure. When symmetrical grid voltage fault occurs, even three-phase short circuit, LVRT can be completed by synthesis method, improving control method; When asymmetry grid voltage drop, Specifically, uses the rotor side and the grid side converter proportional integral resonant(PIR) controller to simplify the traditional low voltage ride through control structures; what’s more adjusting the amount of feedforward through the introduction of two adjustable parameters to achieve multi-objective optimization control of DFIG during asymmetric grid voltage dip, not to achieve the floating control of certain index, but to complete the coordination of multi-objective optimization control of LVRT by changing the quantities of feedforward control signal to change the control objectives. On the basis of carefully researching the model on PSCAD, when the grid voltage asymmetric dip, the simulation results show that the multi-objective optimization control strategies can effectively help DFIG provide LVRT capability. From perspective of practice, the basic control theory and key technology of DFIG under symmetric and asymmetric fault, and make effective theoretical analysis, formula deduction and simulation verification, realizing the comprehensive study of theory and practice.