Research On Suppressing Strategies Of Sub-synchronous Oscillation With DFIG-Based Wind Farms

The large-scale application of wind power is an important symbol of progressing and developing modern power system.Nowadays,with the rapid expansion of China's wind power industry,the problems of wind power connecting to grid become more and more prominent.In order to solve the inverse distribution pattern of wind power endowment and load demands,a large number of flexible regulating devices based on power electronic technology has been adopted,including series compensation equipment which can improve the capacity of transmission lines and enhance the system stability.Doubly-fed induction generator wind farm connecting to grid via series compensation equipment can induce sub-synchronous oscillation.So the research of sub-synchronous oscillation containing DFIG-based wind farm has important practical significance in engineering.First of all,through the basic theory of sub-synchronous oscillation in power system,this paper introduces the related terms and definitions,then puts emphasis on analyzing the elements caused sub-synchronous oscillation and mechanism of action.According to different emphasis of the usages and analysis results,this paper discusses some normal methods and effective strategy of depression.According to the research object and the modified IEEE first benchmark,the mathematical models of wind turbine,doubly-fed induction generator,converter and transmission line with series compensation are studied comprehensively.This paper forms the systematical state equations and establishes the linearized small-signal model further.Based on small signal stability method,the model eigenvalues can be calculated by the system characteristic matrix.The analysis results show that the main factor affecting the sub-synchronous oscillation is series compensation.This paper adopts complex torque coefficient method to analysis the change of electrical damping characteristics.This paper introduces the basic operation principle and the mechanism of depressing sub-synchronous oscillation.The simulation results show that the strategy of subsynchronous damping controller can depress the sub-synchronous oscillation with DFIG effectively.