Research On Transient Stability Enhancement For Wind Farm Combined With SMES Integrated To Multi-machine System

With the increasing capacity of wind power generation units and the increasing proportion of wind power in the system,the grid-connected operation of wind farms puts forward higher requirements for the safe and stable operation of the grid.When short-circuit faults occur in power grid,the output characteristics of the grid-connected point of the fan will also participate in the restoration process of the grid,which will have a certain impact on the transient power angle stability of the system.Rational use of the compensation device equipped with the grid-connected point of the doubly-fed fan(DFIG)to improve the output power of the grid-connected point can effectively improve the transient power angle stability of the system with the fan,while the superconducting energy storage device(SMES)can effectively improve the transient power angle stability of In recent years,it has been widely used in power grid because of its flexible four-quadrant regulation ability and fast responsiveness.Therefore,it is significant to study how to improve the transient stability of multi-machine systems with wind power by using SMES.Based on the topology and operation principle of the doubly fed induction generator,this paper first analyzes the influence of the doubly fed induction generator(DFIG)on the transient power angle stability of the system,and then uses the DFIG equivalent admittance model to modify the nodal admittance matrix of the system,and further deduces the equivalent mechanical power variation and DFIG access location information and DFIG power external characteristics during the system power angle change.Relevance relationship.On this basis,the increasing and decreasing range of equivalent mechanical power is determined by using the zero points of position parameters obtained in advance offline calculation.By analyzing the influence of the increasing and decreasing nature of equivalent mechanical power on the power angle of the system,a comprehensive control strategy of combining SMES to improve the transient power angle stability of multi-generator system with wind power is proposed,which makes full use of the flexibility of SMES.Four-quadrant regulation ability and fast responsiveness can improve the active and reactive power of the grid-connected point of doubly-fed fan during transient period,increase the deceleration area of the system,reduce the acceleration area of the system,and achieve the purpose of improving the transient power angle stability of the system.The MATLAB simulation model of the fan-superconducting energy storage device is built.The simulation results show that the proposed method is superior to the traditional method which only increases or decreases the power angle.Considering the similarity of the structure of doubly-fed fan and converter of superconducting energy storage device,a doubly-fed fan power generation system based on SMES voltage source converter is proposed in this paper.This method can suppress the power fluctuation of DFIG in steady state,absorb unbalanced energy between stator and rotor of doubly-fed fan by superconducting magnet during transient period,maintain the voltage stability of DC bus,make DFIG input and output power to the system according to demand during fault period,and effectively improve the transient stability of the system.Finally,the effectiveness of the proposed system is verified by simulation analysis.