Research On The Influence Of Low Voltage Ride-through Capability Of Doubly-fed Fan On System Transient Power Angle Stability

As the installed capacity of the power system continues to increase and clean energy such as wind power is continuously connected to the grid,the wind power generation characteristics are different from conventional energy which makes the structure of connecting grid more complicated,the power transmission between regions changes and the system transient stability problem is facing more challenges.In order to ensure the safe and stable operation of the system,it is particularly important to perform transient stability analysis on the power system which connected with clean energy such as wind power.In this paper,based on the consideration of the low voltage ride through capability of doubly-fed induction generator,a transient power angle stability analysis is conducted around a clean energy power system with centralized doubly-fed induction generator integrated access.Mainly carried out the following research work:First,the mathematical model and vector control strategy of doubly-fed induction generator are established to provide a theoretical basis for the construction of a detailed grid connection model of doubly-fed induction generator.Then,theoretically analyze the change trend of the fixed rotor flux,fixed rotor current and DC bus voltage of the doubly-fed induction generator during the voltage drop of the grid connection point of the doubly-fed induction generator and derive the expressions of the fixed-rotor flux and current.The problems of fixed rotor overcurrent and DC bus voltage fluctuations during the voltage drop of the network point are theoretically analyzed.The method of using stator series impedance and increasing DC capacitance to achieve low voltage ride through is designed.Aiming at the shortcomings of investing in hardware protection circuits,an improved integrated low voltage ride through strategy for doubly-fed induction generator is designed and a detailed grid-connected model of doubly-fed induction generator is built using PSCAD / EMTDC.The internal variable dynamic response process,the use of stator series impedance with increased DC capacitance capacity and the use of the improved doubly-fed induction generator integrated low voltage ride through strategy to improve the stator and rotor overcurrent and DC bus voltage fluctuations during low voltage ride through were verified by simulation.Finally,it points out the way in which the doubly-fed induction generator access affects the system transient power angle stability.The active and reactive power information of the doubly-fed induction generator is equivalent to ground admittance.Due to the influence of power angle mutual synchronization,different low voltage ride through measures are adopted to make the external characteristics of the doubly-fed induction generator different.Study the different dynamic response processes of the doubly-fed induction generator under different low voltage ride through measures to stabilize the system transient power angle and the effects of the internal dynamics caused by the different low voltage ride through capability of the doubly-fed blower on the transient power angle stability of the multi-machine system are simulated and analyzed.It is pointed out that the doubly-fed induction generator with low voltage ride through capability is more conducive to the system's transient power angle stability than the doubly-fed induction generator without low voltage ride through capability.At the same time,the integrated low voltage ride through strategy of the doubly-fed induction generator designed in this paper is more conducive to the stability of the system's transient power angle than the low voltage ride through strategy of other hardware circuits.This study is of great significance to the stable operation and control of power systems with centralized doubly-fed wind power integration.