Influence Of Grid-connected Direct-drive Wind Farm On Power System Voltage Stability

In recent years,the rapid development of wind power generation,direct drive fan through the rotor field oriented vector control technology,to achieve the generator active power and reactive power independent decoupling control,and through the grid voltage oriented vector control technology,to achieve the active power and reactive power independent decoupling control between the grid side converter and the grid.Therefore,there are more and more direct drive wind farms connected to the grid,and the large-scale access of wind farms will have a significant impact on the voltage stability of the grid.This paper takes the system with large-scale direct drive fan as the research object,and studies the influence of large-scale direct drive fan on the system voltage stability from the static and transient perspectives.An equivalent model of direct drive wind farm is established for static and transient voltage stability analysis.If the static voltage and transient voltage stability of power system including direct drive wind farm are studied,and the response characteristics of all components and control system of direct drive wind farm are fully considered,a very complex process analysis problem will be generated,and the difficulty will become greater.Because the research of direct drive wind farm mainly focuses on the static and transient voltage response of the grid side of direct drive wind turbine,only the grid side response and its determinants are simulated in the modeling of direct drive wind turbine,thus the simplified modeling method of direct drive wind turbine is obtained.According to the working principle and control strategy of direct drive fan,the equivalent model of equivalent unit is established.This paper takes the extended single machine infinite bus system with direct drive wind turbine as an example,analyzes the equivalent model of the system with direct drive wind turbine by two kinds of static power flow calculation methods,and deduces the analytical formula of the bus voltage of the parallel network of the system after the wind power is connected.In BPA,the simulation models of the extended single machine infinite bus system with direct drive wind turbine and the actual grid system are established respectively,and the theoretical calculation results and simulation test results are compared.In this paper,continuous power flow method is used to analyze the influence of the factors such as the permeability of wind power,the position of wind turbine connected to grid,the proportion of load connected and the position of load connected on the static voltage stability of power system under different control modes.Taking the extended single machine infinite bus system with direct drive wind turbine as an example,the equivalent model of the system with direct drive wind turbine is analyzed by ward equivalent calculation method,and the analytical formula of the bus voltage at the parallel point of the system during the symmetrical fault period after the wind power is connected is deduced.In BPA,the simulation models of the extended single machine infinite bus system with direct drive wind turbine and the actual power grid system are established,and the theoretical calculation results and simulation experimental results are compared.The dynamic time-domain simulation method is used to analyze the influence of the bus voltage of the parallel network on the transient voltage stability of the system,such as the permeability of wind power,the position of the grid connected fan,the proportion of load access,the position of load access and the position of short-circuit fault.