| The main types of fans in the wind power market are mainly divided into two categories:constant speed else constant frequency fans and variable speed else constant frequency fans.Cage asynchronous fans and double-fed fans are widely used as representative models of the two fans.For cage-type wind turbines,large-scale wind turbine integration will absorb a large amount of reactive power from the power grid for excitation,and the switching of the wind field will cause voltage dips,voltage flicker and even voltage collapse.Because the direct connection of the stator side of the double-fed fan to the grid,the sensitivity is high.When the system fails,it will run off the grid and cause a transient impact on the grid voltage.In view of the above problems,by using SVG+FC reactive power compensation method with the goal of achieving the optimization of both the compensation effect and economy in this thesis.For cage wind farm grid connection,it takes the cage wind farm into a 10 k V grid under different wind speeds as a research background in this thesis,while ensuring the compensation amount,the grid connection point voltage is stabilized at 10 k V as the control target,and the voltage dropping through signal acquisition is converted into reactive power demand by PI controller,and the best compensation strategy is selected by itself through interval detection.The fixed compensation is carried out through FC.At the same time,under-compensation or over-compensation will be solved by SVG,continuous adjustable compensation is made to ensure that the voltage of the grid connection point is stable and the wind farm meets the grid connection conditions.Researching on the transient faults of the system,the external voltage is increased by SVG + FC equipment to stabilize the reactive power exchange between the cage wind farm and the system,and it can prevent the voltage dropping in greatest ability.For doubly-fed wind farms,a doubly-fed wind system based on Crowbar protection circuit was built,and its transient characteristics during grid faults were studied.Because the instantaneous voltage is decreased during system failure,the doubly-fed fan needs to ensure that it does not operate off-grid within 0.625 s.It can increase the grid-connected electrical voltage from the outside through SVG+FC to suppress the surge current on the rotor side and stabilize the capacitor voltage on the DC side,and improve the low-feeding characteristics of doubly-fed wind turbines and protect the doubly-fed wind energy from off-grid operation.Through theoretical analysis and simulation experiments,the compensation effect of the SVG + FC compensation device is fully verified.Through the construction of PSCAD/EMTDC model and the analysis of simulation results,the results show that: when SVG+FC is connected to the grid,the voltage of the grid connection point is stabilized at 10 k V when the cage wind farm is connected to the grid,and it can choose the best way for different wind speeds.The compensation method of the double-fed fan is significantly improved after the compensation,and the current on the rotor side is also stable within a reasonable range due to the Crowbar protection circuit.With the fault removal,SVG+FC will have a small fluctuation during the removal,and then returned to normal working condition quickly. |
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