Research On Field-Grid Voltage Coordinated Control Theory For Grid Connection Of Doubly-Fed Induction Wind Farm

Recently,as an important form of renewable energy-the use of wind power has developed rapidly.The penetration rate of wind in power grid keeps increasing around the world.However,due to the randomness and intermittency of wind energy,high penetration level of wind power connected to the grid brings a big challenge to the stable operation of the power system.When the grid failure occurs,the voltage on the point of common coupling jumps sharply.The main reason for this situation is the lack of fast reactive power regulation ability provided by the wind power generators in the wind farm.Under severe situations,it may lead to the occurrence of grid voltage failure.Therefore,strict wind power grid connection standards and specifications have been issues in different counties,requiring wind farms to provide quick reactive power during the voltage fluctuation caused by grid failures,enhancing the voltage fault crossing capability of wind farms.Doubly-fed induction generator(DFIG),as one of the most commonly used wind generators,has attracted a lot of efforts on its voltage stability control when it is connected to the power grid.However there is little mention on how to determine the control target values of reactive power generation.To obtain the relationship between wind turbine generation and grid voltage is an important foundation to realize the support from doubly-fed induction generator to the grid voltage.Voltage-power sensitivity matrix is used to express the relationship between the power change by double-fed induction generator and voltage change of the grid,which transforms the complex nonlinear optimization problem into a linear optimization problem.The simplified problem can be solved quickly and accurately to meet the needs of practical engineering application.The higher precision of the sensitivity matrix estimation is,the more accurate the control of the voltage out-of-limit behavior will be.Therefore,the accuracy and timeliness of the voltage-sensitivity calculation is the key to realize the doubly-fed induction wind generator’s support to the grid voltage.In practical engineering,due to the defects such as inaccurate component parameters and not timely update of information,the traditional calculation of voltage-power sensitivity matrix usually has a large calculation error.Therefore,to address this problem,this paper proposes a method to estimate the voltage-power sensitivity in real time by using the recursive least square method,and then to calculate the target value of wind power generation accurately.In order to solve the problem of widely geographical distribution of wind farm and high communication cost,the proposed method is further expanded into a distributed deployment method.The entire effect of other zones is lumped as a single node and then estimated by the local information.This proposed algorithm is proved to control the voltage precisely and efficiently over the simulation by Open DSS and MATLAB.