Stability Analysis Of Renewable-energy Grid-Connected Converter In DC-Link Voltage Time Scale

In order to deal with the problems of energy consumption and environmental protection,the renewable energy generation is developing quickly in China.However,the renewable energy generation in China presents the characteristics of long-distance,large-scale and high concentration,which makes renewable energy generation equipment in local areas replace the traditional synchronous machine as the leading power source,while the more complex characteristics of power electronic equipment bring new challenges to the stable operation of the power system.Grid-connected converter plays an important role in the renewable energy generation as an energy transmission device,and the dynamic behavior of the renewable energy grid-connected converter occurs in the process of converting the DC-side power to the AC-side power and delivering it to the power grid.The disturbance of the system will cause the imbalance of the input and output power of the renewable energy grid-connected converter,and the state of the energy storage element and the controller will change.In above dynamic process,the convergence of the state of the energy storage element and the state of the controller determines the stability of the renewable energy grid-connected converter.Considering the dynamic relationship between unbalanced power and DC-link voltage time scale of new energy grid connected converter,this paper focuses on the static stability and transient stability of renewable energy grid-connected converter in the DC-link voltage time scale,and initially gives the relevant stability theory and analysis method.The specific contents are as follows(1)Based on the typical control strategy of the grid-connected converter,the output power characteristic curve of the AC-side of the renewable energy grid-connected converter is analyzed and the DC-link voltage time scale mathematical model which can describe its power transmission mechanism is established.On this basis,the transmission power limit problem of the renewable energy grid-connected converter under the condition of weak grid is proposed,the static stability of the system and the factors affecting the static stability of the system are studied,and the corresponding stability criterion and static stability margin are proposed.Finally,the theoretical analysis is verified on RT-LAB platform.(2)Considering the influence of the output reactive power of the grid-connected converter on the static stability,this paper analyzes the influence of two different reactive current control strategies on the static stability of the system.This paper reveals the changing trend of the static stability of the grid-connected converter under different reactive current control strategies,and points out that the appropriate reactive power compensation can improve the static stability of the system under the weak grid.And then,the stability is verified by MATLAB simulation.(3)Without considering the switching of control strategy in grid-connected converter,the transient stability of the system under DC-side input power disturbance and remote grid voltage sag is studied.According to the different disturbance scenarios,the change of system operation point and the dynamic behavior of its transient process are analyzed.At the same time,the difference with synchronous machine is compared,and the transient stability limit of the system is given.In addition,based on equal area rule and phase plane analysis method,the transient stability judgment method of grid connected converter is given in this paper.Finally,the theoretical analysis is verified on MATLAB simulation.