Study On Stability Analysis Of AC Microgrids In Island Mode

With the rapid growth of global social production and economic development,energy and environmental crises have become urgent problems to be solved.Microgrids,which rely mainly on new energy as their power source,have become one of the solutions to these problems due to their flexibility and cleanliness.However,because microgrids themselves are small in scale and lack grid rigidity,stability issues are prone to arise,especially when the microgrid system loses support from the public power grid during islanding operation.Therefore,the importance of stability analysis methods for islanded microgrids is increasingly prominent.This thesis focuses on a microgrid system with multiple inverters operating in island mode,and conducts research on key issues such as low-frequency stability,model reduction,and improving system antiinterference ability,with the aim of improving the level of stability analysis for islanded microgrids and enhancing power generation stability and quality.The inverter module is an important basic module of an islanded microgrid.This thesis first designs the filtering circuit parameters of the inverter unit and the parameters of the droop control strategy.Based on frequency domain analysis,the filtering circuit parameters are determined to verify the stability of the system under the designed control parameters.Finally,the feasibility of the designed parameters is verified through simulation,laying a theoretical foundation for system modeling and stability analysis.Next,the stability of a multiple inverter parallel islanded microgrid system is analyzed.The small signal full-order model of the microgrid system is established using a modular modeling method.Further,the eigenvalue method is used to analyze the stability problems of microgrids with different types of loads,clarifying the important characteristics of low-frequency oscillations and verifying the accuracy of the small signal model and the correctness of stability analysis,providing an important theoretical basis for model simplification and reduction.Then,based on singular regression theory and taking the distribution of participating factors as the main basis,this thesis proposes a singular regression reduction method for islanded microgrids modular modeling and establishes a new type of modularized islanded microgrids reduced-order model,including inverter module reduction and load module reduction.Compared with the traditional full-order model,the proposed singular regression reduced-order model of islanded microgrids,which considers pure resistive loads and constant power loads,can significantly reduce the model order while retaining low-frequency dynamics,improving the efficiency of model analysis.The correctness of the proposed reduced-order model is effectively verified through simulation and eigenvalue analysis.Finally,in order to address the low-frequency oscillation problem caused by the droop control and potential stability issues from other sources in the islanded microgrid,an improved droop strategy based on power system stabilizer(PSS)was studied to suppress the low-frequency oscillation of the system.An active disturbance rejection control(ADRC)algorithm was also studied and designed to suppress other stability problems such as load disturbances.The feasibility of the proposed improved algorithms was verified through simulations,providing a research foundation for system modeling and stability analysis.Through the construction of a hardware experimental platform based on inverter networking for islanded microgrids,this thesis verifies the correctness and effectiveness of the stability analysis conclusions and controller design.