Research On Control Strategy And Small Signal Stability Analysis Of DC Microgrid In Island Operation

With the progress and development of society,more and more fields have a higher demand for electric energy,which has led to the gradual acceleration of the consumption of traditional fossil energy.In this context,the distributed generation technology based on renewable energy is widely valued by the state and relevant researchers,and then the concept of microgrid emerges.With the rapid development of DC distributed power generation technology,DC microgrid is expected to become an important framework for intelligent power distribution systems.When it is in island operation state,due to the lack of main power grid support and a large number of power electronic devices and constant power loads are connected internally,it brings greater challenges to the stability of the system.Based on the above background,this paper studies the coordinated control strategy of distributed microsources and the stability of the system in isolated DC microgrid.Droop control is a hotspot technology for realizing coordinated control between microsources in islanded DC microgrids.This paper analyzes the contradiction between power distribution accuracy and voltage adjustment of traditional droop control strategy,and proposes an improved droop control strategy based on power voltage double compensation.In the power compensation strategy,the output current of the microsources is distributed proportionally to their respective capacities through intercept compensation of the droop curve.Based on this,the droop coefficient compensation method is derived,and the same control effect can be achieved by adjusting the slope of the droop curve.In the bus voltage compensation strategy,the bus voltage and load power are shared among the micro sources,and the intercept of the droop curve of each microsource is adjusted to improve the steady-state operation performance of the system.Finally,the effectiveness of this control strategy is verified by Matlab/ Simulink simulation.In order to analyze the stability of DC microgrid under the improved droop control strategy,this paper establishes the mathematical models of parallel microsource and mixed load in turn,and then deduces the small signal model of microgrid system based on Lyapunov stability analysis theory.Then,with the help of the concept of eigenvalue sensitivity in the eigenmatrix,the influence of microsource droop coefficient,constant power load and power compensation controller parameters on system stability is analyzed by eigenvalue analysis method.Compared with the traditional droop control strategy,the improved droop control strategy can improve the small signal stability of the system.Finally,from the perspective of microsource converter control strategy,the parabolic droop control strategy is combined with sliding mode control strategy to reduce the adverse impact of constant power load on the system.The voltage and current double-loop control structure in the traditional droop control is replaced with a sliding mode control structure to enhance the robustness of the system.The bus voltage is linearized near the operating point,the stability of the system under sliding mode control is analyzed,and many factors affecting the stability of the system are obtained.The relationship between the proportion of constant power load allowed to be connected to the islanded DC microgrid and the sliding mode control parameters is emphatically discussed,and the simulation analysis is carried out.In conclusion,this paper proposes a droop control strategy based on power voltage double compensation,and analyzes the small signal stability of the system.Then,the sliding mode controller is designed by combining sliding mode control with droop control,and the factors affecting the stability of the microgrid are discussed in detail,which provides a scheme for the control and stability research of islanding DC microgrid.