Research On Improved VSG Control Strategy For Low Voltage Micro-grid

With the intensification of the world’s energy crisis and the increasingly prominent environmental problems,the penetration rate of renewable energy such as solar and wind energy is constantly increasing,and the resulting power system stability issues have become the focus of attention.As an important interface between distributed energy and power systems,micro-grid inverters have problems such as lack of moment of inertia,difficulty in precise control of voltage and frequency,and difficulty in grid connection.The Virtual Synchronous Generator(VSG)control technology is proposed,which solves the problems of the lack of moment of inertia and damping of the micro-grid inverter,improves the control accuracy and frequency stability of the system,and has broad application prospects.Aiming at the synchronous resonance phenomenon and equivalent negative damping effect in the decoupling strategy of the virtual synchronous generator control system of the low-voltage micro-grid,this paper explores the improved control strategies of VSG of the low-voltage micro-grid by analyzing the power coupling mechanism and the equivalent negative damping mechanism of the system.The main research work and research results obtained in this thesis are summarized as follows:1.Analyzed the structural characteristics of the low-voltage micro-grid,and took the micro-grid inverter as the research object,and constructed a low-voltage micro-grid VSG control system composed of modules such as active-frequency control,reactive-voltage control,VSG control,and virtual impedance.The inverter was made to simulate the characteristics of the moment of inertia and damping of the synchronous generator,the mathematical model of the VSG was established,and the setting of the key parameters of the system and its influence on the stability of the system were analyzed.2.The generation mechanism of VSG’s synchronous resonance is studied and the influence of system resistance characteristics on synchronous resonance is analyzed.After that the approximate calculation of resonance peak is used to characterize the degree of synchronous resonance and the power coupling mechanism of low-voltage micro-grid VSG is studied.Furthermore,the virtual impedance decoupling strategy is introduced,and the influence of synchronous resonance on virtual impedance configuration is studied.At last,a virtual impedance configuration method considering synchronous resonance is proposed.3.The generation mechanism and adverse effects of the negative damping effect of the VSG system of the low-voltage micro-grid are studied.By analyzing the contradiction between the equivalent negative damping effect and the decoupling control strategy,an improved VSG control strategy based on the adaptive damping compensation method is proposed.Optimized the design of the corresponding adaptive damping compensation module based on this compensation method,and analyzed the stability of the system based on this control strategy.4.Based on the MATLAB / Simulink simulation platform,a large number of simulation experiments are carried out on the VSG control strategy and the proposed virtual impedance configuration method.The results verify the effectiveness of the VSG control strategy and the proposed virtual impedance configuration method.Comparing the results of the improved VSG control strategy with the traditional VSG control method and the virtual impedance compensation method,it shows that the system based on this control strategy has stronger stability and faster response speed,which further verifies the effectiveness of the control strategy,and also shows its superiority.