| In the face of the increasing global energy demand and the challenge of environmental pollution,more and more renewable energy has been put into use and developed rapidly in the form of distributed generation.Although distributed generation improves the absorptive capacity of renewable energy and has sufficient flexibility,its characteristics of low inertia and weak damping also bring many adverse effects to the power system.Virtual Synchronous Generator(VSG)technology realizes the complete imitation of the working principle of synchronous generator,and improves the shortcomings of low inertia and weak damping of distributed generation.The problem of frequency and voltage deviation caused by load changes during VSG off grid operation is very important to study the frequency and voltage control during off grid operation;It is necessary to study the pre-synchronization control technology in VSG,which may cause excessive surge current during offline switching;The issue of co frequency resonance during VSG grid connection operation also urgently needs to be addressed.The research content of this article on virtual synchronous generator control is as follows:(1)In order to better simulate the working performance of synchronous generators,a mathematical model of the synchronous generator is established and its mechanical and electrical equations are analyzed.The basic principles of VSG control are obtained through analogy.Based on this,the active frequency controller and reactive voltage controller of VSG are designed,and a voltage current dual closed-loop control inverter bottom control strategy is designed by combining the mathematical model of the threephase inverter.A small signal analysis was conducted on the VSG power control loop,and a tuning method for the moment of inertia and damping coefficient was obtained.At the same time,the impact of the two on the system output performance was analyzed.Finally,the designed VSG control strategy was analyzed and validated using Matlab/Simulink simulation and dSPACE semi physical simulation experiments.(2)In order to improve the output performance of VSG in off grid working mode,the voltage regulation and frequency modulation characteristics of VSG in off grid working mode were analyzed,and improvements were made to address the issue of frequency and voltage deviation.A secondary frequency regulation and voltage regulation control strategy was designed.In response to the problem that traditional control methods cannot meet the smooth switching of inverter parallel and off grid modes,a parallel and off grid switching scheme based on VSG control is proposed,and the pre synchronization control method is improved to enable the frequency,phase,and amplitude of VSG output voltage to quickly track the grid voltage,reduce the impact current during grid connection,and achieve a smooth transition during parallel and off grid mode switching.Finally,the correctness of the proposed control scheme was verified through Matlab/Simulink simulation and dSPACE semi physical simulation experiments.(3)A cross feedforward compensation control strategy was designed to suppress co frequency resonance in response to potential power oscillation issues during VSG grid connection operation.Established a VSG grid connected power transmission model,revealing the synchronous frequency oscillation mechanism of VSG grid connected power.The influence of this resonance phenomenon on system stability was analyzed in the complex frequency domain,and the influence of power coupling on the same frequency resonance problem was further studied.Propose a cross feedforward compensation control strategy that not only eliminates the coupling between active and reactive power,but also eliminates the conjugate poles that cause resonance in the same frequency,fundamentally suppressing the resonance problem of grid connected power in the same frequency.Finally,the superiority of the proposed cross feedforward compensation control strategy was demonstrated through Matlab/Simulink simulation and dSPACE semi physical simulation experiments.There are 85 figures,6 tables and 63 references in this thesis. |
PDF Full Text Request