Research On Modeling And Parameter Tuning Of Grid-connected Inverter Based On Virtual Synchronous Control

With the development of wind and light energy in recent years,the photovoltaic power generation system with large-scale grid-connected inverters as the hub has begun to be integrated into the large grid,which has led to a higher proportion of new energy power generation units in the large grid and began to threaten the dominance of traditional synchronous generators.Affected by the rising penetration rate of new energy,the inertia capacity of the power grid has been greatly weakened,which has led to many safety and stability accidents caused by insufficient system inertia capacity.Therefore,The virtual inertia control represented by the virtual synchronous generator(Virtual Synchronous Generator,VSG)has gradually become research focus in recent years.At the same time,new energy grid-connected standards have evolved from only requiring to participate in power compensation to requiring additional inertia capabilities.First,the model of three-phase voltage-type inverter system is established and the governing equations of voltage loop and current loop are derived.Based on this,the PI controller parameters of voltage loop and current loop are designed.Through the comparative analysis of several typical VSG control structures,a VSG model without damping link is established.This model eliminates the damping link in the traditional model by equivalentizing the damping link and the frequency modulation link without phase lock loop.Based on a good design of the voltage and current loop parameters,the capacitor voltage can track the reference value of the voltage loop without any static error,so that the model can avoid using phase-locked loop to obtain relevant feedback signals.Then,Small signal mathematical model of VSG system is established.Approximate decoupling analysis is performed on the active and reactive loops and the conditions required for decoupling are given.Based on the premise of decoupling,transient and steady-state performance constraints are imposed on the active and reactive loops,so that the relevant parametersmeet the design requirements and the parameter selection range is given.The frequency domain analysis method is used to analyze the influence of active loop parameters on system performance.A simple and feasible pre-synchronization method is given for grid-connected operation of VSG system.By making the amplitude,angular frequency,and phase of the voltage phasors on both sides of the grid-connected switch synchronized,the requirements for smooth transition are achieved.However,this method still needs to use phase-locked loop to obtain grid voltage information.Finally,based on MATLAB/Simulink and dSPACE hardware-in-the-loop simulation platform,the above control strategies were simulated and experimentally verified.The simulation and experimental results prove the effectiveness and feasibility of the proposed control strategy.