Study On The Control Technology Of LCL Grid-connected Inverter Under Non-ideal Power Grid

With the global energy crisis and environmental destruction becoming increasingly prominent,it is imperative to vigorously develop clean energy and promote the development of new energy power generation systems.Grid-connected inverters play an important role in connecting primary energy to large power grids.It is an important part of the new energy power generation system,and its performance directly affects the power quality of the grid.In China,clean energy such as wind energy and photovoltaic are mainly distributed in northern Hebei,Inner Mongolia and northwestern China.These remote areas are rich in clean energy,but the grid is generally fragile.Therefore,this paper conducts in-depth research on the optimal control of LCL grid-connected inverters under non-ideal grid conditions.The paper first analyzes the topology of the inverter.In the balanced state of the power grid,detailed analysis of the mathematical model of the inverter in different coordinate systems.Then introduced the grid voltage vector under different conditions,and pointed out that the phase locked loop is an important part of the grid-connected inverter.Whether the phase-locked loop accurately captures the phase directly affects the grid connection quality.Under grid balance conditions,grid synchronization is relatively simple.However,power grids in remote areas of China are relatively fragile,and imbalances and distortions will occur.In the non-ideal operating state of the power grid,the pre-stage of the phase-locked loop needs to add a filtering link.This paper uses a phase-locking strategy based on the decoupling of complex filter matrices.This method can accurately and quickly extract the positive and negative sequence components of the fundamental wave of the grid voltage in a synchronous rotating coordinate system.Then,the mathematical model of the inverter under the imbalanced state of the power grid and the traditional output current command calculation are analyzed in detail.In order to achieve constant DC-side voltage,constant output instantaneous power,and three-phase current balance,thereby maintaining the goal of power quality.Aiming at the positive and negative sequence current amplitude and phase information,according to the grid-side and converter-side instantaneous power models,a multi-targeted imbalance control strategy is proposed.Based on the traditional grid-connected control,this strategy only introduces negative sequence compensation current,and realizes the conversion of different control targets by adjusting the value of k.Finally,MATLAB simulation analysis of the proposed method.An experimental prototype was set up for experimental verification.Simulation and experimental results show the correctness of the theoretical analysis.There are 43 figures,3 tables and 76 references in this paper.