Research On The Control Of LLCL Filtered Grid-connected Inverter Under PFI Control

In the 21 st century,with the continuous depletion of traditional fossil energy and the negative impact on the ecological environment,people's demand for new energy generation becomes more and more urgent.Among them,grid-connected inverters are the interface devices between new energy generation and traditional large-scale power grids.It is crucial to use new energy generation methods to improve the performance of grid-connected inverters.This paper divides the grid-connected inverter into two parts,the inverting part and the filtering part.On the basis of reading a large number of documents,this article does an in-depth study from these two links so that the grid-connected inverter can operate stably and output high-quality electric energy.The inverting link mainly involves the role of the control strategy on the grid-connected inverter.The filter link mainly involves the suppression of harmonics in the grid-connected current by the filter structure.This paper lists three common control strategies,including PI control,PR control,and RC control.Analyze the shortcomings of its application in grid-connected inverters,and briefly analyze the three filter structures commonly used in grid-connected inverters,including L-type,LC-type,and LCL-type filtering effects,and indicate their respective applications..Through modeling,the root cause of the steady-state error of the output current tracking grid voltage is demonstrated.On this basis,the PFI control is introduced.The analysis of the transfer function shows that the PFI control can achieve zero steady-state error control and can improve the grid voltage versus output current.Impact.At the same time,the LLCL filter structure is introduced on this basis.After analysis and comparison,the filtering effect is better,especially for the harmonics at the switching frequency,and the parameter design method of the LLCL filter structure is introduced.The PFI control strategy is combined with the LLCL filter structure to control the grid-connected inverter to form a closed-loop feedback.However,the introduction of the LLCL structure causes the system to have a resonant peak,and the active damping method is added to suppress it,and eventually a double currentclosed-loop control is formed.In order to further reduce the interference of the grid voltage on the inversion process,the grid voltage feedforward control strategy is introduced to effectively reduce the distortion rate of the grid-connected current.Finally,a 10 KW prototype was built on the Matlab/Simulink simulation platform to verify the simulation results.The grid-connected current waveform and related data were obtained.The results showed that the grid-connected current quickly entered the steady state.The indicators met the technical standards and verified the proposed strategy.The correctness.