Research On Control Strategy Of Single-phase LCL Grid-connected Inverter

As an important technology for grid-connected operation of distributed new energy,phase-locked loop must extract the fundamental wave signal of the grid quickly and accurately under various possible abnormal grid conditions and meet the dynamic and steady-state characteristics.For the grid-connected inverter itself,much attention has been paid to the selection of control strategies,which directly affects whether the grid-connected current can achieve zero steady-state error control and the dynamic and steady-state performance of the inverter system.In recent years,scholars have conducted extensive research on the phase-locked loop(PLL)of quadrature signal generation(QSG),including the second-order generalized integrator(SOGI).Because of its simple structure,it can eliminate the harmonic components in the input signal,which has become the most commonly used method in QSG.This paper first analyzes the structure and characteristics of SOGI-QSG's phase-locked loop.To address its limited ability to suppress grid harmonics,it is proposed to add a moving average filter(MAF)at the front end of the phase-locked loop input to smooth the In addition to the specific sub-grid harmonics in the input signal,at the same time,state feedback is introduced on the basis of the internal PI controller of the phase-locked loop,and the phase-locked loop is maintained with good dynamic performance through appropriate parameter configuration;Control and introduce PID controller to compensate the delay caused by MAF.Finally,build a prototype experiment platform,and verify the feasibility of the above method through simulation and experiment.The main work of this paper is as follows: First,focus on the current research r esults of single-phase PLL at home and abroad,analyze and summarize the advantages and disadvantages of various methods.Secondly,the single-phase LCL grid-connected inverter system is introduced,including the topology of the single-phase grid-connected inverter,the modulation method of the switch,and the selection of the inductance and capacitance components.Secondly,it introduces the structure of SOGI-QSG and analyzes its characteristics.Through simulation,it isverified that its ability to suppress the higher harmonics of the power grid is limited.Then,it is proposed that MAF-QSG can smoothly filter out specific harmonics in the input signal,and the state feedback is introduced inside the loop so that the dynamic performance of the system is not affected and the parameter design is given.Next,MAF is applied to the inverter control to filter out the specific higher harmonics in the feedback error signal.At the same time,the PID controller is intro duced to compensate the delay caused by MAF,and the design method of specific parameters is given.The hardware and software parts of the single-phase LCL grid-connected inverter system are designed again.Finally,by constructing a single-phase LCL grid-connected inverter experimental prototype,the SOGI-QSG and the ability of MAF-QSG to filter the higher harmonics of the power grid is verified first.The simulation waveform and THD analysis of the output signal of the inverter after individual PI control and MAF+PID composite control are also given.Finally,the simulation and experiment verify the grid connection of the single-phase grid-connected inverter under the three abnormal grid conditions of frequency fluctuation,higher harmonics and grid voltage sag,which further proves the feasibility of this study.