Research On Modeling And Control Strategy Of Single Phase Grid Connected Inverter In Low Voltage Distribution Network

With the increasing proportion of new energy power generation and grid connection in the energy structure,grid-connected inverters serve as an important bridge connecting new energy power generation and the grid,and their performance largely determines the quality of grid-connected power.Renewable energy power generation is random,intermittent,and the use of a large number of non-linear power electronic devices will bring complex harmonic problems to the power grid.In this paper,a mathematical model is established for the single-phase LC grid-connected inverter topology,and the improved quasi-proportional resonance control strategy,the fractional-order proportional-integral double-loop control strategy,and the repetitive-proportional control strategy are studied,and the control is verified through simulation and experiments.The effectiveness of the strategy.The specific research content includes:(1)The research background of single-phase grid-connected inverters is explained,and it is clear that reducing the harmonic content of grid-connected inverters,improving the quality of grid-connecting,and improving the performance of inverters mainly include research on new and high-efficiency power electronic devices and improvement of circuit topology.Propose two more perfect control strategies.Then the research status of power electronic devices at home and abroad is analyzed,the advantages and disadvantages of the current mainstream control strategies are compared,and the fractional-order control is introduced;(2)The main circuit topology studied in this paper is introduced,and its working modes are analyzed in detail.For each working mode,a single-phase inverter is established using the state space averaging method and the static operating point small signal method.The fractional-order mathematical model gives the small signal model of the unipolar frequency-doubled SPWM modulator,and obtains the transfer function from the duty cycle to the output voltage and output current.And compared with the integer-order mathematical model;(3)Aiming at the problems that PI control cannot realize the tracking of AC signals without static error and the PR control bandwidth is too narrow,a dual-loop control algorithm based on Quasi-PR is proposed.The outer loop uses PI to control the DC side bus voltage to achieve no static error tracking of the DC voltage and improve the steady-state performance of the system;the inner loop uses Quasi-PR to control the grid-connected current,reduce the harmonic content of the grid-connected current,and pass The voltage feed-forward method offsets the influence of the output voltage on the current loop;a phase-locked loop loop is designed to synchronize the grid-connected voltage and current.A related model was established in the PSIM simulation platform to verify the correctness of the control strategy;(4)The parameter design and calculation process of the LC filter are given,and the double-loop control strategy of Q-PR and PI~αD~βis designed by using the fractional-order transfer function obtained by the fractional-order small-signal model.In order to improve the fitting accuracy of the fractional differential operator,the improved Oustaloup filter is used to perform the fitting of the fractional calculus operator,which improves the accuracy of the fitting frequency band boundary.A simulation model was built in Matlab/Simulink,and external interference was designed to test and verify the robustness and dynamic characteristics of the control system;(5)Aiming at the slow dynamic response of repetitive control,a repetitive-proportional control control strategy is proposed to obtain better steady-state performance and improve the suppression of harmonics.It is verified by simulation that the strategy can quickly adjust and recover on the basis of ensuring the sine waveform when encountering grid voltage fluctuations and current sudden changes,and has good dynamic performance;(6)The composition structure of the experimental platform is introduced.The experimental platform based on PSIM simulation software and DSP28335 is used to verify the designed improved quasi-proportional resonance double closed-loop control strategy.