Research And Design Of Single-phase Power-frequency Grid-connected Inverter

Inverter is the core device of sustainable energy generation and recycling of power,while almost all of the inverter is made up of analog circuit on the market at present, theparameters easily over time and temperature changes in drift, due to differences in eachdevices, analog circuits debugging separately, working too much, control system issingle and not easy upgrade, those are shortcomings of inverter is composed of analogcircuits, so digital inverter is a new development trend. This thesis rely on powerrecycling in lithium battery formation system, digitization of single-phasepower-frequency grid-connected inverter is researched and designed.Firstly, the grid-connected inverter input source and output control way areanalyzed, compared the characteristics of the isolated inverter and the non-isolatedinverter, aiming at the shortcomings of inverter is composed of analog circuits, designedby the digital signal processor TMS320F28335as control system. the DC voltage as theinput source, the inverter output current as feedback control quantity, the isolation ofsingle-phase power-frequency grid-connected inverter topology structure.Secondly, simulation the characteristics of the L, LC, LCL filter in MATLAB, theresults showed that the capacitive current closed-loop feedback of LCL filter can reducethe high harmonic content of the grid-connected current, small volume, comprehensiveperformance is best; In order to control the size and phase of grid-connected current, thegrid-connected current feedback form a closed loop to control, so eventually opted for agrid-connected current and capacitive current double closed loop feedbackgrid-connected current control strategy. TMS320F28335as the core controller design ofthe control grid-connected current size, DSP software phase lock, output of SPWMwave flow chart; and comparative analysis of the anti-islanding detection methods, thenput forward a kind of half cycle active frequency drift method. Established model of thesingle-phase power-frequency grid-connected inverter in Simulink, the simulationresults show that the design of the topological structure and grid-connected currentcontrol strategy is correct, also proved that the half cycle active frequency drift methodcan improve the quality of grid-connected current. On the basis of single-phase power-frequency grid-connected inverter topological structure, design hardware circuitof the main circuit and digital control system.Finally, a low-power single-phase power-frequency grid-connected inverter is setup. The measured abnormal simulation grid voltage or frequency response time of0.09s,inverter in the case of a purely resistive load output voltage and current for50HZsynchronization sine wave，the effective value of the output voltage is220V, the phasedifference of output current and the simulation grid for3°, the total harmonic distortionis3.6%. The experimental results meet the standard requirements of the country, it isprove that the theoretical research and design in the paper is correct and feasible. So theapplication of digital technology inverter will be more stable, convenient to change andupgrade, conducive to production of integrated.