Research On High Reliability Buck-boost Grid-connected Inverter For Wide Input-voltage Range Application

In recent years,with the excessive exploitation of fossil energy,the energy crisis has gradually become prominent,and environmental pollution is becoming increasingly serious.Renewable energy,such as solar energy,fuel cells,and wind energy,is desirable due to their merits of no pollution,regeneration and wide distribution,and has been paid more and more attention.The output of the solar cell or the fuel cell is DC voltage and that of the wind generator is AC voltage with variable frequency,while the grid is AC voltage with constant frequency.Therefore,grid-connected inverters are the important part of distributed generation systems.As the output voltage of fuel cell or solar cell is often low and varies widely,the traditional bridge-type inverter needs to cascade a DC-DC boost converter.However,the control method of two-stage structure is complex,and efficiency of the two-stage system is reduced.In addition,short-through problem exists in the traditional bridge-type inverter,so the reliability of the system is reduced.In order to solve the abovementioned problems,a single-stage high-reliablity buck-boost grid-connected inverter for wide input-voltage range application is proposed.The inverter does not have the shoot-through problem,so it has high reliability.There is no need to set the dead time between switches,so the waveform quality of the grid current is high.The proposed inverter can operate in boost and buck modes,so it is suitable for a wide input-voltage range application.Operating principle of the inverter is analyzed in detail,and the operating principle of four modulation methods is illustrated.The control circuit is designed with the hysteresis current control.The power devices are selected and the LCL filter is designed.The calculation for the reference currents of buck and boost modes is given.The stability of the system is analyzed.The theoretical analysis of the proposed inverter is verified by Saber simulation software.Finally,a 300 W prototype is built and verifies the theoretical analysis.