Design And Implementation Of Two-stage Grid-connected Inverter

At present, two-stage grid-connected inverter is a research hot. Because of the decoupling ofmaximum power point tracking and inverter output, the control statagy is simple. However, due to thetwo power stage, how to improve the efficiency and the reliability of circuit is one of the key issues.Moreover, the output voltage of photovoltaic cell is low, so the DC/DC converter should have highgain to meet the input of the back stage. This dissertation is dedicated to the design of two-stagegrid-connected inverter system. After the theoretical analysis of the topology and control strategy, aphotovoltaic grid-connected inverter system which based on Boost converter with couplinginductance and passive lossless soft-switching dual buck three-level full bridge inverter is designed. Itmeets all the demands of this issue. The essence of this issue can be concluded as follows.Firstly, overall scheme design of two-stage grid-connected inverter has been designed in thispaper, which includes topology building of front and back stage, selection of maximum power pointtracking control strategy, selection of closed-loop control strategy, comparison and selection ofmodulation scheme. Secondly, working principle of the proposed inverter, such as switch workingmodes, maximum power point tracking control strategy and closed-loop control strategy has beenconcretely analyzed. Thirdly, according to overall scheme design, detail designs of the inverter havebeen carried out, including parameter designs of main circuits, control circuits, auxiliary power supplycircuilt and software designs. The control circuits include sampling and conditioning circuits, phaselocked loop circuits, closed-loop control circuits, protection circuits and driving circuits. Thesoftwares finish over-current and over-voltage protection and the maximum power point trackingcontrol. Finally, system simulation using saber software and a prototype of the presented inverter havebeen carried out.Results of simulation and experiment show that the design is reasonable and feasible. Theinverter gets a good performance. The output voltage of the front stage is up to360V, and theefficiency of the front stage is up to90%. The efficiency of the back stage is up to95%. The totalefficiency of the system is up to85%. The echnical qualification is satisfied with the requirements ofthe design.