Research On Single-Phase Transformerless PV Grid-Connected Inverter Based On Model Prediction Control

Single-phase transformerless photovoltaic(PV)grid-connected inverter removes isolated transformer,so it has the advantages of low cost,small volume,light weight and high efficiency,which is of great significance to promote the large-scale application of PV grid-connected system.However,because of the removal of isolation transformer,the parasitic capacitance of PV cells to the ground will form a electrical loop with the filter inductances and capacitances in the system,resulting in leakage current,which will affects the grid-connected effect and may even poses a threat to the safety of people and equipment.Therefore,suppressing the leakage current and improving the grid-connected effect of the inverter is the focus of single-phase transformerless PV grid-connected inverter.In this paper,the topology and control method of single-phase transformerless PV grid-connected inverter with leakage current suppression function are studied.In this paper,the leakage current generation mechanism of single-phase transformerless PV grid-connected inverter is analyzed and the leakage current common-mode equivalent model is established firstly.Then the typical topologies with the function of suppressing leakage current are discussed,which can be divided into the topology based on symmetric inductor configuration and asymmetric inductor configuration.But the application of these typical topologies has some limitations,because the common mode leakage current can not be completely eliminated when considering the parasitic capacitance of the switches.This paper uses the idea of“short circuit parasitic capacitance” to propose a new common ground topology,which can completely eliminate the leakage current.The new topology connects the neutral point of the grid with the negative point of the PV cell,which is equivalent to short circuiting the parasitic capacitance of the PV cell.Based on the analysis of the working mode and common model ability of the new topology,the leakage currentsuppression ability and cost of the new topology are better than those of the traditional topologies.The control system and control block diagram of single-phase transformerless PV grid-connected inverter system are introduced,which are mainly phase-locked loop and control strategy.The model predictive control is applied to the new topology.Compared with the PI,PR control,the model predictive control has the advantages of simple control and quick response.Finally,the experimental prototype of single-phase transformerless PV grid-connected inverter is designed.The overall structure and experimental parameters of the prototype are introduced,and the software and hardware design of the experimental prototype are introduced in detail.The current leakage suppression ability and efficiency of the new common ground topology are studied.The experimental results show the feasibility and superiority of the new topology applied to PV grid-connected system.