Research On Leakage Current Suppression Of Non-isolated Photovoltaic Grid-connected Inverter

With the ever increasing of energy consumption,the shortage of fossil fuels and environmental pollution have become a gravely global issue.Thus the green techs such as the utilization of solar energy gain a great concern of all countries.For many years the photovoltaic power technology has got significant progresses.As a core part of grid-penetrating photovoltaic power systems,non-isolated inverter is widely used for its advantages on its small-size,low cost,light weight,and high efficiency.However because of no transformer,the solar cell units are directly connected to AC grid,and a loop is then formed among parasitic capacitance in the solar cells,the inverter and the AC grid side.This leads to many severe problems such as common-mode leakage current,power loses,power quality and EMI as well.Therefore leakage current suppression for the non-isolated grid-connected photovoltaic inverter is a tantalizing research topic which needs to be conquered urgently.Firstly,the common mode equivalent model of the traditional non-isolated single-phase full-bridge photovoltaic power inverter,is built and simplified in terms of circuitry theory.The influence of parasitic capacitance in the solar cells on circuitry is analyzed,and the causing reason of high-frequency common-mode current is revealed.On the basis of this,three kinds of leakage current suppression methods are summarized out,and the impact of different modulations to the leakage current is also discussed in detail.Secondly,the existing leakage current suppression methods are analyzed for non-isolated photovoltaic power inverters.But the limited effectiveness is found out due to the influence of parasitic capacitance in the switching transistors.Then the characteristics of different clamped structures and the applied range are investigated,and a modified photovoltaic power inverter with the HERIC evolving structures is presented.Then,focusing on a novel-clamped photovoltaic power inverter evolving from the class2 HERIC structure,its operation modes in each phase and the common-mode voltage are analyzed at length,and then its modulation method and the correspondent mathematical model are demonstrated.The control strategy and its design method of the grid-connected inverter are discussed in detail.Matlab/Simulink simulation shows its feasibility and effectiveness in accordance with the theoretical analysis.Finally,a 500 W prototype of the proposed grid-connected photovoltaic power inverter is implemented.All the processes of circuits configuration,control system design,device and parameter selections are described.Eventually the experimental results have verified the excellent performance of the proposed photovoltaic power inverter on the leakage current suppression.