Research On The Topology Of Single-Phase Non-Isolated Photovoltaic Grid-connected Inverter

In order to transmit the energy generated by solar cells to the grid,it is usually necessary to install an inverter between the solar cells and the grid.Compared with the traditional isolated inverters,the non-isolated inverters have the advantages of high conversion efficiency,low cost,small size and light weight,which provide a good solution for grid-connected applications.However,the main disadvantage of non-isolated inverters is the leakage current problem,which will affect the normal operation of inverters,reduce power generation efficiency,and even endanger human safety.This is because the parasitic capacitance between solar cells and the ground can not be neglected.At the same time,there is no electrical isolation between the solar cells and the grid.Common-mode voltage will generate leakage current through the parasitic capacitance.In order to improve the conversion efficiency of grid-connected photovoltaic inverters and solve the leakage current problem,two new single-phase non-isolated inverters are proposed in this paper.Firstly,the generation principle of distributed capacitance of photovoltaic cells is briefly analyzed,and the causes of leakage current are analyzed by establishing common mode circuit model,and the conditions to suppress leakage current are obtained.The traditional full bridge inverter is simulated and analyzed.For the application of non-isolated photovoltaic system and the suppression of leakage current,a novel interleaving parallel single-phase non-isolated MOSFET grid-connected inverter is proposed.The interleaved parallel technology is introduced to reduce the output ripple current and improve the power density of the system without increasing the switching frequency.The output current ripple after interleaved parallel is analyzed in detail.At the same time,the current does not flow through the body diode of the switch during the freewheeling stage,so MOSFET can be used,which has lower switching loss than IGBT.Unipolar modulation strategy is adopted,the ripple current of inductances is small.The principle of the proposed topology and the system loss is analyzed.The closed-loop control strategy and the design of control parameters are described in detail.Thirdly,the family of single-phase non-isolated active clamped H6 topology are proposed.By introducing clamp circuit,the common-mode voltage of the inverter is not affected by the junction capacitance of the switch,which greatly improves the ability of the inverter to suppress common-mode leakage current.Similarly,MOSFET is used to reduce the switching loss of the system.One of the topologies is selected and analyzed in detail,including the working principle,and the change of common-mode voltage.In this paper,the proposed new inverter topologies are simulated by Matlab / simulink,and the theoretical analysis is preliminarily verified.Then two prototypes are built.The experimental results show that the proposed two types of topologies have good leakage current suppression ability and high efficiency,which verifies the correctness of the theoretical analysis.