| At the present stage of global energy transformation,fossil energy causes high carbon emissions,and environmental pollution problems need to be solved urgently.Renewable energy is expected to be the world’s largest source of electricity in the middle of the century.With the development of the times and technological progress,photovoltaic power has become an important branch of the direction of energy development in China.The photovoltaic grid connected inverter is an energy conversion device to transmit power to the power grid,and it has the island protection function when the power grid fails.In a transformerless photovoltaic inverter system,the high-frequency operation of the inverter switching tube will cause the common-mode voltage on the parasitic capacitance to change and form a leakage current.High frequency leakage current greatly increases the number and power loss of grid connected waveform,and even endangers personal safety,so we must undergo strict detection and control.In the application of single-phase inverters,it is a common practice to improve the topology to reduce the leakage current of photovoltaic systems.The method of improving the topology is adding the auxiliary switch,the common mode voltage compensation circuit and the modulation mode to reduce the leakage current.There are usually two ways to improve the topology: improve the DC bypass topology and the improved AC bypass topology.In the topology of application and high efficiency,H5 is an improved DC bypass topology,while Heric,H6,and FB-ZVR belong to the improved AC bypass topology.In this paper,the working principles of several typical topologies are studied and simulated in detail.The efficiency and performance of several commonly used bridge topology are comprehensively analyzed.Based on the existing FB-ZVR topology,an inverter topology with improved AC bypass topology is proposed.The structure of the improved topology and the driving signal of the switch tube are analyzed in detail.The four working states of the improved topology are analyzed according to the different interruption states of the switch tube.In view of the proposed improved FB-ZVR topology,this paper selects the L filter to filter its output and designs the parameters of the L filter in detail.A simulation model of an improved FB-ZVR topology is built in Matlab/Simulink.The main parameters of the output voltage waveform and leakage current waveform of the improved topology are compared with the main parameters list of H5,H6,Heric,andFB-ZVR topology simulation.Through comparison,it is concluded that the improved FV-ZVR topology proposed in this paper can effectively suppress leakage current,improve output voltage waveform,and reduce the waveform distortion rate of output voltage.According to the improvement of the FB-ZVR topology and related performance indicators,inverter parameters calculation,component selection and program design are performed.The simulation results show that the improved FB-ZVR inverter topology has the advantages of low leakage current and low waveform distortion rate. |
