Research On Electromagnetic Interference Of Photovoltaic Grid Connection Based On Z-Source Inverter

With the continuous development of human society,people's increasing energy demand and deteriorating environmental problems form sharp contradictions.Therefore,a series of clean and renewable energy represented by solar energy has become the focus of attention of governments of various countries.In photovoltaic power generation systems,grid-connected inverters are usually required to transfer the electric energy produced by solar photovoltaic panels to the power grid.Due to Z-source inverter's special cascade structure,which can replace inverters and converters,and its unique buck-boost characteristics,the application of Z-source inverter in photovoltaic grid-connected systems has many advantages,such as improving system reliability,improving photovoltaic system efficiency and reducing costs.However,Z-source inverter,like traditional inverter,has serious Electromagnetic Interference(EMI),which leads to distortion of grid-connected current,reduces the reliability of photovoltaic system and brings serious potential safety hazards.Therefore,this thesis takes photovoltaic grid-connected system based on Z-source inverter as the research object,and studies conducted EMI and radiated EMI generated by it.The main research contents are as follows:Firstly,the structure and control principle of photovoltaic grid-connected system based on Z-source inverter are analyzed,and the generation mechanism and coupling path of Common Mode Electromagnetic Interference(CM-EMI)and Differential Mode Electromagnetic Interference(DM-EMI)are analyzed.The parameters such as capacitance and inductance of Z-source inverter network are calculated,and the modulation strategy of Z-source inverter is analyzed based on the existing literature.Finally,the simulation model is built,and the interference voltage and current are analyzed.Secondly,Common Mode Voltage(CMV)generated by single-phase Z-source inverter is deduced,and its leakage current flow path is analyzed,and a high-frequency model of conducting electromagnetic interference path is established.Based on the modulation of unipolar PWM method,this paper adopts a method of changing the switching state of Z-source inverter to suppress CMV.By modulating Fourier transform,CMV after suppression measures are compared with CMV generated by traditional Z-source inverter in frequency domain,which verifies the correctness and effectiveness of the suppression method.Thirdly,according to the three elements of electromagnetic interference,starting from the source of electromagnetic interference,LCL filter is designed for Z-source inverter photovoltaic grid-connected system.Because LCL filter is a third-order filter,resonance problems will inevitably occur in actual use.Therefore,active damping control with capacitive current feedback is adopted to eliminate resonance peaks.Through simulation,the output EMI of the system before LCL filter is connected to the circuit and not connected to the circuit is compared and analyzed.The results show that the LCL filter has good suppression effect on conducted EMI.Finally,the principle of radiated electromagnetic interference of photovoltaic grid-connected system with Z-source inverter is analyzed.Taking Z-source inverter as radiation interference source,a double-loop model of radiation interference is built in Ansoft HFSS simulation software,and the radiation interference generated is analyzed by dipole antenna theory.Finally,the method of shielding the chassis is adopted to suppress radiation interference.