EMI Suppression And Optimization Design Of Magnetic Integration For Grid-connected Inverter

Increasing scarcity of fossil fuels leads to urgent development and utilization of new energy sources such as solar,wind and tide energy.Grid-connected generation based these has become an important measure to alleviate the energy crisis.The grid-connected inverter is an important power-conversion device between the energy source and power grid,its performance directly affects the power quality of the grid.On the other hand,with the updating development of semiconductor materials,wide-band-gap(WBG)semiconductor devices,represented by Si C and Ga N,have been making high-frequency grid-connected inverters.Although the volume and weight of the harmonic filter can be reduced to a certain extent,and the efficiency of the system can be improved,the conducted electromagnetic interference(EMI)issue brought by it cannot be ignored.Therefore,how to better solve the harmonics and EMI issues of the inverter system has become a research hotspot.Aiming at this problem,this paper has optimized the harmonics and EMI filters of the inverter system from the aspects of effect,volume and weight of output filters,and system power density.The main contents of this article are shown as follows:Optimization design of LCL-LC filter’s Electromagnetic compatibility(EMC): through modeling and analysis of LCL,LLCL and LCL-LC grid-connected inverters,the LCL-LC filter is selected as the harmonic filter,and its EMC is optimized to improve EMI suppression performance while maintaining originally satisfied harmonic suppression ability.Besides,in order to handle the system resonance introduced by LCL-LC filter,an active damping strategy based on the feedbacks of capacitor-branch current and grid-side current is used to eliminate resonance and stabilize the system.Meanwhile,a system-corrected method is proposed and utilized for parameters design of the PI controller in such a fifth-order system.Optimization design of EMI filter: the parameter design methods of passive EMI filters are discussed in detail.With the aim to reduce the volume and weight of EMI filter and increase the power density of the inverter,a comprehensive optimization design of EMI filter is carried out through magnetic integration technology,which includes: a.Passive EMI filter(PEF) parameter design method—different from the traditional cut-off frequency method,the single inductor-single capacitor method is used to extract the EMI noise source impedance,based on this,an impedance-matching method is proposed to design the parameters of the EMI filter and its detailed analysis and design procedures are presented;b.Magnetic integration design of PEF—magnetic integration schemes of single-stage and multi-stage EMI filters are designed respectively,with the common-mode(CM)and differential-mode(DM)inductors of the EMI filter integrated into the same single-core unit,significantly reducing the system volume and weight;c.Design of integrated EMI filters based on flexible multilayer foils—based on the single-stage EMI filter,two kinds of integrated EMI filters are preliminarily designed: partially integrated(CM inductors and capacitors integrated in the same single-core unit)and fully integrated(CM inductors,capacitors and DM inductors,capacitors are all integrated in one core unit)filters;d.integrated LCL-EMI filter design—for further reducing the size and weight of the entire output-filter,an LCL-EMI filter integration scheme is proposed,which integrates the harmonic inductor of the LCL filter and the CM inductor of the EMI filter in one core unit.A PLECS-based simulation model of a single-phase inverter is established,the harmonic filtering effects and EMC of the traditional LCL,LLCL,LCL-LC and the improved LCL-LC filter are tested through simulation to verify the feasibility of the modified LCL-LC filter.And the feasibility analysis of various magnetic integration schemes is also conducted by PLECS and Maxwell.Finally,Si-IGBT and Si C-MOSFET single-phase inverters are built as the experimental platforms,and various types of harmonic and EMI filters(traditional LCL,LLCL,LCL-LCL and improved LCL-LC filters;PEFs designed based the cut-off frequency and impedance-matching methods,respectively;discrete single-stage and multi-stage EMI filters and corresponding magnetically integrated EMI filters;LCL-EMI magnetic integrated filter;integrated EMI filters based on FMLFs)are designed for comparative experiments.The SiIGBT inverter is used to verify the superiority of the modified LCL-LC filter and designed double closed-loop control scheme(output power is 2 k W),and the Si C-MOSFET inverter is utilized to verify the valid design of different types of magnetically integrated EMI filters and LCL-EMI filter(output power is 500 W).The experimental results show that the designed improved LCL-LC filter has approximately the same harmonic attenuation performance as the traditional one and with significantly strengthened EMI suppression ability.Besides,the designed double closed-loop control system has good stability and can meet the expected performance;Based on the extracted impedance of EMI noise source,the EMI filter designed by the impedance matching method is more targeted,which can reduce the time cost;The designed magnetically integrated EMI filter can significantly reduce the size and weight of the filter,and improve the system’s power density,especially the LCL-EMI magnetic integration model;The use of FMLFs can further strengthen the integrated degree of traditionally integrated EMI filters,and achieve a satisfied filtering performance.