Magnetic Integration Design Optimization And Stability Of Single-Phase Grid-Connected Converter Based On LCL-EMI Filter

The grid-connected converter is an important unit between the power grid and distributed energy and its working performance directly determines the power quality incorporated into the grid.In recent years,with the technological progress of semiconductor materials,the switching rate of the switch tube in the grid-connected converter is constantly rising.The problems of switching harmonics and electromagnetic interference(EMI)brought by the high-frequency switching devices also become more and more intensified when the power density of system is improved.In order to effectively suppress the switching harmonics and EMI in the converter system,harmonic filter and EMI filter have been widely used.But while the combination of multiple filters improves the output performance of the system,it inevitably increases the overall volume and weight of equipment.Therefore,in order to better solve the switching harmonic and EMI of system,the topology and structure of harmonic filter and EMI filter are optimized,and stability of system is analyzed.The main content is as follows:(1)This paper firstly analyzed L,LC,LCL,LLCL filter and other different high order filter.Based on LCL filter with good filtering effect and low complexity,the mathematical model of single-phase grid converter is established.Secondly,it analyses the source and propagation of conducted EMI in the single-phase grid converter and draws out the differential mode(DM)and common mode(CM)equivalent circuit.Then,the CM interference of single-phase grid-connected converter under three different modulation modes,unipolar SPWM,bipolar SPWM and unipolar frequency doubling is compared in detail,and the simulation is built to verify.(2)Settle filter of single-phase grid-connected converter as the point of penetration,the working principle of traditional harmonic filter and EMI filter is introduced firstly,and the advantages and disadvantages of them are pointed out.Then,the circuit topology and magnetic core structure of traditional magnetic integrated LCL-EMI filter are introduced,and the corresponding magnetic circuit model is established.A more detailed analysis is carried out.Finally,the equivalent harmonic circuit model is obtained.It is pointed out that there may be coupling between grid-side inductor and converter-side inductor,which affects the filter’s suppression effect on the high frequency harmonics.(3)Aiming at the magnetic coupling problem caused by magnetic integration technology,this paper proposes and designs the magnetic core structure of the decoupled symmetric LCL filter,which not only can reduce the filter size,but also can avoid the magnetic coupling between grid-side inductor and converter-side inductor.The decoupled magnetic core can also make use of magnetic coupling of the same side inductor to reduce the number of turns of the inductor.On this basis,combined with EMI filter,the magnetic core structure of decoupled LCL-EMI filter is proposed,and the corresponding magnetic circuit model is established.The decoupled magnetic integration of LCL-EMI not only avoid magnetic coupling between grid-side inductor and converter-side inductor,but also improve the electromagnetic interference suppression ability of the filter.Finally,the correctness and superiority of decoupled LCL-EMI filter are verified through several groups of comparative experiments.