LCL Filter Design And Magnetic Integration Method Research Of Three-phase Voltage Source PWM Inverter

The voltage source PWM inverter(VSI)has a wide range application in fields,such as motor drives,grid inverters,and APFs,etc,because it has many advantages like simple structure and flexible control.The design of the ac port filters(L,LC,LCL)is a key factor in determining reliability and power density of VSI.At the same time,with the development of magnetic material technology,the introduction of magnetic integration technology can further reduce the volume as well as weight of magnetic components in VSI and system power density can be better.Therefore,this paper takes the three phase voltage source PWM inverter as the research model,and studies its ac port inverter side current ripple,LCL filter parameter design and its magnetic integration technology.The main content is from the following aspects:Firstly,through the introduction of PWM modulation technology based on carrier comparison method,this paper expounds the working principle of VSI converter,and analyzes and summarizes the four types of characteristics of VSI ac port power harmonics.Then taking the three phase voltage source PWM inverter as the research object,a simplified mathematical model and time domain analysis method for current ripple calculation are established,and the expressions of current ripple on output voltage,switching time and circuit parameters are obtained,and use the SVPWM method to calculate the current ripple,which provides a theoretical basis for the parameter design of the subsequent LCL filter.On the basis of the current ripple time domain calculation method,the expressions of the peak-to-peak value of the current ripple and the inverter side inductance under different modulation ratios are deduced.This method can calculate the peak-to-peak value of the current ripple under any working condition,and based on this,the inverter side inductance of the LCL filter is designed.At the same time,using the relationship between the ratio of switching frequency and resonant frequency k,the ratio of inverter side inductance to grid side inductance r and harmonic attenuation,it is emphasized that the selection of proportional coefficients r and k is the determining factor for optimizing filter parameters,and the proposed a simple design method of LCL filter parameters.This design approach treats the LCL filter as an integral ac port filtering unit rather than the contribution of individual passive components to current harmonic attenuation.Next,in order to further reduce the volume of the LCL filter and improve the power density of the system,the inverter side inductor and the grid side inductor are integrated on the same magnetic core through magnetic integration technology.However,the integration of the inductor will cause coupling of the capacitor branch of the LCL filter,which will reduce the attenuation of the LCL filter in the high-frequency harmonic part and affect the filtering performance of the filter.Regarding the problem above,this paper analyzes the magnetic circuit of the LCL filter after decoupling.A decoupling inductance is connected in series with the capacitor branch to cancel the inductive coupling.Thus,the active decoupling of the magnetic integration of the LCL filter is realized,and the filtering performance is improved.Finally,through Matlab/Simulink and other softwares and building a three-phase full-bridge VSI experimental prototype test platform.The correctness and effectiveness of the current ripple calculation method,the LCL filter parameter design and the active decoupling of the integrated inductor are verified by experiments in this paper.