Research On LCL Three-level Npc Inverter Based On DM-PIMR Control

With the shortage of traditional energy and the increasing serious pollution,the human demand for developing clean energy and low-carbon environmental protection is also increasing,so the distributed power generation system based on the clean energy such as photovoltaic,wind energy has gradually become a hot topic at home and abroad.Inverter,as an interface device between distributed generation system and power grid,plays an important role.Diode Neutral Point Clamped(NPC)inverter has been widely applied due to its simple topology and good output waveform.However,in view of the phenomenon of voltage deviation at the neutral point and the demand for further improvement of power quality,this paper conducts in-depth research work based on the LCL three-level NPC inverter system,mainly including:Firstly,the working principle of the LCL three-level NPC inverter is described,and the mathematical model of the LCL three-level NPC inverter in the three-phase abc stationary coordinate system,two-phase ?? stationary coordinate system and synchronous dq rotating coordinate system is given.At the same time,aiming at the resonance peak of LCL filter,the active damping method based on capacitance current proportional feedback control is selected through the comparative analysis of passive and active damping methods.Secondly,aiming at the problem of midpoint potential fluctuation of three-level NPC inverter,based on the basic vector classification and the analysis of its effect on midpoint potential,a nine-segment SVPWM modulation strategy based on fuzzy control is introduced.The new medium vector is formed by repartitioning the space vector,and a completely symmetrical nine-segment switch sequence is adopted to eliminate the influence of the medium vector on the potential balance of the midpoint.At the same time,in order to better solve the uncertainty problem of capacitance voltage fluctuation on the dc side,this paper introduces the balance factor method based on fuzzy control,and then realizes the purpose of dynamic regulation of midpoint potential.At last,the feasibility of the proposed strategy is verified by Matlab/Simulink simulation.Thirdly,on the basis of the traditional repetitive control principle and structure analysis,in order to further improve the dynamic performance and steady-state accuracy of the LCL three-level NPC inverter,increasing the inhibition of harmonic disturbance,in this paper,a current double closed loop control strategy based on new DM-PIMR control is proposed,the conditions for the robust stability of the system are analyzed and the corresponding parameters of the design process is presented.The controller not only can suppress the odd and even harmonics separately in the power grid and improve the power quality,but also has good dynamic response performance and robustness.Finally,Matlab/Simulink simulation is used to verify the superiority of the new controller based on SVPWM modulation with nine-segment method.Finally,the experimental prototype of the LCL three-level NPC inverter is built,and the hardware design and software flow of the system are given,including the design and selection of main circuit parameters,the hardware circuit design of each module and the software design flow.The experimental results verify the correctness and superiority of the midpoint potential balance method and the new current controller.