Research On Control Strategy Of Three-phase Three-level VIENNA Rectifier With Neutral Point Potential Balance

With the development of industry,the demand for electric energy is higher and higher,and rectifier is widely used in the field of electric energy conversion.Among many rectifiers,three-phase three-level VIENNA rectifier has the advantages of less switching devices,high power factor,low current harmonic content and can work at high switching frequency,which makes it have high research value.This paper analyzes the working principle of three-phase three-level VIENNA rectifier and derives its mathematical model in two-phase dq rotating coordinate system.Based on the two-level three-level space vector analysis method,the sector judgment of the basic vector of three-phase three-level VIENNA rectifier and the calculation of its action time are simplified,and the SVPWM modulation method of three-phase three-level VIENNA rectifier is obtained,which provides a theoretical basis for the later research.In the two-phase rotating dq coordinate system,the double closed-loop control strategies of voltage outer loop and current inner loop based on particle swarm optimization algorithm are established.The control parameters of traditional current inner loop PI controller are designed offline,while the control parameters of current inner loop PI controller based on particle swarm optimization algorithm are adjusted online by particle swarm optimization algorithm,which makes the control system more adaptive and high control accuracy.At the same time,aiming at the problem of neutral point potential imbalance,a two-step fuzzy PI controller is used to calculate the regulating factor and adjust the action time of positive and negative small vectors to balance the neutral point potential.In the first step,the proportional coefficient and integral coefficient of the PI controller are obtained by collecting the voltage difference between the upper and lower capacitors on the output side and its variation.In the second step,the voltage difference between the upper and lower capacitors on the output side is divided by threshold,and the proportional coefficient and integral coefficient obtained in the first step are adjusted again.Finally,the adjustment factor calculated by the two-step fuzzy PI controller is sent into SVPWM,Adjust the action time of positive and negative small vectors.The parameters of the key components of the main circuit are designed,and the simulation model of the three-phase three-level VIENNA rectifier control system is established by using MATLAB.The double closed-loop control strategy of the outer voltage loop and the inner current loop based on particle swarm optimization algorithm is verified.The DC side output voltage and current have high steady-state precision and small ripple,and the grid side current is sinusoidal and tracking the grid side voltage and strong anti-interference ability;The simulation results of neutral point potential balance show that compared with fuzzy PI control,the fluctuation range of neutral point potential under two-step fuzzy PI control is small,and the regulation speed of two-step fuzzy PI control is faster.