Analysis And Suppression Of Network-side Harmonic Characteristics Of Single-phase Three-level PWM Rectifier

Nowadays,single-phase three-level PWM rectifier has been widely used in railway electric traction field,such as CRH2/CRH380A type traction converter,compared with the traditional two-level topology structure of rectifier,The three-level structure has the advantages of lower switching voltage and higher equivalent switching frequency,so it is more suitable for the working environment of electrified railway.However,in order to reduce the weight and volume of the car body and realize the lightweight design,the high speed EMU cancels the LC resonant filter circuit which can absorb the pulsating voltage effectively,which results in the increase of the harmonic content of the current on the grid side,especially the content of the low harmonic,and the reduction of the current harmonic content on the grid side.The performance of the system.Due to the topological structure of the three-level current,the neutral point potential will drift,which will further increase the current harmonic on the grid side,and may damage the switching device.Therefore,the research on the current harmonic suppression strategy on the grid side of the converter has been widely concerned by scholars at home and abroad.In this paper,the topology,mathematical model and working principle of single-phase three-level PWM rectifier without LC resonant filter loop are introduced,and three common control strategies are studied:transient direct current control,and so on.Based on the principle of predictive current control and current decoupling control in dq coordinate system,the causes of the imbalance between frequency ripple voltage and midpoint potential in the double power grid on the grid side are analyzed,and their effects on the current harmonics on the grid side are analyzed.Secondly,in order to achieve the goal of suppressing current harmonics on the grid side of rectifier,DC voltage dynamic compensation,low-pass filter and N-notch filter are used in the outer voltage loop,respectively.The combination of dynamic compensated low pass filter and low pass filter N times notch filter;The harmonic suppression schemes of multiple quasi-proportional resonant controller with phase compensation and odd repetitive controller are analyzed theoretically in the current inner loop,and the steps of parameter design and the method of discretization are introduced in detail.In addition,a pulse conversion scheme based on hysteresis regulation is introduced to solve the problem of midpoint potential imbalance.Finally,the simulation model of single-phase three-level PWM rectifier is built based on Matlab/Simulink simulation environment.The three conventional control strategies introduced in this paper and different current harmonic suppression schemes on the grid side are simulated under traction and regenerative braking conditions respectively.By analyzing and comparing the simulation data and waveforms of different schemes under different working conditions,the correctness and effectiveness of the proposed current harmonic suppression scheme on the grid side are verified.