Study On Control Method Of Single-phase Cascade H-bridge Power Electronic Transformer

Power Electronic Transformer has topological structure and working principle of the isolation stage DC-DC converter and output stage three-phase inverter are analyzed,and the working state of another kind of Power feature.The power characteristics mentioned here mainly refer to the amplitude,frequency,phase,phase number,phase sequence and waveform of voltage(or current).Single-phase cascade electronic electronic transformer is one of the topologies widely used in THE field of PET.Its topological structure belongs to three levels,which are input level,isolation level and output level respectively.This paper introduces the properties of H bridge cascade transformer.The control strategy of power electronic transformer is studied.The topology structure,working principle topological structure and working principle of the isolation stage DC-DC converter and output stage three-phase inverter are analyzed,and the working state are analyzed from several aspects.The research contents as follows:(1)Firstly,the structure and principle of the input stage are introduced,and the modulation modes of single-phase PWM rectifier and cascade PWM rectifier are analyzed respectively.Then the topological structure and working principle of the isolation stage DC-DC converter and output stage three-phase inverter are analyzed,and the working state of the DC-DC converter with double active bridge under the control of double phase shift is introduced.(2)THE PET input stage object is to enhance power factor of the grid,control strategy,and adopted a score before Xiang Chao repetitive control strategy,the simulation results show that the proposed control strategy can keep the output voltage stability.In this paper,the output control delay and slow response speed of PWM rectifier will be affected by uncertain factors.An improved beat-free control algorithm is proposed and a mathematical model of single-phase PWM rectifier is established.A model predictive control strategy based on difference equation is introduced to reduce the influence of sampling error on current control and improve the accuracy of current prediction.(3)the analysis of the input stage unit H bridge dc output voltage imbalance,in view of the traditional method of voltage sequence number is more,lead to increase in the number of H bridge unit switch problem,an improved capacitor voltage balance control strategy,and by comparing the change of modulation than size and bubble sort method,two kinds of control strategy is verified,the strategy reduced the switching loss.(4)The bridge DC-DC converter shift control are analyzed.Based on the analysis of transmission power and backflow power,an improved two-phase shift control strategy is adopted.The simulation results show that predictive control strategy based on difference equation is introduced to reduce the influence of sampling error on current.Then analyzed about the output stage inverter problems existing in the conventional repetitive control strategy,and adopted a score before Xiang Chao repetitive control strategy,the simulation results show that the proposed control strategy can keep the output voltage stability,and can effectively restrain the rectifier of odd harmonic load,the system has faster response speed and has good dynamic and static performance.