Research And Design Of Power Electronic Transformer With Two Stage Structure

With the development of semiconductor manufacturing technology and power electronics technology,a new type of transformer-power electronic transformer-that combines power electronics and high-frequency transformers is used to replace traditional transformers.PET in addition to realizes the basic functions of traditional transformers such as voltage level conversion,electrical isolation and energy transfer,its outstanding feature is to improve the input power factor,flexibly adjust the output voltage,to achieve a stable isolation voltage.As more and more power equipment is connected to the power grid,the power quality of the power grid is threatened,and the power supply equipment that needs reliable power supply is threatened,the application of PET can effectively improve power quality,improve the reliability of power system,integration and access to distributed power,contribute to the development of smart grid.Therefore,the in-depth study of PET is of great significance and economic value.This paper firstly introduces the research background and development status of PET,the traditional transformer and PET comparative analysis can be seen that the faults of the traditional transformer and advantages of the PET.Based on PET principle and classification,proposed a type of power electronic transformer for two level structure,consisting of AC/DC and DC/AC two level converter,omitted DC/DC converter of the three structure PET.Secondly,according to the two level structure of power electronic transformer analyzes the principle and control strategy from the theory.AC/DC part is mainly composed of a high-frequency transformer and on its both sides of the convertor,analysis its working principle,the input side sinusoidal voltage is firstly modulated into high-frequency voltage with sinusoidal envelope,and then is adjusted to the DC voltage in the two side,uses the open-loop control strategy,given a specific part of the work mode.DC/AC part is single-phase full controlled inverter circuit,analysis of its working principle,circuit mathematical model is deduced,the control strategy is voltage and current double closed loop.Again,set up the hardware circuit of the PET system,including the design of the main power system circuit,driving circuit,signal conditioning circuit,controller and its peripheral circuit and power supply circuit.The design of the software system of TI based on TMS320F28335,including the main program,interrupt service program and control program.Finally,the results were analyzed.The simulation model built by Simulink for thewhole of the two level structure of power electronic transformer,voltage stability,load switching and voltage drop.Simulation experiments were carried out to verify the hardware platform,the results show that the two level structure of power electronic transformer can realize the input side of the high power factor,input and output voltage isolation,AC and DC output voltage stability.The structure is simplified,less devices.