The Research On Power Electronic Transformer Based On Dual PWM Converters

With the continuous development of manufacturing technology of power electronic devices and the gradual maturing of modern power electronic technology,a new type of power transformer—(Power Electronic Transformer, PET),which combined with power electronic technology and transformer technology,is proposed. In addition to the basic functions of traditional transformer,such as voltage regulation, electric isolation and power transmission, the prominent feature of PET is the flexibility to adjust input current, output voltage and input power factor. Because of the advantages,PET can improve system power quality, improve reliability of power supply, facilitate the integration and access of distributed power and contribute to the construction of intelligent power grid. To study PET is of great theoretical significance and practical value.This paper introduces the research background and research situation of PET firstly and analyses some representative structures,then presents a PET of AC/DC/AC topology based on the dual PWM.The PET mainly consists of input stage, isolation stage and output stage. The input state is a three phase voltage PWM rectifier circuit,where input current and output DC voltage both are controlled and can achieve unity power factor control. The isolation stage uses a high-frequency transformer to achieve voltage regulation, electric isolation and power transmission, uses a single phase full bridge invert circuit in the primary side and uncontrolled rectifier circuit in the second side. The output stage is a three phase voltage invert using SVPWM to achieve voltage output. This paper further studies the basic principles of PWM rectifier and the way to work and establishs a mathematical model for the three phase voltage PWM rectifier, then analyzes the specific control strategy and modulation method. Based on Matlab, the simulation model of input stage,output state and the whole system are established and the result of simulation certifies the control strategy correct.Based on the previous theoretical analysis, the entire hardware circuit of system is established, including the design of main circuit,drive circuit for IGBT, flyback power supply, signal sampling and conditioning,and control circuit. Describe the programe flow of input state. Experimental results show that PET can achieve sinusoidal current input and unity power factor control.