Research On The Topology And Control Strategy Of Power Electronic Transformer

Power Electronic Transformer is a kind of new intelligent power voltage device,which combined with power electronic technology and transformer technology.Just like traditional transformer,Power Electronic Transformer can regulate voltage,achieve electric isolation and transfer power,besides,it can adjust input power factor and output voltage,it also can restrain harmonic and so that the system power quality can be improved,and the reliability of power supply can be enhanced.Besides,it has both AC and DC link,which easy for new energy generation to be connected to grid.So,the researches on PET are of great significance.The research background and research situation of PET was introduced in this paper firstly.And then,some typical topologies of PET based on AC/AC and AC/DC/AC were analyzed in the paper and one type of topology based on double PWM was chosen as the research object.The mathematical models of input stage,isolation stage and output stage were built and the control strategies of three stages were studied in the paper.The input stage uses double closed-loop control scheme based on sliding-mode.The isolation stage uses opened-loop control scheme,which inverse DC voltage to high frequency rectangle signal whose duty cycle was 50%.The output stage uses double closed-loop control scheme without the exact value of inductor.Based on the theory above,simulation was made by using Matlab/Simulink,the results show that the current of the input stage of PET can follow the voltage of the input stage,and PET can work under unit power factor.When the system had harmonic,voltage drop or three-phase imbalance,the voltage of the output stage remain stable and its waveform remain in sine.So,it can be known that PET can increase efficiency of power transfer and reduce reactive power loss,and it also can improve system power quality quickly and efficiently and keep the output voltage stable when system failures.