Research On Control Strategy Of Three-to-single Phase Power Electronic Transformer

All kinds of urban residents,petrochemical industry,electrified railway traction system and smelting industry are single-phase loads in our country,which has randomness,overloading and large of harmonics.If it directly gets electricity from three-phase power system,it will be harmful to three-phase power system.From this point,the three-to-single phase power electronic transformer can not only realize equilibrium conversion between single-phase and three-phase,but also can carry on the transformation to the voltage and the power quality.Therefore,in this paper,the control strategies of power electronic transformer are deeply researched to improve the performance of the transformer,and to accelerate its application in actual power grid,which has great of significance.This paper briefly introduces the research backgrounds,research significance and control strategies of the research status of three-to-single phase power electronic transformer.In view of the phenomenon of the actual power grid often appears three-phase voltage unbalance.This paper derived mathematical model of the input stage of power electricity transformer system,analyzed the influence of Three-phase voltage unbalance on the input stage of transformer,and studied the control strategy of the inhibition of negative sequence current,and designed a digital trap which filter 2 harmonic,and made the simulation of input stage.In addition,in order to improve the efficiency of the full bridge DC/DC conversion of the transformer,this paper analyzed the working principle of the control strategy of single-phase-shift and dual-phase-shift,derived transmission power,reflux power and soft switching constraints of Intermediate stage converter;Proposes a dual phase shift control strategy based on optimal reflux power by detecting output power of Intermediate stage to make sure the converter always work in the smallest reflux power mode.At last,this paper compared reflux power of single-phase-shift control,dual-phase control and improved control strategy.This paper introduces the design method of the main parameters of power electronic transformer,and has carried on the simulation to the system as a whole,and verifies correlated characteristics of the system under unbalanced of three-phase voltage system.Finally,on the basis of theoretical study and simulation analysis,build a set of small power experiment system,introduces the hardware design and software design of the experiment system,and the waveforms of transformer were tested.