Control And Realization Of Single Phase Power Electronic Transformer

Nowadays,with the continuous progress of modern power grid technology,power electronic transformer(Power Electronic Transformer,PET)has been widely studied by scholars all over the world.Through power electronics technology,control technology and power switching devices,PET has realized new energy grid-connection,power grid interconnection,power quality control and other functions.Compared with traditional power transformers,PET has the characteristics of light weight,small size,high controllability,easy to form micro grid interface,easy module expansion and so on.It is widely used in new energy systems and smart power grids.In this thesis,the three-stage single-phase PET is taken as the research object,and the control strategy at all levels and the overall starting mode are mainly studied to achieve the goals of power factor regulation,DC side voltage stability,constant voltage and constant frequency of output voltage,etc.The main research is as follows:Firstly,this thesis introduces the overall working principle and topological structure of single-phase PET,studies the working principle of all levels of topologies in detail,and establishes the mathematical model of all levels of topologies.Then,aiming at the influence of DC side voltage fluctuation on the system,a simplified modulation strategy is developed to compensate the DC voltage.In addition,in order to improve the phase-locked capability of the system,a virtual two-phase phase-locked loop method with a second-order generalized integrator is used to phase lock the voltage on the grid side.Secondly,the topological control method of single-phase PET at all levels is studied in detail.In order to solve the problem of current distortion caused by secondary ripple of DC voltage in single-phase PET input stage with traditional d-q vector control method,a notch filter and quasi-proportional resonance(Proportional Resonant,PR)control strategy is used to reduce current harmonics on the grid side,and unit power factor rectification and DC voltage stability are realized.A single phase shift control method of DC-DC converter is studied to realize voltage stability on the low voltage side.In order to realize constant voltage and constant frequency of the output voltage,a constant output voltage control method is adopted for the output stage.In addition,this thesis studies the overall start-up control of single-phase PET,and builds the overall simulation of single-phase PET using Simulink to verify the steady-state and dynamic performance of the system.Finally,the circuit parameters,hardware circuit and software program of singlephase PET system are designed,and the whole experiment platform of single-phase PET is established.The single-phase PET input stage and the whole operation of the single-phase PET system are experimented,and the correctness of the control strategy studied in this thesis is illustrated by comparing with the simulation analysis.