Research On Full Bridge Converter ISOP Combined System And Its Control Algorithm

With the improvement of scientific and technological level,power electronic technology has been widely used in various cutting-edge scientific and technological fields,and penetrated into industrial production,power system and other aspects.In the process of power system transformation to new energy,there are more and more DC transmission lines.the voltage level of power grid is also continuously improved.the high-voltage power electronic integration technology is developing rapidly.In order to meet the performance requirements of power range and voltage stress of power electronic devices,the integration,standardization and modularization technology of power electronic system still needs to be deeply studied.Among them,the input series output parallel(ISOP)combined system of polytropic converter module can be used to solve the design problems caused by high voltage or high current,which has become the leading direction of scientific research in last several years.This paper will further study and optimize the control algorithm of the ISOP system on the basis of the selection and working characteristic analysis of the single module converter of the ISOP system.The paper has completed the following research work:Firstly,the design and working characteristics of single module converter are completed.It aims at saving electric energy and reducing energy consumption.The full bridge DC/DC converter most suitable for high voltage and high power is selected.The working process of the converter under phase-shifting control is analyzed,and the conditions for realizing soft switching are established.Then,the parameters of each element are calculated according to the input and output indexes,and the detailed parameters of each element are obtained.On this basis,the mathematical model of the unit module is established..In addition,the small signal model of the converter is established by deriving the small signal expression under weak interference.Secondly,the input voltage sharing and output current sharing control strategies of ISOP system are theoretically studied,and the feasibility of the control strategies is verified.On the basis of establishing the small signal model of the three module ISOP system,the transfer function of the small signal model of the three module ISOP system is derived.Then a three loop control strategy is proposed based on the small signal model,and the two closed loop controllers after decoupling are designed respectively: the input voltage sharing loop and the output voltage current loop.In view of the large number of three loop control parameters and difficult regulation,this paper improves the output voltage loop control algorithm based on particle swarm optimization(PSO),and gives the algorithm flow chart and the improved program block diagram.Finally,according to the performance index of the system and the component data,the single module phase shifted full bridge converter and the three module ISOP system are built on the Simulink platform by MATLAB simulation software,and the implementation of phase-shift control soft switching is verified.Comparing the output waveforms of three loop control and three loop control improved by particle swarm optimization algorithm,the superiority of the improved control strategy is verified.The simulation experiment is carried out under the condition of sudden change of input voltage and inconsistent transformation ratio of transformer.The results show that the control strategy and optimization method established in this paper have good control effect,so that the system has excellent voltage and current sharing performance while ensuring steady-state operation,and achieves the design goal.