| DC high voltage converters are widely used in DC microgrids,deep sea long-distance power supply systems and other applications.The combination of multiple converter input series output parallels(ISOP)into a new type of converter is an effective way to solve this problem.The key technical issue of the ISOP converter is how to ensure the input voltage sharing and output current sharing of each module during the system operation.In this dissertation,the following work has been carried out on the design and research of the ISOP combined converter.Firstly,the phase shifted full bridge topology is selected as the basic module of the ISOP combined converter.Theoretical analysis and research are carried out on the characteristics of the converter’s commutation process,wide range soft switching technology and duty cycle loss suppression measures,etc.The converter parameters are designed based on technical indicators such as withstand voltage level,transmission efficiency and application occasions,and the key components are selected.On this basis,the small signal model of the two-module ISOP combined converter is established to provide a theoretical basis for the determination of the stability of the subsequent control strategy.According to the design criteria of the loop compensator,the open-loop Bode diagram of the system is corrected and the phase-shifted fullbridge voltage-current double closed-loop control system is designed.Secondly,in order to cope with the complex operating environment and improve the modularity of the system,the dissertation adopts an interconnector-free control scheme including voltage feedforward,voltage shifting and current dispersion reverse droop strategies,and conducts a theoretical derivation and comparative analysis of the basic operation and voltage regulation characteristics of the above control strategies.Among them,the current dispersion reverse droop control strategy does not need to collect the input-side voltage,which can reduce the isolation devices in the control system and improve the system reliability.However,when the output-side current of the system is large,the output voltage steady-state deviation rate is high.The difference between the output current of each module and the average value of the total output current is superimposed on the outer loop of the control system by a certain percentage.On this basis,a simulation model of the two-module ISOP system is built to analyze its voltage equalization effect and the output voltage steady-state deviation rate and other technical indicators to verified the correctness and effectiveness of the theoretical analysis of the anti droop control strategy based on the average system output current and compensation for the deviation of single module output current.Finally,the main circuit and control circuit hardware systems are designed,the two-module ISOP combined converter experimental platform is built,and the steady-state and dynamic performance of the system is tested under different control strategies.The results show that the adopted average current dispersion inverse sag control strategy can effectively ensure the stable operation of the ISOP system.The research results significantly improve the reliability of the system. |
