Research On Multi-module Parallel DC-DC Converters

Aeronautical high voltage DC(HVDC)power system is one of the main structures of future multi-electric aircraft power supply system.In order to ensure the load demand of multi-electric aircraft,in the 270V high-voltage DC system,there is a certain need for 270V conversion to the 28V.More and more modular ideas are used in the design of aviation DC converters in high-power application.It makes a single converter into a sub-module with universal properties,and achieves a power level improvement through a multi-module parallel structure.In this way,the redundancy of the system can be realized,the reliability of the power system can be improved and the stress of the switching device can be reduced.On the other hand,it is convenient to realize the power superposition and improve the scalability of the system.In this paper,the aviation DC converter adopts a two-stage structure.The front stage is a LLC-DCX converter based on matrix transformer,and the latter stage is an interleaved synchronous rectification Buck converter.Short-circuit control and multi-module parallel current sharing control can be realized by controlling the latter stage Buck converter.Based on the analysis of the starting characteristics of the front stage LLC-DCX converter and the latter stage Buck converter,the paper proposes the soft start scheme and designs the startup sequence of the cascade system.In order to solve current spike problem at the short-circuit moment,a short-circuit control scheme based on the output voltage feedforward is adopted,which can effectively suppress the short-circuit transient current spike and improve reliability of the system.For high-power applications,this paper further studies multi-module parallel technology.After comparing and analyzing the common parallel current sharing control schemes,considering the factors of current sharing accuracy,current sharing response speed and reliability,this paper chooses the maximum current sharing method as the parallel current sharing control scheme between modules,and the adjustment structure of the current sharing loop outside the voltage loop is designed on this basis.In this paper,the fault analysis of multi-module DC converter system is carried out,and the fault module elimination scheme is designed to improve the fault tolerance of the system.Finally,an aviation DC converter with rated power of 3kW was developed,and three modules were connected in parallel.The experiment verified the correctness of the theoretical analysis and the design scheme.