Research On Modularized Three-port DC-DC Conversion System

With the increasing demand of space power systems,standalone renewable power systems and DC microgrids,research and exploration on novel topologies of power converter and new structures of system have been promoted.This paper mainly focuses on the research of topology derivation of high-performance three-port converter(TPC),modularized TPC power systems and the common power control strategies for them,to meet the growing requirement of high power density,high reliability and modularization of the space power systems.A family of novel partly-isolated TPC topologies is proposed and the method for the derivation of TPC topologies is given.Based on the high-frequency pulsating voltage caused by two-switch bridge of the interleaved Buck/Boost converter(IBBC),steady and controlable voltage can be generated with the help of bridgeless boost rectifier(BBR)and be served as the third power port.To achive the galvanic isolation,power transformer can be inserted between the IBBC and BBR,and a family of partly-isolated TPC topologies can be derived with different structures of BBR.The detailed operational principle,output characteristics and soft-switching analysis of the proposed topology are presented,and the power control and its implementation are given.With the control strategy of pulse-width modulation plus phase-shift modulation,the power-flow control of primary side and secondary side can be decoupled.At the same time,the current ripple of the PV port can be greatly reduced,and both the primary-side and secondary-side switches can achieve soft switching,which help to improve the efficiency of the converter.With the proposed topology and power control method,the converter can achieve smooth swtiching among different operation conditions when the input or output power varies,while the output voltage keeps steady which meets the demand of the space power system.The system structure and power control of modular three-port converter(MTPC)power system are studied.Since the TPC has three power ports,various flexible structures of MTPC system can be obtained for different power demands.The basic structure of MTPC is the parallel connection of all the three power ports of the TPC modules,and the current-sharing(CS)control strategy of the system is studied.The operations and control requirements of the system are analyzed in detail,then the general idea of power control of the paralleled MTPC system is given,that is,CS control is required for two of the three power ports simultaneously while the third port achieves CS naturally.Since the focus of the CS control for paralleled MTPC system is the same as that of paralleled system with two-port converters,the existing CS control methods can be extended to the paralleled TPC system.As an example,detailed implementation of the CS control based on the average-current method on both the bidrectional ports and the output ports are presented.The structure of the MTPC power system with separated power sources and its power control strategy are proposed.With the isolated input ports of TPC modules connecting to the distributed sources respectively,the system can achieve distributed maximum power point tracking of the sources.The system is composed of several TPC modules,interfacing the distributed sources,which helps to achieve distributed maximum power point tracking of the sources.The system architecture,operation conditions and power control demands are illustrated in depth.To achieve power management of the system,a novel hybrid power control strategy is proposed,that is,CS control on the bidirectional ports when the energy-storage device(ESD)discharges,and power distribution based on the power ability of the separated sources when the ESD charges.With the proposed power control strategy,reliable and stable operations of the system within all of the operation conditions can be achieved.A novel MTPC power system with separated loads and its power management are proposed,which features that there is no common voltage bus on the load side.Distributed loads are connected to each TPC modules,and single-stage power conversion can be achieved from both the input port and bidirectional port to the output port.To achieve optimal power distribution of the system,a novel hybrid system-level power control strategy is proposed,i.e.,CS control on the bidirectional ports when the ESD charges and power distribution based on power requirements of the separated loads when the ESD discharges.With the proposed power control strategy,the system can achieve stable operations under different operation conditions and smooth switching among them when the input or output power changes.Prototypes are built with both the simulation and experimental results in detail to verify the analysis mentioned above,respectively.