| With the rapid development of space technology,the functions of spacecraft become more and more complex,which puts forward higher requirements for the power system of spacecraft.The partially isolated three-port DC-DC converter(TPC)has the advantages of small size,high integration,and high power density,it can be used as an effective topology to integrate primary energy,energy storage device,and power equipment in spacecraft power systems.The partially isolated TPC which integrates dual Buck/Boost with dual active bridge(DAB)is researched as the object,and because the switching loss is one of the main loss sources,and the mismatch of high-frequency transformer primary side voltage of the high-voltage port and the secondary side voltage will lead to the increase of leakage current stress,and it will increase the conduction loss of the switch and the core loss of high-frequency transformer,therefore,it is of great significance to study the soft-switching method and the current stress optimal control method for improving the power transmission efficiency.This dissertation aims to provide a more efficient solution for the power conversion of the spacecraft power system.The main research contents and innovation points of this dissertation are as follows:(1)This dissertation proposes a soft-switching Buck/Boost converter topology based on coupled inductors and dual diode.Detailed analysis of the working process of the converter during a switching cycle is given;and the implementation conditions for soft-switching,key parameters(coupling inductance,switch parallel capacitance)design points,and control principles are provided;the input source current ripple analysis and loss analysis are carried out;a 120 k Hz,500 W experimental prototype is built,and the experimental results show that the efficiency at full load is improved by more than 1.2%(Buck mode)and 1.3%(Boost mode)compared to traditional Buck/Boost converter.Both the main switch and auxiliary switch of this topology can achieve soft-switching,and compared with the existing zero-voltage-switching(ZVS)Buck/Boost converter based on coupled inductors,the input source current has less ripple,thus,it is more suitable for the connection of energy storage device and spacecraft power system.In addition,a family of Buck/Boost converter topologies based on coupled inductors and dual diode is obtained by changing the connecting positions of the coupled branches in the main circuit,similar to the existing ZVS Buck/Boost converter,it provides more topology choices for practical applications.Taking two topologies as examples,the working principle analysis,loss analysis,and key parameters design of the converter are carried out,two 100 k Hz,1000 W experimental prototypes are built,the feasibility and soft-switching performance of these two converters are verified by experiments.(2)According to the research on soft-switching technology based on coupled inductors mentioned above,in order to further suppress the ripple of the input source current,a novel active clamp soft-switching Buck/Boost converter topology based on coupled inductors is proposed.The working process of the converter in a switching cycle is analyzed in detail,and the soft-switching conditions,key parameters(transformer parameters,clamp capacitance,switch parallel capacitance),and control principle are given,and a 100 k Hz,800 W experimental prototype is built,and the experimental results show that the full-load efficiency is 1.2% higher than that of the conventional Buck/Boost converter.The main switch can realize ZVS and the auxiliary switch can realize zero-current-switching(ZCS).The phase-shifting control between the main switch and the corresponding auxiliary switch is used to minimize the conduction loss of the auxiliary circuit.Compared with the current ZVS method based on coupled inductors used in Buck,Boost,and Buck/Boost converters,this method can completely avoid the large ripple of input source current caused by the introduction of the auxiliary current.(3)For the TPC which integrates dual Buck/Boost and DAB,in addition to the duty cycle of the original side arm and the phase-shift angle between the original and secondary side full-bridge circuits,the phase-shifting angle between the secondary bridge arms can be used as the third control variable to participate in the optimal control.This dissertation presents a current stress optimal control method for the TPC which integrates dual Buck/Boost and DAB.The mathematical model of current stress optimization is established,and the optimization problem is transformed into an extremum problem with constraint conditions.A 50 k Hz,500 W TPC experimental prototype is built,and it is verified that the peak leakage inductor current of the highfrequency transformer can be suppressed by introducing optimal control,the system loss can be reduced,and the power transmission efficiency can be improved.In the case of light load,the current stress optimal control method can achieve more obvious results.(4)Based on the research of the soft-switching technology of the Buck/Boost converter,the auxiliary circuit is introduced into the TPC which integrates dual Buck/Boost and DAB,the TPC topology based on the coupled inductors and dual diode,and the active clamp TPC topology based on coupled inductors are constructed.For these two TPC topologies,the realization conditions of ZVS are given,and the switching states of the main switch and auxiliary switch in a switching cycle are given,the soft-switching range of the primary side main switch before and after introducing the auxiliary circuit is compared under different matching degree between the primary side high-voltage port voltage and the secondary side voltage,and the reasonable parameter design can realize ZVS in full load range,two 60 k Hz,750 W coupled inductor-based TPC prototypes(the type of dual diode and the type of active clamp)are built,which can effectively extend the ZVS range of the main switch.The two TPC topologies have the advantage of low current ripple at the energy storage port,which can avoid the adverse effect of large current ripple on the life of energy storage devices(such as lithium batteries)when applied to spacecraft power systems. |
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