| Because of the function of efficiently delivering energy among multiple DC ports,multi-port DC-DC converters are widely demanded in emerging industry applications such as DC microgrids,electric vehicles,aerospace,etc.The existing multi-port DC-DC converters mainly consist of two types,including sharing the common switch and the common magnetic core.The former one successfully realizes independent control of N outputs by utilizing only N+1 switches.However,because switches occupy relatively smaller volume when compared with other components such as the magnetic element with bulky magnetic cores,the volume optimization of former one can be further improved.Compared with the former one,the latter has higher power density due to sharing only one magnetic core.Therefore,it is widely concerned and chosen as the research topic of this paper.Through multiplexing inductor current,only one inductor is required to realize energy conversion among multiple DC ports,thus decreasing the costs and the volume.Nevertheless,the limited number of this type of converters cannot meet the demand of practical applications.Moreover,when single inductor multi-output DC-DC converters are operated in continuous conduction mode(CCM),the severe cross-regulation problem exists.This problem can be solved in discontinuous conduction mode(DCM),however,large peak current occurs when the load is heavy.That may cause large undesired conduction loss.In addition,the switches are usually hardswitching when single inductor multi-input multi-output DC-DC converters are operated in CCM,resulting in large switching loss and harmful electromagnetic interference.Based on existing researches on magnetic core shared multi-port DC-DC converters,the main work of this paper composes the following three aspects:(1)A simple derivation method of single inductor multi-input multi-output(SI-MIMO)DCDC converters is proposed.According to it,a large quantity of topologies with various good performance can be obtained through only three steps.Firstly,three basic cells consisting of a single inductor,multiple sets of unidirectional switches and input/output ports are proposed based on inductor current multiplexing.Secondly,integrate them with the conventional two-port converters by selecting demanded basic cells and connecting their suspension points with different circuit nodes.Finally,implement the topology simplification by removing unnecessary switches/diodes.Based on the proposed principle,a large number of SI-MIMO DC-DC converters with different characteristics are derived from buck,boost,buck-boost and non-inverting buckboost converters to meet the demand of different applications.(2)To simultaneously alleviate the cross-regulation problem under CCM and the large spike output current problem under DCM in SI-MIMO DC-DC converters,this paper also presents a scheme of coupled inductor based multi-output DC-DC converters which is suitable for applications with unbalanced loads.This kind of converters is derived from the typical two-port DC-DC converters by substituting their output inductor with coupled inductor based multi-output branch,without increasing the number of magnetic cores.The coupled inductor based multioutput branch consists of multiple paralleled output branches with unidirectional switches and one coupled inductor whose turns ratio is 1:1.The dotted terminals of both primary and secondary windings of coupled inductor are connected to output nodes in original two-port DC-DC converters.Therefore,the original output current equals to continuous magnetizing current so that the spike output current can be successfully depressed even under heavy load.In addition,the paralleled output branches are connected to another terminal of secondary winding through unidirectional switches.Accordingly,the leakage inductor current can be assigned to these output branches with the control of switches so that the output voltages can be independently regulated when under light loads.Moreover,the cross-regulation problem between the original output port and the added ones is improved because they harvest energy from magnetizing inductor and leakage inductor,respectively.Based on example traditional two-port DC-DC converters which are buck,zeta and cuk,their corresponding coupled inductor based multi-output DC-DC converters for unbalanced loads are derived.The original output port is suitable for a heavy load,and other added output ports are for light loads.(3)By means of duality,the dotted terminals of primary and secondary windings are turned to be connected to the input node of original two-port DC-DC converters rather than output node in(2).And the new coupled inductor based multi-output branch is used to substitute the input inductor in two-port DC-DC converters.After replacing,the derived multi-output DC-DC converters can similarly obtain a good cross-regulation.Differently,the continuous current is changed to be the input one rather than the output one due to replacing the input inductor.Moreover,the current of primary winding could be negative because it is changed from the sum of the magnetizing current and the leakage inductor current to the difference between them.According to it,after replacing the diode in original two-port DC-DC converters with a synchronous rectifier switch,the soft-switching can be achieved,contributing to lower switching losses.Taking the traditional two-port DC converters boost,sepic,and cuk with input inductors as examples,this paper also derived corresponding soft-switching multi-output DC-DC converters from them.After the derivation of SI-MIMO DC-DC converters,the coupled inductor based multi-port DC-DC converters for unbalanced loads and the soft-switching multi-output DC-DC converters,this paper selects one example topology from each of these three types of DC-DC converters.The operation principles,the circuit characteristics,design considerations,etc.based on the three examples are introduced in detail.At last,the experiments are implemented to verify the correctness of theoretical analysis. |
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