Research On Topology Derivation And Generalized Analysis Of Non-Isolated DC-DC Converters Based On Unified Model Method

As an essential part of power electronics,dc-dc converters attract an extensive attention from both academic and industrial researches since they have been widely used in various applications.For each practical application,comparison among different viable dc-dc converter topologies should be conducted to search for an optimum choice.Therefore,there are two stringent requirements for the topology research:(1)more viable topology configurations should be provided and(2)their comparison process should be easy.In order to obtain more topologies,several systematic topology derivation methods including duality,extension and combination,have been proposed.However,they have some limitations.Additionally,because the characteristics analyses of different topologies are performed one-by-one which will result in a lot of work,the comparison and selection process is complicated.In order to better provide and choose a preferred topology for the practical non-isolated application,a systematic unified model methodology of topology derivation and generalized analysis is employed in this paper.Firstly,according to system requirements,a unified model of the corresponding converter is proposed,from which multiple possible topologies can be derived with different connecting relationships.Then operation principle of the converter is introduced in detail,and the restrictions to guarantee normal operation are derived,with which all possible connections are judged to select out viable topology configurations.Finally,steady-state characteristics and small-signal models of all proposed topologies are simultaneously achieved from the aforementioned operation principle.Therefore,with the unified model methodology,not only more viable topology configurations are derived,but also their performance characteristics are simultaneously yielded.After the review of zero-voltage-switching(ZVS)dc-dc converters and integrated three-port converters,the unified model method is applied in the magnetic coupling soft-switching non-isolated dc-dc converters and the integrated three-port non-isolated dc-dc converters with reduced switches,to derive more topologies and achieve generalized analysis.All derived magnetic coupling dc-dc converters can achieve soft-switching operation without any additional magnetic core,and all obtained integrated three-port dc-dc converters can realize independent control among three ports with only three switches.In the paper,theoretical analysis and experimental verification are presented in detail,which show that the unified model methodology of topology derivation and generalized analysis is systematic,practical,general and extendable.Firstly,the unified model method is introduced in detail.In the paper,a basic cell consisting of two switches and one inductor instead of a specific converter,is utilized as the research objective,which makes research more general because it is a common part of many non-isolated dc-dc converters.According to the ZVS realization principle,a unified model of magnetic coupling soft-switching dc-dc converter based on the basic cell is proposed.With simple modifications,other three type of unified models are further developed.In all above unified models,12 possible configurations exist according to the connecting relationship between main circuit and auxiliary circuit.Likewise,from the operation principle of integrated three-port converter with reduced switches,its unified model is also presented and there are 1728 possible configurations.After the deduction of above five unified models,the systematic unified model methodology of topology derivation and generalized analysis is illustrated in detail.With the method,several viable topologies along with their performance characteristics can be easily obtained for non-isolated dc-dc converters inclusive of the basic cell.Secondly,the unified model method is employed in the magnetic coupling soft-switching dc-dc converter to achieve topology derivation and generalized analysis.Its operation principle is introduced on the basis of unified model,and constraints of normal operation are also obtained.According to the constraints,5 viable magnetic coupling soft-switching topologies are derived from 12 possible connections,among which 4 topologies are firstly proposed in the paper.Moreover,generalized analysis is also performed to simultaneously achieve the steady-state characteristics and small-signal models of all proposed topologies.Performance characteristics of each topology can be easily obtained by substituting into corresponding parameters.Hence,comparison among these viable topology configurations can be easily conducted,which is beneficial for engineers to select an optimum one in the practical design.In the paper,the magnetic coupling soft-switching buck converter is taken as an example to compare its 5 different configurations under different voltage gains.From the comparison result,an optimum one is chosen for the specific application with 48V input and 24V output and its prototype circuit is built.Also,experimental waveforms are demonstrated to verify the correctness of theoretical analysis.Thirdly,the unified model of the magnetic coupling soft-switching dc-dc converter is modified to generate three extended unified models,which are suitable for different applications.The magnetic coupling soft-switching unidirectional and bidirectional dc-dc converters with controlled auxiliary circuits can achieve lower conduction losses and higher efficiency.The magnetic coupling dc-dc converters with controlled auxiliary circuits can also realize soft-switching operation for switches in non-synchronous applications.And the magnetic coupling soft-switching dual-output dc-dc converters can independently regulate two output voltages without additional components.Likewise,the operation principle analysis and topology derivation for each unified model are performed,and a family of viable topologies are respectively obtained,among which most topologies are firstly proposed in the paper.Meanwhile,experiment of a typical one from each type of converters is conducted to verify the theoretical analysis.Because all above unified models are derived from a same model,their characteristics are similar.Therefore,generalized analysis of these unified models can also be performed,which can help to better understand their relationships.Finally,the unified model methodology is also applied to the integrated three-port dc-dc converter,which can expand the breadth and depth of the research.Because the connecting relationships are more complicated in the integrated three-port converter,there are theoretically 1728 possible configurations and it is difficult to judge their effectiveness one-by-one.In order to derive all viable topologies quickly and precisely,mathematical modelling is employed in the paper.The restrictions of normal operation are transformed into mathematical relations,with which 16 feasible solutions are acquired.For all proposed three-port dc-dc converters,simple structure and low cost are obtained due to the reduced number of switches.Likewise,voltage gains,soft-switching operation and small-signal models of all proposed topologies are simultaneously achieved with the generalized analysis.And a typical prototype circuit with 48V input and 24V/2A,36V/3A outputs is built as an example to validate the effectiveness of proposed converters.From above,this paper systematically introduces the significance,theoretical knowledge and practical applications of the unified model methodology.In order to perfect the existing topology derivation methods and provide more favorable topologies along with convenient designs,the unified model method is employed to achieve topology derivation and generalized analysis for non-isolated dc-dc converters in the paper.Detailed content of the method is introduced,and its advantages are also summarized that it is systematic,practical,general and extendable.Afterwards,the magnetic coupling soft-switching dc-dc converter and integrated three-port dc-dc converter with reduced switches are taken as examples to show how the method works.From the magnetic coupling soft-switching dc-dc converter,unified models of other three type of dc-dc converters are further derived.Their topology derivation and analysis process are similar,but they are suitable for different applications due to the different characteristics.Moreover,the topology derivation of integrated three-port dc-dc converter further explores the solution to quickly select out all viable topologies under a complicated connection condition with mathematical modelling.This paper not only generate multiple new preferred topologies for practical applications,but also can revolutionize a new way for topology derivation and theoretical analysis.