Multiple Operating Mode Analysis of Power Converter based on Graph Theory

Power converters are the typical switched systems which operate based on the alternate switching of the semiconductor switches.The operating mode of power converters consists of several operating stages in one switching period.Each operating stage refers to a sub-circuit or equivalent circuit where different sub-circuits are switched in a fixed order according to the control strategy design.Power converter may operate in different operating modes even with the same control scheme,for example,the DC-DC converter has differing performance under the continuous conduction mode(CCM)and discontinuous conduction mode(DCM).Thus,it is necessary to have a comprehensive understanding of the converter’s characteristics in advance to avoid undesired operation in practice.In this paper,the power converter is considered as a graph made up of several meshes.All sub-circuits in power converter can then be obtained by the mesh combination algorithm,and the operating mode can be constructed by considering the preset switching ON/OFF scheme.Ultimately,the typical waveforms in different modes can be predicted,which is useful to identify abnormal phenomena.Cúk converter is taken as an example to demonstrate the proposed multiple mode analysis method.It is found that there are four kinds of phenomena in addition to the well-known CCM and DCM.Finally,the experimental results are provided and show good agreement with the theoretical analysis.