Abstract: The concepts of hybrid dynamic system (HDS)and switched linear system (SLS)were introduced into studying the controllability and reachability of Buck converter .In this paper , the switched linear system model of Buck converter was first built , and then the controllability and reachability definitions and theorems of the switched linear system with the same systematic matrix and different input matrices were presented according to the characteristics of the switched linear system model for Buck converters .Afterwards, the controllability and reachability of Buck converter was strictly proved based on the switched linear system model .Finally , the relationship among the controllability , reachability and output controllability was discussed and it is pointed out that the three items are in good concordance. Moreover , the controllability of Buck converter was verified by experiments, there by concluding that , with load current step , the output of Buck converter is completely controllable and is kept stable in the designed reference .This is in concordance with the controllability analysis result of Buck converter as a switched linear system model .The proposed method is also adaptable to the investigation of the controllability and reachability of other power converters .

Key words: Buck converter, switched linear system, controllability, reachability