Discretisation performance analysis of sliding mode controlled DC-DC buck converter via zero-order holder

Abstract

This study investigates the discretisation effects of the zero-order holder (ZOH) on DC-DC buck converters under the direct ON/OFF control of sliding mode (SM), and the two core issues of stability and periodicity for the discrete system are focused on. The optimal parameter for the SM controller is first given on the basis of stability and response speed in the continuous-time domain, following its ZOH discretisation. Restricted by the existence condition of discrete SM, the guaranteed stability is investigated and compared with that of the continuous system in the phase plane, proving that the sampling time of ZOH affects its stability region. Meanwhile, the periodic dynamics, including the system state and the symbolic sequence of switching control law, is further studied via analysing the steady limit cycle of state in phase plane; and the existence condition of multi-periodicity is also deduced. Innovatively this study establishes the influence relationship of the periodic dynamics with the performances of the steady-state error of output voltage and switching frequency. Simulation and experiment results are presented to validate the theoretical and practical value of the proposed research.