Modelling and analysis of multicell converters using discrete time models

The main drawback of the discrete time models reported in the literature for predicting nonlinear phenomena in power electronic circuits is their complexity which make their use in system design very minted. The availability of approximated discrete time models that retain the accuracy of the exact model and at the same time makes the system design simple would give new perspectives in the control design of such systems. In this paper we give a detailed analytical study of a two-cell DC-DC buck converter for high voltage applications by using discrete time formulation. Different operating modes are possible and they can be modeled by a unified discrete time model. A digital controller is considered for the system. This controller includes a dynamic compensator in the form of digital integrator for the output variable regulation. An approximated discrete time model in the form of current recurrence equation which accurately describes the dynamical behavior of the system is derived. This model is use to predict instabilities when some design parameters are varied. The Jury test is applied to the characteristic polynomial in order to obtain boundary of stability in the design parameter space. Numerical simulations confirm the theoretical predictions