Decoupling and Optimal Control of Multilevel Buck DC–DC Converters With Inverse System Theory

Abstract

Multilevel buck dc–dc converters have advantages of low switching voltage stress, small inductor size, and high power density. To take an advantage of these properties, the flying capacitor voltage must be balanced at appropriate voltage references value. However, the multilevel buck dc–dc converters are a multi-input multioutput nonlinear strongly coupled control system. To address the problems associated with the complexity of strongly coupled voltages while maintaining control, in this article we propose a decoupled optimal control strategy with an inverse system theory. On the basis of establishing a large signal average model, a universal method to choose the output function for full linearization is proposed with the help of the inverse system method. Furthermore, the linearization and decoupling of the system are achieved, and a number of single-input, single-output pseudolinear subsystems are obtained. Based on the linearized system, multiple optimal controllers are designed to control the subsystems, which significantly reduces the difficulty in controller design. Numerical simulation results show that compared to proportional integral control with linear decoupling, the proposed control strategy has better dynamic regulation performance and stronger robustness under a six-level buck dc–dc converter. Finally, the proposed approach is further verified with the experimental results of a three-level buck dc–dc converter prototype.