Multiple boundaries sliding mode control applied to capacitor voltage-balancing systems

摘要

Capacitor voltage-balancing systems are usually applied to power electronic circuits. The main issue in these systems is equalising the voltage of a large number of capacitors connected to a voltage source in serial or parallel arrangements. A particular application of the capacitor voltage-balancing systems is found in modular multilevel converters (MMC). The voltage balancing of the floating capacitors in the submodules of the MMC during its pre-charging operating stage is a key issue since it is a critical task for the correct operating of these converters. The stability analysis of an active voltage balancing strategy for pre-charging MMCs is addressed in this paper. The adopted voltage-balancing strategy consists in adding a resistance to each submodule of the MMC by means of a controlled switch. These switches are being controlled by a sliding mode control algorithm with multiple boundaries (discontinuity surfaces of high co-dimension). These systems are essentially discontinuous piecewise smooth dynamical systems (Filippov systems) commanded by electronic switches. In this paper, the local stability of the voltage balanced system is analytically proven for an arbitrary number of submodules. In addition, a detailed analysis of the global dynamics of this system with two submodules and two switching boundaries sliding mode control is presented. Simulation results obtained on a MMC with 10 submodules are shown to validate the theoretical analysis. (C) 2020 Elsevier B.V. All rights reserved.