Feedback Linearization Based Current Control Strategy for Modular Multilevel Converters

Modular Multilevel Converters (MMCs) are multi-input-multi-output (MIMO) nonlinear systems. The control systems for MMCs are required to simultaneously achieve multiple control objectives. Existing cascaded control strategies for MMCs are complex and the controller parameter design is not straightforward for the nonlinear systems with highly coupled states. In view of this, a feedback linearization based current control strategy is proposed for an MMC system in this paper. The nonlinear state function model of the MMC is presented and transformed to a linearized form with the help of the feedback linearization technique. Simple linear controllers are employed for the linearized system to regulate the output and inner differential currents of the MMC, which significantly reduces the difficulty in current controller design. The experimental results show that the proposed feedback linearization control strategy is able to achieve excellent steady-state and dynamic performance.