Decoupled Current Control via Feedback Linearization Technique for a Grid-Connected Modular Multilevel Converter

As the MMC is a highly coupled Multi-Input Multi-Output (MIMO) nonlinear system, classical linear controllers only achieve zero steady-state error and good dynamic performance at a limited linear range around an operation point. Else, its dynamic performance highly depreciates. This paper uses the Input-Output Feedback Linearization (IOFL) technique to decouple the meshed state-dependent inputs of the grid-connected MMC current dynamics model. This method independently controls the DC-, AC-, and Circulating currents with desired performance through the whole operation range. The internal dynamics are analyzed and proven stable. From this analysis, the conduction losses for steady-state operation are obtained as a by-product. Simulation results validate the controller performance under different power and energy exchange scenarios.