Real-Time Hierarchical MPC Applied to an MMC in Grid-Forming Mode: Implementation and Validation in Power Hardware-in-The-Loop

Modular Multilevel Converters (MMC) are now expected to fulfill AC and DC grid stability functions while at the same time they must ensure their own operation. In this article, we propose a new MIMO control structure to coordinate the AC/DC power exchange and MMC internal energy control using a hierarchical MPC. This controller is tested on an AC/DC system where the MMC works in grid-forming mode on the AC side and controls the DC-grid voltage at the same time. This MPC solution is implemented in a real-time controller to operate a physical mockup of a 6 kVA MMC which contains 60 submodules and interfaces a 400 V DC grid and a 120 V (line-to-ground) AC grid. The MPC solution shows similar tracking performance with the state-of-the-art dual PI control solution based on two PI controllers working in parallel, and exhibits a better disturbance rejection capacity than this dual PI.