Control Allocation for Optimal and Resilient Operation of the MMC

The article proposes a new approach to modular multilevel converter (MMC) control. A key feature is the use of real-time optimization for arm voltage regulation and for balancing of the capacitor voltages in the submodules (SMs). The control allocation (CA) method automatically and optimally distributes the control requirements among a large number of switches. As a benefit, the algorithm can be adapted with almost no modification to accommodate failures. First, a control-oriented approach is used to derive the necessary models. Then, the MMC control architecture is designed. Simulations demonstrate the effectiveness of the approach on an MMC with 50 SMs per arm. Test cases include steady state and transient conditions, as well as operation without and with multiple SM faults.