Adaptive Fast-Optimization Predictive Control of MMC With Improved Hybrid Control Framework

Modular multilevel converters (MMC) are widely used in voltage-sourced converter-based high-voltage dc due to their modular design, ease of scale, and fault tolerance capabilities. The multivariable control objectives of MMCs can be achieved by model predictive control (MPC) due to MPC's fast dynamic response and ease of implementation. Nonetheless, conventional MPC techniques for MMC have shortcomings, including high computational requirements and poor circulating current suppression. First, this study proposes an adaptive fast-optimization MPC that adapts the number of candidate combinations to the steady and transient states, significantly reducing the computational burden. Second, an improved hybrid combination of MPC with proportional resonance controller is used to enhance the circulating current suppression performance. Simulations and experimental case studies on a three-phase grid-connected MMC validate the proposed techniques.