arXiv:2611.07734v1 Announce Type: new Abstract: Model-based design (MBD) is a mature framework for designing the current controllers of modular multilevel converters (MMCs) in high-voltage direct current (HVDC) transmission systems. In MBD, linear state-space models are preferred for their good trade-off between accurate dynamics prediction and simplicity. However, first-principle derivations often neglect relevant MMC dynamics, which can hinder controller performance. Data-driven (DD) methods can deliver less biased models that capture parameter uncertainties, control-loop interactions, and grid dynamics, yet they remain under-exploited for controlling MMC currents. This paper studies DD current control method based on integral Subspace Predictive Control (iSPC), synthesized directly from input--output data measured in a high fidelity real-time digital simulator (RTDS), and proposes an initial guideline outlining the main steps for its systematic application to MMC current control. The proposed iSPC is compared against state-of-the-art DD solution, and the findings are validated through simulation studies in MATLAB/Simulink.