This work proposes an model-predictive-control (MPC) strategy applied to Modular Multilevel Matrix Converter (M3C) for Low-Frequency AC (LFAC) transmission systems. This work considers a current, local-cluster balancing (LCB) and inter-cluster balancing (ICB) control based on MPC for a LFAC transmission system which is composed by at least one grid-forming and grid-following control for M3Cs. The novelty of the proposal is the designed ICB control for grid-forming and grid following M3Cs to regulate the cluster energies using circulating currents and common-mode voltage while keeping the power converter under safe limits. Simulations are presented to validate the proposed strategy for both M3Cs. The first M3C generates the low-frequency voltage grid, and the second M3C moves power from one side to the other.