A Multistage and Increased-Level Model Predictive Control Method for Modular Multilevel Converters

In the per-phase model predictive control (MPC) methods, capacitor voltage balancing control had to be introduced to ensure the stable operation of the modular multilevel converter (MMC) due to the inability to directly control the DC-link current. This limits the system's ability to achieve overall optimal control performance, particularly evident in the MPC methods at 2N+1 levels. Therefore, a multistage and increased-level MPC method is proposed. The method combines both per-phase and three-phase models, and achieves the overall control performance by controlling the DC-link current within a reasonable range. Meanwhile, the method is less computationally intensive and independent of the number of submodules (SMs). Finally, the superiority of the method is verified by simulation of a three-phase MMC inverter.