Dynamic Performance Evaluation and Optimization of Common HFAC Bus Lightweight MMC-SST

The common high-frequency ac bus modular multilevel converter–based solid-state transformer (MMC-SST) scheme featured by synchronous modulation could realize the lightweight design of module capacitance without complicating the control strategy and circuit structure. However, in the lightweight MMC-SST system, the substantial reduction of submodule capacitance leads to the strong coupling between ac and dc ports. The study of tracking and antidisturbance performances of the lightweight MMC-SST based on the dynamic average model shows that the tracking performance difference could be compensated by the regulator, but the antidisturbance performance is weakened when the capacitance is reduced. A predictive controller is proposed for optimizing the antidisturbance performance, which could improve the response speed and then decrease dc-link voltage deviation. The feasibility of low inertia operation of the lightweight MMC-SST in a hybrid ac–dc distribution network, medium voltage dc power transmission system, and photovoltaic and energy storage joint power supply system is also evaluated; it shows that the normal operations of MMC-SST are not deteriorated by the inertia reduction both in the power router and generator modes. Finally, the effectiveness of the optimization strategy is verified by simulations and experiments.