A global inertia sharing control scheme for hybrid five-port power electronic transformer to achieve energy coordination, transient switching, and submodule balancing

In high-power hybrid AC/DC distribution systems, multi-port power electronic transformer (PET) encounters challenges such as energy coordination, transient switching, and submodule balancing. In order to address these issues, especially improving transient dynamic performance, this paper proposes a global inertia sharing (GIS) control scheme for a hybrid five-port PET based on modular multilevel converter (MMC), dual active bridge (DAB), and energy storage system (ESS). Firstly, the scheme introduces an inertia sharing (IS) characteristic among internal submodules and external ports based on the capacitor's properties, analyzing the control quantities and degrees of freedom for controlling IS. Next, according to the mathematical model of the PET, four IS controllers and three balancing controllers are designed for the GIS control scheme to achieve coordinated energy control, optimization of transient performance of the system, balance between submodules, and effectively reduce the number of control parameters and sampling hardware circuits. Additionally, the operation region of the system, power flow modes, and controller parameter selection are analyzed. Validation results in extreme conditions and numerous operating mode switching demonstrate that the proposed GIS control scheme enables seamless switching and submodule balancing under uninterrupted power supply, significantly enhancing system transient dynamic performance and enriching power flow modes.