Multiport Power Management Method with Partial Power Processing in a MV Solid-State Transformer for PV, Storage, and Fast-Charging EV Integration

This paper proposes, a control method to enable partial power processing (PPP) for increased efficiency of a multiport solid-state transformer (SST). Multiport SSTs are promising in integrating multiple LV DC/AC sources/loads such as photovoltaic (PV), storage, and electric vehicles (EV) into the grid without bulky line-frequency transformers. However, considering ~98.5% efficient line-frequency transformers, efficiency is one major challenge of the SST. For multiport MV LV SSTs, it is revealed in this paper that enabling direct energy exchange between two LV ports is more efficient than circulating power from one LV port into the transformer and back to another LV port. With the PPP, most power exchange between LV ports is processed by only part of the converter. This paper describes a modulation and control scheme for PPP of a current-source SST. The fundamental idea is to select appropriate space vectors that enable direct LV ports power exchange. With the proposed PPP control, the converter efficiency can increase by ~0.37%-1.28% in a wide-range of operating points in this paper. Simulation and experimental results verify the proposed PPP control scheme. The simulation results can be evaluated by using Matlab/Simulink 2018a Software.

Keywords: Three-port power electronic transformer (PET), current-source converter (CSC), isolated bidirectional converter, differential power processing (DPP), battery energy storage system (BESS), ultrafast charging, extreme fast charging, modular soft switching solid-state transformer (M-S4T).