Скачать или смотреть webinar 44th #1 Research on the Modular Multilevel Converter based Solid-State Transformer

The solid-state transformer (SST), also known as the power electronic transformer or the smart transformer, is an emerging technology, which acts as an interface between the medium-voltage AC grid and the low-voltage DC bus with galvanic isolation at medium/high frequency. The input-series output-parallel (ISOP) structure is the basic SST configuration for achieving the voltage transformation. The series-connected converters are used for sharing the relatively high grid-side voltages, and the parallel-connected converters are used for shifting the isolation requirements to medium/high frequency.
In this presentation, the so-called modular multilevel converter (MMC) is open-circuited at the DC link, and the open-DC MMC based SST is developed for integrating both PV panels and EV chargers together. The developed SST features the flexibility in addressing opposite power flow directions. Detailed power flow analysis on the open-DC MMC is carried out to clarify the control freedoms, and thus the corresponding control scheme can be designed. It is further found that the operational burden of the developed SST under unbalanced grid conditions can be greatly reduced if the DC-side powers are properly regulated. The laboratory test results are provided to validate the effectiveness of the developed SST, especially under unbalanced grid conditions.