MVDC multi-terminal grids: a valid support for distribution grids improvement

Medium Voltage Direct Current (MVDC) technology can be very helpful in meshing traditional AC distribution grids by means of multi-terminal DC links; this way, power flows among different feeders can be redistributed, as similar as transmission lines. Moreover, MVDC converters can easily interface renewable generators (e.g. photovoltaic farms) with AC, handling at the same time reverse power flows. This paper presents an overview of such technology, from initial concept and state-of-the-art to some innovative projects, including advanced protection schemes between MVDC links and existing distribution grid. The examples include active current limiter devices, hybrid circuit breakers and a communication layer for the coordination of these protection devices and power converters (logic selectivity), making MVDC a valuable support for AC grid improvement.