Using a 4-leg three phase Inverter to connect the AC Grid with a Bipolar DC Grid

Abstract:
With an increasing number of decentralised renewable energy resources and electric DC loads, DC microgrids typically provides a better alternative compared to the conventional AC grid in terms of efficiency and controllability. By implementing DC microgrids, AC and DC grids will coexist resulting in a need for a converter that can enable a power transfer between these two grids. This paper discusses the implementation of this converter. By using a four-leg three phase inverter this converter can enable a power transfer between the grids and directly supply single phase loads on the AC side of the grid. Furthermore, this converter gives the opportunity to create an islanded bipolar DC grid from the three phase AC grid, or create an islanded AC grid from a bipolar DC grid. A low voltage test setup with a 4-leg converter is shown which can power an unbalanced AC load from a DC source. A simulation model in Caspoc of the required control to power unbalanced loads in the AC grid from the DC grid is shown. Lastly, a prototype has been developed to test this converter in a real life setting in future studies.