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A DC Grid Without The Application of DC Breakers

With increasing demand for renewable energy integration, engineering crew is currently managing to expand the application of two-terminal HVDC into multi-terminal HVDC or DC grid. Similar as AC grid, it is necessary for DC grid to possess the ability to deal with DC fault rapidly. While at the present stage, the performance of DC breaker is far away from the standard of comprehensive engineering applying in both economic and technical aspect. At the same time, hybrid MMC equipped with HSS requires coordinate from all the converters paralleled to the grid to cut off the fault line or fault converter, which causes power outage of entire grid, so this alternative scheme can be applied to multi-terminal HVDC in a limited scale, but cannot be adopted directly to DC grid. This paper proposed a DC grid without the application of DC breakers and its corresponding control and protection strategy. Divided into several sub-grids according to their voltage classes and port characteristics, the proposed DC grid is able to handle DC fault in situ without the help of DC breakers, by inserting fault isolation devices into the sub-grid connecting lines. Simulation results validate the proposed DC grid and its corresponding control and protection strategy.