Background: With the increasing development of voltage source converter based high voltage direct current (HVDC), it will become reality to interconnect different DC networks into DC grid with DC-DC converters.
Method: In this paper, three operation scenarios for the DC grid with DC-DC converters are proposed, by which the DC networks can reinforce each other with relative independence. In order to achieve the flexible switching of the proposed scenarios, the DC-DC combined control and principle of parameter selection is presented. In addition, two coordination control for different scenarios are given to optimize the distribution of unbalanced power when the disturbances occur in the grid. With the proposed scenarios and control strategy, the impacts caused by the disturbances are alleviated and the uninterrupted operation of the grid is guaranteed.
Result: A simulation model is established on the PSCAD/EMTDC and the simulation results verify the effectiveness of the proposed operation scenarios and control strategy.