The book reports in detail on the approaches used to estimate the new steady-state operation limits of the expanded system and examines the factors influencing them, revealing new operation limits in the process. Further, the book explains how to coordinate the converters to stay within the limits after there has been a disturbance in the system. In closing, it describes the current DC grid control concept, including how to implement it in an MTDC system, and introduces a new DC grid control layer, the primary control interface (IFC).