Low Order Response Model-based Secondary Control for the AC-MTDC Grids

The holistic nature of primary and secondary control leads to the satisfactory operation of the AC surrounded Multi-Terminal HVDC (AC-MTDC) grids. In this paper, a Lower Order Response Model  (LORM) is developed and utilized in the hierarchical control structure. The LORM based secondary control is proposed while operating primary control in droop for a requisite operation of the AC-MTDC grids. The objective of this secondary control is to ensure reduced frequency and DC-voltage deviation with enhanced stability of the AC-MTDC grids. Further, the stability margins of the AC-MTDC grid are identified by employing an eigenvalue analysis of the LORM. These margins decide the droop value limits, which are utilized in secondary control for the stable operation of the AC-MTDC grid. The proposed framework is validated in MATLAB and PSCAD/EMTDC co-simulation platforms while considering two case studies and an AC-MTDC test system consisting of five terminals integrated into a two-area power system.