Primary — Secondary control strategy for meshed HVDC transmission grids at steady state

HVDC (High Voltage DC) transmission systems are believed to be a key to integrate more renewable energy sources, especially from remote area and offshore environment, into power systems. In this paper, a steady state control strategy that can be used in a meshed HVDC grids is presented. The control strategy combines local primary controllers and a central secondary or supervisory controller. The objective of the primary controllers is to enable shared management of required changes in bus powers as a result of a disturbance in the system. The objective of the secondary controller is to change voltage and power settings of the primary controllers so that power flows in the transmission cables of the system are kept within the thermal limits after the disturbance. The primary controllers react first when there are disturbances in the system followed by the secondary controller which acts only when necessary.