Power flow analysis in multi-terminal HVDC grid

Recent interests in developing a new type of grid have suggested the idea of the dc grid. However, the dc grid has less degrees of freedom than an ac grid which restricts its power flow control ability. To overcome this situation, an auxiliary dc voltage controller that would vary the voltage on a dc line can be inserted to provide additional degrees of control freedom. This paper investigates the benefits of adding such controller on a dc grid. The region of operation for a system with and without the auxiliary dc voltage controller is calculated. Two configurations are studied: a 3 terminals system with 3 lines and a 4 terminals system with 5 lines. The analysis confirms the enlargement of the region of operation for both systems and high sensitivity to voltage variations caused by the controller is explored.