Algebraic model and control of embedded multi-terminal DC network in meshed AC power system

Multi-terminal DC grid can be embedded in meshed AC grid to increase power transmission capability and control power flow of AC grid. In addition to economic benefits especially in congested areas, the proposed solution can provide back-up for the AC grid and enhance power transmission capacity and flexibility. From the supervisory control point of view, a control algorithm is required to set the reference values for controlling the DC grid power flow based on the desired operating points of meshed AC grid. In this paper, the algebraic model of the DC grid is derived and validated in meshed AC power systems. Algebraic model will present the behavior of AC grid with respect to various operating points of the DC grid, and it is used for steady state analysis. This paper also proposes a droop control structure with dead-band controller for the DC grid. To verify the algebraic model and the control structure, dynamic performance of the embedded multi-terminal DC grid in a reduced order three-bus AC equivalent NYPA power system is investigated in PSCAD/EMTDC environment.