A generalized unified power flow algorithm for AC/DC networks containing VSC-based multi-terminal DC grid

The voltage source converter (VSC) based multi-terminal DC (MTDC) grid becomes an attractive solution of renewable energy integration and AC grids interconnection. Steady state power flow analysis is the basis of further research about the AC/DC grid. The main contribution of this paper is the proposed generalized unified power flow algorithm for AC/DC grids containing VSC-based MTDC. It can also deal with different DC voltage control schemes. This paper investigates the steady state VSC station model and MTDC grid model. According to the power balance of VSC, the relationship between AC grid and DC grid is derived precisely. Secondly, considering diverse control modes of VSC, different DC voltage control schemes, such as constant voltage control, voltage margin control and voltage droop control are presented. At last, we define the mismatch equations of AC gird, VSC and MTDC grid. Employing the Newton-Raphson method, all the unknown state variables of AC, VSC and MTDC can be solved simultaneously with only one Jacobian Matrix. Several simulations with different DC voltage control schemes are set up to clarify the validity, efficiency and feasibility of the proposed unified power flow algorithm.