A Power Flow Calculation Method for Multi-Voltage Level DC Power Grid Considering the Control Modes and DC/DC Converter

Compared with traditional DC power flow analysis; multi-voltage level DC grid power flow analysis is more complex due to its diverse operation methods. This article proposes the power flow calculation method in multi-voltage level DC grid considering the control modes. To take into account the control mode of the different AC/DC and DC/DC converter stations, the basic control characteristic of multi-voltage level DC grid is studied at first. After obtaining the DC transformers' influence in power flow analysis, the multi-voltage level DC grid is then partitioned in different sub-grids according to different converter's and DC transformer's control modes. Based on such method, the steady-state equivalent model of the multi-voltage level DC grid can be established for power flow calculation. Finally, the node admittance matrix and power flow equation are established through Newton Iterative method. To verify the proposed method, a three-voltage level DC grid with 13 terminals are established in PSCAD software. Based on such model, the correctness of the method is verified and the impact of the DC transformers is also analyzed.