Power Flow Calculation Method for Hybrid Cascaded HVDC Transmission System

There are various technical schemes of Hybrid High-voltage Direct Current (HVDC) transmission, and the topology of DC system is complex. The existing power flow algorithms are difficult to establish the mathematical model for complex DC system. Therefore, this paper studies the power flow calculation of hybrid cascaded HVDC system. Firstly, the topology and steady-state control mode of hybrid cascaded HVDC system are analyzed. Then, according to the numerical relationship of state variables between the converter station and a single converter, the bipolar and multivalve converter stations are equivalent, and the power flow model of the hybrid converter station composed of line commutated converter (LCC) and modular multilevel converter (MMC) is derived. On this basis, by analyzing the internal relationship between the power flow models of converter stations, the method of establishing the power flow model of hybrid cascaded HVDC system is given. Finally, the modified IEEE 39 bus AC/DC system is solved based on the alternating iteration algorithm, and the effectiveness of the proposed model and algorithm are verified.