Power Flow Calculation of AC/DC System With LCC-MMC Series/Parallel Hybrid HVDC

Abstract

There are various technical schemes for the hybrid HVDC transmission, and rather complex structures for the topology of the DC system. Meanwhile, it is difficult for the current power flow algorithm to establish a mathematical model in the complex DC system. Therefore, this paper studies the power flow calculation of the series and parallel hybrid AC/DC system. Firstly, the topologies and steady-state control modes of the hybrid DC systems in the Baihetan and the Kunliulong projects are analyzed. Then, according to the numerical relationship of state variables between the converter station and the single converters, the bipolar and the multi-valve converter stations are equivalent, deriving the power flow model of the converter station based on the line commutated converter (LCC) and the modular multilevel converter (MMC). On this basis, by analyzing the internal relationship between the converter station power flow models, the establishment method of the power flow models of the series and parallel hybrid DC system is given. A LCC-MMC series/parallel hybrid AC/DC system power flow alternating iterative algorithm is proposed. Finally, the effectiveness of the proposed model and algorithm is verified by the modified IEEE 39-node series/parallel AC/DC system.