Alternating Iterative Power-Flow Algorithm for Hybrid AC-DC Power Grids Incorporating LCCs and VSCs

AC-DC power-flow calculation is the basis for studying HVDC systems. Since traditional iterative methods need many alternative iterations and have convergence problems, this paper proposes an alternating iterative power-flow algorithm for hybrid AC-DC power grids incorporating line-commutated converters (LCCs) and voltage source converters (VSCs). Firstly, the algorithm incorporates the converter interface model into the AC side, considering the influence of the DC side on the AC side, and establishes an AC-augmented Jacobian matrix model with LCC/VSC interface equation variables. Then, according to the type of converter, control mode, and DC grid control strategy, a DC grid power-flow calculation model under various control modes is established for realizing the power-flow decoupling calculation of AC-DC power grids incorporating LCCs and VSCs. The accuracy and effectiveness of the improved algorithm are evaluated using modified IEEE 57 bus AC-DC networks and the CIGRE B4 DC grid test system. The improved algorithm is applicable to various DC grid control modes and considers the reasonable adjustment of the DC grid variable constraints and operating modes.