Equilibrium Point Analysis for the MMC-HVDC System with Trust-region Algorithm

As a promising topology, modular multilevel converters (MMCs) are widely deployed for high voltage direct current (HVDC) systems. To directly calculate the equilibrium point of MMC-HVDC, this paper establishes the system model considering the dynamics of the capacitor voltages, the output current and the circulating current. The established model is then analyzed to exhibit the interactions between the state and the control variables. Without simulations, a trust-region algorithm is proposed to determine the equilibrium point of the MMC-HVDC system, which decreases the time cost compared with the simulation. For the verification of developed method, an MMC-HVDC system is tested. The results demonstrate that the derived model and the proposed algorithm can provide accurate equilibrium point with high efficiency. On the basis of the developed algorithm, the model and parameter impacts are also analyzed.