Modelling and simulation of a high voltage-level modular multilevel converter (MMC) is challenging due to large amount of semiconductor switches, various submodule (SM) circuits, and different operating conditions. Several equivalent models have been proposed for modelling and simulation in system level, which did not consider an industrial or digital controller. To accelerate MMC station design, a highly efficient model is needed with considering control parameters/strategies and accurate dynamics of voltage/current. In this study, an improved equivalent circuit model (ECM) is developed for large-scale system simulation and MMC station design. The proposed ECM considered the MMCs based on various SM circuits under different operating conditions. It can generate bipolar arm voltage and simulate static compensator under dc fault condition. Based on the proposed ECM, the influences of simulation time step on accuracy/efficiency are investigated by considering the sample period and voltage balancing strategies. This research is conducted based on an MMC-HVDC system in the PSCAD/EMTDC software. The study results demonstrate the effectiveness of the proposed ECM and show the relationship between simulation accuracy/efficiency and control/simulation parameters for determining simulation time step. Based on study results, the computational efficiency of proposed model is not significantly affected by the complexity of SM circuit.

中文翻译：

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改进的MMC等效电路模型及仿真时间步长的影响分析

由于大量的半导体开关，各种子模块（SM）电路和不同的工作条件，高电压级模块化多电平转换器（MMC）的建模和仿真具有挑战性。对于系统级的建模和仿真，已经提出了几种等效模型，这些模型没有考虑工业或数字控制器。为了加快MMC站的设计，需要一个高效的模型，同时考虑控制参数/策略和准确的电压/电流动态。在这项研究中，为大型系统仿真和MMC站设计开发了一种改进的等效电路模型（ECM）。提出的ECM考虑了在不同工作条件下基于各种SM电路的MMC。它可以产生双极臂电压并在直流故障条件下模拟静态补偿器。基于提出的ECM，通过考虑采样周期和电压平衡策略，研究了仿真时间步长对精度/效率的影响。这项研究是基于PSCAD / EMTDC软件中的MMC-HVDC系统进行的。研究结果证明了所提出的ECM的有效性，并显示了仿真精度/效率与控制/仿真参数之间的关系，以确定仿真时间步长。根据研究结果，所提模型的计算效率不受SM电路复杂度的影响很大。研究结果证明了所提出的ECM的有效性，并显示了仿真精度/效率与控制/仿真参数之间的关系，以确定仿真时间步长。根据研究结果，所提模型的计算效率不受SM电路复杂度的影响。研究结果证明了所提出的ECM的有效性，并显示了仿真精度/效率与控制/仿真参数之间的关系，以确定仿真时间步长。根据研究结果，所提模型的计算效率不受SM电路复杂度的影响。