Unified Multi-Level Modeling and High-Fidelity Real-Time Simulation of Modular Multi-Level Converter

Real-time simulation plays an important role in the development and verification of modular multi-level converter (MMC) systems, especially for the rapid and low-risk evaluation of control and protection functions in medium- and high-voltage applications. However, MMC validation often requires simulation models with different fidelity levels for different testing purposes, while detailed device-level representation further imposes stringent constraints on computational efficiency. To address these issues, this paper develops a multi-level real-time modeling framework for MMCs, in which switch models of different accuracy can be incorporated within a unified architecture and flexibly selected according to the target test scenario. On this basis, a device-level real-time simulation method is further established to capture the nonlinear switching transients of MMCs under the proposed framework. By combining network decoupling with FPGA-oriented implementation, the framework can achieve a minimum simulation step of 50 ns under fully parallel hardware allocation. Considering FPGA resource optimization, the prototype implemented in this work is validated with a 100 ns time-step. A three-phase MMC with four submodules per arm is used as the validation case and implemented on an FPGA platform. Both waveform comparisons and quantitative error analysis demonstrate close agreement between the proposed real-time model and offline reference models. In addition, closed-loop real-time experiments are conducted to further confirm the effectiveness of the developed MMC model in realistic real-time simulation-based testing applications.