A Software-Based Fault-Tolerant Strategy for Modular Multilevel Converter Using DC Bus Voltage Control

A software-based method is proposed in this article to enhance the fault-tolerant capability of modular multilevel converters (MMCs). In the proposed approach, dc bus voltage is considered as a controllable parameter in a way to maximize the line-to-line voltage amplitude at the postfault condition. In comparison with the previous works, the proposed method maintains a larger line-to-line voltage in various fault states. Several drawbacks such as high amount of common-mode voltage, power-factor limitations, and electromagnetic interference problems existing in the previous works are alleviated in the proposed method. Another advantage of the proposed method is that the line-to-neutral voltages of the MMC remain balanced in the postfault condition. This feature makes it possible to utilize third-harmonic injection technique to maintain larger line-to-line voltage after the fault occurrence in the MMC. Moreover, the proposed method can be applied to both three-phase and single-phase systems. A general formulation of the proposed method is derived, and at the end, comparative simulation and experimental results are provided to validate the effectiveness of the proposed method.

Automated summary

The article proposes a software-based method to enhance the fault-tolerant capability of modular multilevel converters (MMCs) by controlling the DC bus voltage. The method maintains larger line-to-line voltage in various fault states and balances the line-to-neutral voltages of the MMC in the postfault condition. Additionally, it addresses common-mode voltage, power-factor limitations, and electromagnetic interference issues seen in previous works.