Submodule (SM) open-circuit failures severely affect the reliable operation of modular multilevel converter (MMCs). A comprehensive SM open-circuit failure diagnosis process includes three steps with failure detection, localization, and classification. However, the existing diagnosis methods perform these steps separately, which makes the diagnosis processcomplicated. Furthermore, the efficiency is relatively low with separate diagnosis steps. To address this issue, a diagnosis method with variance measurement is proposed in this paper to combine failure detection, localization, and classification. The proposed method makes use of two fault characteristics of SM open-circuit failures: 1) SM capacitor voltages have distinct distributions upon different faulty IGBTs; 2) Numerous SMs in the MMC make the failure diagnosis equivalent to statistical outlier analysis. On account of the fault characteristics, a variance-based index called VAR is proposed to evaluate the distributions of SM capacitor voltages. The VAR values are then analyzed with quartile analysis, which is a statistical outlier analysis method, to complete the diagnosis process. The proposed failure diagnosis method features high reliability, high compatibility, and high cost-effectiveness. Finally, the feasibility of the proposed method is verified through both simulations and experiments under various failure scenarios.

中文翻译：

---

具有方差测量的模块化多电平转换器（MMC）的统计子模块开路故障诊断方法

子模块（SM）断路故障严重影响模块化多电平转换器（MMC）的可靠运行。全面的SM开路故障诊断过程包括故障检测，定位和分类三个步骤。然而，现有的诊断方法分别执行这些步骤，这使得诊断过程变得复杂。此外，通过单独的诊断步骤，效率相对较低。为了解决这个问题，本文提出了一种结合方差测量的诊断方法，将故障检测，定位和分类相结合。所提出的方法利用了SM开路故障的两个故障特征：1）SM电容器电压在不同故障IGBT上的分布不同；2）MMC中的大量SM使故障诊断等同于统计异常值分析。考虑到故障特征，提出了一种基于方差的指标VAR，用于评估SM电容器电压的分布。然后使用四分位数分析（一种统计异常值分析方法）分析VAR值，以完成诊断过程。提出的故障诊断方法具有高可靠性，高兼容性和高成本效益的特点。最后，通过仿真和实验，验证了该方法在各种故障场景下的可行性。这是一种统计异常值分析方法，可以完成诊断过程。提出的故障诊断方法具有高可靠性，高兼容性和高成本效益的特点。最后，通过仿真和实验，验证了该方法在各种故障场景下的可行性。这是一种统计异常值分析方法，可以完成诊断过程。提出的故障诊断方法具有高可靠性，高兼容性和高成本效益的特点。最后，通过仿真和实验，验证了该方法在各种故障场景下的可行性。