Seok-Min Kim, "멀티레벨 컨버터 기반 직류 배전 시스템의 신뢰성 향상을 위한 전압 변조 및 고장 허용제어," 아주대학교 공학박사 학위 논문, 2020. > Paper

This thesis presents switch fault-tolerant strategies for cascaded H-bridge multilevel converter (CHMC) and modular multilevel 

converter (MMC). The proposed tolerant methods are categorized in two different methods to handle open- and short-circuit faults

separately. Most of fault-tolerant methods uses the reserved submodules installed in a multilevel converter. The proposed tolerant 

method in this thesis can maintain the balanced three-phase line-to-line voltages and currents without reserved submodules under

faulty switch condition. Additionally, the rotation scheme is introduced to mitigate unbalanced power distribution among

submodules. The life-time of a power semiconductor relies on its temperature and switching loss is converted as a source of the

temperature. This thesis proposes a modulation method for MMCs to reduce the switching loss while the MMC produces high

quality output voltage and current. The proposed modulation scheme includes discontinuous modulation period to reduce the

switching loss, however, the period causes severe deviation of submodule capacitor voltage. In order to balance the submodule

capacitor voltage, the proposed method conducts rotation method using clamping operation and reconfigured sinusoidal

modulation both. By applying the clamping operation, the MMC can reduce the switching loss effectively and maintain balanced

capacitor voltages. In this thesis, the effectiveness of the proposed control methods is verified by the simulation and experimental

results.