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Fault‑tolerant capability of MMC with novel structure of middle submodules
Duc Dung Le,Dong-Choon Lee,Eui-Cheol Nho 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.9
In this paper, an improved modular multilevel converter (MMC) topology has been proposed with fault-tolerant capability and reduced submodule capacitor voltage fluctuation (SMCVF) in a low frequency operating range. In the proposed converter, a novel middle SM, which has salient features, is inserted between the upper and lower arms. For regular operation, the middle SM is applied to mitigate the power fluctuations in both arms by providing distribution of high-frequency power components, which reduces the AC voltage fluctuation on the SM capacitor. When a fault occurs in any SM in the upper or lower arms, a new half-bridge SM can be configured from the middle SM to replace the faulty SM without any interruption, which means the converter is operated in the fault-tolerant mode. Therefore, the performance of the converter is maintained well, and the system reliability is enhanced. Simulation and experimental results have verified the effectiveness of the proposed topology and control strategy.
Duc Dung Le,Dong-Choon Lee 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
This paper proposes a modified hybrid modular multilevel converters based on half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs) for mediumvoltage applications. The FBSMs are used to reduce the submodule (SM) capacitor voltage fluctuations in low fundamental frequency operations by balancing the power difference between the upper and lower arms through flying inductors without the common-mode voltage injected. In addition, the FBSM can substitute a faulty HBSM if a failure in HBSM is detected and then the converter keeps its operation continuously. The viability of the proposed topology as well as the effectiveness of the control scheme have been confirmed by the simulation and experiment results.
Three-phase flying-capacitor MMC with six coupled inductors
Le, Duc Dung,Lee, Dong-Choon,Kim, Heung-Geun The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.4
In this paper, the design and integration of coupled inductors have been proposed for a flying-capacitor (FC) modular multilevel converter (MMC) for induction motor drive applications. In the conventional three-phase FC-MMC, twelve discrete inductors are needed for three legs. However, by integrating one coupled inductor with two windings in two half-arms, the number of inductors required is reduced from 12 to 6. Accordingly, the overall volumes and weights of cores and windings can be reduced by 41.7% and 41.4% when compared with discrete inductors. To confirm the validity of the proposed coupled inductor, a 4160-V/1-MW simulation model of a FC-MMC and a 220-V/3-kW scaled-down prototype have been built, of which performance for induction motor drives has been tested from standstill to the rated speed.
Duc Dung Le,Sihyeong Hong,Dong-Choon Lee 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.6
In this paper, an IGBT open-circuit fault detection and fault-tolerant control strategy are proposed for a fl ying-capacitor modular multilevel converter (FC-MMC) feeding induction motor drives. Fault occurrence is detected by monitoring the sum of measured AC-circulating currents. In the fault case, the phase with the faulty device is identifi ed through the errors between the measured and estimated output currents of the converter. In this phase, then, a localization of a faulty submodule (SM) is performed by investigating the SM capacitor voltages. Thereafter, the fault-tolerant control method is applied to reconfi gure the converter structure, where the faulty SM is isolated and the converter can operate as normal. In addition, an SM capacitor voltage-balancing control scheme is proposed, where the number of current sensors is reduced to six from nine. Therefore, the system cost is lowered, and the communication burden is lightened. The viability of the proposed control scheme is confi rmed by experimental results for an FC-MMC-fed induction motor drive system.