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The novel hybrid advanced traction power supply device (NH-ATPSD), which consists of a traction transformer and a “two-phase-parallel-input to single-phase-cascaded-output” (2AC-AC) converter, has been proposed recently. It provides opportunities for solving the neutral section and negative-sequence power quality problems. However, different from the single-level power electronic device with a cascade structure, the negative-sequence current and healthy module overload may occur when the input- or output-module fault occurs in NH-ATPSD. Thus, a dynamic fault-tolerant control for NH-ATPSD is proposed in this article. For input module faults, the healthy module overload is avoided by the proposed dynamic modulation coefficient, which can dynamically adjust the power allocation between output port modules. In addition, the negative-sequence current is suppressed by controlling the partial power imbalance between the 2AC input modules. For output module faults, the active bypass of faulty modules and increased voltage methods are adopted to keep the rated voltage and power output. Finally, the simulation and experiment results verify the effectiveness and efficiency of the proposed control strategy under different fault types.

The traditional cascaded multilevel converter has the problems of many submodules, low power density and high loss. Therefore, this paper proposes a hybrid cascaded multilevel converter (HCMC) topology based on Si and SiC devices. The HCMC consists of a cascaded H-bridge (CHB) unit mixed with Si IGBT and SiC MOSFET devices in series with a three-level neutral point clamped (NPC) unit of all-Si IGBT devices. Then, a special high- and low-frequency hybrid modulation strategy is presented for this topology, which gives full play to the advantages of low conduction loss of Si IGBT and low switching loss of SiC MOSFET. Further, the parameter optimization design of the HCMC is given. In addition, an alternation voltage balancing control method is presented to avoid the problem of capacitor voltage imbalance in submodules. Finally, the simulation and experiment are conducted under the reactive power compensation condition of the 6 kV system, and the effectiveness of the proposed topology and modulation strategy is proved. Moreover, the loss comparison between HCMC and existing cascaded multilevel converters proves that the proposed HCMC topology greatly reduces the operating loss while ensuring the output performance.