Abstract: Serial methods may easily lead to the accumulation of algorithm complexity and diagnostic time. A parallel open-circuit fault diagnosis method is proposed for cascaded full-bridge neutral point clamped (NPC) inverters employing carrier phase shifted modulation in this paper, which can achieve independent online diagnosis of multiple faults in different submodules. The complexity and diagnosis time remain unchanged as the submodule number increases. The voltage changes and divergence trends of submodule capacitors under normal and fault conditions are analyzed and compared. The corresponding relationship between the abnormal voltage deviation and the faulty device is summarized. The fault detection is achieved based on the output current and voltage deviation, which also reduces the fault location range. Considering capacitance differences and low-frequency fluctuations of the DC voltage, high-precision extraction of abnormal voltage changes is derived. Hypo-thesis and validation methods are used to calculate the voltage deviation caused by the undetermined devices, and the fault location is further achieved by comparing them with the extracted results. Finally, the feasibility and effectiveness of the proposed method are verified on the experimental prototype containing three submodules.