Hierarchical Open-Circuit Fault Diagnosis in VSC-MTDC Transmission Systems Based on Passive Sliding-Mode State Estimation

This paper proposes a passive sliding-mode state estimator (PSMSE)-based hierarchical open-circuit fault diagnosis scheme for identifying the open-circuit fault and locating the faulty power semiconductor device in voltage source converter-based multi-terminal direct current (VSC-MTDC) transmission systems. Fault detection and isolation (FDI) is one of the most crucial processes in the VSC-MTDC operation. The energy storage function in passivity theory is constructed for analyzing the system stability and preserving the system passivity property. Then the additional inputs are designed to reshape energy and guarantee the global asymptotic convergence to the sliding surface. Four layers are established in the proposed hierarchical fault diagnosis scheme for precise fault identification and localization. The enhanced observation dynamics are provided compared with the conventional sliding-mode method because of the extra damping injections. Meanwhile, the fault detection time is also reduced with enhanced immunity. Simulation cases on healthy transient conditions and faulty conditions are executed to verify the effectiveness of the proposed PSMSE-based hierarchical open-circuit fault diagnosis scheme.