Design of a highly reliable fault-tolerant unified power flow controller for enhanced voltage regulation

The rapid proliferation of inverter-based resources (IBRs) has complicated the power system infrastructure and required efficient Flexible Alternating Current Transmission System (FACTS) devices to ensure dynamic power flow in the grid. Among these, the unified power flow controller (UPFC) has superior performance; however, it is vulnerable to capacitor degradation that connects the Static Synchronous Series Compensator (SSSC) and Static Synchronous Compensator (STATCOM) converters, as well as open-circuit faults to the IGBT switches of the inverter in series and parallel converters. These faults can deteriorate the performance of the UPFC converter, which can undermine the stability of the system. This paper introduced a fault-tolerant UPFC architecture based on the redundant capacitor and N + 1 IGBT switches that ensure the resilience and robustness of the converter in the event of a fault. A seamless mechanism is designed that can reconfigure the control to bypass the faulty component and connect the healthy component using the fault detection and isolation (FDI) block of the fault-tolerant control (FTC). The simulations in MATLAB/Simulink clearly illustrate that the proposed N + 1 strategy ensures the constant capacitor voltage in the event of faults in IGBT switches. As compared to the conventional control strategies, this method reduces the settling time to 60 ms, ensuring the continuous voltage regulation of the grid. This result demonstrates that the proposed solution enhanced the operational reliability and robustness of the UPFC in critical transmission corridors.