Fast Fault Protection Based on Direction of Fault Current for the High-Surety Power-Supply System

The high-surety power-supply system, super uninterruptable power supply (Super-UPS), is an evolution of the traditional uninterruptible power supply. It consists of multiple sources, multiple energy storages, and redundant power converters to improve the reliability of the power-supply system significantly. In this paper, a fast fault-protection scheme based on direction of fault current without the assistance of communication for Super-UPS is presented. It achieves fast and selective fault detection and ensures the uninterruptible load power when short-circuit faults occur. The directional fault-current detection and the coordination between the circuit breakers and converters are investigated. The protection threshold settings are also discussed. In addition, an improved fault-current measurement method, which can suppress the influence of stray inductance of the solid-state circuit breaker, is presented to guarantee an accurate operation of the protection scheme for rapidly rising fault current. Finally, the proposed protection scheme and the improved fault-current measurement method for Super-UPS are verified by experiments.