Vibration identification of fiber optic current sensors based on dual closed-loop feedback and VMD

In this paper, a dual closed-loop feedback scheme is employed to divide the FOCS into two operational cycles. The 1st cycle, similar to traditional methods, maintains the bias phase at the high-sensitivity operating point of ±π/2 for measuring current. However, in the 1st cycle, it is impossible to distinguish between current and vibration. Therefore, the 2nd cycle is proposed to determine whether vibration has occurred. The bias phase in the 2nd cycle is maintained at the lowsensitivity operating point of 0 through feedback, and only vibration signals above the fundamental square wave frequency are received. Then, the data collected from both cycles are decomposed using the VMD method. By comparing the times of the burst points, it can be determined whether the fluctuations in the 1st cycle are due to vibrations. If the signal is due to vibration, the trip operation will not be initiated, thereby avoiding false tripping incidents.