Compensation of Phase Modulation Disturbance in All Fiber-Optical Current Transformer

In order to improve measurement accuracy of all fiber-optical current transformer (FOCT), an improved demodulation algorithm was proposed for a sine modulation. The formula for effective phase modulation depth (EPMD) was firstly presented, and three kinds of potential external disturbance in EPMD were analyzed. To overcome the current measurement error induced by these EPMD disturbances, we put forward an improved algorithm for time-dependent measurement of EPMD by second- and fourth-order harmonic component of optoelectronic signal. A simulation experiment in different disturbance intensity were carried out, and the results showed that when measured current is between 200A~1500A,the proposed algorithm can enhance the current measurement accuracy by over 30 times than the conventional algorithm, and measurement relative deviation can be maintained below 0.2% if the disturbance intensity is below 5%.