Study on Performance of DC Optical Current Transformer Based on Fast Variable Optical Attenuator

As a diffractive Micro-Opto-Electro-Mechanical system device, the grating light valve has high optical modulation efficiency and fast modulation rate, which can form many applications such as display and communication, and fast variable optical attenuator (FVOA) is one of the important ones. Benefiting from the low power consumption and polarization insensitivity characteristics of FVOA, an FVOA-based optical current transformer (FVOA-OCT) for high-voltage direct current measurement is proposed. A closed-loop optical feedback structure combining square-wave and step-wave is designed, which can track the phase shift introduced by the measured current in real time through the compensation phase shift generated by the step-wave, so as to solve the nonlinear problem of FVOA, and then improve the linearity, dynamic range and sensitivity. The solution eliminates the need for a laser energy supply system, which increases the reliability. A prototype with a rated current of 800 A is developed, and the test results show that the ratio error (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RE</i>) fluctuation range is -0.35%-0.38% at 80 A, -0.04%--0.01% at 960 A, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RE</i> and phase displacement of 1200 Hz harmonic current are -2.2% and 70 μs, respectively, and the step response rising time in the range of 0.1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p.u.</i>-0.9 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p.u.</i> is about 135 μs. These confirm that the prototype meets the error limit requirements of class 0.2% specified in GB/T 26216.1-2019.