Linear Time-Invariant Optical Voltage Sensor for Harmonic Measurement

Traditional voltage transformers exhibit nonlinear distortion and frequency dependence in harmonic measurements. The optical voltage sensor (OVS) theoretically enables to measure harmonics, but its practical performance is unsatisfactory due to the limited measurement linear range and temperature drift issue. To fix these issues, this article presents a linear time-invariant OVS (LTI-OVS). Based on the Pockels electrooptic effect, the LTI-OVS linearly converts various harmonic voltages into polarization angle variations, which are then mapped into linear displacements using a slit aluminum plate grating (SAPG). In addition, a square-wave differential detection method is employed to dynamically compensate for quasi-static phase noise caused by crystal temperature drift. Experimental validations demonstrate that the proposed LTI-OVS achieves ratio errors below 0.2% and phase errors within $10'$ in single-frequency harmonic measurements. For composite harmonic signals, the spurious-free dynamic range (SFDR) reaches 44.87 dB. The results show that the LTI-OVS to multifrequency input signals strictly adheres to the linear superposition principle of individual frequency components, effectively verifying its harmonic measurement characteristics.