Enhanced Inflection Points Retrieval Method Applied to an Optical Voltage Sensor

Abstract

The optical voltage transducer offers several advantages over traditional inductive and capacitive transformers, such as wide bandwidth, complete galvanic isolation, and immunity to electromagnetic interference. These voltage transformers can be designed using electro-optical amplitude modulators, which are based on the Pockels effect in crystals such as lithium niobate. The quadrature switching method is employed to obtain two signals from the photodetected one. Inflection points from these two signals are then retrieved using the Discontinuity Point Judgment (DPJ) method. Based on the preliminary converted signal and the identified inflection points, an orthogonal signal is constructed. This approach achieves the quadrature condition without the need for a feedback control loop. The two resulting quadrature signals are subsequently analyzed using the high-gain and sliding mode control approach, which involves employing the control system to fully compensate for the phase shifts induced by the voltage applied to the sensor crystal. Data were collected using a myRIO card and stored in. lvm files; later, they were compiled offline using Matlab. Sinusoidal signals ranging from 7 kV to 14 kV (peak-to-peak) were tested, with amplitude relative errors remaining below 1 % when compared to a high-voltage (HV) probe reference.