Design and Measurement Verification of Elasto-Optical Sensor Adapted to Space Charge Measurement Method Based on Optoelectronics

The alternative electrical power system equipment such as power electronic transformer is the core component of the distributed and renewable energy grid, facing the development needs to large capacity, compact and high voltage level. However, the development of power electronics technology reduces the size of electrical equipment, but also puts higher requirements on its insulation performance. Compared to the traditional electrical equipment, due to the direct exposure to the high frequency class sine wave, transient PWM switching pulse and other strong field special electrical stress, the operating condition of the alternative electrical power system equipment is worse. To support the reliable insulation design and state evaluation of alternative electrical power system equipment under the complex transient stress, based on the narrow pulse width and high signal-to-noise ratio characteristics of terahertz wave and the principle of the ellipsometry detection method, a space charge measurement method with high spatial and temporal resolution is proposed, and the transmission model of photo-electro-mechanical charge measurement signal is constructed. The model analysis points out that the space charge elastic wave generated by the perturbation of the electric field is approximately proportional to the light intensity difference detected by the balanced detector. Combined with the terahertz photoelectric field characterization model, it is feasible to recover space charge distribution by measuring the light intensity difference. The related work verified the feasibility of the proposed method from the theoretical level. Aiming to the key sensing detection part of the measurement system, based on molecular dynamics simulation, the design and modification of the elasto-optical sensor substrate material are carried out. Meanwhile, the modified design idea of sensor material based on SU-8 photoresist and hydroxylated functionalized graphene is proposed. The simulation results point out that the elastic modulus and Poisson's ratio of the SU-8/HFGR composite system shows a decreasing trend with the increase of temperature. Compared with the unmodified system, the mechanical stability of the composite system is improved. The average elastic modulus of the composite system is 4.420 9 GPa with a mean squared error of 0.146 6, and the average Poisson's ratio is 0.208 1 with a mean squared error of 0.009 8. Further, based on the photolithography principle, the highly reliable elasto-optical sensor is prepared. Further, based on the proposed optical measurement method, an ellipsometry measurement platform is designed and built. Since the charge perturbation elastic wave presents kHz repetition frequency and picosecond pulse width waveform characteristics, the piezoelectric actuator is selected as the kHz level repetition sinusoidal elastic wave input source, and the femtosecond laser is selected as the femtosecond pulse width pulsed elastic wave input source, so as to respectively simulate the space charge perturbed to produce kHz frequency and fs pulse width elastic wave scenarios. Then, the measurement results of the ellipsometry measurement platform are compared with the piezoelectric sensing module of the conventional electroacoustic pulse measurement system to verify the measurement performance of the developed sensor. The experimental results shows that the output voltage of the balanced detector is mV level, which is consistent with the traditional PEA piezoelectric sensor module. At the same time, the sensor could be used in optical measurement with high reliability to catch the kHz repeated elastic waves and fs pulse width elastic waves. Compared with the piezoelectric sensor module, the measurement waveform of the elasto-optical sensor is smoother and less distortion. © 2023 Chinese Machine Press. All rights reserved.