The Development Of High-frequency Two Phase Power Supply For Induction Thermography

In the eddy-current thermography detection system,the performance of the excitation power affects the detection rate and thermal contrast of the defect crack of the test object.Aiming at the problems such as strong dependence on crack orientation and the low sensitivity in the conventional single-channel excitation,a two-phase orthogonal excitation power supply system was proposed to detect different crack of sample.The key technology of excitation probe structure,hardware circuit and dual frequency search algorithm was studied deeply.A two-phase high-frequency power supply for induction thermography was developed.Based on the theory of rotating magnetic field,a compound double U-shaped excitation probe structure with two U-shaped cores and two excitation coils was proposed.With establishing the simulation model of the probe structure and the sample established,the distribution characteristics of the transient magnetic field on the sample surface were analyzed by finite element software,it is verified that the excitation probe can generate a magnetic field whose amplitude is constant and the direction changes periodically.According to the characteristics of two-phase series resonant load,the hardware circuit of high frequency power supply was designed,including the dual H bridge circuit of MOSFET,the high-side bootstrap driving circuit of integrated chip,the control system circuit of AVR and FPGA and the impedance matching transformer.By adjusting the number of turns of the two excitation coils,the inductance of the load circuit were equal.According to the load voltage and current phase difference and based on the dichotomy of the digital phase-locked loop,automatic fast search for two load resonant frequencies is achieved.Based on the above technologies,the two-phase orthogonal excitation power supply for induction thermography was developed.The waveforms of the control signal,the voltage and current waveforms when the MOSFETs are turned on and off,and the load voltage and current waveforms at the resonant time were tested,it is verified that the power system is reliable.In order to verify the heating effect of the two-phase orthogonal excitation power system on different direction crack,a eddy current thermography testing platform was set up to detect the 30 mm ? 0.35 mm penetrating crack on the surface of 45# steel,and the detection rate and heat Contrast experimental results show that the power system can effectively reduce the dependence on crack direction and improve the detection sensitivity of defect crack in eddy thermal imaging,which satisfies the thermal excitation requirement of detecting crack in any direction.