The Development Of High Frequency Power Supply For The Pulsed Eddy Current Thermography

Pulsed eddy current thermography technology is combined with the pulsed eddy current testing technology and the active thermography technology. Due to the discontinuity of electrical conductivity and permeability, the basic principle of detection is that the eddy current field of the metallic sample to be heated will be abnormal in the defect position, then the joule heat caused by the eddy current will be different from other regions, which result in the temperature abnormity. The results of temperature information can be observed by the infrared thermal imager and then be conducted quantitative evaluation. Compared with the regular nondestructive testing, pulsed eddy current thermography technology has the advantages of non-contact, good space differentiating, a larger detection area at one time and an intuitionistic result, and so forth.Pulsed eddy current testing system mainly includes three modules: induction heating, thermal imaging, data analysis. The induction heating module consists of a sample, an excitation coil and a high frequency power supply, which can realize the conversion from electrical energy to heat energy. Its performance directly affects the final detection result. The water-cooled copper coil is mainly applied in the induction heating fields, which has disadvantages of low energy transfer, poor incentive uniformity, coil shade thermal imager view, high sensitive to the coil, etc.This dissertation introduces magnetism gathering device to the eddy current thermography system, which is excited by U-shaped magnetic gather device. Through modeling and simulation based on ANSYS, the lift-off distance has a smaller influence of heating power, greater energy transfer and incentive uniformity for the magnetism gathering device compared with the water-cooled copper excitation,The series resonance topology for power supply is selected in this dissertation. The power of each hardware module is designed, which consists of rectifier filter circuit, LC resonance circuit, impedance matching transformers, H-bridge driving circuit, current sampling circuit, etc., to realize the power of different load drivers. Through the lift-off height impact experiment, heating uniformity experiment, the crack detection of 45# and 304# steel experiment, the results prove the high frequency power supply with the magnetism gathering device can greatly improve the efficiency of energy transfer, keep a good uniformity of excitation, reduce the sensitivity of the lift-off distance, and at the same time eliminate the shade of the coil on the thermal imager, simplify the system structure, and better realize metal material surface crack detection as well.