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The pulsed eddy current (PEC) is an effective method for the online detection of laser welding seam defects. The joint wavelet dictionary learning method is proposed for solving the separation problem of the broad frequency harmonic and local non-smooth distortion of the PEC signal. The Haar and Gabor wavelet is adopted to be the basic function, which is extended to be the over complete wavelet dictionary library by cyclic migration. The sparse representation of the defect PEC signal is obtained by combining the joint wavelet dictionary with the orthogonal matching pursuit algorithm. The feature parameters of the PEC signal are calculated and inputted into the support vector machine to detect the laser welding seam defect intelligently. The validity of the proposed method is further verified by the experimental results, demonstrating the effectiveness of the classification identification and quantitative assessment of the pore and crack.

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Pulsed eddy current testing is suitable for non-contact detection of conductor structural defect, which is an effective method to realize online detection of welding structural defect of power battery pack. Aiming at the circular laser weld structure between the bus-bar and the terminal of the power battery pack, a three-dimensional finite element simulation model of pulsed eddy current testing is established. According to the structural parameters of the pulsed eddy current excitation coil, which are the inner diameter, outer diameter, height and number of turns, the pulsed eddy current voltage responses of the laser welding defect structure of the battery pack bus-bar are calculated, respectively. By analyzing the influence of the excitation coil parameters on the pulsed eddy current detection results, the pulsed eddy current excitation coil parameters are determined for the testing of laser welding structural defects. It provides a method and basis for the optimal design of the pulsed eddy current detection system for the laser weld structural defect of the battery pack bus-bar.

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