In this paper, a non-contact degradation evaluation method for insulated gate bipolar transistor (IGBT) modules is proposed based on eddy current pulsed thermography approach. In non-contact heat excitation procedures, a high-power induction heater is introduced to generate heat excitation in IGBT modules. The thermographs of the whole temperature mapping are recorded non-invasively by an IR camera. As a result, the joint degradation of IGBT modules can be evaluated by the transient thermal response curves derived from the recorded thermographs. Firstly, the non-destructive evaluation principle of the eddy current pulsed thermography (ECPT) system for an IGBT module with a heat sink is introduced. A 3D simulation module is built with physical parameters in ANSYS simulations, and then thermal propagation behavior considering the degradation impact is investigated. An experimental ECPT system is set up to verify the effectiveness of the proposed method. The experimental results show that the delay time to peak temperature can be extracted and treated as an effective indicative feature of joint degradation.

Aiming to calculate the winding parasitic capacitance for high-frequency high-voltage application, this paper proposes an improved energy method by dividing the electrostatic field into several energy regions. Analytical models of the divided energy regions are established based on the assumed electric field distribution. The stored electrostatic energy in the specified regions covers not only the energy between adjacent turns but also the non-adjacent turns, and a compensation factor is introduced to correct the layer misalignment problem of the standard winding, which makes the analytical energy fairly accurate. Following closely, a calculation procedure of parasitic capacitance is demonstrated. In the end, the accuracy and effectiveness of this method are verified by finite element simulations and measurements.

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