Implementation of real-time health assessment and thermal management of insulated gate bipolar transistors (IGBTs) require thermal equivalent circuit models that can be used to predict the junction temperature of the modules. Solder aging in IGBT’s has a substantial impact on the accuracy of junction temperatures estimated by the models. This paper proposes an adaptive thermal equivalent circuit model that can estimate the junction temperature of IGBTs with precision under solder aging conditions. Firstly, the solder aging process is monitored in real time by the temperature gradient of the baseplate of the IGBT module, which is easily implement by placing two thermal sensors at the interface between the baseplate and the cold plate. Then, when the solder aging is detected, the actual junction temperature obtained by an on-state collector-emitter voltage of the IGBT is utilized to update model parameters based on the thermal behavior of the device. By combining the two stages, the effect of solder aging on the accuracy of the junction temperature estimate is removed in time. Simulation and experimental results are provided to verify the effectiveness of the proposed method.

Planar transformers have often been mistaken to essentially have lower leakage inductances. The “radial effect” is a nature characteristic for planar windings due to a higher aspect ratio of conductor width to conductor thickness, which gives a reduction in leakage inductance. Traditional formulas for leakage inductance in traditional transformers where the winding width is much smaller than the winding height are not suitable for planar transformers. This paper specifically tailors the traditional 1-D solution of leakage inductance by decomposing the leakage flux into longitudinal and transversal flux. In this manner the “eddy current effect” and the “radial effect” in leakage inductance can be analyzed individually. The proposed new formula including both ac (high frequency eddy current effect) and dc effects (radial effect) offers an accurate prediction of leakage inductance in planar transformers. Finite Element Analysis (FEA) and measurements are carried out to validate the proposed formula.

A model for the online estimation of junction temperature based on the gate pre-threshold voltage in high-power insulated-gate bipolar transistors (IGBTs) was proposed. Firstly, the turn-on behavior and temperature dependence of the gate-emitter voltage during the turn-on delay period were studied. It was revealed that the turn-on waveform of the gate-emitter voltage exhibits a point of inflection after which the voltage between the gate and emitter increases significantly; at this point, the relationship between the voltage and the temperature changes from a positive correlation to a negative correlation. Meanwhile, Analyses on the basis of semiconductor physics revealed that the negative correlation between gate-emitter voltage and temperature is caused by the temperature dependence of the flatband voltage. Finally, a model for estimating the junction temperature was established based on a combination of the turn-on delay time and the gate pre-threshold voltage which is negatively correlated with the temperature, to eliminate the effect of the bus voltage.

This paper proposes an improved partially interleaved structure for high-voltage (several kV) high-frequency (several hundred kHz) multiple-output applications. The proposed transformer structure is compared with other typical structures with the leakage inductance, AC capacitance, AC resistance and the ratio of AC/DC resistance taken into consideration. The proposed structure features lower leakage inductance, smaller AC capacitance, lower AC resistance and lower ratio of AC-DC resistance, which is suitable for high-frequency high-efficiency applications. A planar transformer with the proposed structure was built and tested in an LCLC resonant converter, where the input voltage is 40 V, output is 4800 V, switching frequency 500 kHz and the efficiency is 96.8%, which validates the analysis.

The performance factor (PF) for magnetic materials originated with S.A. Mulder [1] to compare different grades of ferrite materials. It essentially consists of a plot of the product of the frequency (f) and flux density (B) versus frequency at a specified level of power loss per unit volume.

Insulated gate bipolar transistors (IGBTs) are widely used in new energy fields, such as wind power converters and electric vehicles. The junction temperature characteristics and junction temperature measurements greatly influence the reliability of the IGBT. During switching, the electrical parameters of the IGBT undergo considerable change. The thermo sensitive electrical parameter (TSEP) method has been commonly used to extract junction temperature. The TSEP method has the inherent advantages of being able to take measurements quickly and accurately, in a non-intrusive manner. The junction temperature estimate under the on-state condition cannot reflect the reliability of the IGBT during the dynamic switching process. The solution to this dilemma is to measure the junction temperature using the dynamic TSEP method during the IGBT turn-off process. The junction temperature is measured by the reverse voltage peak between the auxiliary emitter and power emitter, which forms during the IGBT turn-off process. The feasibility of the proposed method has been experimentally verified.