Search for: All records

Emerging applications of compact high-voltage SiC modules pose strong challenges in the module package insulation design. Such SiC module insulations are subjected to both high voltage DC and PWM excitations between different terminals during different switching intervals. High dV/dt strongly interferes with partial discharge (PD) testing as it is hard to distinguish PD pulses and PWM excitation induced interferences. This paper covers both the testing and modeling of PD phenomena in high-voltage power modules. A high dV/dt PD testing platform is proposed, which involves a Super-High-Frequency (SHF, >3GHz) down-mixing PD detection receiver and a high-voltage scalable square wave generator. The proposed method captures SHF PD signatures and determines PDIV for packaging insulation. Using this platform, this paper provides a group of PDIV comparisons of packaging insulation under DC and PWM waveforms and discloses discrepancies in these PDIV results with respect to their excitations. Based on these PD testing results, the paper further provides a model using space charge accumulation to explain the PD difference under DC and PWM waveforms. Both simulation and sample testing results are included in this paper to support this hypothesis. With this new model, the paper includes an updated insulation design procedure for high-voltage power modules. 

Li-ion diffusion and lithiation kinetics in MnO/C nanocomposites were systematically investigated by monitoring the change in the charge transfer resistance and the ion diffusion coefficient, and the kinetically predominant process at various charge/discharge states. Crystal field analysis and density functional theory (DFT) calculations were introduced to reveal the relationship between the electronic structure of the phase compositions, the displayed electrochemical potential and its profile. The split 3d orbitals in the Mn ion determine the ordering of the electron migration and energy difference, leading to the different potential profiles in the lithiated/delithiated process. The phase compositions strongly affect the intrinsic properties of the MnO/C nanocomposites, increasing the ion diffusion coefficient from ∼10 −15 to 10 −11 cm 2 s −1 when the electrode progressed from the fully charged to fully discharged state, while both the surface redox reaction and the solid-state diffusion could be the limiting process depending on the lithiation/delithiation states. In addition, the MnO/C anode delivers an energy efficiency of 90% in a Li-ion hybrid capacitor, suggesting a promising and competitive application in the future.