2 research outputs found
In Situ Diagnosis of Multichip IGBT Module Wire Bonding Faults Based on Collector Voltage Undershoot
Condition monitoring of IGBT modules is an effective way to improve the transient performance and reliability of modular multilevel converters (MMC). This paper proposes a novel bond wire failure monitoring method for the multichip IGBT modules in the MMC half-bridge submodule structure. The collector voltage undershoot VCA(np) of the complementary IGBT switch is measured during the turn-off switching transition of the controlled IGBT switch. VCA(np) is sensitive to the induced voltage over the stray inductance of the IGBT bond wires and provides high sensitivity as a health indicator. The non-intrusive measurement technique is demonstrated using a half-bridge circuit during the turn-off transition of the controlled IGBT, while its complementary switch (i.e., the device under test) is in the off state. Theoretical analysis and experimental results show that the parametric drift due to wire bonding failures can be effectively monitored with high specific relative sensitivity and granularity. To ensure its effectiveness in practical applications, the influence of load current, submodule capacitor voltage, and junction temperature is discussed. In addition, a readout circuit is designed featuring the integrated desaturation detection and voltage peak detection, which offers both the short-term overcurrent fault protection and long-term bond wire aging monitoring functions.</p
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Translation of Ligand-Centered Hydrogen Evolution Reaction Activity and Mechanism of a Rhenium-Thiolate from Solution to Modified Electrodes: A Combined Experimental and Density Functional Theory Study
The homogeneous,
nonaqueous catalytic activity of the rhenium-thiolate complex ReL<sub>3</sub> (L = diphenylphosphinobenzenethiolate) for the hydrogen evolution
reaction (HER) has been transferred from nonaqueous homogeneous to
aqueous heterogeneous conditions by immobilization on a glassy carbon
electrode surface. A series of modified electrodes based on ReL<sub>3</sub> and its oxidized precursor [ReL<sub>3</sub>]Â[PF<sub>6</sub>] were fabricated by drop-cast methods, yielding catalytically active
species with HER overpotentials for a current density of 10 mA/cm<sup>2</sup>, ranging from 357 to 919 mV. The overpotential correlates
with film resistance as measured by electrochemical impedance spectroscopy
and film morphology as determined by scanning and transmission electron
microscopy. The lowest overpotential was for films based on the ionic
[ReL<sub>3</sub>]Â[PF<sub>6</sub>] precursor with the inclusion of
carbon black. Stability measurements indicate a 2 to 3 h conditioning
period in which the overpotential increases, after which no change
in activity is observed within 24 h or upon reimmersion in fresh aqueous,
acidic solution. Electronic spectroscopy results are consistent with
ReL<sub>3</sub> as the active species on the electrode surface; however,
the presence of an undetected quantity of catalytically active degradation
species cannot be excluded. The HER mechanism was evaluated by Tafel
slope analysis, which is consistent with a novel Volmer–Heyrovsky–Tafel-like
mechanism that parallels the proposed homogeneous HER pathway. Proposed
mechanisms involving traditional metal-hydride processes vs ligand-centered
reactivity were examined by density functional theory, including identification
and characterization of relevant transition states. The ligand-centered
path is energetically favored with protonation of cis-sulfur sites
culminating in homolytic S–H bond cleavage with H<sub>2</sub> evolution via H atom coupling