Zheyu Zhang

Photovoltaic (PV) inverters are critical yet vulnerable components in modern energy systems, often acting as reliability bottlenecks that increase the levelized cost of energy (LCOE). To address this, this paper presents a comprehensive Failure Mode and Effects Analysis (FMEA) tailored for PV inverters. Leveraging field data and literature, we identify failure-prone components, such as capacitors, and relays, and prioritize their risks based on quantitative Risk Priority Numbers (RPNs). The analysis reveals that surge-induced MOV short circuits, capacitor degradation, and environmental cooling fan failures dominate the risk profile. These findings provide a targeted framework for reliability improvement, guiding future efforts in predictive diagnostics, design optimization, and accelerated life testing strategies.

CCryogenic power electronics have emerged as a critical technology for applications ranging from superconducting systems to deep-space exploration. To ensure reliable low-temperature operation, the thermal and electrical management of the cryogenic apparatus is essential, where the design of conduction leads acts as a governing factor. This paper presents an analytical modeling framework for the temperature profile of cryogenic conduction leads, designed to balance thermal load against electrical voltage drop and power loss. The model is grounded in the linearization of temperature-dependent material properties, augmented by a novel error compensation method. This approach extends predictive accuracy down to 50 K. Furthermore, sensitivity analysis reveals the lead resistance as the metric most susceptible to parameter uncertainties. Experimental validation demonstrates that the model predictions align closely with measurement data, achieving R² consistently above 0.98. Notably, the relative error remains below 3% at 50 K across different operating currents. While numerical benchmarks confirm that thermal radiation induces deviations under high-temperature overload conditions, its impact is negligible within standard cryogenic operating ranges. Finally, based on this validated model, a systematic design methodology is proposed to optimize the conduction lead geometry for both pulse-based characterization and continuous operation, ensuring compliance with strict thermal and electrical constraints.

Future electrified aircraft propulsion (EAP) requires solid-state circuit breaker (SSCB) to be: 1) extremely light, efficient, fast and reliable; 2) suitable for both longer-term higher voltage (>10 kV dc) or shorter-term lower voltage (1 to 2 kV dc) systems; 3) suitable for cryogenic cooling enabled by liquified natural gas or liquid hydrogen fuel; and 4) highly flexible, intelligent and easy for protection coordination. This article summarizes the research effort led by the University of Tennessee team of applying gallium nitride (GaN) devices to a cryogenically-cooled SSCB for EAP applications. With the careful device selection, characterization, packaging and system-level integration and control, the developed SSCB reached an extremely high efficiency ( $>99.96$ % in a 40kft altitude chamber with liquid nitrogen cooling), high density (>336 kW/kg for a 750V/100A rating per module), high scalability (able to be configured in the range of 1kV to 10kV and 100A to 1000A), and intelligent and coordinated fault protections, e.g., $10\times $ fault current interruption and i2t protection, polarity-sensitive and voltage-dependent fault detection, and current limiting functions.

Regio- and stereoselective switchable synthesis of (E)- and (Z)-N-carbonylvinylated pyrazoles is first developed by using the Michael addition reaction of pyrazoles and conjugated carbonyl alkynes. Ag₂CO₃ plays a key role in the switchable synthesis of (E)- and (Z)-N-carbonylvinylated pyrazoles. Ag₂CO₃-free reactions lead to thermodynamically stable (E)-N-carbonylvinylated pyrazoles in excellent yields whereas reactions with Ag₂CO₃ give (Z)-N-carbonylvinylated pyrazoles in good yields. It is noteworthy that (E)- or (Z)-N¹-carbonylvinylated pyrazoles are obtained with high regioselectivity when asymmetrically substituted pyrazoles react with conjugated carbonyl alkynes. The method can also extend to the gram scale. A plausible mechanism is proposed on the basis of the detailed studies, wherein Ag⁺ acts as coordination guidance.