Browsing by Author "Jimenez, Sergio Julian"

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    Design of a Medium-Voltage High-Current Super-Cascode Power Module
    (University of Alabama Libraries, 2023) Jimenez, Sergio Julian; Lemmon, Andrew
    Wide bandgap (WBG) semiconductors are garnering significant attention due to their exceptional characteristics that facilitate the development of high-efficiency, high-power converters. However, several limitations including cost, manufacturability, and technical limitation have hindered the realization of Medium Voltage (MV) devices utilizing WBG technology. In light of this, the super-cascode switch (SCS) emerges as one of the most promising candidates to bridge this technological gap in the short term. The significance of the SCS is underscored by its capability to attain MV ratings through the utilization of low-voltage (LV) semiconductors, which have been available in the market for over a decade.This dissertation delves into a comprehensive examination of the SCS, proposing enhancements to an existing super-cascode topology, thereby facilitating advancements in both the static and dynamic performance of the SCS. This dissertation provides a comprehensive theoretical treatment of the operating principles governing the SCS, which have only been partially unveiled in existing literature. Moreover, a novel set of figures of merit have been established to properly evaluate the performance and operation of the SCS. These metrics yield insights into the performance of the SCS, elucidating characteristics previously obscured due to the absence of appropriate metrics to evaluate the SCS. Integrating all the previous information, a 6.5 kV – 400 A super-cascode power module was designed, implemented, and experimentally evaluated.
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    On the Triggering Mechanism for Self-Sustained Oscillation in Wide Band-Gap Semiconductors
    (University of Alabama Libraries, 2021) Jimenez, Sergio Julian; Lemmon, Andrew N.; University of Alabama Tuscaloosa
    Wide bandgap (WBG) semiconductors are very attractive due to the outstanding characteristics that enable high-efficiency power electronics converters. However, due to the achievable fast transitions, these devices can suffer from unintended behavior such as under-damped ringing, voltage and current overshoot, half-bridge shoot-through, increased electromagnetic interference (EMI), and self-sustained oscillation (SSO).This thesis provides an analytical treatment of the triggering mechanism leading to SSO, which is an undesired phenomenon that may occur during turn-off transitions of WBG transistors due to their fast switching performance. For this analysis, a large signal model has been developed in state-space form to determine the likelihood of forced cycles in a simplified application circuit. Forced cycles are known to be a necessary but not sufficient condition for SSO to occur. In this sense, preventing the occurrence of forced cycles eliminates any possibility of destabilizing the circuit. Forced cycles occur when the gate-source voltage of the active switch rings back above threshold and causes channel conduction. The model presented in this thesis is capable of predicting the maximum gate-source voltage ring-back for any level of intrinsic parasitics and operating conditions. The model presented in this thesis is empirically validated with an application circuit utilizing GaN high electron mobility transistors (HEMTs). GaN HEMTs are known for very high switching speed, which also introduces susceptibility to SSO. The modeling framework introduced in this thesis is expected to be useful to application designers in creating application circuits that take maximum advantage of the attractive properties of WBG devices while ensuring immunity to the SSO phenomenon by some intentionally selected design margin.