Switching Trajectory Control for High Voltage Silicon Carbide Power Devices with Novel Active Gate Drivers

The penetration of silicon carbide (SiC) semiconductor devices is increasing in the power industry due to their lower parasitics, higher blocking voltage, and higher thermal conductivity over their silicon (Si) counterparts. Applications of high voltage SiC power devices, generally 10 kV or higher, can significantly reduce the amount of the cascaded levels of converters in the distributed system, simplify the system by reducing the number of the semiconductor devices, and increase the system reliability. However, the gate drivers for high voltage SiC devices are not available on the market. Also, the characteristics of the third generation 10 kV SiC MOSFETs with XHV-6 package which are developed by CREE are approaching those of an ideal switch with high dv/dt and di/dt. The fast switching speed of SiC devices introduces challenges for the application since electromagnetic interference (EMI) noise and overshoot voltage can be serious. Also, the insulation should be carefully designed to prevent partial discharge. To address the aforementioned issues, this work investigates the switching behaviors of SiC power MOSFETs with mathematic models and the formation of EMI noise in a power converter. Based on the theoretical analysis, a model-based switching trajectory optimizing three-level active gate driver (AGD) is proposed. The proposed AGD has five operation modes, i.e., faster/normal/slower for the turn-on process and slower/normal for the turn-off process. The availability of multiple operation modes offers an extra degree of freedom to improve the switching performance for a particular application and enables it to be more versatile. The proposed AGD can provide higher switching speed adjustment resolution than the other AGDs, and this feature will allow the proposed AGD to fine tune the switching speed of SiC power devices. In addition, a novel model-based trajectory optimization strategy is proposed to determine the optimal gate driver output voltage by trading the EMI noise against the switching energy losses. For the 10 kV SiC power MOSFET, the detailed design considerations of the proposed AGD are demonstrated in this dissertation. The functionalities of the 3-L AGD are validated through the double pulse tests results with 1.2 kV and 10 kV SiC power MOSFETs

A novel active gate driver for improving SiC MOSFET switching trajectory

The trend in power electronic applications is to reach higher power density and higher efficiency. Currently, the wide band-gap devices such as silicon carbide MOSFET (SiC MOSFET) are of great interest because they can work at higher switching frequency with low losses. The increase of the switching speed in power devices leads to high power density systems. However, this can generate problems such as overshoots, oscillations, additional losses, and electromagnetic interference (EMI). In this paper, a novel active gate driver (AGD) for improving the SiC MOSFET switching trajectory with high performance is presented. The AGD is an open-loop control system and its principle is based on gate energy decrease with a gate resistance increment during the Miller plateau effect on gate-source voltage. The proposed AGD has been designed and validated through experimental tests for high-frequency operation. Moreover, an EMI discussion and a performance analysis were realized for the AGD. The results show that the AGD can reduce the overshoots, oscillations, and losses without compromising the EMI. In addition, the AGD can control the turn-on and turn-off transitions separately, and it is suitable for working with asymmetrical supplies required by SiC MOSFETs.Postprint (author's final draft

Active gate drivers for high-frequency application of SiC MOSFETs

The trend in the development of power converters is focused on efficient systems with high power density, reliability and low cost. The challenges to cover the new power converters requirements are mainly concentered on the use of new switching-device technologies such as silicon carbide MOSFETs (SiC). SiC MOSFETs have better characteristics than their silicon counterparts; they have low conduction resistance, can work at higher switching speeds and can operate at higher temperature and voltage levels. Despite the advantages of SiC transistors, operating at high switching frequencies, with these devices, reveal new challenges. The fast switching speeds of SiC MOSFETs can cause over-voltages and over-currents that lead to electromagnetic interference (EMI) problems. For this reason, gate drivers (GD) development is a fundamental stage in SiC MOSFETs circuitry design. The reduction of the problems at high switching frequencies, thus increasing their performance, will allow to take advantage of these devices and achieve more efficient and high power density systems. This Thesis consists of a study, design and development of active gate drivers (AGDs) aimed to improve the switching performance of SiC MOSFETs applied to high-frequency power converters. Every developed stage regarding the GDs is validated through tests and experimental studies. In addition, the developed GDs are applied to converters for wireless charging systems of electric vehicle batteries. The results show the effectiveness of the proposed GDs and their viability in power converters based on SiC MOSFET devices.La tendencia en el diseño y desarrollo de convertidores de potencia está enfocada en realizar sistemas eficientes con alta densidad de potencia, fiabilidad y bajo costo. Los retos para cubrir esta tendencia están centrados principalmente en el uso de nuevas tecnologías de dispositivos de conmutación tales como, MOSFETs de carburo de silicio (SiC). Los MOSFETs de SiC presentan mejores características que sus homólogos de silicio; tienen baja resistencia de conducción, pueden trabajar a mayores velocidades de conmutación y pueden operar a mayores niveles de temperatura y tensión. A pesar de las ventajas de los transistores de SiC, existen problemas que se manifiestan cuando estos dispositivos operan a altas frecuencias de conmutación. Las rápidas velocidades de conmutación de los MOSFETs de SiC pueden provocar sobre-voltajes y sobre-corrientes que conllevan a problemas de interferencia electromagnética (EMI). Por tal motivo, el desarrollo de controladores de puertas es una etapa fundamental en los MOSFETs de SiC para eliminar los problemas a altas frecuencias de conmutación y aumentar su rendimiento. En consecuencia, aprovechar las ventajas de estos dispositivos y lograr sistemas más eficientes y con alta densidad de potencia. En esta tesis, se realiza un estudio, diseño y desarrollo de controladores activos de puerta para mejorar el rendimiento de conmutación de los MOSFETs de SiC aplicados a convertidores de potencia de alta frecuencia. Los controladores son validados a través de pruebas y estudios experimentales. Además, los controladores de puerta desarrollados son aplicados en convertidores para sistemas de carga inalámbrica de baterías de vehículos eléctricos. Los resultados muestran la importancia de los controladores de compuerta propuestos y su viabilidad en convertidores de potencia basados en carburo de silicio

Non-intrusive methodologies for characterization of bias temperature instability in SiC power MOSFETs

The gate oxide reliability of SiC power MOSFETs remains a challenge, despite the improvements of the new generation power devices. The threshold voltage drift caused by Bias Temperature Instability (BTI) has been subject of different studies and methods have been proposed to evaluate the real magnitude of the threshold voltage shift. These methodologies usually focus on the characterization of the threshold voltage shift, rather than its implications to the operation or how the threshold voltage shift can be detected during the application. This paper presents two non-intrusive methodologies which can assess and determine the impact of BTI-induced. The proposed methodologies are able to capture the peak shift and subsequent recovery after stress removal

Static Current Unbalance of Paralleled SiC MOSFET Modules in the Final Layout

Silicon Carbide (SiC) MOSFETs enable enhanced performance of power converters in several applications. Parallel connection of SiC MOSFETs become mandatory for medium power applications due to the current rate of existing modules. A balanced current sharing between paralleled MOSFETs is desired to maximize the power capability of each device, maximizing the power capability of the whole system. This work studies the static current unbalance of two paralleled 1200V-400A SiC MOSFET modules with individual gate driver. Experimental measurements are done focused on parasitic inductance caused by electromechanical layout

Modeling, Measurement and Mitigation of Fast Switching Issues in Voltage Source Inverters

Wide-bandgap devices are enjoying wider adoption across the power electronics industry for their superior properties and the resulting opportunities for higher efficiency and power density. However, various issues arise due to the faster switching speed, including switching transient voltage overshoot, unstable oscillation, gate driving and evaluation difficulty, measurement and monitoring challenge, and potential load insulation degradation. This dissertation first sets out to model and understand the switching transient voltage overshoots. Unique oscillation patterns and features of the turn-on and turn-off overvoltage are discovered and analyzed, which provides new insights into the switching transient. During the experimental characterization, a new unstable oscillation pattern is found during the trench MOSFET\u27s turn-off transient. The MOSFET channel may be falsely turned back on, resulting in severe oscillation and possible loss of control. Time-domain and large-signal analytical models are established, which reveals the negative impact of common-source inductances and unconventional capacitance curve of trench MOSFET. Besides the devices themselves, another determining part in their switching transient behavior is the gate driver. A programmable gate driver platform is proposed to readily adapt to different power semiconductors and driving schemes, which can greatly facilitate the evaluation and comparison of different devices and driving schemes. The faster switching speed of wide-bandgap devices also requires more demanding measurement and monitoring solutions. A novel combinational Rogowski coil concept is proposed, which leverages the self-integrating feature to further increase the bandwidth. Prototypes achieved more than 300 MHz bandwidth, while keeping the cross-sectional area less than 2.5 mm$^2$. Finally, the very high voltage slew rate of wide-bandgap devices may negatively impact the motor load insulation. Attempting to fully utilize the higher switching frequency capability, sinewave and $dv/dt$ filters are compared. It is shown that sinewave filters can achieve higher efficiency and power density than $dv/dt$ filters, especially for high frequency applications

Analysis and optimization of the hardware design of a sic mosfet based power converter with sic schottky diodes utilizing a split output topology

In recent years, the use of power electronic devices for energy conversion with semiconductors such as silicon carbide (SiC) or gallium nitride (GaN) are replacing silicon due to their high thermal conductivity, efficiency, resistance, and the possibility of smaller and thinner designs. For this reason, in order to evaluate the improvement potential of these systems, it is beneficial to realize experimental setups that emulate real operating conditions in order to verify the correct performance of these systems. In this context and based on the previous work done by Giorgio Ferrara, this thesis focuses on the analysis and identification of improvements of a SiC MOSFET-based power electronic converter with the aim of suggesting and studying different solutions that ensure a high-performance operation that allows its correct implementation in motor traction and grid-connected applications. During the thesis work, it is carried out an in-depth analysis of the voltage peaks between drain and source originated by the fast switching of the MOSFET to evaluate the use of Snubber capacitors and it is made a new hardware design of the gate driver board using isolated gate drivers to improve the dynamic behaviour in the switching transients of the SiC transistors and provide safety and robustness to the system. Finally, maintaining the original design of the converter, it implements the split output topology to evaluate possible solutions to the problems of electromagnetic interference (EMI) and the crosstalk effect that occurs with high frequency switchingNegli ultimi anni, l'uso di dispositivi elettronici di potenza per la conversione dell'energia con semiconduttori come il carburo di silicio (SiC) o il nitruro di gallio (GaN) sta sostituendo il silicio grazie alla sua elevata conducibilità termica, all'efficienza, alla resistenza e alla possibilità di realizzare disegni più piccoli e sottili. Per questo motivo, al fine di valutare il potenziale di miglioramento di questi sistemi, è utile realizzare set-up sperimentali che emulino le condizioni operative reali, in modo da poter eseguire diversi test per verificare il corretto comportamento di questi sistemi. In tale contesto e a partire dal precedente lavoro effettuato per Giorgio Ferrara, la presente tesi si concentra nell' analisi e nidentificazione di miglioramenti di un convertitore di potenza DC-AC a commutazione, al fine di proporre e studiare diverse soluzioni che garantiscano le elevate prestazioni che assicurano la sua corretta implementazione in applicazioni di trazione a motore e di connessione alla rete. Durante il lavoro di tesi, si analizza in dettaglio il fenomeno di picchi di tensione tra drain e source causato per la commutazione veloce del MOSFET e si valuta l'utilizzo di condensatori snubber; in più si realizza un nuovo disegno hardware della board di gate driver utilizzando gate driver isolati per migliorare il comportamento dinamico nei transitori di commutazione dei transistor SiC e per fornire sicurezza e robustezza al sistema. Per finire, mantenendo il disegno originale del convertitore, implementa la topologia di uscita Split Output per valutare possibili soluzioni ai problemi di interferenza elettromagnetica (EMI) e all'effetto diafonia che si produce con la commutazione ad alta frequenzaObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.5 - Augmentar la investigació científica i millorar la capacitat tecnològica dels sectors industrials de tots els països, en particular els països en desenvolupament, entre d’altres maneres fomentant la innovació i augmentant substancialment, d’aquí al 2030, el nombre de persones que treballen en el camp de la investigació i el desenvolupa­ment per cada milió d’habitants, així com la despesa en investigació i desenvolupament dels sectors públic i priva

Analysis and optimization of the hardware design of a sic mosfet based power converter with sic schottky diodes utilizing a split output topology

In recent years, the use of power electronic devices for energy conversion with semiconductors such as silicon carbide (SiC) or gallium nitride (GaN) are replacing silicon due to their high thermal conductivity, efficiency, resistance, and the possibility of smaller and thinner designs. For this reason, in order to evaluate the improvement potential of these systems, it is beneficial to realize experimental setups that emulate real operating conditions in order to verify the correct performance of these systems. In this context and based on the previous work done by Giorgio Ferrara, this thesis focuses on the analysis and identification of improvements of a SiC MOSFET-based power electronic converter with the aim of suggesting and studying different solutions that ensure a high-performance operation that allows its correct implementation in motor traction and grid-connected applications. During the thesis work, it is carried out an in-depth analysis of the voltage peaks between drain and source originated by the fast switching of the MOSFET to evaluate the use of Snubber capacitors and it is made a new hardware design of the gate driver board using isolated gate drivers to improve the dynamic behaviour in the switching transients of the SiC transistors and provide safety and robustness to the system. Finally, maintaining the original design of the converter, it implements the split output topology to evaluate possible solutions to the problems of electromagnetic interference (EMI) and the crosstalk effect that occurs with high frequency switchingNegli ultimi anni, l'uso di dispositivi elettronici di potenza per la conversione dell'energia con semiconduttori come il carburo di silicio (SiC) o il nitruro di gallio (GaN) sta sostituendo il silicio grazie alla sua elevata conducibilità termica, all'efficienza, alla resistenza e alla possibilità di realizzare disegni più piccoli e sottili. Per questo motivo, al fine di valutare il potenziale di miglioramento di questi sistemi, è utile realizzare set-up sperimentali che emulino le condizioni operative reali, in modo da poter eseguire diversi test per verificare il corretto comportamento di questi sistemi. In tale contesto e a partire dal precedente lavoro effettuato per Giorgio Ferrara, la presente tesi si concentra nell' analisi e nidentificazione di miglioramenti di un convertitore di potenza DC-AC a commutazione, al fine di proporre e studiare diverse soluzioni che garantiscano le elevate prestazioni che assicurano la sua corretta implementazione in applicazioni di trazione a motore e di connessione alla rete. Durante il lavoro di tesi, si analizza in dettaglio il fenomeno di picchi di tensione tra drain e source causato per la commutazione veloce del MOSFET e si valuta l'utilizzo di condensatori snubber; in più si realizza un nuovo disegno hardware della board di gate driver utilizzando gate driver isolati per migliorare il comportamento dinamico nei transitori di commutazione dei transistor SiC e per fornire sicurezza e robustezza al sistema. Per finire, mantenendo il disegno originale del convertitore, implementa la topologia di uscita Split Output per valutare possibili soluzioni ai problemi di interferenza elettromagnetica (EMI) e all'effetto diafonia che si produce con la commutazione ad alta frequenzaObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.5 - Augmentar la investigació científica i millorar la capacitat tecnològica dels sectors industrials de tots els països, en particular els països en desenvolupament, entre d’altres maneres fomentant la innovació i augmentant substancialment, d’aquí al 2030, el nombre de persones que treballen en el camp de la investigació i el desenvolupa­ment per cada milió d’habitants, així com la despesa en investigació i desenvolupament dels sectors públic i priva