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Modeling and Characterization of Circuit Level Transients in Wide Bandgap Devices

Koganti, Naga Babu

Abstract Details

2018, Master of Science, University of Toledo, Electrical Engineering.
Wide bandgap devices (GaN) are an enabling technology for high frequency and high efficiency power electronics. Especially, the combination of low on-resistance and high breakdown voltages relates to high power-density capabilities of GaN devices and makes them a potential alternative for silicon devices in high power conversion applications. Also, GaN devices are intrinsically very fast with low switching losses due to high saturation velocities and can achieve higher efficiencies in hard switching applications. On the contrary, low inherent capacitance makes them more vulnerable to high dv/dt transitions and can cause undesired circuit level issues such as voltage overshoot, ringing, and false turn-on. Any unchecked external parasitic impedances will further exacerbate the device transient behavior and run the risk of device failure under circuit level implementation. Therefore, this thesis work presents a detailed analytical framework to address some of the circuit level challenges associated with GaN. The analytical framework lays a foundation to optimize device safety and performance. The first part of this thesis work deals with mitigation of false turn-on of the synchronous-FET in a half bridge buck converter operated at 1 MHz frequency. The study presents a detail investigation of false turn-on event and proposes its mitigation by modifying the control-FET gate resistance. An analytical circuit model with intrinsic device components and external parasitic parameters has been considered to develop a relationship between control-FET gate resistance and false turn-on induced voltage of the synchronous-FET. The results of the analytical method proposed in this study show good agreement with the experimental results. The model can then be used to predict false turn-on at varying values of high-side gate resistance. The second part of this thesis focuses on the development of an improved model to predict voltage overshoot in normally-off GaN devices. As the GaN device requires lower gate bias to fully turn-on when compared to its counterpart (Si), there is a narrow margin between recommended (5V) and max gate voltage rating (6V). Any voltage spike beyond the maximum gate voltage could cause device breakdown and catastrophic failure. Therefore, to avoid such failures and safeguard the GaN device, proper prediction methodologies are required. In this study, a higher order (fourth order) analytical method is developed that allows for the calculation of gate resistances necessary for a desired amount of overshoot. The non-linear capacitances of the device are modeled and considered in the analysis. The model is validated with a double-pulse tester and a boost converter. The developed method was compared with known second order and circuit simulation models and found to yield improved results. The two studies detailed here lay the foundation for optimizing the performance of GaN devices while keeping them in their safe operating regions.
Raghav Khanna (Committee Chair)
Mansoor Alam (Committee Member)
Vijay Devabhaktuni (Committee Member)
106 p.

Recommended Citations

Citations

  • Koganti, N. B. (2018). Modeling and Characterization of Circuit Level Transients in Wide Bandgap Devices [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo153311831687909

    APA Style (7th edition)

  • Koganti, Naga Babu. Modeling and Characterization of Circuit Level Transients in Wide Bandgap Devices. 2018. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo153311831687909.

    MLA Style (8th edition)

  • Koganti, Naga Babu. "Modeling and Characterization of Circuit Level Transients in Wide Bandgap Devices." Master's thesis, University of Toledo, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo153311831687909

    Chicago Manual of Style (17th edition)