Browsing by Author "Lai, J. S."

Now showing 1 - 4 of 4
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    Cascode GaN HEMT Gate Driving Analysis
    Heumesser, V.; Lai, J. S.; Hsieh, H. C.; Hsu, J.; Yang, C. Y.; Chang, E. Y.; Liu, C. Y.; Chieng, W. H.; Hsieh, Y. T. (IEEE, 2023-01-01)
    The aim of this paper is to analyze the conventional cascode gate driving to understand the switching transition and to provide a design guide for the GaN HEMT and its associated packaging. A double-pulse tester has been designed and fabricated with minimum parasitic inductance to avoid unnecessary parasitic ringing. The switching behaviors in both turn-on and -off are analyzed through topological study and explained through SPICE simulation. Two different cascode devices were tested to show the impact of threshold voltage and low-voltage Si MOSFET selection.
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    D-Mode GaN HEMT with Direct Drive
    Heumesser, V.; Lai, J. S.; Hsieh, H. C.; Hsu, J.; Yang, C. Y.; Chang, E. Y.; Ko, H. K.; Liu, W. H.; Lin, Y. M. (IEEE, 2023-01-01)
    A direct-driven gate driver circuit has been developed for the depletion-mode gallium nitride (d-mode GaN) high electron mobility transistor (HEMT), which is a'normally on'' device and is typically connected in series with a low-voltage power MOSFET to prevent shoot-through faults. The switching of such a''cascode'' device is substantially delayed due to a large MOSFET input capacitance. This paper introduces a charge-pump based direct-driven approach to provide a negative voltage in the gate drive loop so that the device becomes 'normally off The switching characteristics of the direct-driven HEMT is analyzed through computer simulation and hardware testing. Results indicate that the switching delays due to MOSFET gating is eliminated, and the voltage slew rate can be directly controlled by the gate resistance.
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    Impact of Automation on the Reliability of the Athens Utilities Board's Distribution System
    Lawler, J. S.; Lai, J. S.; Monteen, L. D.; Patton, J. B.; Rizy, D. T. (IEEE, 1989-01-01)
    In this paper we discuss the reliability effects of distribution automation on the Athens Utilities Board (AUB) in Athens, Tennessee. This investigation is part of the Athens Automation and Control Experiment sponsored by the U. S. Department of Energy, Office of Energy Storage and Distribution, Electric Energy Systems Program. In this experiment, distribution feeder equipment on twelve feeders connected to three substations is being remotely controlled from a central dispatch center, A supervisory control and data acquisition system provides substation and feeder monitoring and remote control of feeder circuit breakers, power reclosers, and load break switches. An analytical study is presented to show the improvement in conventional distribution system reliability indices that are achieved at AUB as a function of the penetration of automation equipment. The value of automation predicted by the study is highly sensitive to the historical outage data used in the analysis and to the economic worth of reliability assigned by the utility. These sensitivities are well known and account, at least in part, for the reluctance of some upper utility managers to invest in automation systems. Operating experience with the AUB automation system has shown that there are significant intangible reliability benefits and tangible cost savings associated with automation that are outside the scope of conventional distribution reliability indices. Eight case studies are described, from actual AUB operations, where the automation system resulted in significant cost savings and reliability benefits that are not captured by conventional reliability indices, Other utilities should expect similar benefits, which will be difficult to quantify analytically but, which add to the value of and justification for distribution automation.
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    Optimum Current Control for a High Speed Axial Gap Permanent Magnet Synchronous Motor
    Lai, J. S.; Bailey, J. M.; Young, R. W.; Sohns, C. W.; Hawsey, R. A. (IEEE, 1989-01-01)
    A high-speed (20,000 r/min) axial-gap permanent magnet (PM) synchronous motor constructed and controlled using a novel algorithm is described. An optimization algorithm using the Newton-Raphson method is proposed to solve the maximum torque/amp problem for salient-type PM motors. The optimum voltage and torque angle for different speeds are further derived from optimum dq-axes currents so that decoupled control can be applied to a six-step inverter. The complete drive system can be implemented using open-loop optimum voltage and torque angle trajectories or closed-loop control with one variable controlled by a lookup table and the other variable controlled by a closed-loop controller. The open-loop and closed-loop control systems are simulated. Although torque pulsation cannot be avoided with a six-step inverter, acceleration is quite smooth due to high load inertia.