Jarod Delhotal

Miniature high voltage, high temperature component package development

With the next generation of semiconductor materials in development, significant strides in the Size, Weight, and Power (SWaP) characteristics of power conversion systems are presently underway. In particular, much of the improvements in system-level efficiencies and power densities due to wide-bandgap (WBG) and ultra-wide-bandgap (UWBG) device incorporation are realized through higher voltage, higher frequency, and higher temperature operation. Concomitantly, there is a demand for ever smaller device footprints with high voltage, high power handling ability while maintaining ultra-low inductive/capacitive parasitics for high frequency operation. For our work, we are developing small size vertical gallium nitride (GaN) and aluminum gallium nitride (AlGaN) power diodes and transistors with breakdown and hold-off voltages as high as 15kV. The small size and high power densities of these devices create stringent requirements on both the size (balanced between larger sizing for increased voltage hold-off with smaller sizing for reduced parasitics) and heat dissipation capabilities of the associated packaging. To accommodate these requirements and to be able to characterize these novel device designs, we have developed specialized packages as well as test hardware and capabilities. This work describes the requirements of these new devices, the development of the high voltage, high power packages, and the high-voltage, high-temperature test capabilities needed to characterize and use the completed components. In the course of this work, we have settled on a multi-step methodology for assessing the performance of these new power devices, which we also present.

Evaluation of PV frequency-watt function for fast frequency reserves

Increasing the penetration of distributed renewable sources, including photovoltaic (PV) sources, poses technical challenges for grid management. The grid has been optimized over decades to rely upon large centralized power plants with well-established feedback controls, but now non-dispatchable, renewable sources are displacing these controllable generators. By programming autonomous functionality into distributed energy resources-in particular, PV inverters-the aggregated PV resources can act collectively to mitigate grid disturbances. This paper focuses on the problem of frequency regulation. Specifically, the use of existing IEC 61850-90-7 grid support functions to improve grid frequency response using a frequency-watt function was investigated. The proposed approach dampens frequency disturbances associated with variable irradiance conditions as well as contingency events without incorporating expensive energy storage systems or supplemental generation, but it does require some curtailment of power to enable headroom for control action. Thus, this study includes a determination of the trade-offs between reduced energy delivery and dynamic performance. This paper includes simulation results for an island grid and hardware results for a testbed that includes a load, a 225 kW diesel generator, and a 24 kW inverter.

Stability of high-bandwidth power electronic systems with transmission lines

In most distributed power electronic systems, the transmission line effects associated with cabling are neglected due to the expectation that cables are sufficiently short to be modeled as a lumped parameter model. However, as converter switching speeds and control bandwidth increase, especially in large distributed power electronic based systems, the transmission line effects may become an important consideration when establishing margins of stability. In this work, immittance based stability analysis is applied to power electronic systems with long cables between source and load converter. In particular, the Energy Systems Analysis Consortium (ESAC) method is utilized to compute limits on cable length so as to maintain prescribed stability margins. Simulation results are presented in support of the approach.

DC link bus design for high frequency, high temperature converters

Advancements in IGBT device performance and reliability have been important for widespread electric vehicle (EV) and hybrid electric vehicle (HEV) adoption. However, further improvements in device performance are now limited by silicons (Si) inherent material characteristics. New improvements are being realized in converter efficiency and power density with wide bandgap materials, such as silicon-carbide (SiC) and gallium nitride (GaN), which permit faster switching frequencies and higher temperature operation. On the horizon are ultra-wide bandgap materials such as aluminum nitride (AlN) and aluminum gallium nitride (AlGaN) which hold the potential to push the envelope further. As device operating temperatures and switching frequencies increase, however, the balance of the power conversion system becomes more important: DC bus design, filter components and thermal management. This paper considers a typical 6-puIse inverter application common in EV and HEV power systems and provides an alternative, cost-effective solution to the design of a low-impedance DC bus. In contrast to systems that use bus bars with film or electrolytic dc link capacitors, the proposed high-frequency (HF) bus design reduces parasitic resistance and inductance, tolerates higher temperature and is potentially scalable to MHz frequencies. A prototype was built and compared in simulation to the DC bus design documented for the 2010 Toyota Prius.

Optimization of a Virtual Power Plant to Provide Frequency Support.

Increasing the penetration of distributed renewable sources, including photovoltaic (PV) sources, poses technical challenges for grid management. The grid has been optimized over decades to rely upon large centralized power plants with well-established feedback controls, but now non-dispatchable, renewable sources are displacing these controllable generators. This one-year study was funded by the Department of Energy (DOE) SunShot program and is intended to better utilize those variable resources by providing electric utilities with the tools to implement frequency regulation and primary frequency reserves using aggregated renewable resources, known as a virtual power plant. The goal is to eventually enable the integration of 100s of Gigawatts into US power systems.