Publications

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This report details the test setup, process, and results for radiated susceptibility testing of multicrystalline silicon photovoltaic (PV) modules as part of the EMP-Resilient Electric Grid Grand Challenge Laboratory Directed Research and Development (LDRD) project at Sandia National Laboratories. Testing was conducted over October 10-17, 2019, where 8 photovoltaic modules were exposed to E1 transient pulses with peak field levels up to 100 kV/m. Modules were terminated in a resistive load representing connected components. State of health testing conducted via I-V curve tracing of the photovoltaic modules showed no observable loss of device function due to large electric field transients. Differential mode currents were measured on the order of 10's of amps for up to a microsecond following the radiated field pulse. Common mode currents took the form of a damped sinusoid with a maximum peak of 10's to 100's of amps with a resonance near 60 MHz.

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Inverters using phase-locked loops for control depend on voltages generated by synchronous machines to operate. This might be problematic if much of the conventional generation fleet is displaced by inverters. To solve this problem, grid-forming control for inverters has been proposed as being capable of autonomously regulating grid voltages and frequency. Presently, the performance of bulk power systems with massive penetration of grid-forming inverters has not been thoroughly studied as to elucidate benefits. Hence, this paper presents inverter models with two grid-forming strategies: virtual oscillator control and droop control. The two models are specifically developed to be used in positive-sequence simulation packages and have been implemented in PSLF. The implementations are used to study the performance of bulk power grids incorporating inverters with gridforming capability. Specifically, simulations are conducted on a modified IEEE 39-bus test system and the microWECC test system with varying levels of synchronous and inverter-based generation. The dynamic performance of the tested systems with gridforming inverters during contingency events is better than cases with only synchronous generation.

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Historically, photovoltaic inverters have been grid-following controlled, but with increasing penetrations of inverter-based generation on the grid, grid-forming inverters (GFMI) are gaining interest. GFMIs can also be used in microgrids that require the ability to interact and operate with the grid (grid-tied), or to operate autonomously (islanded) while supplying their corresponding loads. This approach can substantially improve the response of the grid to severe contingencies such as hurricanes, or to high load demands. During islanded conditions, GFMIs play an important role on dictating the system's voltage and frequency the same way as synchronous generators do in large interconnected systems. For this reason, it is important to understand the behavior of such grid-forming inverters under fault scenarios. This paper focuses on testing different commercially available grid-forming inverters under fault conditions.

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Modern power grids include a variety of renewable Distributed Energy Resources (DERs) as a strategy to comply with new environmental and renewable portfolio standards (RPSs) imposed by state and federal agencies. Typically, DERs include the use of power electronic (PE) interfaces to interactwith the power grid. Recently this interaction has not only been focused on supplying maximum available energy, but also on supporting the power grid under abnormal conditions such as low voltage/frequency conditions or non-unity power factor. Over the last few years, grid-following inverters (GFLIs) have proven their value while providing these ancillary grid-support services either at residential or utility scale. However, the use of grid-forming inverters (GFMIs) is gaining momentum as the penetration-level of DERs increases and system inertia decreases. Under abnormal operating conditions, GFMIs tend to better preserve grid stability due to their intrinsic ability to balance loadswithout the aid of coordination controls. In order to gain and propose fundamental insights into the interfacing of GFMIs to real time simulation, this paper analyzes the dynamics of two different GFMI simulation models in terms of stability and load changes using a Power Hardware-in-the-Loop (PHIL) simulation testbed.

Historically, photovoltaic inverters have been grid-following controlled, but with increasing penetrations of inverter-based generation on the grid, grid-forming inverters (GFMI) are gaining interest. GFMIs can also be used in microgrids that require the ability to interact and operate with the grid (grid-tied), or to operate autonomously (islanded) while supplying their corresponding loads. This approach can substantially improve the response of the grid to severe contingencies such as hurricanes, or to high load demands. During islanded conditions, GFMIs play an important role on dictating the system's voltage and frequency the same way as synchronous generators do in large interconnected systems. For this reason, it is important to understand the behavior of such grid-forming inverters under fault scenarios. This paper focuses on testing different commercially available grid-forming inverters under fault conditions.

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The purpose of the International Technology Roadmap for Wide-Bandgap Power Semiconductors (ITRW) Materials and Devices Working Group, which considers the materials science of Wide-and Ultra-Wide-Band-Gap (WBG and UWBG) semiconductors, in addition to device design, fabrication, and evaluation, is to formulate a long-term, international roadmap for WBG and UWBG materials and devices, consistent with the packaging and applications working groups of ITRW. The working group is co-chaired by Victor Veliadis (primarily representing silicon carbide (SiC) and related materials) and Robert Kaplar (primarily representing gallium nitride (GaN) and related materials, as well as emerging ultra-WBGs) and is split into four sub-working-groups, which are: 1) SiC materials and devices (co-chairs Jon Zhang and Mietek Bakowski). 2) Lateral GaN materials and devices (co-chairs Sameh Khalil and Peter Moens). 3) Vertical GaN materials and devices (co-chairs TBD). 4) Emerging UWBG materials and devices (co-chairs Mark Hollis). The first two subgroups represent technology that is far more mature than that of the latter two, and devices are available as commercial products in power applications. The primary focus of this article will be on developments in subgroups 1 and 2, with only brief descriptions of the latter two sub-groups, including future activities as they mature technologically.

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