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Photovoltaic Inverter Momentary Cessation: Recovery Process is Key

Conference Record of the IEEE Photovoltaic Specialists Conference

Pierre, Brian J.; Elkhatib, Mohamed E.; Hoke, Andy

Momentary cessation refers to an inverter control mode. When the inverter terminal voltage falls below (or exceeds) a certain level, the inverter ceases to output any current, but attempts to maintain (or quickly regain) phase-locked loop synchronization to allow for quick reinjection of current when the voltage recovers to a certain point. This paper presents a photovoltaic (PV) momentary cessation model developed in PSS/E. Simulations are presented for a high voltage transmission line fault contingency in the Hawaiian island of Oahu power system on a validated PSS/E model, modified to include a custom distributed PV inverter model, and different near-future distributed PV penetration levels. Simulations for the island power system include different penetration levels of PV, and different recovery times (ramp rates and delays) after momentary cessation. The results indicate that during low voltage events, such as faults, momentary cessation can produce severe under frequency events, causing significant load shed and shortly thereafter, in some cases, over frequency events that cause generation to trip offline. The problem is exacerbated with higher penetration levels of PV. If momentary cessation is used (as is typically the case for distribution-connected resources), the recovery process after momentary cessation should be carefully considered to minimize impacts to bulk power system stability.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

Bulk Power System Dynamics with Varying Levels of Synchronous Generators and Grid-Forming Power Inverters

Conference Record of the IEEE Photovoltaic Specialists Conference

Pierre, Brian J.; Villegas Pico, Hugo N.; Elliott, Ryan T.; Flicker, Jack D.; Lin, Yashen; Johnson, Brian B.; Eto, Joseph H.; Lasseter, Robert H.; Ellis, Abraham E.

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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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

Segmentation certainty through uncertainty: Uncertainty-refined binary volumetric segmentation under multifactor domain shift

IEEE Computer Society Conference on Computer Vision and Pattern Recognition Workshops

Martinez, Carianne M.; Potter, Kevin M.; Smith, Matthew D.; Donahue, Emily D.; Collins, Lincoln; Korbin, John P.; Roberts, Scott A.

Deep learning segmentation models are known to be sensitive to the scale, contrast, and distribution of pixel values when applied to Computed Tomography (CT) images. For material samples, scans are often obtained from a variety of scanning equipment and resolutions resulting in domain shift. The ability of segmentation models to generalize to examples from these shifted domains relies on how well the distribution of the training data represents the overall distribution of the target data. We present a method to overcome the challenges presented by domain shifts. Our results indicate that we can leverage a deep learning model trained on one domain to accurately segment similar materials at different resolutions by refining binary predictions using uncertainty quantification (UQ). We apply this technique to a set of unlabeled CT scans of woven composite materials with clear qualitative improvement of binary segmentations over the original deep learning predictions. In contrast to prior work, our technique enables refined segmentations without the expense of the additional training time and parameters associated with deep learning models used to address domain shift.

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TYPE Conference Poster YEAR 2019
OSTIScopus

Visualization Methods for Quasi-Static Time-Series (QSTS) Simulations with High PV Penetration

Conference Record of the IEEE Photovoltaic Specialists Conference

Azzolini, Joseph A.; Reno, Matthew J.; Lave, Matthew S.

Distribution system analysis requires yearlong quasi-static time-series (QSTS) simulations to accurately capture the variability introduced by high penetrations of distributed energy resources (DER) such as residential and commercial-scale photovoltaic (PV) installations. Numerous methods are available that significantly reduce the computational time needed for QSTS simulations while maintaining accuracy. However, analyzing the results remains a challenge; a typical QSTS simulation generates millions of data points that contain critical information about the circuit and its components. This paper provides examples of visualization methods to facilitate the analysis of QSTS results and to highlight various characteristics of circuits with high variability.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

Comparison of Ideal Transformer Method and Damping Impedance Method for PV Power-Hardware-In-The-Loop Experiments

Conference Record of the IEEE Photovoltaic Specialists Conference

Summers, Adam; Hernandez Alvidrez, Javier H.; Darbali-Zamora, Rachid; Reno, Matthew J.; Johnson, Jay B.; Gurule, Nicholas S.

The Ideal Transformer Method (ITM) and the Damping Impedance Method (DIM) are the most widely used techniques for connecting power equipment to a Power-Hardware-in-the-Loop (PHIL) real-time simulation. Both methods have been studied for their stability and accuracy in PHIL simulations, but neither have been analyzed when the hardware is providing grid-support services with volt-var, frequency-watt, and fixed power factor functions. In this work, we experimentally validate the two methods of connecting a physical PV inverter to a PHIL system and evaluate them for dynamic stability and accuracy when operating with grid-support functions. It was found that the DIM Low Pass Lead Filter (LPF LD) method was the best under unity and negative power factor conditions, but the ITM LPF LD method was preferred under positive power factor conditions.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

Differential Analysis of the Angle of Incidence Response of Utility-Grade PV Modules

Conference Record of the IEEE Photovoltaic Specialists Conference

King, Bruce H.; Robinson, Charles D.

Anti-reflective coatings (ARCs) are commonly applied to commercial modules to reduce reflection losses and improve energy harvest. Relative performance at low incidence angle is often indistinguishable between different modules and it is only at high incidence angle that performance becomes differentiated. It is also precisely in this range that accurate measurements are the most difficult to obtain, complicating efforts to compare the benefits of different coatings. In this study, the performance of multiple commercial modules with different coatings were compared. A differential approach was employed, facilitating relative comparisons between test devices and a common reference. Using this method, performance differences at high incidence angles could be visualized and quantified. Differential analysis was extended to multiple system performance models in order to predict and quantify potential improvements in annual energy harvest. Improvements were observed upwards of 1% seasonally and 0.5% annually for the best performing coatings. 10° fixed tilt systems were seen to potentially benefit the most from ARCs, while single axis trackers benefitted the least.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

Differences in Snow Shedding in Photovoltaic Systems with Framed and Frameless Modules

Conference Record of the IEEE Photovoltaic Specialists Conference

Riley, Daniel R.; Burnham, Laurie B.; Walker, Bevan; Pearce, Joshua M.

Energy losses due to snow coverage can be high in climates with large annual snowfall. These losses may be reduced with region-specific system design guidelines. One possible factor in snow retention on PV systems could be frame presence and/or shape. Sandia is studying the effect of module frame presence on photovoltaic module snow shedding for a pair of otherwise-identical PV systems in Vermont. The results of this study provide a summary of the findings after the 2018-2019 winter period. The results clearly show that the presence of a frame inhibits PV performance in mild winter conditions.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

AMI Data Quality and Collection Method Considerations for Improving the Accuracy of Distribution Models

Conference Record of the IEEE Photovoltaic Specialists Conference

Blakely, Logan; Reno, Matthew J.; Ashok, Kavya

Spectral clustering is applied to the problem of phase identification of electric customers to investigate the data needs (resolution and accuracy) of advanced metering infrastructure (AMI). More accurate models are required to accurately interconnect high penetrations of PV/DER and for optimal electric grid operations. This paper demonstrates the effects of different data collection implementations and common errors in AMI datasets on the phase identification task. This includes measurement intervals, data resolution, collection periods, time synchronization issues, noisy measurements, biased meters, and mislabeled phases. High quality AMI data is a critical consideration to model correction and accurate hosting capacity analyses.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

Effects of Photovoltaic Module Materials and Design on Module Deformation under Load

Conference Record of the IEEE Photovoltaic Specialists Conference

Hartley, James Y.; Maes, Ashley M.; Owen-Bellini, Michael; Truman, Thomas; Elce, Edmund; Ward, Allan; Khraishi, Tariq; Roberts, Scott A.

Static structural finite element models of an aluminum-framed crystalline silicon (c-Si) photovoltaic (PV) module and a glass-glass thin film PV module were constructed and validated against experimental measurements of deflection under uniform pressure loading. Parametric analyses using Latin Hypercube Sampling (LHS) were performed to propagate simulation input uncertainties related to module material properties, dimensions, and manufacturing tolerances into expected uncertainties in simulated deflection predictions. This exercise verifies the applicability and validity of finite element modeling for predicting mechanical behavior of solar modules across architectures and enables computational models to be used with greater confidence in assessment of module mechanical stressors and design for reliability. Sensitivity analyses were also performed on the uncertainty quantification data sets using linear correlation coefficients to elucidate the key parameters influencing module deformation. This information has implications on which materials or parameters may be optimized to best increase module stiffness and reliability, whether the key optimization parameters change with module architecture or loading magnitudes, and whether parameters such as frame design and racking must be replicated in reduced-scale reliability studies to adequately capture full module mechanical behavior.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

Predicting Photovoltaic Module Series Resistance based on Indoor-Aging Tests and Thermal Cycling Cumulative Exposure Estimates

Conference Record of the IEEE Photovoltaic Specialists Conference

Jones, Christian B.; Hobbs, William B.; Libby, Cara; Gunda, Thushara G.; Hamzavy, Babak

The IEC 61215 and Qualification Plus indoor aging tests are recognized as valuable assessment procedures for identifying photovoltaic (PV) modules that are prone to early-life failures or excessive degradation. However, it is unclear how well the tests match with reality, and if they can predict in-field performance. Therefore, the present work performed indoor-aging thermal cycling tests on pristine-condition modules and evaluated, using in-field current and voltage (I-V) curve scans, modules of the same make and model exposed to the actual environment within a production field. The experiment included the estimate of the overall exposure to thermal cycling in both indoor and outdoor environments, the extraction of the series resistance from the I-V curves, the development of a model based on the indoor results, and finally the testing of the model on outdoor exposure amounts to predict actual changes in resistance. Index Terms - photovoltaic, accelerated aging, series resistance.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus
Results 21201–21400 of 96,771
Results 21201–21400 of 96,771