Irradiance and Temperature Transient Sensitivity Analysis for Photovoltaic Control

Katherine A. Kim,Philip T. Krein,Jay J. Lee,Hyunsu Bae,Bo-Hyung Cho 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

This paper analyzes control scheme sensitivity to changes in irradiance and temperature around the maximum power point (MPP) for photovoltaic (PV) panels. Conventional control schemes such as constant voltage, current, and resistance, as well as a newly introduced voltage-offset resistance control (VRC) are compared. Based on experimental PV data and a validated model, VRC is found to have the lowest sensitivity to typical transients. Stability analysis of a buck and boost converter under VRC indicate that some ranges of the equivalent resistance are stable while others can cause instability. Two established PV control methods are assessed in terms of transient stability and three additional low-sensitivity methods utilizing VRC are outlined. These methods are applicable to PV controllers taking infrequent measurements that hold the control line steady between samples.

Reexamination of Photovoltaic Hot Spotting to Show Inadequacy of the Bypass Diode

Kim, Katherine A.,Krein, Philip T. IEEE 2015 IEEE journal of photovoltaics Vol.5 No.5

<P>Hot spotting is a reliability problem in photovoltaic (PV) panels where a mismatched cell heats up significantly and degrades panel performance. High temperatures due to hot spotting can damage cell encapsulant and lead to second breakdown; both cause permanent damage to the PV panel. Although bypass diodes are used for protection and qualification tests are used to reduce cell mismatch, these strategies are shown to be insufficient for hot spot prevention. This paper reexamines the hot spot problem in PV strings through simulation and load-line analysis. Results show that cells in typical panel string lengths are susceptible to hot spotting because of reverse bias behavior. A number of existing and emerging solutions aimed at hot spot prevention are discussed and evaluated. Commercially available active bypass switches are an improvement over passive diodes but do not prevent hot spotting. Cells with low breakdown voltages limit power dissipation but are not fully vetted as a long-term solution. A combination of hot spot detection and open-circuit protection is a complete solution to hot spotting.</P>

A Smart Setup for Craniospinal Irradiation

Jennifer L. Peterson,Laura A. Vallow,Siyong Kim,Henry E. Casale,Katherine S. Tzou 한국의학물리학회 2013 의학물리 Vol.24 No.4

To present a novel technique for delivering craniospinal irradiation in the supine position using a perfect match,field-in-field (FIF) intrafractional feathering, and simple forward-optimization technique. Computed tomographysimulation was performed with patients in the supine position. Half-beam, blocked, opposed, lateral, cranialfields with a collimator rotation were matched to the divergence of the superior border of an upper-spinal field. Fixed field parameters were used, and the isocenter of the upper-spinal field was placed at the samesource-to-axis distance (SAD), 20 cm inferior to the cranial isocenter. For a lower-spinal field, the isocenterwas placed 40 cm inferior to the cranial isocenter at a constant SAD. Both gantry and couch rotations for thelower-spinal field were used to achieve perfect divergence match with the inferior border of the upper-spinalfield. A FIF technique was used to feather the craniospinal and spinal-spinal junction daily by varying the matchline over 2 cm. The dose throughout the target volume was modulated using the FIF simple forward optimizationtechnique to obtain homogenous coverage. Daily, image-guided therapy was used to assure and verify the setup. Our supine-position, perfect match craniospinal irradiation technique with FIF intrafractional feathering and dosemodulation provided a simple and safe way to deliver treatment while minimizing dose inhomogeneity.

Design Methodology of Bidirectional Flyback Converter for Differential Power Processing Modules in PV Applications

Seungbin Park,Mina Kim,Hoejeong Jeong,Katherine A. Kim,Taewon Kim,A-Rong Kim,Jee-Hoon Jung 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

A bidirectional flyback converter is a suitable topology for a PV-to-bus differential power processing (DPP) module in PV applications because of its electrical isolation capability, bidirectional power transfer, high step-up ratio, and simple circuit structure. Bidirectional flyback converters differ from the conventional flyback converters, which has power switches and snubber circuits on both the primary and secondary sides for bi-directional operations. The poor reverse recovery characteristics of the anti-parallel diode of the secondary (output) side power switch increase the switching loss and reduce the reliability. This paper proposes the design methodology of the bidirectional flyback converter for operating under the boundary conduction mode (BCM), which can show low power loss from the reverse recovery issue. The suitable magnetizing inductance is obtained by calculating the power losses in the bidirectional operation at the rated load. The validity of the proposed design methodology is verified using a 25.6-W bidirectional flyback converter prototype.

Photovoltaic Hot Spot Mitigation Using Voltage-Threshold Control At The Panel Level

Katherine A. Kim,Jonathan Ehlmann,Philip T. Krein 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

Maximum power point tracking (MPPT) for photovoltaic (PV) panels is primarily implemented at the panel level in presently-installed PV systems. Each panel typically consists of three subpanel strings with a bypass diode connected over each subpanel. When a panel becomes partially-shaded, the MPPT control may bypass a substring to optimize power, however, bypassing increases hot spotting risk. This paper introduces a voltage-threshold control that works with existing MPPT to mitigate hot spotting. The control imposes a lower voltage limit that prevents a compromised subpanel string from being bypassed. Simulation results show that voltage-threshold control is effective in limiting hot spotting for both typical Type A and Type B PV cells, with only minimal reduction in energy output.

Bioinformatics-driven discovery of rational combination for overcoming EGFR-mutant lung cancer resistance to EGFR therapy

Kim, Jihye,Vasu, Vihas T.,Mishra, Rangnath,Singleton, Katherine R.,Yoo, Minjae,Leach, Sonia M.,Farias-Hesson, Eveline,Mason, Robert J.,Kang, Jaewoo,Ramamoorthy, Preveen,Kern, Jeffrey A.,Heasley, Lynn Oxford University Press 2014 Bioinformatics Vol.30 No.17

<P><B>Motivation:</B> Non–small-cell lung cancer (NSCLC) is the leading cause of cancer death in the United States. Targeted tyrosine kinase inhibitors (TKIs) directed against the epidermal growth factor receptor (EGFR) have been widely and successfully used in treating NSCLC patients with activating EGFR mutations. Unfortunately, the duration of response is short-lived, and all patients eventually relapse by acquiring resistance mechanisms.</P><P><B>Result:</B> We performed an integrative systems biology approach to determine essential kinases that drive EGFR-TKI resistance in cancer cell lines. We used a series of bioinformatics methods to analyze and integrate the functional genetics screen and RNA-seq data to identify a set of kinases that are critical in survival and proliferation in these TKI-resistant lines. By connecting the essential kinases to compounds using a novel kinase connectivity map (K-Map), we identified and validated bosutinib as an effective compound that could inhibit proliferation and induce apoptosis in TKI-resistant lines. A rational combination of bosutinib and gefitinib showed additive and synergistic effects in cancer cell lines resistant to EGFR TKI alone.</P><P><B>Conclusions:</B> We have demonstrated a bioinformatics-driven discovery roadmap for drug repurposing and development in overcoming resistance in EGFR-mutant NSCLC, which could be generalized to other cancer types in the era of personalized medicine.</P><P><B>Availability and implementation:</B> K-Map can be accessible at: http://tanlab.ucdenver.edu/kMap.</P><P><B>Contact:</B> aikchoon.tan@ucdenver.edu or finiganj@njhealth.org</P><P><B>Supplementary information:</B> Supplementary data are available at <I>Bioinformatics</I> online.</P>

A Smart Setup for Craniospinal Irradiation

Peterson, Jennifer L.,Vallow, Laura A.,Kim, Siyong,Casale, Henry E.,Tzou, Katherine S. Korean Society of Medical Physics 2013 의학물리 Vol.24 No.4

Our purpose is to present a novel technique for delivering craniospinal irradiation in the supine position using a perfect match, field-in-field (FIF) intrafractional feathering, and simple forward-optimization technique. To achieve this purpose, computed tomography simulation was performed with patients in the supine position. Half-beam, blocked, opposed, lateral, cranial fields with a collimator rotation were matched to the divergence of the superior border of an upper-spinal field. Fixed field parameters were used, and the isocenter of the upper-spinal field was placed at the same source-to-axis distance (SAD), 20 cm inferior to the cranial isocenter. For a lower-spinal field, the isocenter was placed 40 cm inferior to the cranial isocenter at a constant SAD. Both gantry and couch rotations for the lower-spinal field were used to achieve perfect divergence match with the inferior border of the upper-spinal field. A FIF technique was used to feather the craniospinal and spinal-spinal junction daily by varying the match line over 2 cm. The dose throughout the target volume was modulated using the FIF simple forward optimization technique to obtain homogenous coverage. Daily, image-guided therapy was used to assure and verify the setup. This supine-position, perfect match craniospinal irradiation technique with FIF intrafractional feathering and dose modulation provides a simple and safe way to deliver treatment while minimizing dose inhomogeneity.

Comprehensive Electric-Thermal Photovoltaic Modeling for Power-Hardware-in-the-Loop Simulation (PHILS) Applications

Xuan Hung Mai,Sang-Kyu Kwak,Jee-Hoon Jung,Kim, Katherine A. Institute of Electrical and Electronics Engineers 2017 IEEE transactions on industrial electronics Vol.64 No.8

<P>This paper presents a dynamic, electricthermal model for a photovoltaic (PV) cell that combines electrical and thermal parameters to accurately emulate PV panels in real time for power-hardware-in-the-loop simulation (PHILS). In this model, the irradiance and ambient temperature are used to calculate the PV cell temperature based on a five-layer thermal model. The cell temperature is then used in the electrical model to accurately adjust the PV electrical characteristics. A custom experimental setup is built to test and verify the electrical and thermal characteristics of the PV cell model. This electric-thermal model is validated using experimental data in realistic scenarios. The model is also tested with PHILS using a real-time simulator and a programmable dc power supply to emulate PV power generation under various load changes. The model is well matched to the experimental measurements with an error within 2.4% for the electrical aspects and within 1.5% for the thermal aspects in the tested scenarios.</P>

Realistic Circuit Modeling Using Derating Factors for Triboelectric Nanogenerators in Energy Harvesting Applications

Bo-Kyung Yoon,Jee-Hoon Jung,Jeong Min Baik,Katherine A. Kim 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

As the internet of things (IoT) gains popularity, many sensors and devices for a variety of applications need to be powered. Energy harvesting produces electric power from surrounding energy and is the key to powering many IoT devices. A triboelectric nanogenerator (TENG) is a newly-introduced device that harvests electric energy from vibrational energy using the principle of electrostatic energy. Here, the characteristics of the TENG are determined to model and simulate under realistic operation using derating factors. Simulations using the ideal TENG’s circuit model diverge significantly from the actual experimental results. Thus, derating factors are introduced to minimize error between simulation and experimental results. Derating factors of the internal voltage source and the capacitor of the TENG are defined and swept over a range of values to find the values that best fit to the experimental results. For the contact-mode TENG, a voltage derating of 0.0054 and capacitor derating value of 1 resulted in the lowest error in terms of power output. The comparison of the simulation and experiment shows that the they are matched with an error of 1.14×10<SUP>-13</SUP> A for current, 0.157 V for voltage, and 3.81×10<SUP>-13</SUP> W for power.

FAULT DETECTION DEVELOPMENTS FOR SMART GRID PHOTOVOLTAIC SYSTEMS

Katherine A. KIM 한국신재생에너지학회 2015 AFORE Vol.2015 No.11