Method of adaptive solar tracking using variable step size

A method for controlling a photovoltaic (PV) panel in a PV system including a computing device that provides motor control signals and implements an iterative adaprtive control (IAC) algorithm for adjusting an angle of the PV panel. The IAC algorithm relates P at a current time k (P(k)), an elevation angle of the PV panel at k (0s(k)), P after a next step (P(k+1)) and an elevation angle of the PV panel at k+1 (0s(k+1)). The algorithm generates a perturbed power value P(k+1) to provide a power perturbation to P(k), and calculates 0s(k+1) using P(k+1). The motor control signals cause the motor to position the PV panel to achieve 0s(k+1). A change in P resulting from the positioning is compared to a predetermined change limit, and only if the change in P is greater than/equal to the change limit, again sensing P, and repeating the generating, calculating and positioning

Iterative Adaptive Solar Tracking Having Variable Step Size

A system controller for position controlling a photovoltaic (PV) panel in a PV system including a power sensor sensing output power (P), and a motor for positioning the PV panel. The system controller includes a computing device having memory that provides motor control signal and implements an iterative adaptive control (IAC) algorithm stored in the memory for adjusting an angle of the PV panel. The IAC algorithm includes an iterative relation that relates P at current time k (P(k)), its elevation angle at k (?s(k)), P after a next step (P(k+1)) and its elevation angle at k+1(?s(k+1)). The IAV algorithm generates a perturbed power value P(k+1) to provide a power perturbation to P(k), and calculates a position angle ?s(k+1) of the PV panel using the perturbed power value. The motor control signals from the computing device cause the motor to oposition the PV panel to achieve ?s(k+1)

Thrombocytopenia and disseminated histoplasmosis in immunocompetent adults

Disseminated histoplasmosis among immunocompetent patients is rare, but may be associated with clinically significant refractory thrombocytopenia. Platelet counts often return to normal levels following antifungal therapy. Therefore, the most important management of this refractory thrombocytopenia is the recognition and treatment of histoplasmosis infection

Postoperative Atrial Fibrillation and Flutter in Liver Transplantation: An Important Predictor of Early and Late Morbidity and Mortality

Postoperative atrial fibrillation/flutter (POAF) is the most common perioperative arrhythmia and may be particularly problematic after liver transplantation (LT). This study is a single‐center retrospective analysis of POAF to determine its incidence following LT, to identify risk factors, to assess its impact on clinical outcomes, and to summarize management strategies. The records of all patients who underwent LT between 2010 and 2018 were reviewed. Extracted data included pre‐LT demographics and cardiac evaluation, in‐hospital post‐LT cardiac events, early and late complications, and survival. Among 1011 patients, the incidence of post‐LT POAF was 10%. Using binary logistic regression, pre‐LT history of atrial fibrillation was the strongest predictor of POAF (odds ratio [OR], 6.72; 95% confidence interval [CI], 2.00‐22.57; P < 0.001), followed by history of coronary artery disease (CAD; OR, 2.52; 95% CI, 1.10‐5.81; P = 0.03). Cardiac stress testing abnormality and CAD on cardiac catheterization were also associated with higher risk. Median time to POAF onset after LT was 3 days with 72% of cases resolving within 48 hours. POAF patients had greater hospital length of stay, death during the LT admission, and 90‐day and 1‐year mortality. POAF was an independent risk factor for post‐LT mortality (OR, 2.0; 95% CI, 1.3‐3.0; P < 0.01). Amiodarone was administered to 73% of POAF patients with no evidence of increased serum alanine aminotransferase levels. POAF occurred in 10% of post‐LT patients with early onset and rapid resolution in most affected patients. POAF patients, however, had significant morbidity and mortality, suggesting that POAF is an important marker for worse early and late post‐LT outcomes

Pre‐Liver Transplant Cardiac Catheterization is Associated with Low Rate of Myocardial Infarction and Cardiac Mortality

Background A previous study at Indiana University demonstrated a reduction in myocardial infarction (MI) incidence with increased frequency of cardiac catheterization (CATH) in liver transplant (LT) candidates. A strict protocol for performing CATH based upon predefined risk factors, rather than non‐invasive testing alone, was applied to a subgroup (2009‐2010) from that study. CATH was followed by percutaneous coronary intervention (PCI) in cases of significant coronary artery disease (CAD; ≥50% stenosis). The current study applies this screening protocol to a larger cohort (2010‐2016) to assess post‐LT clinical outcomes. Results Among 811 LT patients, 766 underwent stress testing (94%), and 559 underwent CATH (69%) of whom 10% had CAD requiring PCI. The sensitivity of stress echocardiography in detecting significant CAD was 37%. Predictors of PCI included increasing age, male gender and personal history of CAD (p<0.05 for all). Compared to patients who had no CATH, patients who underwent CATH had higher mortality (p=0.07), and the hazard rates (HR) for mortality increased with CAD severity [normal CATH (HR: 1.35 [95% CI: 0.79, 2.33], p=0.298); non‐obstructive CAD (HR: 1.53 [95% CI: 0.84, 2.77], p=0.161); and significant CAD (HR: 1.96 [95% CI: 0.93, 4.15], p=0.080)]. Post‐LT outcomes were compared to the 2009‐2010 subgroup from the previous study and showed similar 1‐year overall mortality (8% and 6%, p=0.48); 1‐year MI incidence (<1% and <1%, p=0.8); and MI deaths as portion of all deaths (3% and 9%, p=0.35). Conclusion Stress echocardiography alone is not reliable in screening LT patients for CAD. Aggressive CAD screening with CATH is associated with low rate of MI and cardiac mortality and validates the previously published protocol when extrapolated over a larger sample and longer follow‐up period

CAD-LT score effectively predicts risk of significant coronary artery disease in liver transplant candidates

Background & Aims Patients with cirrhosis and significant coronary artery disease (CAD) are at risk of peri-liver transplantation (LT) cardiac events. The coronary artery disease in liver transplantation (CAD-LT) score and algorithm aim to predict the risk of significant CAD in LT candidates and guide pre-LT cardiac evaluation. Methods Patients who underwent pre-LT evaluation at Indiana University (2010-2019) were studied retrospectively. Stress echocardiography (SE) and cardiac catheterization (CATH) reports were reviewed. CATH was performed for predefined CAD risk factors, irrespective of normal SE. Significant CAD was defined as CAD requiring percutaneous or surgical intervention. A multivariate regression model was constructed to assess risk factors. Receiver-operating curve analysis was used to compute a point-based risk score and a stratified testing algorithm. Results A total of 1,771 pre-LT patients underwent cardiac evaluation, including results from 1,634 SE and 1,266 CATH assessments. Risk-adjusted predictors of significant CAD at CATH were older age (adjusted odds ratio 1.05; 95% CI 1.03–1.08), male sex (1.69; 1.16–2.50), diabetes (1.57; 1.12–2.22), hypertension (1.61; 1.14–2.28), tobacco use (pack years) (1.01; 1.00–1.02), family history of CAD (1.63; 1.16–2.28), and personal history of CAD (6.55; 4.33–9.90). The CAD-LT score stratified significant CAD risk as low (≤2%), intermediate (3% to 9%), and high (≥10%). Among patients who underwent CATH, a risk-based testing algorithm (low: no testing; intermediate: non-invasive testing vs. CATH; high: CATH) would have identified 97% of all significant CAD and potentially avoided unnecessary testing (669 SE [57%] and 561 CATH [44%]). Conclusions The CAD-LT score and algorithm (available at www.cad-lt.com) effectively stratify pre-LT risk for significant CAD. This may guide more targeted testing of candidates with fewer tests and faster time to waitlist. Lay summary The coronary artery disease in liver transplantation (CAD-LT) score and algorithm effectively stratify patients based on their risk of significant coronary artery disease. The CAD-LT algorithm can be used to guide a more targeted cardiac evaluation prior to liver transplantation

A generalized program for extracting the control characteristics of resonant converters via the state-plane diagram

This paper presents a generalized computer program that can be used to derive the control characteristics of resonant converters from their state-plane trajectories. It has been shown that the geometrical properties of the state-plane trajectory can be used to derive the control characteristics of a given resonant converter topology. These characteristics are essential in determining the design parameters such as the converter gain, component stresses, and required feedback controller. The main program consists of several subroutines, each of which is associated with a segment of the state-plane trajectory. Such a program will make it faster and easier for a design engineer to obtain the design parameters of any given resonant topology

High Frequency Low Cost Dc-Ac Inverter Design With Fuel Cell Source For Home Applications

This paper presents a new design of high frequency Dc/Ac inverter for home applications using fuel cells or photovoltaic array sources. A battery bank parallel to the DC link is provided to take care of the slow dynamic response of the source. The design is based on a push-pull dc/dc converter followed by a full-bridge PWM inverter topology. The nominal power rating is 10 kW. Actual design parameters, procedure and experimental results of a 1.5 kW prototype are provided. The objective of this paper is to explore the possibility of making renewable sources of energy utility interactive by means of low cost power electronic interface

Adaptive Sun Tracking Algorithm For Incident Energy Maximization And Efficiency Improvement Of Pv Panels

In recent times, sun tracking systems are being increasingly employed to enhance the efficiency of photovoltaic panels by constantly tracking the elevation and azimuth angles of the sun. In this paper, a novel adaptive digital signal processing and control algorithm is presented that optimizes the overall PV system output power by adjusting the position angles of the solar panel on both the elevation and azimuth axes. Since the proposed approach is adaptive in nature, the optimal position angles for the solar panel are iteratively computed using the adaptive gradient ascent method, until the incident solar radiation, and hence the output power is maximized. Furthermore, a Taylor\u27s series approximation is employed for generating a unique optimal position angle increment/decrement at each iteration. Simulation results show that the proposed technique demonstrates fast convergence and excellent tracking accuracy at all times of the day. © 2010 Elsevier Ltd

Analysis And Optimization Of Bcm Peak Current Mode Control Techniques For Microinverters

This paper presents a detailed power loss model for a microinverter with three different zero voltage switching (ZVS) boundary conduction mode (BCM) current modulation methods. The model is used to calculate the optimum peak current boundaries for each modulation method. Based on the power loss model, a dual-zone modulation method is proposed to further improve the microinverter efficiency. The proposed modulation method provides two main benefits: the addition of one more soft switching transition and low peak current boundary. The additional soft switching transition reduces switching losses by means of zero current switching (ZCS). The lower peak current boundary reduces inductor rms current and conduction losses as well as allowing the output filter inductor to be smaller and more efficient. An improved BCM peak current control method was proposed and implemented on a microinverter prototype. The control circuit provides a highly accurate representation of the filter inductor current waveform and also provides galvanic isolation which simplifies control circuit design. The experimental results on a 400-W three-phase half-bridge microinverter validate the theoretical analysis of the power loss distribution and demonstrate that further improvement in efficiency can be achieved by using the proposed dual-zone modulation method