Steady State And Dynamic Analysis And Optimization Of Single-stage Power Factor Correction Converters

With the increased interest in applying Power Factor Correction (PFC) to off-line AC-DC converters, the field of integrated, single-stage PFC converter development has attracted wide attention. Considering the tens of millions of low-to-medium power supplies manufactured each year for today\u27s rechargeable equipment, the expected reduction in cost by utilizing advanced technologies is significant. To date, only a few single-stage topologies have made it to the market due to the inherit limitations in this structure. The high voltage and current stresses on the components led to reduced efficiency and an increased failure rate. In addition, the component prices tend to increase with increased electrical and thermal requirements, jeopardizing the overarching goal of price reduction. The absence of dedicated control circuitry for each stage complicates the power balance in these converters, often resulting in an oversized bus capacitance. These factors have impeded widespread acceptance of these new techniques by manufacturers, and as such single stage PFC has remained largely a drawing board concept. This dissertation will present an in-depth study of innovative solutions that address these problems directly, rather than proposing more topologies with the same type of issues. The direct energy transfer concept is analyzed and presented as a promising solution for the majority of the single-stage PFC converter limitations. Three topologies are presented and analyzed based on this innovative structure. To complete the picture, the dynamics of a variety of single-stage converters can be analyzed using a proposed switched transformer model

The IDENTIFY study: the investigation and detection of urological neoplasia in patients referred with suspected urinary tract cancer - a multicentre observational study

Objective To evaluate the contemporary prevalence of urinary tract cancer (bladder cancer, upper tract urothelial cancer [UTUC] and renal cancer) in patients referred to secondary care with haematuria, adjusted for established patient risk markers and geographical variation. Patients and Methods This was an international multicentre prospective observational study. We included patients aged ≥16 years, referred to secondary care with suspected urinary tract cancer. Patients with a known or previous urological malignancy were excluded. We estimated the prevalence of bladder cancer, UTUC, renal cancer and prostate cancer; stratified by age, type of haematuria, sex, and smoking. We used a multivariable mixed-effects logistic regression to adjust cancer prevalence for age, type of haematuria, sex, smoking, hospitals, and countries. Results Of the 11 059 patients assessed for eligibility, 10 896 were included from 110 hospitals across 26 countries. The overall adjusted cancer prevalence (n = 2257) was 28.2% (95% confidence interval [CI] 22.3–34.1), bladder cancer (n = 1951) 24.7% (95% CI 19.1–30.2), UTUC (n = 128) 1.14% (95% CI 0.77–1.52), renal cancer (n = 107) 1.05% (95% CI 0.80–1.29), and prostate cancer (n = 124) 1.75% (95% CI 1.32–2.18). The odds ratios for patient risk markers in the model for all cancers were: age 1.04 (95% CI 1.03–1.05; P < 0.001), visible haematuria 3.47 (95% CI 2.90–4.15; P < 0.001), male sex 1.30 (95% CI 1.14–1.50; P < 0.001), and smoking 2.70 (95% CI 2.30–3.18; P < 0.001). Conclusions A better understanding of cancer prevalence across an international population is required to inform clinical guidelines. We are the first to report urinary tract cancer prevalence across an international population in patients referred to secondary care, adjusted for patient risk markers and geographical variation. Bladder cancer was the most prevalent disease. Visible haematuria was the strongest predictor for urinary tract cancer

The SIB Swiss Institute of Bioinformatics' resources: focus on curated databases

The SIB Swiss Institute of Bioinformatics (www.isb-sib.ch) provides world-class bioinformatics databases, software tools, services and training to the international life science community in academia and industry. These solutions allow life scientists to turn the exponentially growing amount of data into knowledge. Here, we provide an overview of SIB's resources and competence areas, with a strong focus on curated databases and SIB's most popular and widely used resources. In particular, SIB's Bioinformatics resource portal ExPASy features over 150 resources, including UniProtKB/Swiss-Prot, ENZYME, PROSITE, neXtProt, STRING, UniCarbKB, SugarBindDB, SwissRegulon, EPD, arrayMap, Bgee, SWISS-MODEL Repository, OMA, OrthoDB and other databases, which are briefly described in this article

Recent Advances In Single-Stage Power Factor Correction

This paper presents an overview of various interesting power factor correction techniques for single-phase applications. The discussion includes commonly-used control strategies and various types of converter topologies. Included is a comparative study of these strategies, with the major advantages and disadvantages is highlighted. We will emphasize the single-stage topologies, its drawbacks and some promising solutions. ©2003 IEEE

Unified Flyback Switching-Cell Model Including The Leakage Inductance Effects For Spice Simulation

A unified behavioral model based on the flyback transformer, including its leakage inductance, is presented in this paper. The proposed switched transformer model is applicable to simulate topology-independent converters under both continuous (CCM) and discontinuous (DCM) conduction modes. The model can be used in modeling more complicated converter topologies with non-idealities, such as leakage inductance and snubber networks. Simulation results using the proposed model show the over-looked effect of the transformer leakage inductance on the high frequency transfer function response of the flyback converter. The time domain simulation results show a good accuracy and significant reduction in the simulation time

Universal Input Single-Stage Pfc Ac/Dc Converter With Reduced Dc-Bus Voltage Stress

High DC bus voltage stress and low conversion efficiency limit the practical application for single stage Power Factor Correction (PFC) AC-DC converter. This paper presents a cost-effective approach to alleviate these issues based on conventional BIFRED AC/DC converter. In the proposed topology, a Flyback transformer and a small serial connected inductor are implemented to replace traditional input PFC inductor, and a cost-efficient lossless snubber is also proposed to reduce the turn-off spike of the main switch. The experimental result of a 20v≰.5A prototype indicates that the proposed technique can suppress the DC voltage below 400V through the entire universal input range while keeping the efficiency and power factor stay above 81% and 0.95 respectively

Asymmetric Half Bridge Soft-Switching Pfc Converter With Direct Energy Transfer

A single stage Power Factor Correction (PFC) AC/DC converter with direct energy transfer feature is proposed in this paper. An asymmetric Half-Bridge topology is used as the DC-DC cell for its inherent ZVS capability, and a direct energy transfer PFC cell is introduced to improve the conversion efficiency. Its operational principles are discussed in detail, simulation and experimental results are also presented to verify the functionality of this converter

Efficient High Power Factor Single-Stage Ac/Dc Converter

A near flat-top input current waveform and direct energy transferring AC/DC converter which features high efficiency and high power factor is described. In the proposed converter, energy transfers in hybrid mode which means that when the instant line voltage exceeds the preset value, energy is transferred directly to the output side from the input line; otherwise the energy storage capacitor power the output load. The performance of the proposed concept was evaluated on a 200W (48V≰.17A) experimental prototype. It is shown that the efficiency is increased significantly over the case without the direct energy concept. Proof of the concept was verified theoretically and experimentally

Five-Terminal Average Modeling And Ac Analysis Of Pfc Converters In Pspice

A simple and accurate five-terminal switched transformer average model was used to perform the AC analysis of single-stage Power Factor Correction (PFC) converter using PSPICE. Unlike other models presented in literature, the proposed switching cell includes the transformer leakage inductance, the intermediate bus input, and still addresses both continuous and discontinuous conduction modes. The developed PSPICE model is very relevant to isolated converters including the PFC example provided here, which are not easily handled by other models. © 2005 IEEE