Active input-voltage and load-current sharing in input-series and output-parallel connected modular DC-DC converters using dynamic input-voltage reference scheme

This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.     

IEEE Power Engineering Review

In this paper, the author describes how solving three-phase power system voltage sag problems requires cooperation between electric utilities and end-users, with support from equipment manufacturers and standards-setting organizations.     

Novel soft-switching DC-DC converter with full ZVS-range andreduced filter requirement. II. Constant-input, variable-outputapplications

For pt.I see ibid., vol.16, no.2, p.184-92 (2001). The performance of the hybrid converter featuring zero-voltage-switching (ZVS) down to no-load and significant reduction in the filter requirement, proposed in Part I of this paper, is analyzed here for constant-input, variable-output applications. For these applications, the main drawback of the hybrid converter, namely the increased transformer rating is eliminated. The advantages of the hybrid configuration like the reduction in filter rating and full-load ZVS with negligible penalty on conduction loss, are retained. An extension of the basic hybrid converter-a combination of two full-bridges using six switches is proposed. This configuration is well suited for applications above a few kilowatts, and results in significant reduction in the ripple current rating of the input filter capacitor. Experimental results obtained from a 1 kW/100 kHz prototype are presented     

Single nucleotide polymorphism spectra in newborns and centenarians: identification of genes coding for rise of mortal disease

Some single-nucleotide polymorphisms (SNPs) increase the risk of mortal disease. Identifying these SNPs and the genes in which they reside is an important area in human genomics. Such qualitative observations are important in themselves. However, an accurate assessment of the numerical distribution and age-dependent decline of SNPs in the population would permit calculation of the rises represented by each SNP. Such analyses have not been attempted because of a lack of an efficient and cost-effective method to detect multiple SNPs in a large number of individuals and a large number of genes. Here, we suggest the use of an analytical procedure that can scan for SNPs in 100-bp DNA sequences from as many as 10000 donors' blood cell samples, or 20000 alleles, simultaneously. Our suggestion is based on technology developed for studies of somatic mutations in human tissue DNA for point mutations at frequencies equal to or greater than 10(-6). In a simplified version of this technology, any SNP arising at frequencies at or above 5x10(-4) would be identified with useful precision. A gene would be represented by 10 or more sections of 100bp. This strategy includes splice-site mutations that represent a significant fraction of gene inactivating point mutations and would not be observed in strategies using cDNA. To illustrate the logic of the suggested approach, we use American mortality records to calculate the expected decrease in SNPs coding for premature mortality in newborns and centenarians. We consider several elementary cases: SNPs in one gene only, any of several genes, or all of several genes that create a risk of death by pancreatic cancer. The fraction of expressed polymorphisms affecting mortality should be simultaneously increased in probands and decreased in the aged relative to newborns. Silent polymorphisms in the same gene would remain unchanged in all three groups and serve as internal standards. A key point is that scanning a gene, in which loss of gene function creates the risk of mortality is expected to reveal not one, but multiple SNPs, which decline with age, as carriers die earlier in life than non-carriers. Several SNPs in a scanned gene would suggest that the decreasing SNP was genetically linked to a different polymorphism that creates the disease risk.     

Catalytic-assisted synthesis, characterization and low frequency AC conduction of nanostructured conducting polyaniline

Polymerizations of aniline at the reaction temperatures of 25 and 50 °C have been performed in the presence of iron catalyst. The prepared conducting polyaniline at different reaction periods was investigated for physicochemical and electrical properties, through X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR) and frequency-dependent electrical conductivity measurements, respectively. XRD studies established the improved nanostructured crystalline nature for the polymer prepared at 50 °C. Size of the particles ranging from 10 to 20 nm was calculated for the prepared polyaniline. SEM analysis shows the cauliflower-like morphology for optimized reaction temperature. The study further establishes the attainment of uniform distribution of polyaniline at the reaction temperature of 50 °C. The charge transitions between benzenoid (B-band) and quinonoid (Q-band) bands were witnessed by UV–Vis spectrum analysis. The band gap analysis revealed the narrow band gap direct transition semiconducting nature of the conducting polymer. Quinonoid and phenylene rings were identified through vibrational bands between 1570 and 827 cm^?1 via FTIR spectroscopy analysis. The AC conductivity of the sample synthesized at 50 °C showed 1.50 × 10^?1 S cm^?1. Enhancement in conductivity with increasing temperature represented the improved crystalline nature of the polyaniline prepared at 50 °C.     

Common-duty-ratio control of input-series connected modular DC-DC converters with active input voltage and load-current sharing

This paper proposes a simple control method to achieve active sharing of input voltage and load current among modular converters that are connected in series at the input and in parallel at the output. The input-series connection enables a fully modular power-system architecture, where low voltage and low power modules can be connected in any combination at the input and/or at the output, to realize any given specifications. Further, the input-series connection enables the use of low-voltage MOSFETs that are optimized for very low R/sub DSON/, thus, resulting in lower conduction losses. In the proposed scheme, the duty ratio to all the converter modules connected in input-series and output-parallel (ISOP) configuration is made common. This scheme does not require a dedicated input-voltage or load-current-share controller. It relies on the inherent self-correcting characteristic of the ISOP connection when the duty ratio of all the converters is the same. The proposed scheme is analyzed using the average model of a forward converter. The stability and performance of the scheme are verified through numerical simulation, both in frequency domain and in time domain. The proposed control method is also validated on an experimental prototype ISOP system comprising of two forward converters.     

Advanced bus-clamping PWM TechniquesBased on space vector approach

Conventional space vector pulsewidth modulation (CSVPWM) employs conventional switching sequence, which divides the zero vector time equally between the two zero states in every subcycle. Existing bus-clamping PWM (BCPWM) techniques employ clamping sequences, which use only one zero state in a subcycle. This paper deals with a special type of switching sequences, termed here as "double-switching clamping sequences," which use only one zero state and apply an active vector twice in a subcycle. The present work brings out a class of bus-clamping PWM techniques, which employ such sequences. It is shown analytically as well as experimentally that the proposed BCPWM techniques result in reduced harmonic distortion in the line currents over CSVPWM as well as existing BCPWM techniques at high modulation indices for a given average switching frequency of F/sub SW/. At high modulation indices, the dominant harmonic components in the line voltages are around 2F/sub SW/ with the proposed BCPWM techniques, while the dominant components are around F/sub SW/ and 1.5F/sub SW/, respectively, with CSVPWM and existing BCPWM techniques. The proposed techniques also reduce the inverter switching losses at high power factors over CSVPWM and existing BCPWM techniques.     

A Comprehensive Analysis of Hybrid Phase-Modulated Converter With Current-Doubler Rectifier and Comparison With Its Center-Tapped Counterpart

A hybrid phase-modulated converter (HPMC) is a recent innovation in the family of soft-switching converters. It is a promising solution to most soft-switching issues. The principal bottleneck in achieving higher efficiency with this topology is the secondary side loss-mainly the losses in the transformer and the rectifier. For low-voltage high-current power supplies, the current-doubler rectification of HPMC addresses both the transformer conduction losses and the rectifier losses. The presence of an additional path for quiescent current in this scheme gives rise to a third mode of operation. There is also the possibility of magnetic integration of all the magnetic components into one, which can cause substantial reduction in magnetic requirements. These facts make the analysis of current doubler important. In this paper, all the operating modes are identified and corresponding equations and equivalent circuits that aid in filter and control design are derived. The zero-voltage-switching (ZVS) characteristics, filter requirement, small-signal transfer characteristics, device ratings, and magnetics size requirement are considered to compare this configuration with its center-tapped counterpart. The current-doubler scheme is found to have superior soft-switching characteristics in that it can achieve ZVS at lighter loads with a much lower peak magnetizing current in the transformer and leakage inductance. Also, a judicious choice of output current ripple can give an overall reduced magnetics requirement. The analyses are verified by simulation and hardware implementation. HPMC is found to be most advantageous for applications with input voltages essentially constant, but the output voltage widely varying, for example in battery chargers and converters with power factor correction front end