Dynamic modeling of pwm and single-switch single-stage power factor correction converters

The concept of averaging has been used extensively in the modeling of power electronic circuits to overcome their inherent time-variant nature. Among various methods, the PWM switch modeling approach is most widely accepted in the study of closed-loop stability and transient response because of its accuracy and simplicity. However, a non-ideal PWM switch model considering conduction losses is not available except for converters operating in continuous conduction mode (CCM) and under small ripple conditions. Modeling of conductor losses under large ripple conditions has not been reported in the open literature, especially when the converter operates in discontinuous conduction mode (DCM). In this dissertation, new models are developed to include conduction losses in the non-ideal PWM switch model under CCM and DCM conditions. The developed model is verified through two converter examples and the effect of conduction losses on the steady state and dynamic responses of the converter is also studied. Another major constraint of the PWM switch modeling approach is that it heavily relies on finding the three-terminal PWM switch. This requirement severely limits its application in modeling single-switch single-stage power factor correction (PFC) converters, where more complex topological structures and switching actions are often encountered. In this work, we developed a new modeling approach which extends the PWM switch concept by identifying the charging and discharging voltages applied to the inductors. The new method can be easily applied to derive large-signal models for a large group of PFC converters and the procedure is elaborated through a specific example. Finally, analytical results regarding harmonic contents and power factors of various PWM converters in PFC applications are also presented here

The combination approach of SVM and ECOC for powerful identification and classification of transcription factor

<p>Abstract</p> <p>Background</p> <p>Transcription factors (TFs) are core functional proteins which play important roles in gene expression control, and they are key factors for gene regulation network construction. Traditionally, they were identified and classified through experimental approaches. In order to save time and reduce costs, many computational methods have been developed to identify TFs from new proteins and to classify the resulted TFs. Though these methods have facilitated screening of TFs to some extent, low accuracy is still a common problem. With the fast growing number of new proteins, more precise algorithms for identifying TFs from new proteins and classifying the consequent TFs are in a high demand.</p> <p>Results</p> <p>The support vector machine (SVM) algorithm was utilized to construct an automatic detector for TF identification, where protein domains and functional sites were employed as feature vectors. Error-correcting output coding (ECOC) algorithm, which was originated from information and communication engineering fields, was introduced to combine with support vector machine (SVM) methodology for TF classification. The overall success rates of identification and classification achieved 88.22% and 97.83% respectively. Finally, a web site was constructed to let users access our tools (see Availability and requirements section for URL).</p> <p>Conclusion</p> <p>The SVM method was a valid and stable means for TFs identification with protein domains and functional sites as feature vectors. Error-correcting output coding (ECOC) algorithm is a powerful method for multi-class classification problem. When combined with SVM method, it can remarkably increase the accuracy of TF classification using protein domains and functional sites as feature vectors. In addition, our work implied that ECOC algorithm may succeed in a broad range of applications in biological data mining.</p

Three-dimensional array of microbubbles sonoporation of cells in microfluidics

Sonoporation is a popular membrane disruption technique widely applicable in various fields, including cell therapy, drug delivery, and biomanufacturing. In recent years, there has been significant progress in achieving controlled, high-viability, and high-efficiency cell sonoporation in microfluidics. If the microchannels are too small, especially when scaled down to the cellular level, it still remains a challenge to overcome microchannel clogging, and low throughput. Here, we presented a microfluidic device capable of modulating membrane permeability through oscillating three-dimensional array of microbubbles. Simulations were performed to analyze the effective range of action of the oscillating microbubbles to obtain the optimal microchannel size. Utilizing a high-precision light curing 3D printer to fabricate uniformly sized microstructures in a one-step on both the side walls and the top surface for the generation of microbubbles. These microbubbles oscillated with nearly identical amplitudes and frequencies, ensuring efficient and stable sonoporation within the system. Cells were captured and trapped on the bubble surface by the acoustic streaming and secondary acoustic radiation forces induced by the oscillating microbubbles. At a driving voltage of 30 Vpp, the sonoporation efficiency of cells reached 93.9% ± 2.4%

Impact of regulatory intervention and consumer environmental concern on product introduction

To meet consumer expectations for greener and better quality products and to ensure effective compliance with emissions regulations, firms have begun investing in improving the quality and greenness (low carbon level) of existing products. Emissions regulations currently restrict carbon emissions from product manufacturing rather than the emissions from the use of sold products. However, a large amount of carbon may be emitted from the use of products. Motivated by these issues, we analytically investigate the impact of environmental concern and the policies of regulators, and consumer environmental concern on product introduction. Our results show that (i) whether emissions trading regulations benefit firms depends on the quality improvement capability, and the interaction between emissions price and allowed emissions cap; (ii) the environmental concern of consumers helps firms obtain higher profits when quality improvement capability is relatively high, and always benefits environmental performance; and (iii) relatively low environmental concern set by regulators is detrimental to the maximization of social welfare, whereas high regulator environmental concern helps to maximize social welfare but at the expense of reducing firms’ profits

Correcting The Pspice Large-Signal Model For Pwm Converters Operating In Dcm

It is shown that an incorrect parameter limit in the existing Pspice pulsewidth modulated (PWM) switch model has been detected. The main objective of this work is to alert users of such models to a potential source of simulation error under certain parameter specifications as shown here. Simulation of the boost converter operating in discontinuous conduction mode (DCM) based on this incorrect model results in either convergence problems or wrong results. Correction of the model is provided and its validity is verified using a specific converter example. The results illustrate how the old and corrected models produce different results when the boost converter is subjected to some transients under sudden load variations

DC-to-DC converter with no magnetic elements and enhanced regulation

A switched-capacitor-based (SC) step-up dc converter is proposed. It contains no inductors and transformers, thus it can be realized in small size, exhibiting low weight and high power density. Two switched-capacitor circuits, operating in antiphase in each half-cycle, are used to control the energy flow from an unregulated voltage source to a regulated output. The capacitors are charged and discharged according to a designed sequence. To enhance the line and load regulation capability, in each half-cycle, each charging interval is split into two subintervals,: which are followed by noncharging subintervals whose duration is dictated by the pulsewidth modulation (PWM) feedback circuit. The new converter is advantageous for applications in which significant line drops are likely to occur. © 1997 IEEE