Leakage inductance calculation of complex transformer constructions based on a simple two-coil inductor model

The paper presents a set of systematic matrices operation derived from Kirchhoff s Node Law with the base of a simple two-coil inductor model to deduce leakage inductances of windings seen from the schematic point of view. This method provides a platform in calculating leakage inductances of complex transformer structures. Its robustness covers different kinds of concentric winding structures where by getting accurate values of mutual inductances between all combinations of winding elements in a pair-wise sense, accurate leakage inductances can be deduced through the matrices operation without any computational simulations. In essence, such operation reduces lots of difficult magnetic problems within a transformer into determination of mutual and self inductances of winding elements through a simple two-coil inductor model. The approach has been implemented on PowerESIM [5] [6], a web base server type power converter design program, for reader to test.published_or_final_versio

Interleaved boost power factor corrector operating in discontinuous-inductor-current mode

This paper presents the basic operation of the Discontinuous-Inductor-Current-Mode (DICM) boost PFC and the improvement achieved by interleaving technique. The PFC is constructed by at least two boost cells, each cell is kept running in DICM. Input current of the PFC is analyzed by numerical method and the optimum power factor is calculated in different modes of operation. The calculated result is verified by experiment and presented in graphical form with detailed discussion. The result shows that interleaving technique can alleviate the ripple current and improve the power factor. The improvement is obvious for the number of boost cells equal to 2 or 3 and the ripple alleviation is better when the PFC is operated in fixed frequency mode. The optimum power factor is improved up to 0.99 even without an input filter.published_or_final_versio

Fast response Full Bridge Power Factor Corrector

A fast response Full Bridge Power Factor Corrector (FBPFC) is presented in this paper. The converter is combined by two interleaved boost cells and a conventional full bridge converter. As the interleaving technique is applied, the input ripple current of FBPFC are reduced. Experimental result shows that the maximum power factor is 0.98 even without input filter.published_or_final_versio

Experimental study on turbulence characteristics of a slot jet impingement on semi-circular surfaces

2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

DSP controlled power converter

A digital controller is designed and implemented by a Digital Signal Processor (DSP) to replace the Pulse Width Modulator (PWM) and error amplifier compensation network in a two wheeler forward converter. The DSP controller is designed in three approaches: a) Discretization of analog controller - the design is based on the transfer function of the error amplifier compensation network. b) Digital PID controller design - the design is based on the general form of the pulse transfer function of PID controller. c) Deadbeat controller design - the design is based on the open-loop pulse transfer function of the power converter. The controller design is optimised by running computer simulation with the MATLAB numerical calculation package and the experimental results agree with the simulated analysis.published_or_final_versio

Analysis of the resonance modes of PZT/epoxy 1-3 composite rings

Author name used is this publication: C. P. ChongRefereed conference paper2001-2002 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

Validation of the Abbreviated Mental Test (Hong Kong version) in the elderly medical patient

The Abbreviated Mental Test is a useful screening test for abnormal cognitive function in the elderly patient. It is widely used in UK geriatrics practice. A modified local version of the Abbreviated Mental Test is also commonly used in Hong Kong. In the present study, the local version of the 10-question Abbreviated Mental Test was validated against clinical diagnoses of normal/abnormal cognitive function (by DSM III R criteria). Sixty-nine patients (aged 65 years and older) referred to the Acute Geriatric Assessment Team at the Queen Mary Hospital were assessed. Nine patients (13%) were excluded because of language barrier, deafness, dysphasia and/or severe dysarthria. Sixty patients completed the test and the clinical assessment. An incorrect answer in each of the test items was found to be significantly associated with abnormal cognitive function (P<0.005). For the Abbreviated Mental Test score, the best cut-off point was found to be six (below six was considered abnormal); this yielded a sensitivity of 96% and a specificity of 94%.published_or_final_versio

Design consideration of a multi-function otoacoustic emission measurement system

A new approach for recording otoacoustic emissions (OAEs) is described in the paper. The system is based on a personal computer equipped with INTEL Pentium CPU. A single chip microcomputer INTEL 8096 is developed to be a stimulus generator. Some critical problems and circuit parameters in the design of this system are presented in the paper. The main advantages of the system are (1) it can record three kinds of OAEs which have many clinical applications; (2) it can save raw data for further analysis, as most researchers need; (3) plenty of analysis functions can be developed in this system. With the use of the newly developed system, SOAEs, TEOAEs, and DPOAEs have been successfully measured.published_or_final_versio

Development of a micromanipulator-based loading device for mechanoregulation study of human mesenchymal stem cells in three-dimensional collagen constructs

Mechanical signal is important for regulating cellular activities, including proliferation, metabolism, matrix production, and orientation. Bioreactors with loading functions can be used to precondition cells in three-dimensional (3D) constructs so as to study the cellular responses to mechanical stimulation. However, full-scale bioreactor is not always an affordable option considering the high cost of equipments and the liter-sized medium with serum and growth factor supplements. In this study, a custom-built loading system was developed by coupling a conventional camera-equipped inverted research microscope with two micromanipulators. The system was programmed to deliver either cyclic compressive loading with different frequencies or static compressive loading for 1 week to investigate the cellular responses of human mesenchymal stem cells (hMSCs) entrapped in a 3D construct consists of reconstituted collagen fibers. Cellular properties, including their alignment, cytoskeleton, and cell metabolism, and properties of matrix molecules, such as collagen fiber alignment and glycosaminoglycan deposition, were evaluated. Using a MatLab-based image analysis program, reorientation of the entrapped cells from a random distribution to a preferred alignment along the loading direction in constructs with both static and cyclic compression has been demonstrated, but no such alignment was found in the free-floating controls. Fluorescent staining on filamentous actin cytoskeleton also confirmed the finding. Nevertheless, the collagen fiber meshwork entrapping the hMSCs remained randomly distributed, and no change in cellular metabolism and glycosaminoglycans production was noted. The current study provides a simple and affordable option toward setting up a mechanoregulation facility based on existing laboratory equipments and sheds new insights on the effect of mechanical loading on the alignment of hMSCs in 3D collagen constructs. Copyright © 2010, Mary Ann Liebert, Inc.published_or_final_versio

Fast tracking of evoked potential variations using correlated scale function designed by multiresolution analysis

Fast tracking of evoked potential variations is of great importance in clinical operation. The paper describes a method whereby an ensemble averaged signal is used as the prototype of the scale function and designs a correlated scale function based on multiresolution analysis. Hence, an effective low pass digital filter having powerful tracking capability is obtained. Results show that the filter designed filters out the noise more effectively than that using general wavelet filtering, and the tracking of the peak of evoked potential is easily obtained.published_or_final_versio