Reliability analysis and performance degradation of a boost converter

pre-printIn general, power converters are operated in closed-loop systems, and any characteristic variations in one component will simultaneously alter the operating point of other components, resulting in a shift in overall reliability profile. This interdependence makes the reliability of a converter a complex function of time and operating conditions; therefore, the application may demand periodic replacement of converters to avoid downtime and maintenance cost. By knowing the present state of health and the remaining life of a power converter, it is possible to reduce the maintenance cost for expensive high-power converters. This paper presents a reliability analysis for a boost converter, although this method could be used to any power converter being operated using closed-loop controls. Through the conducted study, it is revealed that the reliability of a boost converter having control loops degrades with time, and this paper presents a method to calculate time-varying reliability of a boost converter as a function of characteristic variations in different components in the circuit. In addition, the effects of operating and ambient conditions have been included in the reliability model as well. It was found that any increase in the ON-state resistance of the MOSFET or equivalent series resistance of the output capacitor decreases the overall reliability of the converter. However, any variation in the capacitance has a more complex impact on the converter's reliability. This paper is a step forward to the power-converter reliability analysis because the cumulative effect of multiple degraded components has been considered in the reliability model

Energy efficient residential house wall system

The energy consumption and greenhouse gas emission by the residential housing sector are considered to be one of the largest in economically developed countries. The larger energy consumption and greenhouse gas emission not only put additional pressure on finite fossil fuel resources but also cause global warming and climate change. Additionally, the residential housing sector will be consuming more energy as the house demand and average house floor area are progressively increasing. With currently used residential house wall systems, it is hard to reduce energy consumption for ongoing house space heating and cooling. A smart house wall envelope with optimal thermal masses and insulation materials is vital for reducing our increasing energy consumption. The major aim of this study is to investigate thermal performance and energy saving potential of a new house wall system for variable climate conditions. The thermal performance modelling was carried out using commercially developed software AccuRate®. The findings indicate that a notable energy savings can be accomplished if a smart house wall system is used

Comparison between caudal epidural block and popliteal nerve block for postoperative analgesia in children undergoing foot surgery: a randomized controlled trial

Background: Pain following surgery in children cause discomfort, restlessness and agitation in the postoperative period which may result in an increased incidence of nausea, vomiting and maladaptive behavioural changes. Regional anaesthesia is commonly used as an adjunct to general anaesthesia for perioperative analgesia in children as part of a multimodal approach of pain relief. This study is to compare between caudal epidural block and popliteal nerve block for postoperative analgesia in children undergoing foot surgery.Methods: A prospective randomized single blind study was carried out on 30 children aged 1-12 years of either sex undergoing foot surgery. Patients were randomly assigned into caudal epidural block group and Popliteal nerve block group, 15 children each. Both groups receive 1 ml/kg of 0.25% bupivacaine. Foot surgery was carried out under general anesthesia along with regional block for all children. After completion of surgery, children were shifted to PACU and HR, BP, SPO2 were monitored. Patient was discharged from PACU after CHEOPS (1-5 years) or VAS (6-12 years) <4. Parental satisfaction, sedation score, PONV, and any other side effects were recorded.Results: Demographic data and baseline vital signs were comparable between two groups. Statistically significant difference (p=0.025) in number of attempts in giving block in group A (1.20±0.41) than group B (1.80±0.86). The mean postoperative pain scores, CHEOPS and VAS were comparable in both groups.Conclusions: Both caudal epidural block and popliteal nerve block provides comparable and adequate analgesia in children undergoing elective foot surgery

Bifacial Si heterojunction-perovskite organic-inorganic tandem to produce highly efficient (η T * ~ 33%) solar cell

As single junction photovoltaic (PV) technologies both Si heterojunction (HIT) and perovskite based solar cells promise high efficiencies at low cost. Intuitively a traditional tandem cell design with these cells connected in series is expected to improve the efficiency further. Using a self-consistent numerical modeling of optical and transport characteristics however we find that a traditional series connected tandem design suffers from low JSC due to band-gap mismatch and current matching constraints. Specifically a traditional tandem cell with state-of-the-art HIT ( η=24% ) and perovskite ( η=20% ) sub-cells provides only a modest tandem efficiency of ηT~ 25%. Instead we demonstrate that a bifacial HIT/perovskite tandem design decouples the optoelectronic constraints and provides an innovative path for extraordinary efficiencies. In the bifacial configuration the same state-of-the-art sub-cells achieve a normalized output of η∗T  = 33% exceeding the bifacial HIT performance at practical albedo reflections. Unlike the traditional design this bifacial design is relatively insensitive to perovskite thickness variations which may translate to simpler manufacture and higher yield

PV-Transformer-Less Inverter Topology for Battery-Equivalent DC Supply from Leakage Current

Solar panels used for electricity generation have got inverters as their core components. Such inverters are made from switching devices coupled with additional circuit component configured in a transformer-less topology in recent reported works. A transformer-less topology suffers from the drawbacks of lack of isolation leading to leakage current flow from various points of it down to ground. The leakage in inverters might be troublesome as it may lead to loss in power, and may cause malfunctioning of analog devices normally used in power inverters. In this work, we identify possible leakage currents in a given transformer-less topology using the circuit analysis principles. The conversion of so obtained leakage currents into a useful DC voltage is carried out in this work. This work focuses on converting leakage current into small DC voltage in the range of ~1.1004V using recently reported rectifier circuits, supplying a load of 200Ω in the mW range. Although small in magnitude, such voltage sources could be used for battery charging purposes or driving small loads

Manufacturing of agricultural machinery in Bangladesh: opportunities and constraints

Despite numerous limitations, agricultural machinery (AM) manufacturing sub-sector inBangladeshis growing quite satisfactorily and has potential to make substantial contribution to much needed non-farm economic growth, employment generation, mechanization of on and off-farm agricultural activities, and as a whole orientation in the national development.  This study made an attempt to take account of AM manufacturers, importers, traders/wholesalers and retailers, their associations, assess market potential and identify serious bottlenecks associated with this sub-sector.  Stratified random sampling technique was used for identifying respondents in quantitative survey, while focus group discussions (FGDs) and Key Informant Interviews (KIIs) were conducted for qualitative investigation.  In recent years, there are about 70 foundries, 800 agricultural machinery manufacturing industries and workshops, 1,500 spare parts manufacturing workshops, and about 20,000 repair and maintenance workshops are engaged in AM sub-sector of the country.  The annual estimated market size of AM and spare parts in the country is about US$802.3 million with an US$ 105.2 million annual repair and maintenance service market, estimating an annual total AM market size of about US$907.5 million of which local production market share is about     US$ 402.7 million.  The spare parts market size in the country is about US$309.3 million of which domestic production of spare parts is estimated US$ 237.9 million.  The significant shift in the supply of spare parts in the country underlines the growth potential of the local spare parts manufacturing sub-sector and potential for substitution of imported spare parts.  Bogra has emerged as the center of manufacturing AM and spare parts especially for irrigation pumps, threshers, maize shellers, piston, liner and numerous spare parts of small diesel engines and machines, casting of machine components etc. and contributing about 80% of the local production in the country.  However, infrastructures for production of AM and spare parts in Bogra and elsewhere in the country are still inadequate. The study recommends declaration of Borga and Jessore as ‘Agri-machinery districts’ and establishment of special ‘Agri-machinery Production Zones (APZ)’ in these areas.  To promote export market to Indian subcontinent and other developing countries, tariff and non-tariff restrictions would be waved on AM through bilateral negotiations and border markets (hats) withIndiato be allowed for AM sales. 

Adaptive Critic Network for Person Tracking Using 3D Skeleton Data

Analysis of human gait using 3-dimensional co-occurrence skeleton joints extracted from Lidar sensor data has been shown a viable method for predicting person identity. The co-occurrence based networks rely on the spatial changes between frames of each joint in the skeleton data sequence. Normally, this data is obtained using a Lidar skeleton extraction method to estimate these co-occurrence features from raw Lidar frames, which can be prone to incorrect joint estimations when part of the body is occluded. These datasets can also be time consuming and expensive to collect and typically offer a small number of samples for training and testing network models. The small number of samples and occlusion can cause challenges when training deep neural networks to perform real time tracking of the person in the scene. We propose preliminary results with a deep reinforcement learning actor critic network for person tracking of 3D skeleton data using a small dataset. The proposed approach can achieve an average tracking rate of 68.92±15.90% given limited examples to train the network

Numerical Study on Bubble Dynamics and Two-Phase Frictional Pressure Drop of Slug Flow Regime in Adiabatic T-junction Square Microchannel

In this study, bubble dynamics and frictional pressure drop associated with gas liquid two-phase slug flow regime in adiabatic T-junction square microchannel has been investigated using CFD. A comprehensive study on the mechanism of bubble formation via squeezing and shearing regime is performed. The randomness and recirculation profiles observed in the squeezing regime are significantly higher as compared to the shearing regime during formation of the slug. Further, effects of increasing gas velocity on bubble length are obtained at fixed liquid velocities and simulated data displayed good agreement with available correlations in literature. The frictional pressure drop for slug flow regime from simulations are also obtained and evaluated against existing separated flow models. A regression correlation has also been developed by modifying C-parameter using separated flow model, which improves the prediction of two-phase frictional pressure drop data within slug flow region, with mean absolute error of 10 %. The influences of fluid properties such as liquid viscosity and surface tension on the two-phase frictional pressure drop are also investigated and compared with developed correlation. The higher liquid viscosity and lower surface tension value resulted in bubble formation via shearing regime. This work is licensed under a Creative Commons Attribution 4.0 International License

Performance Analysis of Solar Adsorption Cooling System - Effect of Position of Heat Storage Tank

An insulated storage tank has been added with adsorption cooling system run by solar heat collected by CPC panel. It has been expected and seen that the storage tank has a vital contribution in the performance of the chiller. The storage tank is connected with a solar heat driven single stage two bed basic adsorption chillers activated with silica gel-water pair in two ways. The tank is connected in such a way that (i) the solar collectors supply hot water to the desorption bed, the outflow of the desorber is collected in the reserve tank. The reserve tank supplies water to the collector and complete the heat transfer cycle. (ii) The solar collector supply hot water which is collected in the storage tank first and then supplied to the desorber. The outflow of the desorber is carried to the collector again. Comparative studies have been conducted at the steady state for both of the systems with heat storage. It has been observed that the system is robust with design (i) while with design (ii) performance enhances beyond the sunset time with heat storage