• Journal of Power Electronics
• /
• v.19 no.4
• /
• pp.869-880
• /
• 2019

Due to the inherent feedforward of load current, capacitor current (CC) control shows a fast transient response that makes it suitable for the power supplies used in various portable electronic devices. However, considering the effect of the outer voltage loop, the stable range of the duty-cycle is significantly diminished in CC controlled buck converters. To investigate the stability effect of the outer voltage loop on buck converters, a CC controlled buck converter with a proportion-integral (PI) compensator is taken as an example, and its second-order discrete-time model is established. Based on this model, the instability caused by the duty-cycle is discussed with consideration of the outer voltage loop. Then the dynamical effects of the feedback gain of the PI compensator and the equivalent series resistance (ESR) of the output capacitor on the CC controlled buck converter with a PI compensator are studied. Furthermore, the design-oriented closed-loop stability criterion is derived. Finally, PSIM simulations and experimental results are supplied to verify the theoretical analyses.

• Journal of Energy Engineering
• /
• v.15 no.3 s.47
• /
• pp.154-159
• /
• 2006

An experimental study has been performed to investigate the correlation on compressor discharge temperature of capacity modulated system A/C in cooling mode. Indoor and outdoor temperatures, the cooling capacity, compressor discharge temperature and loading time are measured by the psychrometric calorimeter. The system is controlled by applying the scroll compressor operated by PWM valve and loading duty. With decreasing outdoor temperature, the cooling capacity increases. But, with decreasing indoor temperature, it decreases. According to the increase in outdoor temperature and loading duty, compressor discharge temperature increases. From these experimental data, the correlation on compressor discharge temperature is proposed. The correlation obtained from the present study is agreed with the experimental data within $3^{\circ}C$.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.13 no.2
• /
• pp.89-93
• /
• 2014

Variable polarity (VP) arc welding is known as an effective solution for aluminum thanks to the cleaning effect, which means oxide removal, during the DCEP (direct current electrode positive) period. In this research, VP GTAW (gas tungsten arc welding) is adopted for lap joint fillet welding of 3mm thickness 5052 aluminum alloy. Various welding currents and DCEP duty cycles are applied as welding conditions with a fixed welding speed to investigate the influence of DCEP characteristics on weld bead formation. Results show a tendency of higher heat input for higher DCEP duty cycle, which result does not follow conventional arc theory because it is known that DCEN (DC electrode negative) polarity is more efficient for heat input than is DCEP. This phenomenonhas recently been reported by several VP-GTA researchers and is still controversial because the mechanism of oxide removal is not yet clear except for the previous, well-known idea of "ion bombardment", which cannot explain the situation. Finally, proper usage conditions for VP-GTAW are suggested; then, further, related theoretical topics in the field of cathode physics are brieflyintroduced.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.12 no.10
• /
• pp.4889-4902
• /
• 2018

It is a challenging issue to improve the energy efficiency of neighbor discovery in WSNs. This paper proposes an optimal discovery model (ODM) for the first time. Based on the model, we investigate the influence of the relative size of two unequal active slots on the energy efficiency. ODM provides the energy optimal value of the length of the larger active slot at a given duty cycle. Other than existing methods, the worst-case latency bound of ODM is only one period. This is a subversive conclusion, because almost all other related methods are based on a wake-up schedule that contains several periods. We theoretically deduce that ODM can reduce worst-case discovery latency by 43.89% compared to Searchlight-Trim when their duty cycles are the same. The simulations verify the advantage of ODM.

• Smart Structures and Systems
• /
• v.14 no.4
• /
• pp.617-641
• /
• 2014

The energy constraint is still a common issue for the practical application of wireless sensors, since they are usually powered by batteries which limit their lifetime. In this paper, a practical compound energy efficiency strategy is proposed and realized in the implementation of a real time wireless sensor platform. The platform is intended for wireless structural monitoring applications and consists of three parts, wireless sensing unit, base station and data acquisition and configuration software running in a computer within the Matlab environment. The high energy efficiency of the wireless sensor platform is achieved by a proposed adaptive radio transmission power control algorithm, and some straightforward methods, including adopting low power ICs and high efficient power management circuits, low duty cycle radio polling and switching off radio between two adjacent data packets' transmission. The adaptive transmission power control algorithm is based on the statistical average of the path loss estimations using a moving average filter. The algorithm is implemented in the wireless node and relies on the received signal strength feedback piggybacked in the ACK packet from the base station node to estimate the path loss. Therefore, it does not need any control packet overheads. Several experiments are carried out to investigate the link quality of radio channels, validate and evaluate the proposed adaptive transmission power control algorithm, including static and dynamic experiments.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.11 no.2
• /
• pp.63-68
• /
• 2003

The purpose of this study was to investigate reduction of exhaust gas temperature in LPG conversion engine from diesel. A conventional diesel engine was modified to a LPG(Liquified Petroleum Gas) engine that diesel fuel injection pump was replaced by the LPG fuel system. The research was peformed with measurement of exhaust gas temperature by varying spark ignition timing, air-fuel ratio, compression ratio, EGR ratio and different compositions of butane and propane. The major conclusion of this work were followed. (i) Exhaust gas temperature was decreased and power was increased with the advanced spark ignition timing. (ii) Exhaust gas temperature was decreased with lean and rich air-fuel ratio. (iii)Exhaust gas temperature was decreased and power was increased with the higher compression ratio. (iv) Engine power and exhaust temperature were not influenced by varied butane/propane fuel compositions. (v) Finally, one of the important parameters in reduction of exhaust gas temperature is spark ignition timing among the parameters in this study.

• Journal of Welding and Joining
• /
• v.25 no.5
• /
• pp.64-71
• /
• 2007

The aim of this paper is to investigate the effects of welding parameters on the weld shape in seal-welding of STS304L capsule for manufacturing a radioisotope source which is widely used in nondestructive testing of metal structures using gamma ray. Pulsed gas tungsten arc (Pulsed GTA) welding is performed for thin cross sectional area of the capsule. Seven welding parameters including current waveform parameters and arc length etc. are selected as main process parameters using design of experiment. The weld shape such as bead width, penetration depth, weld area, aspect ratio and area rate is investigated to assess the effects of welding parameters. As results, the combination of pulse duty/welding speed largely affects on bead width, penetration depth, area and aspect ratio. Finally, it is concluded that the key parameters are the combination of pulse duty/welding speed, base current and arc length, and their optimal conditions are 50%/1.77mm/s, 6.4A and 1 mm.

• The Journal of Korean Academy of Sensory Integration
• /
• v.15 no.2
• /
• pp.1-21
• /
• 2017

Objective : The aims of the this study is to identify job characteristics, to generate job description, and additionally to investigate duty task of the job for Korean pediatric occupational therapist focused on sensory integration intervention. Methods : In the first stage, job analysis of pediatric occupational therapist focused on sensory integration intervention was performed by an advisory committee consist of the DACUM panel. Through the job analysis, job description with definition was established. In the second stage, a survey was performed for 141 pediatric occupational therapist using a questionnaire based on the job description in order to investigate importance, frequency and difficulty of duty task and task elements of the job. This process was done from May to September 2017. Results : The job definition drew from this study was 'Pediatric occupational therapist provides occupational therapy services to children and adolescents to support occupational performance and social participation including daily activities and play". Through the job description established in this study, 9 duties (consulting, evaluation, intervention plan, intervention, document, education, self-development, management, and administration), 28 tasks and 169 task elements were drew. In the survey, among the duty tasks and task elements, 'ensure physical safety' and 'perform a session' were selected as the most important task, and 'ensure safety of children, sensory integrative equipment and environment' and 'prepare a safe environment' were selected as the most important element. Conclusion : This study defined job demands and characteristics of pediatric occupational therapist who performs sensory integration intervention. It is expected that this study can be used a resource to develop and/or improve educational program related.

• Transactions of the Korean hydrogen and new energy society
• /
• v.30 no.1
• /
• pp.76-82
• /
• 2019

This study was investigate the characteristics of GHGs ($CO_2$, $CH_4$, and $N_2O$) emissions of diesel medium duty trucks according to their various driving modes. GHGs emissions decreased as vehicle speed increased, and emissions increased after 64.7 km/h. The 4.5 ton trucks show higher values of $CO_2$, $CH_4$, $N_2O$, 35%, 25%, and 57%, respectively, comparing of the 2.5 ton trucks. Also, $CO_2$ emissions under WHVC mode were 20% lower than those under the NEDC mode. In the case of cold start condition, $CO_2$ emissions were 12-13% higher than those for hot start condition. In the future, the result of present study will provide basic data to set up GHGs emission standards for medium and heavy duty vehicles.

• Korean Journal of Biological Psychiatry
• /
• v.22 no.2
• /
• pp.55-62
• /
• 2015

Objectives Social workers can suffer from occupational stress resulting from dealing with clients, which might lead to metal health problems. We aimed to investigate the association of duty-related traumatic experiences and stress coping strategies with post-traumatic stress symptoms among social workers in public sector. Methods A total of 110 social workers in public sector (men 30.9%, $36.5{\pm}7.6$ yrs) participated in this study. All subjects were evaluated the frequency and the impact of duty-related traumatic events. Additionally, they completed questionnaires including the Impact of Event Scale-Revised for post-traumatic stress symptoms, the Beck Depression Inventory-II for depressive symptoms, the Scale for Suicidal Ideation for suicide symptoms and the Ways of Coping Checklist for stress coping strategies. Results The most frequent traumatic events were "Violent or abusive language from a client" (95.0%) and "Client made a fuss" (94.5%). The most distressing traumatic event was "Seeing a dead body on duty" (7.6 out of 10), which predicted post-traumatic stress symptoms (odds ratio 4.04 ; 95% confidence interval, 1.79-9.11). Among 4 types of stress coping strategies, the emotion-focused coping was positively correlated with post-traumatic stress symptoms after controlling age and sex (${\beta}$ = 0.50, p < 0.001). Conclusions Social workers in public sector showed high level of post-traumatic stress symptoms. Duty-related traumatic events and the emotional-focused coping strategies were associated with the severity of post-traumatic stress symptoms. The modification of stress coping strategies would alleviate post-traumatic stress symptoms in social workers in public sector.