저신장율 대향류확산화염에서 진동불안정성을 갖는 에지화염의 동적거동

박준성(June Sung Park),김현표(Hyun Pyo Kim),박정(Jeong Park),김정수(Jeong Soo Kim),길상인(Sang In Keel) 한국연소학회 2006 KOSCOSYMPOSIUM논문집 Vol.- No.-

Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Critical mole fraction at flame extinction is examined with velocity ratio and global strain rate. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate and added nitrogen mole fraction to fuel stream (fuel Lewis number). It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations in low strain rate flames are experimentally described well and are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames. Important contribution of lateral heat loss even to edge flame oscillation is clarified.

Dual-mode Inverting Buck-boost Converter using Set-time Variable PWM Method

Hak-Yun Kim,Myeong-Hak Lee,Young-Ho Shin,Jin-Won Kim,Nam-Soo Kim,Ho-Yong Choi 대한전자공학회 2018 Journal of semiconductor technology and science Vol.18 No.4

This paper proposes a dual-mode inverting buck-boost DC-DC converter using a set-time variable PWM (SPWM) method. To obtain high efficiency in all load ranges, this dual-mode converter operates in the PWM mode under heavy load, and in the SPWM method under light load in which the switching frequency of the set-time is modulated in proportion to the load current in the PWM mode. In this PWM-SPWM dual mode, it is possible to realize a small circuit by adding only the additional circuit using a voltage-controlled oscillator which varies the switching frequency under light load, based on the PWM mode. Also, the converter can vary output voltage by changing its reference voltages and has variable maximum and minimum switching frequencies for a number of applications. The converter was fabricated with 0.35 μm standard CMOS process technology and occupies an area of 0.93 mm ´ 0.90 mm. The experimental results show that when the input voltage range is 2.9 V ~ 4.2 V, the circuit produces an output voltage range of -1.0 V ~ - 0.7 V with a ripple voltage of 3 mV and has a power efficiency of 68% ~ 82.1% for a load current of 5 mA ~ 250 mA.

표면연소기의 저주파 연소진동음의 특성

한희갑,이근희,권영필 한국소음진동공학회 2000 소음 진동 Vol.10 No.6

The objective of this study is to examine the onset condition and the frequency characteristics of the low-frequency combustion oscillation in a surface burner. For this purpose, extensive parametric studies have been performed experimentally and the effects of size of each section, the equivalence ratio, and the entrance velocity on oscillatory behavior explored. The experimental results were discussed in comparison with the other combustors associated tilth the low-frequency combustion oscillation. The combustion mode is driven at high combustion rate by the lift of unstable flame near the lower limit of the combustible equivalence ratio. The oscillation frequency is dependent not on the burner geometry but on the equivalence ratio and the combustion load. Low-frequency combustion mode was formed to be divided into two different modes, named C1 and C2 respectively. Two modes occurred individually, simultaneously or transitionally according to the equivalence ratio and combustion load. The characteristics of low-frequency oscillation is different from each other depending on the type of combustors. The surface burner has also its own characteristics of low -frequency oscillation.

빠른 응답특성을 갖는 DC/DC 컨버터 하이브리드 전류 모드 제어기

오승민,백승우,김학원,조관열 전력전자학회 2019 전력전자학회 논문지 Vol.23 No.2

A wide-bandwidth current controller is required for fast charging/discharging of super capacitor applications. Peak current mode is generally used to accomplish fast charging/discharging because this mode has fast response characteristics. However, the peak current mode control must have a slope compensation function to restrain sub-harmonics oscillation. The slope must be changed accordingly if the controlled output voltage is varied. However, changing the slope for every changed output voltage is not easy. The other solution, selecting the slope as the maximum value, causes a slow response problem to occur. Therefore, we propose a hybrid mode controller that uses a peak current and a newly specified valley current. Through the proposed hybrid mode control, the sub-harmonic oscillation does not occur when the duty is larger than 0.5 because of the fast response.

A Novel Interleaving Control Scheme for Boost Converters Operating in Critical Conduction Mode

Yang, Xu,Ying, Yanping,Chen, Wenjie The Korean Institute of Power Electronics 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.2

Interleaving techniques are widely used to reduce input/output ripples and to increase the power capacity of boost converters operating in critical conduction mode. Two types of phase-shift control schemes are studied in this paper, the turn-on time shifting method and the turn-off time shifting method. It is found that although the turn-off time shifting method exhibits better performance, it suffers from sub-harmonic oscillations at high input voltages. To solve this problem, an intensive quantitative analysis of the sub-harmonic oscillation phenomenon is made in this paper. Based upon that, a novel modified turn off time shifting control scheme for interleaved boost converters operating in critical conduction mode is proposed. An important advantage of this scheme is that both the master phase and the slave phase can operate stably in critical conduction mode without any oscillations in the full input voltage range. This method is implemented with a FPGA based digital PWM control platform, and tests were carried out on a two-phase interleaved boost PFC converter prototype. Experimental results demonstrated the feasibility and performance of the proposed phase-shift control scheme.

A Novel Interleaving Control Scheme for Boost Converters Operating in Critical Conduction Mode

Xu Yang,Yanping Ying,Wenjie Chen 전력전자학회 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.2

Interleaving techniques are widely used to reduce input/output ripples and to increase the power capacity of boost converters operating in critical conduction mode. Two types of phase-shift control schemes are studied in this paper, the turn-on time shifting method and the turn-off time shifting method. It is found that although the turn-off time shifting method exhibits better performance, it suffers from sub-harmonic oscillations at high input voltages. To solve this problem, an intensive quantitative analysis of the sub-harmonic oscillation phenomenon is made in this paper. Based upon that, a novel modified turn off time shifting control scheme for interleaved boost converters operating in critical conduction mode is proposed. An important advantage of this scheme is that both the master phase and the slave phase can operate stably in critical conduction mode without any oscillations in the full input voltage range. This method is implemented with a FPGA based digital PWM control platform, and tests were carried out on a two-phase interleaved boost PFC converter prototype. Experimental results demonstrated the feasibility and performance of the proposed phase-shift control scheme.

Hydrodynamic characteristics of internal waves induced by a heaving body in a two-layer fluid

Min, Eun-Hong,Koo, Weoncheol Elsevier 2017 Ocean engineering Vol.145 No.-

<P><B>Abstract</B></P> <P>The stratification of fluid caused by the change of water densities can generate two water waves on each fluid boundary. One is the surface wave on the free surface, and the other is the internal wave on the interface between the fluid layers. Two wave modes exist in the two-layer fluid: barotropic mode and baroclinic mode. This study develops a numerical model to simulate the surface and internal waves in the time domain. The time histories of the water waves on both surface boundaries are simulated using the numerical wave tank (NWT) technique by an oscillating circular body located on the free surface or underwater in the lower fluid domain. The NWT technique is based on the boundary element method with properly defined boundary conditions, including interface boundaries. The leapfrog method is used for the time integration of the water surface boundary conditions. The time-varying generated waves are disassembled through the Fast Fourier Transform (FFT). Each wave component is compared with analytic solutions. The relative magnitudes of the generated waves on both fluid layers are examined according to each wave mode. The dominant wave mode varies according to the oscillating body frequencies. The amplitude ratios of the two waves are compared for various density ratios and fluid depths.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A numerical model was developed to simulate the surface and internal waves in the time domain. </LI> <LI> Two wave modes were observed in the two-layer fluid: barotropic and baroclinic modes. </LI> <LI> The dominant wave mode varied according to the oscillating body frequencies. </LI> <LI> The amplitude ratios were compared for various density ratios and fluid depths. </LI> </UL> </P>

Switching-Mode BJT Driver for Self-Oscillated Push-Pull Inverters

Borekci, Selim,Oncu, Selim The Korean Institute of Power Electronics 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.2

Self oscillating current fed push pull resonant inverters can be controlled without using special drivers. Dc current flows through the choke coil and the power switches, although the driving signals of the power switches are sinusoidal. When the base current is near zero, the transistors cannot be operated in switching mode. Hence higher switching power losses and instantaneous peak power during off transitions are observed. In this study, an alternative design has been proposed to overcome this problem. A prototype circuit has been built which provides dc bias current to the base of the transistors. Experimental results are compared with theoretical calculations to demonstrate the validity of the design. The proposed design decreases the peak and average power losses by about 8 times, when compared to conventional designs.

Switching-Mode BJT Driver for Self-Oscillated Push-Pull Inverters

Selim Borekci,Selim Oncu 전력전자학회 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.2

Self oscillating current fed push pull resonant inverters can be controlled without using special drivers. Dc current flows through the choke coil and the power switches, although the driving signals of the power switches are sinusoidal. When the base current is near zero, the transistors cannot be operated in switching mode. Hence higher switching power losses and instantaneous peak power during off transitions are observed. In this study, an alternative design has been proposed to overcome this problem. A prototype circuit has been built which provides dc bias current to the base of the transistors. Experimental results are compared with theoretical calculations to demonstrate the validity of the design. The proposed design decreases the peak and average power losses by about 8 times, when compared to conventional designs.

Using Input Shaping to Repress Two-mode Residual Vibration on Aerial Lifts

Jia Hongxia,Zhu Fumin,Joshua Vaughan 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10

Aerial lifts are machines that enable human workers to comfortably work at heights that might otherwise be inaccessible. They typically have multiple long-reach arms to enable working at such heights. There is typically enough flexibility in these arms to result in deflections of the lift endpoint, the bucket where the operators are located. These deflections can be excited by either motion of the operators within the bucket or by operator commands moving the bucket around the workspace. Input shaping is one method that can drastically reduce the motion-induced oscillation. This paper investigates the application of input shaping to one category of aerial lifts, commonly called cherrypickers. When input shaping is used, the endpoint vibration is reduced. However, it is not completely eliminated due to the nonlinear nature of the system.