• Title/Summary/Keyword: modulation instability

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Analysis of Voltage Delay and Compensation for Current Control in H-Bridge Multi-Level Inverter (H-브릿지 멀티레벨 인버터의 전압 지연 해석 및 전류 제어 보상)

  • Park, Young-Min;Ryu, Han-Seong;Lee, Hyun-Won;Jung, Myung-Gil;Lee, Se-Hyun
    • The Transactions of the Korean Institute of Power Electronics
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    • v.15 no.1
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    • pp.43-51
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    • 2010
  • This paper proposes an analysis of voltage delay and compensation for current control in H-Bridge Multi-Level (HBML) inverters for a medium voltage motor drive with vector control. It is shown that the expansion and modularization capability of the HBML inverter is improved in case of using Phase-Shifted Pulse Width Modulation (PSPWM) since individual inverter modules operate more independently. But, the PSPWM of HBML has a phase difference between reference voltage and real voltage, which can cause instability in the current regulator at high speed where the ratio of the sampling frequency to the output frequency is insufficient. This instability of the current regulator is removed by adding a proposed method which compensate a phase difference between reference voltage and real voltage. The proposed method is suitable for HBML inverter controlled by PSPWM with low switching frequency and high speed motor drive. The validity of the proposed method is verified experimentally on 6,600[V] 1,400[kW] induction motor fed by an 13-level HBML inverter.

Numerical Simulation of the Effect of Pressure Fluctuation on the Modulation of Equivalence Ratio at the Fuel Injection Hole (압력변동이 연료 분사구에서의 당량비 변동에 미치는 영향에 관한 수치 해석)

  • Kim, Hyeon-Jun;Hong, Jung-Goo;Shin, Hyun-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.3 s.258
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    • pp.292-299
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    • 2007
  • In gas turbine technology, the flame stability is inherently greater in conventional diffusion type combustion over a wider range fuel to oxidizer ratio. However, premixed type combustion which has narrow flame stability region, is widely used due to environmental reason. It has been observed in experiments that combustion instability of low frequency (${\sim}10Hz$) results from the modulation of equivalence ratio at fuel injection hole when a pressure fluctuation propagates upwards along the channel of the burner under an unchoked fuel flow condition. In this study, a commercial program was used to determine how the fuel flow rate changed with respect to the pressure, velocity of the fuel flow and the mass fraction in a choked and an unchoked condition. The calculation focuses on the upstream of the dump plane to know how the forced pressure with the fuel injection conditions affects the modulation of the equivalence ratio. Therefore, it is found that pressure fluctuation leads to oscillation of mass flow rate and then results in equivalence ratio modulation under the unchoked fuel flow condition.

Effects of Changes in Equivalence Ratio and Modulation Condition on Flame Transfer Function (당량비 및 섭동 조건 변화가 화염 전달 함수에 미치는 영향)

  • Kim, Dae-Sik
    • Journal of the Korean Society of Propulsion Engineers
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    • v.15 no.4
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    • pp.35-40
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    • 2011
  • An experimental study of the flame response in a turbulent premixed combustor has been conducted in order to investigate mechanisms for combustion instabilities in a lean premixed gas turbine combustor. A lab-scale combustor and mixing section system were fabricated to measure the flame transfer function. Measurements are made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The results show that the flame transfer functions are greatly dependent on the modulation frequency as well as operating conditions such as equivalence ratio. Flame dynamics can be generalized as a function of Strouhal number which is a ratio of flame length to modulation wave length.

Experimental Study of Deep-Water Wave Instability : Part 2. Evolution of The Initially-Modulated Wave Train (심해파의 불안정성에 관한 실험 연구 -제2부 : 초기변형파의 불안정성)

  • Cho, Won Chul
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.1
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    • pp.203-211
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    • 1993
  • Experiment on the instability and breaking of the initially modulated deep-water wave train (in wave amplitude or in wave frequency) is performed to investigate the effect of the initial modulation on nonlinear wave evolution. Wave amplitude and frequency modulations are developed earlier and larger than in the case of the uniform deep-water wave trains. However, for small wave steepness in the initially amplitude-modulated wave train, the wave train becomes demodulated and nearly returns to the original wave form at the end of the wave evolution far downstream from the breaking region, with energy returning to the fundamental wave frequency.

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Stability Analysis and Control of Nonlinear Behavior in V2 Switching Buck Converter

  • Hu, Wei;Zhang, Fangying;Long, Xiaoli;Chen, Xinbing;Deng, Wenting
    • Journal of Power Electronics
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    • v.14 no.6
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    • pp.1208-1216
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    • 2014
  • Mismatch between switching frequency and circuit parameters often occurs in industrial applications, which would lead to instability phenomena. The bifurcation behavior of $V^2$ controlled buck converter is investigated as the pulse width modulation period is varied. Nonlinear behavior is analyzed based on the monodromy matrix of the system. We observed that the stable period-1 orbit was first transformed to the period-2 bifurcation, which subsequently changed to chaos. The mechanism of the series of period-2 bifurcations shows that the characteristic eigenvalue of the monodromy matrix passes through the unit circle along the negative real axis. Resonant parametric perturbation technique has been applied to prevent the onset of instability. Meanwhile, the extended stability region of the converter is obtained. Simulation and experimental prototypes are built, and the corresponding results verify the theoretical analysis.

Fabrication Uncertainty and Noise Issues in High-Precision MEMS Actuators and Sensors

  • Cho, Young-Ho;Lee, Won-Chul;Han, Ki-Ho
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.2 no.4
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    • pp.280-287
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    • 2002
  • We present technical issues involved in the development of actuators and sensors for applications to high-precision Micro Electro Mechanical System (MEMS). The technical issues include fabrication uncertainty and noise disturbance, causing major difficulties for MEMS to achieve high-precision actuation and detection functions. For nano-precision actuators, we solve the fabrication instability and electrical noise problems using digital actuators coupled with nonlinear mechanical modulators. For the high-precision capacitive sensors, we present a branched finger electrodes using high-amplitude anti-phase sensing signals. We also demonstrate the potential applications of the nanoactuators and nanodetectors to high-precision positioning MEMS.

Frequency Stabilization of Femtosecond Lasers for Dimensional Metrology (거리 및 형상 측정을 위한 펨토초 레이저의 주파수 안정화)

  • Kim Young-Jin;Jin Jong-Han;Kim Seung-Woo
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.10a
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    • pp.188-191
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    • 2005
  • A common feature in various methods of optical interferometry for absolute distance measurements is the use of multiple monochromatic light components either in sequence or in parallel at the same time. Two or multiple wavelength synthesis has been studied though its performance is vulnerable to the frequency instability of the light source. Recently continuous frequency modulation is considered a promising method with availability of wide band tunable diode lasers, which also have frequency instability errors. We can lock frequencies of these third-party light sources to the modes of the femtosecond laser which is stabilized to the precision of the standard radio frequency. To this end, we have stabilized all the modes of the femtosecond laser to the atomic frequency standard by using powerful tools of frequency-domain laser stabilization.

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Stabilizing Control of DC/DC Buck Converters with Constant Power Loads in Continuous Conduction and Discontinuous Conduction Modes Using Digital Power Alignment Technique

  • Khaligh Alireza;Emadi Ali
    • Journal of Electrical Engineering and Technology
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    • v.1 no.1
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    • pp.63-72
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    • 2006
  • The purpose of this raper is to address the negative impedance instability in DC/DC converters. We present the negative impedance instability of PWM DC/DC converters loaded by constant power loads (CPLs). An approach to design digital controllers for DC/DC converters Is presented. The proposed method, called Power Alignment control technique, is applied to DC/DC step-down choppers operating in continuous conduction or discontinuous conduction modes with CPLs. This approach uses two predefined state variables instead of conventional pulse width modulation (PWM) to regulate the output voltage. A comparator compares actual output voltage with the reference and then switches between the appropriate states. It needs few logic gates and comparators to be implemented thus, making it extremely simple and easy to develop using a low-cost application specific integrated circuit (ASIC) for converters with CPLs. Furthermore, stability of the proposed controllers using the small signal analysis as well as the second theorem of Lyapunov is verified. Finally, simulation and analytical results are presented to describe and verify the proposed technique.

A study of the spatial amplification of the Type II instability for the Rotating-disk flow (회전원판 유동의 제2형 불안정성 공간증폭에 관한 이론적 연구)

  • Lee, Yun-Yong;Lee, Kwang-Won;Hwang, Young-Kyu
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.481-486
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    • 2001
  • The hydrodynamic instability of the three-dimensional boundary layer on a rotating disk introduces a periodic modulation of the mean flow in the form of stationary cross flow vortices. Detailed numerical values of the growth rates, neutral curves and other characteristics have been calculated for the Type II-instabilities. Presented are the neutral stability results concerning the two instability modes by solving new linear stability equations reformulated not only by considering whole convective terms but by correcting some errors in the previous stability equations. The present stability results are agree with the previously known ones within reasonable limit. The spatial amplification contours have been calculated for the moving disturbance wave, whose azimuth angle is between $\varepsilon=-10^{\circ}$ and $-20^{\circ}$. The transition flow of the moving disturbance wave will be developed at $\varepsilon=-15^{\circ}$ and Re=352 corresponding at the growth rates n = 5.8 from the spatial amplification contours.

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Flame Dynamic Response to Inlet Flow Perturbation in a Turbulent Premixed Combustor (난류 예혼합 연소기에서의 흡입 유동 섭동에 대한 화염의 동적 거동)

  • Kim, Dae-Sik
    • Journal of the Korean Society of Combustion
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    • v.14 no.4
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    • pp.48-53
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    • 2009
  • This paper describes the forced flame response in a turbulent premixed gas turbine combustor. The fuel was premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. To impose the inlet flow velocity, a siren type modulation device was developed using an AC motor, rotating and static plates. Measurements were made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The test results showed that flame length as well as geometry was strongly dependent upon modulation frequency in addition to operating conditions such as inlet velocity. Convection delay time between the velocity perturbation and heat release fluctuations was calculated using phase information of the transfer function, which agreed well with the results of flame length measurements. Also, basic characteristics of the flame nonlinear response shown in the current test conditions were introduced.

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