• 제어로봇시스템학회논문지
• /
• 제20권2호
• /
• pp.186-192
• /
• 2014

Recently wind energy penetration into power systems has increased. Wind power, as a renewable energy source, plays a different role in the power system compared to conventional power generation units. As long as only single and small wind power units are installed in the power system, wind power does not influence power system operation and can easily be integrated. However, when wind power penetration reaches a significantly high level and conventional power production units are substituted, the impact of wind power on the power system becomes noticeable and must be handled. The connection of large wind turbines and wind farms to the grid has a large impact on grid stability. The electrical power system becomes more vulnerable to and dependent on wind energy production, and therefore there is an increased concern about the large wind turbines impact on grid stability. In this work, a new type of fuzzy logic controller for the frequency control of wind farms is proposed and its performance is verified using SimWindFarm toolbox which was developed as part of the Aeolus FP7 project.

• Structural Engineering and Mechanics
• /
• 제34권6호
• /
• pp.755-778
• /
• 2010

Near-fault ground motion with directivity or fling effects is significantly influenced by the rupture mechanism and substantially different from ordinary records. This class of ground motion has large amplitude and long period, exhibits unusual response spectra shapes, possesses high PGV/PGA and PGD/PGA ratios and is best characterized in the velocity and the displacement time-histories. Such ground motion is also characterized by its energy being contained in a single or very few pulses, thus capable of causing severe damage to the structures. This paper investigates the characteristics of near-fault pulse-like ground motions and their implications on the structural responses using new proposed measures, such as, the effective frequency range, the energy rate (in time and frequency domains) and the damage indices. The paper develops also simple mathematical expressions for modeling this class of ground motion and the associated structural responses, thus eliminating numerical integration of the equations of motion. An optimization technique is also developed by using energy concepts and damage indices for modeling this class of ground motion for inelastic structures at sites having limited earthquake data.

• ETRI Journal
• /
• 제46권4호
• /
• pp.581-594
• /
• 2024

In this study, a planar printed circuit board (PCB) coil with FR4 substrate was designed and simulated using the finite element method, and the results were analyzed in the frequency domain. This coil can be used in wireless power transfer (WPT) as a transmitter or receiver, eliminating wires. It can also be used as the receiver in radio frequency energy-harvesting (RF-EH) systems by optimizing the planar PCB coil to convert radio-wave energy into electricity, and it can be employed as an excitation (transmitter) or receiver coil in nuclear magnetic resonance (NMR) spectroscopy. This PCB coil can replace the conventional coil, yielding a reduced occupied volume, a fine-tuned design, reduced weight, and increased efficiency. Based on the calculated gain, power, and electromagnetic and electric field results, this planar PCB coil can be implemented in WPT, NMR spectroscopy, and RF-EH devices with minor changes. In applications such as NMR spectroscopy, it can be used as a transceiver planar PCB coil. In this design, at frequencies of 915 MHz and 40 MHz with 5 mm between coils, we received powers of 287.3 μW and 480 μW, respectively, which are suitable for an NMR coil or RF-EH system.

• 한국태양에너지학회 논문집
• /
• 제27권2호
• /
• pp.37-44
• /
• 2007

As photovoltaic(PV) power generation system becomes more common, it will be necessary to investigate islanding detection method for PV systems. Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and reactive power of the load and PV system are closely matched, islanding detection by Passive methods becomes difficult. Also, most active methods lose effectiveness when there are several PV systems feeding the same island. The active frequency drift positive feedback method(AFDPF) enables islanding detection by forcing the frequency of the voltage in the island to drift up or down. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF considering output power quality and islanding prevention performance are performed by simulation and experiment according to IEEE Std 929-2000 islanding test.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2008년도 제39회 하계학술대회
• /
• pp.1246-1247
• /
• 2008

With recent advanced in portable electric devices, wireless sensor, MEMS and bio-Mechanics device, the new typed power supply, not conventional battery but self-powered energy source is needed. Particularly, the system that harvests from their environments are interests for use in self powered devices. For very low powered devices, environmental energy may be enough to use power source. Therefore, in other to made piezoelectric energy harvesting device, PMN-PZT thick film was formed by the screen printing method on the Ag/Pd coated alumina substrate. The layer was 8 layers and slurry where a-terpineol, ethycellulose, ferro B-75001 as Vehicle, PMN-PZT powder used are fabricated by ball mill. The output power quality was be also investigated by changing the load resistance, weight and frequency. The made piezoelectric energy harvesting device was resulted from the conditions of 33$k{\Omega}$, 0.25g, 197Hz respectively. The thick film was prepared at the condition of 2.75Vrms, and its power was 230${\mu} W$ and its thickness was 56${mu}m$. The piezoelectric energy harvesting device output voltage was increased, when the load weight, load resistance was increasing and resonance frequency was diminishing. The other side, resonance frequency was diminished, when the weight was increasing. And output power was continuously it changed by load resistance, output voltage, weight and resonance frequency.

• 대한기계학회논문집
• /
• 제18권4호
• /
• pp.1050-1056
• /
• 1994

When a vibration data for a rotating machine such as a pump or a compressor is concerned, the frequency fluctuation of the energy contents at an instant time may provide useful information on understanding the vibration characteristics of the rotating machinery, rather than the averaged energy distribution along the frequency axis. Especially, when a periodic signal has different spectral contents, the approach to use the averaged frequency distribution, called the normal frequency analysis, may not be appropriate to extract vibration source characteristics of the structure. This paper introduces a way to analyze the signal based on an instant time. In order to evaluate the performance of the various approach, the investigatation compares three different algorithms which are frequently implemented in the instantaneous frequency analysis. Also for the noise effect embodied in the true signal, various cases for different SN ratio have been examined. The result shows that the noise level is crucial to evalute the instantaneous frequency analysis. In order to implement the instantaneous frequency analysis, the extraction of the relevant information from the measured signal should have the high S/N ratio, i, e., 40 dB or above.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
• /
• pp.193-193
• /
• 2008

Wearable and ubiquitous micro systems will be greatly growing and their related devices should be self-powered in order to avoid the replacement of finite power sources, for example, by scavenging energy from the environment. With ever reducing power requirements of both analog and digital circuits, power scavenging approaches are becoming increasingly realistic. One approach is to drive an electromechanical converter from ambient motion or vibration. Vibration-driven generators based on electromagnetic, electrostatic and piezoelectric technologies have been demonstrated. Among various generator types proposed so far, piezoelectric generator possesses considerable potential in micro system. To overcome low mechanical-to-electric energy conversion, the piezoelectric device should activate in resonance mode in response to external vibration. Normally, the external vibration excretes at low frequency ranging 0.1 to 200 Hz, whereas the resonant frequencies of the devices are fixed as constant. Therefore, keeping their resonant mode in varying external vibration can be one of important points in enhancing the conversion efficiency. We investigated the possibility of use of multi-bender type piezoelectric devices. To match the external vibration frequency with the device resonant frequency, the various devices with different resonant frequency were chosen.

• 한국전기전자재료학회논문지
• /
• 제24권5호
• /
• pp.416-421
• /
• 2011

Nowadays, the increasing demands upon mobile devices such as wireless sensor networks and the recent advent of low power electrical devices such as MEMS make such renewable power sources attractive. A vibration-driven MEMS lead zirconate titanate $Pb(Zr,Ti)O_3$ (PZT) cantilever device is developed for energy harvesting application. This paper presents a piezoelectric based energy harvester which is suitable for power generating from conventional vibration and has in providing energy for low power electron ic devices. The PZT cantilever is used d33 mode to get the electrical power. The PZT cantilever based energy harvester with the dimension of 7 mm${\times}$3 mm${\times}$0.03 mm is fabricated using micromachining technologies. This PZT cantilever has the mechanical resonance frequency with a 900 Hz. With these conditions, we get experimentally the 37 uW output power from this device with the application of 1g acceleration using the 900 Hz vibration. From this study, we show the feasibility of one of energy harvesting candidates using PZT based structure. This PZT energy harvester could be used for various applications such a batteryless micro sensors and micro power generators.

• 한국음향학회지
• /
• 제25권8호
• /
• pp.370-374
• /
• 2006

음성인식의 특징벡터로서 멜-주파수 켑스트럴 계수 (MFCC, mel-frequency cepstral coefficients)가 가장 널리 사용되고 있다. FMCC 추출과정은 입력되는 음성신호를 푸리에 변환한 후, 주파수 대역별로 필터를 취하여 에너지 값을 구하고 이산 코사인 변환을 하여 그 계수 값을 구한다. 본 논문에서는 멜-스케일 된 주파수 대역필터를 취할 때 가중함수에 의해서 구해진 각 대역필터별 가중치를 적용하여 필터의 출력 에너지를 계산한다. 여기서 가중치를 구하기 위해 사용된 가중함수는 포만트가 존재하는 대역을 중심으로 인접한 대역들이 가우시안 분포를 가지는 함수이다. 제안한 방법으로 실험한 결과, 잡음이 거의 없는 음성신호에 대해서는 기존의 MFCC를 사용했을 때와 비슷한 인식률을 보이고 잡음성분이 많을수록 가중치가 적용된 방법이 인식률에서 보다 높은 성능 향상을 가져온다.

• 한국전기전자재료학회논문지
• /
• 제16권7호
• /
• pp.593-598
• /
• 2003

In this paper, 3rd overtone mode energy-trapped filter using modified PbTiO$_3$ system ceramics was manufactured to apply for intermediate frequency(IF) SMD type fillet with splitted electrode and gap size. To investigate the effects of splitted electrode and gap size on filter characteristics of 3rd overtone mode energy-trapped filter, ceramic wafers were fabricated by etching splitted rectangular electrode size(b$\times$d) of b=0.4, 0.6, 0.8, 1mm, d=0.3, 0.4, 0.5, 0.6mm and gap size(c) c=0.2, 0.3, 0.4, 0.6mm, respectively. And then, SMD type ceramic filter were fabricated with the size of 3.7$\times$3.1$\textrm{mm}^2$. SMD type ceramic filter with the size of b=0.8mm, d=0.4mm and gap(c)=0.4mm, which showed insertion loss of 2.951dB, 3dB bandwidth of 54.7kHz and 20dB stop bandwidth of 129.27kHz, was suitable for IF bandpass filter application.