• Title, Summary, Keyword: Speed Deviation

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Adaptive Gain-based Stable Power Smoothing of a DFIG

  • Lee, Hyewon;Hwang, Min;Lee, Jinsik;Muljadi, Eduard;Jung, Hong-Ju;Kang, Yong Cheol
    • Journal of Electrical Engineering and Technology
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    • v.12 no.6
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    • pp.2099-2105
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    • 2017
  • In a power system that has a high wind penetration, the output power fluctuation of a large-scale wind turbine generator (WTG) caused by the varying wind speed increases the maximum frequency deviation, which is an important metric to assess the quality of electricity, because of the reduced system inertia. This paper proposes a stable power-smoothing scheme of a doubly-fed induction generator (DFIG) that can suppress the maximum frequency deviation, particularly for a power system with a high wind penetration. To do this, the proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while guaranteeing the stable operation of a DFIG, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WTG under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.

Alternative robust estimation methods for parameters of Gumbel distribution: an application to wind speed data with outliers

  • Aydin, Demet
    • Wind and Structures
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    • v.26 no.6
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    • pp.383-395
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    • 2018
  • An accurate determination of wind speed distribution is the basis for an evaluation of the wind energy potential required to design a wind turbine, so it is important to estimate unknown parameters of wind speed distribution. In this paper, Gumbel distribution is used in modelling wind speed data, and alternative robust estimation methods to estimate its parameters are considered. The methodologies used to obtain the estimators of the parameters are least absolute deviation, weighted least absolute deviation, median/MAD and least median of squares. The performances of the estimators are compared with traditional estimation methods (i.e., maximum likelihood and least squares) according to bias, mean square deviation and total mean square deviation criteria using a Monte-Carlo simulation study for the data with and without outliers. The simulation results show that least median of squares and median/MAD estimators are more efficient than others for data with outliers in many cases. However, median/MAD estimator is not consistent for location parameter of Gumbel distribution in all cases. In real data application, it is firstly demonstrated that Gumbel distribution fits the daily mean wind speed data well and is also better one to model the data than Weibull distribution with respect to the root mean square error and coefficient of determination criteria. Next, the wind data modified by outliers is analysed to show the performance of the proposed estimators by using numerical and graphical methods.

Estimation of Allowable Path-deviation Time in Free-space Optical Communication Links Using Various Aircraft Trajectories

  • Kim, Chul Han
    • Current Optics and Photonics
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    • v.3 no.3
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    • pp.210-214
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    • 2019
  • The allowable path-deviation time of aircraft in a free-space optical communication system has been estimated from various trajectories, using different values of aircraft speeds and turn rates. We assumed the existence of a link between the aircraft and a ground base station. First, the transmitter beam's divergence angle was calculated through two different approaches, one based on a simple optical-link equation, and the other based on an attenuation coefficient. From the calculations, the discrepancy between the two approaches was negligible when the link distance was approximately 110 km, and was under 5% when the link distance ranged from 80 to 140 km. Subsequently, the allowable path-deviation time of the aircraft within the tracking-error tolerance of the system was estimated, using different aircraft speeds, turn rates, and link distances. The results indicated that the allowable path-deviation time was primarily determined by the aircraft's speed and turn rate. For example, the allowable path-deviation time was estimated to be ~3.5 s for an aircraft speed of 166.68 km/h, a turn rate of $90^{\circ}/min$, and a link distance of 100 km. Furthermore, for a constant aircraft speed and turn rate, the path-deviation time was observed to be almost unchanged when the link distance ranged from 80 to 140 km.

Comparative analysis of the wind characteristics of three landfall typhoons based on stationary and nonstationary wind models

  • Quan, Yong;Fu, Guo Qiang;Huang, Zi Feng;Gu, Ming
    • Wind and Structures
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    • v.31 no.3
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    • pp.269-285
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    • 2020
  • The statistical characteristics of typhoon wind speed records tend to have a considerable time-varying trend; thus, the stationary wind model may not be appropriate to estimate the wind characteristics of typhoon events. Several nonstationary wind speed models have been proposed by pioneers to characterize wind characteristics more accurately, but comparative studies on the applicability of the different wind models are still lacking. In this study, three landfall typhoons, Ampil, Jongdari, and Rumbia, recorded by ultrasonic anemometers atop the Shanghai World Financial Center (SWFC), are used for the comparative analysis of stationary and nonstationary wind characteristics. The time-varying mean is extracted with the discrete wavelet transform (DWT) method, and the time-varying standard deviation is calculated by the autoregressive moving average generalized autoregressive conditional heteroscedasticity (ARMA-GARCH) model. After extracting the time-varying trend, the longitudinal wind characteristics, e.g., the probability distribution, power spectral density (PSD), turbulence integral scale, turbulence intensity, gust factor, and peak factor, are comparatively analyzed based on the stationary wind speed model, time-varying mean wind speed model and time-varying standard deviation wind speed model. The comparative analysis of the different wind models emphasizes the significance of the nonstationary considerations in typhoon events. The time-varying standard deviation model can better identify the similarities among the different typhoons and appropriately describe the nonstationary wind characteristics of the typhoons.

Effects of Sending Text Message and Searching Navigation on Skin Conductance Level and Deviation of Vehicle Speed during Driving (문자 메시지 전송 및 내비게이션 명칭 검색이 운전 중 피부전도수준과 속도편차에 미치는 영향)

  • Yang, Jae-Woong;Lee, Su-Jeong;Kim, Ji-Hye;Choi, Mi-Hyun;Choi, Jin-Seung;Kim, Han-Su;Ji, Doo-Hwan;Tack, Gye-Rae;Chung, Soon-Cheol;Min, Byung-Chan
    • Journal of the Society of Korea Industrial and Systems Engineering
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    • v.34 no.1
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    • pp.9-13
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    • 2011
  • The purpose of this study was to investigate the effects of the secondary tasks such as sending text message (STM) and searching navigation (SN) on skin conductance level (SCL) and deviation of vehicle speed during driving. The participants included 30 healthy adults; 14 males aged $25.2{\pm}0.9$ with $1.9{\pm}1.8$ years of driving experiences and 16 females aged $22.6{\pm}1.9$ with $1.2{\pm}0.8$ years of driving experiences. All subjects were instructed to keep a constant speed (80km/h or 100km/h). SCL and deviation of vehicle speed were measured during driving only and driving with secondary tasks. SCL and deviation of vehicle speed were more increased during the driving with secondary tasks than driving only. Secondary tasks increased an activation of sympathetic nerve system and decreased driving performance. However, there were no significant differences in the SCL and deviation of vehicle speed according to gender and speed.

A study on the Finishing Characteristics of Ultra-precision System (초정밀 가공시스템의 염마 가공 특성에 관한 연구)

  • Bae, Myung-Il;Kim, Hong-Bae
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.10
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    • pp.11-16
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    • 1999
  • In this study, Ultra-precision finishing system using micro abrasive film experimented using experimental variable film feed speed and grinding speed and structural steel(SM45C) with respect to 12~3{\mu}m$ micro abrasive film. the result are follows; (1) Experimental condition must setup dissimilar about each micro abrasive film. (2) To measurement deviation the smallest machined condition are 20mm/min in 12{\mu}m$, 5mm/min and 15mm/min in 9{\mu}m$ and 5{\mu}m$, 5mm/min in 3{\mu}m$ in film feed speed. (3) To measurement deviation the smallest machined condition are 180m/min in 12{\mu}m$, 84m/min in 9{\mu}m$, 56 and 84m/min in 5{\mu}m$, 104m/min in 3{\mu}m$ in grinding speed.

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Analysis on wind condition characteristics for an offshore structure design (해상풍력 구조물 설계를 위한 풍황 특성분석)

  • Seo, Hyun-Soo;Kyong, Nam-Ho;Vaas, Franz;Kim, Hyun-Goo
    • 한국신재생에너지학회:학술대회논문집
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    • pp.262-267
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    • 2008
  • The long-term wind data are reconstructed from the short-term meteorological data to design the 4 MW offshore wind park which will be constructed at Woljeong-ri, Jeju island, Korea. Using two MCP (Measure-Correlate-Predict) models, the relative deviation of wind speed and direction from two neighboring reference weather stations can be regressed at each azimuth sector. The validation of the present method is checked about linear and matrix MCP models for the sets of measured data, and the characteristic wind turbulence is estimated from the ninety-percent percentile of standard deviation in the probability distribution. Using the Gumbel's model, the extreme wind speed of fifty-year return period is predicted by the reconstructed long-term data. The predicted results of this analysis concerning turbulence intensity and extreme wind speed are used for the calculation of fatigue life and extreme load in the design procedure of wind turbine structures at offshore wind farms.

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An Analysis on Compliance of Variable Speed Limit under Foggy Conditions using Driving Simulator (차량 시뮬레이터를 이용한 안개 도로 가변제한속도 순응 경향 분석)

  • Kim, Soullam;Lee, Sukki;Kim, Yongseok
    • The Journal of The Korea Institute of Intelligent Transport Systems
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    • v.16 no.2
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    • pp.116-127
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    • 2017
  • A fog on road is known as a weather factor that affects traffic flow. The method in order to solve the problem, recently, Variable Speed Limit(VSL) which provide reasonable speed limit by road and weather conditions in real time is introduced. However, if drivers do not comply with VSL, the road safety more decrease than without VSL because individual vehicle's speed deviation is larger than without VSL. Therefore, this paper aims to analyze to speed limit compliance and traffic characteristics under foggy conditions with and without VSL. A test using driving simulator divides into normal and foggy condition with visibilities are 200m, 150, 50~100m. The test results showed that 70 subjects's average speed mostly obeyed speed limit, but speed deviation generally declined with VSL. Especially, the speed deviation more reduced under foggy conditions. According to this study, compliance of VSL clearly rose in low visibility and VSL helped improve road safety due to reduction of speed deviation. The results of this study are expected to make use of reasonable speed limit for reference.

Influence of track irregularities in high-speed Maglev transportation systems

  • Huang, Jing Yu;Wu, Zhe Wei;Shi, Jin;Gao, Yang;Wang, Dong-Zhou
    • Smart Structures and Systems
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    • v.21 no.5
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    • pp.571-582
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    • 2018
  • Track irregularities of high-speed Maglev lines have significant influence on ride comfort. Their adjustment is of key importance in the daily maintenance of these lines. In this study, an adjustment method is proposed and track irregularities analysis is performed. This study considers two modules: an inspection module and a vehicle-guideway coupling vibration analysis module. In the inspection module, an inertial reference method is employed for field-measurements of the Shanghai high-speed Maglev demonstration line. Then, a partial filtering, integration method, resampling method, and designed elliptic filter are employed to analyze the detection data, which reveals the required track irregularities. In the analysis module, a vehicle-guideway interaction model and an electromagnetic interaction model were developed. The influence of the measured line irregularities is considered for the calculations of the electromagnetic force. Numerical integration method was employed for the calculations. Based on the actual field detection results and analysis using the numerical model, a threshold analysis method is developed. Several irregularities modalities with different girder end's deviations were considered in the simulations. The inspection results indicated that long-wavelength irregularities with larger girder end's deviations were the dominant irregularities. In addition, the threshold analysis of the girder end's deviation shows that irregularities that have a deviation amplitude larger than 6 mm and certain modalities (e.g., M- and N-shape) are unfavorable. These types of irregularities should be adjusted during the daily maintenance.

Power Smoothing of a Variable-Speed Wind Turbine Generator Based on the Rotor Speed-Dependent Gain (회전자 속도에 따라 변하는 게인에 기반한 가변속 풍력발전기 출력 평활화)

  • Kim, Yeonhee;Kang, Yong Cheol
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.65 no.4
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    • pp.533-538
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    • 2016
  • In a power grid that has a high penetration of wind power, the highly-fluctuating output power of wind turbine generators (WTGs) adversely impacts the power quality in terms of the system frequency. This paper proposes a power smoothing scheme of a variable-speed WTG that can smooth its fluctuating output power caused by varying wind speeds, thereby improving system frequency regulation. To achieve this, an additional loop relying on the frequency deviation that operates in association with the maximum power point tracking control loop, is proposed; its control gain is modified with the rotor speed. For a low rotor speed, to ensure the stable operation of a WTG, the gain is set to be proportional to the square of the rotor speed. For a high rotor speed, to improve the power smoothing capability, the control gain is set to be proportional to the cube of the rotor speed. The performance of the proposed scheme is investigated under varying wind speeds for the IEEE 14-bus system using an EMTP-RV simulator. The simulation results indicate that the proposed scheme can mitigate the output power fluctuation of WTGs caused by varying wind speeds by adjusting the control gain depending on the rotor speed, thereby supporting system frequency regulation.