• 전자공학회논문지B
• /
• 제33B권2호
• /
• pp.47-55
• /
• 1996

A microwave incoherent imaging method for a conducting cyliner by using multi-frequency tiem-harmonic field is presented in this study. In this paper, an incoherent intensity pattern of th econducting cylinder is obtained by averagin gout the multi-frequency intensities of the coherent field such as the time-harmonic field scattered from this cylinder. This phenomenon is hsown numerically in scattering by a conducting circular cylinder illuminated by the time-harmonic plane wave, and is interpreted analytically by the mutual coherence functon defined as a frequency-averaged intensity of the time-harmonic fields in th frequency domain.

• 조명전기설비학회논문지
• /
• 제27권3호
• /
• pp.43-49
• /
• 2013

Recently harmonics flowing into power system is increasing as the usage of semiconductor equipments and switching mode power equipments are increasing. Harmonics cause problems such as heat increasing and reduction in capacity of transformers, especially the harmonics flowing into a distribution transformer can lead to the lifetime reduction of transformer. In this paper, we are about to develop a device that can monitor harmonics in real-time as it is affixed to a distribution transformer. Unlike the existing expensive harmonic analysis device, a new harmonic analysis algorithm is proposed in order to implement low-cost equipment. The real-time harmonic analysis algorithm proposed in this paper allows implementation on low performance microcontrollers, thus it can monitor the harmonic in real-time as it is individually affixed to the transformer. Therefore, it would improve the reliability of the transformer and stable power system operation would be possible as it can prevent the transformer accidents in advance.

• Journal of Power Electronics
• /
• 제14권3호
• /
• pp.572-579
• /
• 2014

As a non-linear time variant system, the four-quadrant line converter of an electric multiple unit (EMU) was expressed by linear time periodic functions near an operating point and modeled by a steady-state harmonic domain matrix. The components were then combined according to the circuit connection and relations of the feedback control loops to form a complete converter model. The proposed modeling method allows the study of the amplitude of harmonic impedances to explore harmonic coupling. Moreover, the proposed method helps provide a better design for the converter controllers, as well as solves the problem in coordination operation between the EMUs and the AC supply. On-site data from an actual $CRH_2$ high-speed train were used to validate the modeling principles presented in the paper.

• 조명전기설비학회논문지
• /
• 제23권4호
• /
• pp.29-38
• /
• 2009

GHP(Gas Heating Pump) 시스템은 가스 엔진으로 구동되는 압축기로 구성되는 효율적인 냉/난방기이고, 학교나 사무용 빌딩에 널리 쓰이고 있다. GHP는 느린 응답, 큰 시정수와 시간에 따라 변하는 시스템으로 제어하기가 어렵다. 이들 비선형 부하는 고조파 전류를 발생시키고, 전력계통의 정현파 전압을 왜곡시킨다. 고조파 측정 결과로 고조파는 시간에 따라 변하는 특성이 관측되었다. 시간에 따라 변하는 고조파를 해결하기 위해서 쓰이는 가장 보편적인 방법은 누적확률을 사용하는 것이다. 본 논문에서는 GHP부하의 고조파 특성, IEC 61000-3-2에 의한 고조파 평가와 사례연구 시스템의 고조파 시뮬레이션 및 고조파 필터 적용을 심도있게 다루고자 하였다.

• Bulletin of the Korean Chemical Society
• /
• 제23권2호
• /
• pp.355-356
• /
• 2002

• 조명전기설비학회논문지
• /
• 제25권4호
• /
• pp.124-134
• /
• 2011

A new dead time compensation scheme that can exactly estimate the dead time and inverter nonlinearity under parameter variations is proposed for a PWM inverter-fed PMSM drive. The proposed scheme uses the fact that the sixth harmonic component in total disturbance estimated under the presence of various uncertainties is mainly caused by the dead time and inverter nonlinearity. The total disturbance due to the parameter variations as well as the dead time and inverter nonlinearity is estimated by the adaptive scheme. The sixth harmonic component is extracted from this total disturbance through harmonic analysis. The obtained sixth harmonic is processed by the PI controller to estimate the disturbance caused by the dead time and inverter nonlinearity in the stationary reference frame. The effectiveness of the proposed scheme is verified. Without requiring an additional hardware, the proposed scheme can effectively compensate the dead time and inverter nonlinearity even under the parameter variations.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
• /
• pp.479-483
• /
• 1997

In general, motor parameters can be divided into mechanical/electrical parameters and harmonic parameters. Mechanical/electrical parameters identification of motor have been studying systematically for a long time. But, systematical study on harmonic parameters analysis for efficient motor drive system are very poor. The goal of this paper is to propose analyzing method of harmonic parameters for motor drive system with various experimental graphic screens and numerical results and to develope harmonic parameters analyzer. A developed analyzer is made up 586-PC and DSP (digital signal processor) board, motor drive system, power and harmonic parameters analyzing software for windows. Harmonic parameters are analyzed using correlation signal processing techniques based on the correlation between voltage and current waveforms. Analysis results are visualized by 3-D current coordinates, and it is compared and evaluated with conventional time/frequency domain. To verify the validity of the proposed system, 1/4HP capacitor run type single phase induction motor and thyristor speed controller is used for analyzing. Harmonic parameters of motor drive system is analyzed and verified, with varying fire angle of thyristor speed controller, and the proposed approach is to confirm validity.

• 대한원격탐사학회지
• /
• 제35권4호
• /
• pp.573-587
• /
• 2019

A multi-temporal approach using remotely sensed time series data obtained over multiple years is a very useful method for monitoring land covers and land-cover changes. While spectral-based methods at any particular time limits the application utility due to instability of the quality of data obtained at that time, the approach based on the temporal profile can produce more accurate results since data is analyzed from a long-term perspective rather than on one point in time. In this study, a multi-temporal approach applying a multi-periodic harmonic model is proposed for classification of remotely sensed data. A harmonic model characterizes the seasonal variation of a time series by four parameters: average level, frequency, phase, and amplitude. The availability of high-quality data is very important for multi-temporal analysis.An satellite image usually have many unobserved data and bad-quality data due to the influence of observation environment and sensing system, which impede the analysis and might possibly produce inaccurate results. Harmonic analysis is also very useful for real-time data reconstruction. Multi-periodic harmonic model is applied to the reconstructed data to classify land covers and monitor land-cover change by tracking the temporal profiles. The proposed method is tested with the MODIS and GOCI NDVI time series over the Korean Peninsula for 5 years from 2012 to 2016. The results show that the multi-periodic harmonic model has a great potential for classification of land-cover types and monitoring of land-cover changes through characterizing annual temporal dynamics.

• Bulletin of the Korean Chemical Society
• /
• 제25권2호
• /
• pp.285-288
• /
• 2004

A canonical transformation changes variables such as coordinates and momenta to new variables preserving either the Poisson bracket or the commutation relations depending on whether the problem is classical or quantal respectively. Classically canonical transformations are well established as a powerful tool for solving differential equations. Quantum canonical transformations have been defined and used relatively recently because of the non-commutativeness of the quantum variables. Three elementary canonical transformations and their composite transformations have quantum implementations. Quantum canonical transformations have been mostly used in time-independent Schrodinger equations and a harmonic oscillator with time-dependent angular frequency is probably the only time-dependent problem solved by these transformations. In this work, we apply quantum canonical transformations to a harmonic oscillator in which both angular frequency and equilibrium position are time-dependent.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2001년도 하계종합학술대회 논문집(2)
• /
• pp.281-284
• /
• 2001

This paper describes an analog multi-phase delay-locked loop (DLL) to solve the harmonic lock problem using current-starved inverter and shunt-capacitor delay cell. The DLL can be used not only as an internal clock buffer of microprocessors and memory It's but also as a multi-phase clock generator for gigabit serial interfaces. The proposed circuit was simulated in a 0.25${\mu}{\textrm}{m}$ CMOS technology to solve harmonic lock problem and to realize fast lock-on time and low-jitter we verified time interval less than 40 ps as the simulation results.