• 전기학회논문지P
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• 제59권3호
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• pp.253-257
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• 2010

The frequency is an important operation parameter for the control, protection, and stability of a power system. The frequency as a key index of power quality can be indicative of system abnormal conditions and disturbances. Due to the sudden change in generation and loads or faults in power system, the frequency is supposed to deviate from its nominal value. It is essential that the frequency must be maintained very close to its nominal frequency. An accurate monitoring of the power frequency is essential to optimal operation and prevention for wide area blackout. As most conventional frequency estimation schemes are based on DFT filter, it has been pointed out that the gain error could cause defects when the frequency is deviated from nominal value. This paper presents an advanced frequency estimation technique using gain compensation to improve the performance of DFT filter based techniques. To evaluate performance of the proposed algorithm, the 765kV T/L system in Korea is simulated by EMTP-RV software. The proposed technique can reduce the gain error caused when the power system frequency deviates from nominal value.

• KEPCO Journal on Electric Power and Energy
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• 제4권2호
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• pp.107-114
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• 2018

In recent years, ESS (Energy Storage System) has been widely used in various parts of a power system. Especially, due to its fast response time and high ramp rate, ESS is known to play an important role in regulating grid frequency and providing rotational inertia. As the number of installed and commercially operating ESSs increases, the reliability becomes an important issue. This paper introduces control schemes and presents its test method for grid-connected ESS for primary frequency regulation. The test method allows to verify the control operation in the individual operation mode and state. A validation of the method through actual ESS test in a electrical substation is presented in the case study section.

• Journal of Electrical Engineering and Technology
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• 제5권1호
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• pp.28-35
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• 2010

This paper presents new Adaptive Linear Combination Structure (ADALINE) for tracking/estimating voltage-current phasor and frequency of power system. To estimate the phasors and frequency from sampled data, the algorithm assumes that orthogonal coefficients and speed of angular frequency of power system are unknown parameters. With adequate sampled data, the estimation problem can be considered as a linear weighted least squares (LMS) problem. In addition to determining the phasors (orthogonal coefficients), the procedure estimates the power system frequency. The main algorithm is verified through a computer simulation and data from field. The proposed algorithm is tested with transient and dynamic behaviors during power swing, a step change of frequency upon islanding of small generators and disconnection of load. The algorithm shows a very high accuracy, robustness, fast response time and adaptive performance over a wide range of frequency, from 10 to 2000 Hz.

• Journal of Power Electronics
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• 제13권5호
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• pp.798-805
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• 2013

This paper presents the control and implementation of the dual-stator-winding induction generator for variable frequency AC (VFAC) generating system. This generator has two sets of stator windings embedded into the stator slots. The power winding produces the VFAC power to feed the loads, and the control winding is connected to the static excitation controller to control the generator for output voltage regulation with speed and load variations. On the basis of the idea of power balance, an instantaneous slip frequency control (ISFC) strategy using the information of both the output voltage and the output power is used in this system. A series of experiments is carried out on a 15 kW prototype for verification. Results show that the system has good static and dynamic performance in a wide speed range, which demonstrates that the ISFC strategy is suitable for this system.

• 전기학회논문지
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• 제62권7호
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• pp.891-897
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• 2013

The power system frequency plays an important role in monitoring and controlling the power system. The frequency can be measured through discrete Fourier transform (DFT) coefficients of its positive fundamental frequency. The accuracy of the frequency estimate is severely affected by noise in the power system signal and the leakage effect of the negative fundamental frequency in DFT. This paper proposes a DFT-based frequency estimation algorithm to cope with the noise as well as the leakage effect. In this algorithm, two suitable digital filters are introduced to reduce efficiently frequency estimate error due to the noise. These filters are designed to use a digital bandpass filter and a second-degree integrator. The effectiveness of the proposed algorithm in reduction of frequency estimate error is verified through simulations on noise, harmonics and frequency deviation.

• 한국산학기술학회논문지
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• 제10권8호
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• pp.1824-1831
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• 2009

본 논문은 대규모 전력 송전망에서 발전기가 사고로 인해 순간적으로 전력공급을 중단하게 되었을 때 과도기간 동안 나타나는 전력계통 주파수의 급강하가 탈락된 발전기의 위치로부터 전력 송전망 전체로 파급되어 가는 전파속도를 분석한다. 이러한 전력계통 주파수 동요의 전파속도는 전력계통 고유의 특성에 따라 다르게 나타나기 때문에 광역적 측면에서 전력 수송망의 특성을 이해하는데 중요한 파라미터이며, 최근 미국의 전력 송전망을 대상으로 운영중인 광역 전력계통 주파수 감시스템(FNET)을 활용한 전력 IT 적용연구에서 중요한 파라미터로 활용되고 있다. 본 논문에서는 방대한 규모를 가진 미 동부의 전력송전 연계계통에 대해 최근의 동적모델을 사용하여 다양한 위치에서의 발전기 탈락을 모의한 후 이에 따른 전력계통주파수 동요의 전파 특성을 분석하고 그 전파속도를 제시한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 학술대회 논문집 전문대학교육위원
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• pp.185-190
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• 2006

Frequency and phasor are the most important quantities in power system operation because they can reflect the whole power system situation. Frequency reflects the dynamic energy balance between load and generating power, while operators use phasor to constitute the state of system and, moreover, phasor based line relays are currently used in most power systems. So frequency and phasor are regarded as indices for the operating power systems in practice. The proposed technique is suitable for estimation near-nominal, nomina), and off-nominal frequencies. It is useful in designing microprocessor-based relays and meters that need to measure power system frequency. Performance test results, using signals from EMTP source and Excel program, indicate that the proposed technique can provide accurate estimates within 16ms. Maximum estimation errors observed during testing are of the order of 0.006Hz for nominal, near-nominal, and off-nominal frequencies. The proposed technique provides accurate estimates in presence of noise and harmonics and in case ground fault. The rate change of the phase angle is used for estimation. To confirm the validity of the proposed algorithm, the simulation studies carried out on a typical 154[KV] double T/L system by using EMTP software. Some test results are presented in the paper.

• Journal of Advanced Marine Engineering and Technology
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• 제35권6호
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• pp.861-866
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• 2011

본 논문에서는 파도의 상하운동에 의해 발전되는 형발전시스템과 진동발전시스템이 결합된 하이브리드 발전방법을 제안한다. 선형발전시스템은 권선과 영구자석으로 구성되어있고, 파도의 상하운동속도를 직접적으로 사용하므로 파도의 주파수에 관계없이 안정적인 발전을 한다. 그리고 진동발전시스템은 진동시스템인 영구자석, 스프링과 발전시스템인 영구자석, 권선으로 구성되어 있다. 진동발전시스템은 파도의 주파수와 진동시스템의 고유진동수를 일치시킨 공진대역에서 구동함으로써 파도의 상하운동 속도보다 더 큰 속도를 이용하여 더 많은 전기에너지를 얻을 수 있다. 따라서 본 연구에서 제안한 하이브리드 파력발전방법은 공진영역에서 더 많은 전기에너지를 얻을 수 있을 뿐만 아니라 공진영역을 벗어난 대역에서도 안정적으로 발전할 수 있는 장점을 가짐을 알 수 있다.

• 전기학회논문지
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• 제57권2호
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• pp.268-275
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• 2008

In this paper, we introduce a new method for detecting and estimating faults on a power line using the time-frequency domain reflectometry system. The system rests upon time-frequency signal analysis and uses a chirp signal which is multiplied by Gaussian envelope. The chirp signal is used as a reference signal, and we can get the reflected signal from a fault on a wire. To detect and estimate faults, we analyze the reflected signal by Wigner time-frequency distribution function and normalized time-frequency cross correlation function. In this paper we design an optimal reference signal for power line and implement a system for estimating fault distance on a power line with the TFDR implemented by PXI equipments. This approach is verified by some experiments with HIV 2.25mm power lines.

• 전기학회논문지
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• 제57권11호
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• pp.1946-1953
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• 2008

Power system of Jeju is interconnected to the mainland using HVDC and that is also interconnected to three wind farms. It will be difficult to control of Jeju power system if HVDC is disconnected or HVDC is overhauled under large scale wind farms interconnected. We measured and analysed the power quality of two substation and two wind farms to assess that wind farms have an effect on Jeju system during the HVDC overhaul last May. We concentrated on the power quality like frequency, voltage variation, voltage harmonics, current harmonics, flicker. We can found that the frequency of Jeju system is very unstable during overhaul, so the frequency of Jeju system can be variated easily by wind farm's rapid output power variation. There are some benefits and weak points in power quality between two wind farms because each wind farm is consist of different wind turbines.