• Proceedings of the KIPE Conference
• /
• 2013.07a
• /
• pp.216-217
• /
• 2013

This paper presents an algorithm for a phase-segregated active power filter for three-phase electric system. Due to the symmetrical characteristic of three-phase system and the specialty of distribution system, the proposed algorithm focuses on the extraction of harmonic component of load current in each phase and simulations have been done by PLECS software to verify the validity of the proposed algorithm while loads are nonlinear.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
• /
• 1993.07a
• /
• pp.142-145
• /
• 1993

쇄파대 내에서는 여러가지 흐름이 상호 간섭하면서 작용하기 때문에 극히 복잡한 흐름장이 형성 된다. 해빈의 제반 동역학에 있어서 최우선되는 작용력은 파동 이지만, 흐름 또한 표사와 확산현상을 지배하는 중요한 요인이다. 특히 쇄파대 내외의 천수역에서는 해류나 조류 등 지구 물리학적 크기의 흐름보다는 소위 해빈류가 문제가 되는 경우가 많다. 해빈류계는 그 평면적인 흐름의 형태에 따라 연안류계(longshore current system), 순환류계(symmetrical celluar system), 사행류계(meandering system) 등 3가지로 분류된다(Basco, 1982). (중략)

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.41 no.9
• /
• pp.1031-1041
• /
• 1992

Existing current-controlled inverters with hysteresis controller (HC) result in the dependence of the inverter on its load characteristics, poor inverter utilization due to too much or too little supply voltage, and the current error in the hysteresis band(HB) which causes deterioration of operation of the supplied motor. In this paper, techniques and results of modeling the operation of current-controlled three phase power inverter with HC are presented. Four symmetrical control schemes are considered: the so called three independent control, three semi-dependent control(a), three semi-dependent control(b) and three dependent control each using three current controller. The dependence of the inverter on its load has been studied. To overcome this difficulty, an inner feedback control has been introduced and optimum parameter has been determined. With the addition of an inner feedback control, adjustment of the switching frequency to a desired value is possible. Also, this modification improves operating characteristics of inverter by enforcing a switching pattern of low dependence on the load, resulting in significantly improved quality of the output current.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.51 no.10
• /
• pp.510-517
• /
• 2002

The use of underground transmission cables has continuously increased in densely inhabited urban and suburban area. Due to a increasing demand of underground cables, two or more circuits are installed in parallel for several kilometers. It, however, has not been realized that the sheath circulating current is generated in the system where a large number of cables are laid in the same route. In this paper, sheath circulating current is analyzed by the EMTP and compared with the measured values. Unbalance arrangement of cables or cross-bonding length causes a significant effect on the magnitude of the sheath current. Sheath circulating current could be greatly reduced by the symmetrical configuration of cables and installation of the impedance reduction system. Especially, with the impedance system of 1Ω installed, the sheath circulating current is reduced by 85.7%.

• Proceedings of the KIPE Conference
• /
• 2014.07a
• /
• pp.215-216
• /
• 2014

This paper proposes a control algorithm for permanent magnet synchronous generator with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage offshore wind power system under unbalanced grid conditions. The proposed control algorithm particularly compensates for the unbalanced grid voltage at the point of common coupling in a collector bus of offshore wind power system. This control algorithm has been formulated based on the symmetrical components in positive and negative rotating synchronous reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power are described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of ac input current is injected to the point of common coupling in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm makes it possible to provide a balanced voltage at the point of common coupling resulting in the generated power of high quality from offshore wind power system under unbalanced network conditions.

• Korean Journal of Optics and Photonics
• /
• v.14 no.4
• /
• pp.399-405
• /
• 2003

We manufactured a clamp-type optical current transformer (COCT) head using FD10 glass. It was manufactured of two parts of FD10 glass with symmetrical structure and was designed so that light propagates along the critical angle in order to avoid a phase difference with the light within the sensor head at reflection. Also, we measured and analyzed the current of conductor from 0 to 1,000 AT, change of optical power with incidence angle of light, temperature and polarization of light, long-term current measurement using COCT head, and demonstrated the feasibility of manufactured COCT through those experiments.

• Journal of Power Electronics
• /
• v.18 no.1
• /
• pp.171-184
• /
• 2018

Unbalanced and distorted grid voltages cause the grid side current of a current source PWM rectifier to be heavily distorted. They can also cause the DC-link current to fluctuate with a huge amplitude. In order to enhance the performance of a current-source PWM rectifier under unbalanced and harmonic grid voltage conditions, a mathematical model of a current-source PWM rectifier is established and a flexible multi-objective control strategy is proposed to control the DC-link current and grid-current. The fundamental positive/negative sequence, $5^{th}$ and $7^{th}$ order harmonic components of the grid voltage are first separated with the proposed control strategy. The grid current reference are optimized based on three objectives: 1) sinusoidal and symmetrical grid current, 2) sinusoidal grid current and elimination of the DC-current $2^{nd}$ order fluctuations, and 3) elimination of the DC-current $2^{nd}$ and $6^{th}$ order fluctuations. To avoid separation of the grid current components, a multi-frequency proportional-resonant controller is applied to control the fundamental positive/negative sequence, $5^{th}$ and $7^{th}$ order harmonic current. Finally, experimental results verify the effectiveness of proposed control strategy.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.41 no.9
• /
• pp.953-959
• /
• 1992

As the TC(time-current) curve corresponding to symmetrical time invariant RMS value has been traditionally chosen and used for setting the relay, it has caused the misoperation errors on relay coordination because of CT secondary current being actually an asymmetrical time varying RMS value. In this paper, an algorithm for calculating the relay operating time is developed to study the asymmetrical effect using the step-by-step method. We represent the relay operating time errors between with and without DC offset versus PSM(plug setting multiplier), TMS(time multiplier setting) and X/R ratio. And also we present the correction factor. Finally we confirm the validity of this technique through the case study.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.56 no.4
• /
• pp.716-723
• /
• 2007

This paper suggests of a 3-phase 3-wire unified active power filter. The system is composed of a series active power filter and a parallel active power filter. The proposed series active power filter compensating unbalance source voltage and current harmonics of the parallel active power filter improves power factor. The proposed algorithm which improves for power factor and harmonic reduction are calculated by the performance function, and which compensates for the unbalanced source voltage is calculated based on the symmetrical component analysis. We composed a combined system of the series active power filter and parallel active power filter to confirm a validity of the proposed control methods. The effectiveness of the proposed algorithm is confirmed by the experiments.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.6 no.3
• /
• pp.12-23
• /
• 1969

In this paper, the current distribution on a 6 points fed linear antenna is theoretically introduced. The antenna that we call the 6 points fed linear antenna is an antenna which are fed by emf E1 at the first two points, emf E2 at the second two points, and emf E3 at the third two points. symmetrical with respect to the center. In this analysis, Hallens theory has been extended with the approximation in the same order.