• KEPCO Journal on Electric Power and Energy
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• 제2권2호
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• pp.307-310
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• 2016

The operational cost for maintaining the superconductivity of high-temperature superconducting (HTS) cables needs to be reduced for feasible operation. It depends on factors such as AC loss and heat transfer from the outside. Effective operation requires design optimization and suitable operational conditions. Generally, it is known that critical currents increase and AC losses decrease as the operational temperature of liquid nitrogen ($LN_2$) is lowered. However, the cryo-cooler consumes more power to lower the temperature. To determine the effective operational temperature of the HTS cable while considering the critical current and AC loss, critical currents of the HTS cable conductor were measured under various temperature conditions using sub-cooled $LN_2$ by Stirling cryo-cooler. Next, AC losses were measured under the same conditions and their variations were analyzed. We used the results to select suitable operating conditions while considering the cryo-cooler's power consumption. We then recommended the effective operating temperature for the HTS cable system installed in an actual power grid in KEPCO's 154/22.9 kV transformer substation.

• 한국산업융합학회 논문집
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• 제24권4_2호
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• pp.491-499
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• 2021

Batteries are widely used for energy storage, such as ESS(Energy Storage System), electric vehicles, electric aircraft, and electric powered ships. Among them, a submarine uses a high power battery for an energy storage. When the battery of a submarine is discharged, a diesel generator generates AC power, and then AC/DC power converter change AC power to DC power for charging the battery. Therefore, in order to lower the current capacity of the diesel generator, it is necessary to use an AC/DC converter with a high input power factor. And, a power converter with a large power capacity must have high stability because it can lead to a major accident when a failure occurs. However, the control algorithm using the traditional PI controller is difficult to satisfy stability and dynamic characteristics. In this paper, we design the high power AC/DC converter with high input power factor for battery charging systems. And, we propose a stable control algorithm. The validity of the proposed method is verified through simulation and experiments.

• 조명전기설비학회논문지
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• 제28권1호
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• pp.16-28
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• 2014

This paper presents a novel high-power-factor circuit topology of AC to AC current-fed type high frequency resonant inverter which includes the function of power factor correction(PFC) in the proposed inverter to operate the AC input block with high power factor. The proposed circuit topology of AC to AC current fed type high resonant inverter removes DC link electrolytic capacitor and has also the one of power factor correction(PFC) in the inverter circuit without an additional PFC circuit since the input current by constituting it in parallel as an unit inverter, which assumes the class-E high frequency resonant inverter of conventional current-fed type, flows in the form of the resultant current flowing through each constant current reactor($L_{d1}$, $L_{d2}$). The circuit analysis of proposed inverter is generally described by adopting the normalized parameters and the evaluation of its operating characteristics are conducted by using the parameters such as the ratio of switching and resonant frequency(${\mu}$), coupling coefficient(k) and so on. An example of procedure for circuit design based on the characteristic values obtained from the theoretical analysis is presented. To confirm the validity of the theoretical analysis, the experimental results are also presented. In the future, the proposed inverter shows it can be practically used as power supply system for induction heating application, DC-DC converter etc.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.524-526
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• 2005

As a research activity of the project of "Verification Test of Superconducting Power Cable", we measured the AC loss of a short length superconducting power cable. The rating and the length of the cable were 22.9kV, 1,250A and 2.2m. The voltage taps for measuring the AC loss were attached to both ends of the conductor of the superconducting cable. Through the voltage taps and a lock-in amplifier we measured the in-phase component of the voltage($V_x$) with the load current(I). The AC loss was measured by multiplying the in-phase component of the voltage($V_x$) by the load current(I). The value of the AC loss of the superconducting power cable was 1.18W/m/phase/kA at 77.3K, 1atm.

• 한국산업정보학회논문지
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• 제24권2호
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• pp.57-63
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• 2019

점차적으로 늘어나는 전력 수요의 공급을 원활히 하기 위해서 발전 설비 뿐만 아니라 전력을 전송하기 위한 전력케이블의 증설도 반드시 필요하다. 하지만 대부분의 도심지에 전력을 공급하기 위한 전력케이블의 증설은 추가적인 케이블의 설치공사를 위한 공간을 필요로 하고 현재 국내 도심지에 케이블 설치를 위한 공간이 부족한 실정이다. 이에 동일한 사이즈로 더 많은 전력을 전송할 수 있는 초전도 전력 케이블은 부족한 케이블의 설치공간을 극복할 수 있는 대안으로 등장하였다. 하지만 대용량의 전력 전송의 이점을 가지고 있는 초전도 전력케이블은 교류 시스템에서의 일부 손실을 가지고 있다. 따라서 교류 전력 전송 시스템에서 초전도 전력 케이블을 도입하기 위해서는 교류손실의 설계 및 분석이 반드시 필요하다. 이에 본 논문에서는 다양한 초전도 전력케이블의 교류 손실 분석을 통하여 실제 초전도 전력 케이블의 제조 및 실계통 적용에 고려하고자 한다. 단일 초전도 선재에 대한 교류 손실의 이론적인 계산 방법은 존재하지만 많은 수로 구성된 초전도 전력 케이블의 교류손실 계산은 쉽지가 않다. 저자는 초전도의 E-J (Electric field-current density) 특성이 고려된 전자기적 유한요소해석법을 이용하여 다양한 종류의 초전도 전력케이블 교류 손실을 분석하고자 한다. 또한 본 초전도 전력케이블의 교류손실 특성 분석은 실계통에 적용될 초전도 전력케이블의 설계 및 개발에 중요한 요소로 작용될 것이다. [1-4].

• Journal of Power Electronics
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• 제18권3호
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• pp.694-701
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• 2018

This paper proposes a new single-phase power converter topology for changing the frequency of AC voltage. The proposed single-phase frequency converter (SFC) includes a T-type multi-level power converter (TMPC), a frequency decoupling transformer (FDT) and a digital signal processor (DSP). The TMPC can convert a 60 Hz AC voltage to a DC voltage and then convert the DC voltage to a 50 Hz AC voltage. Therefore, the output currents of the two T-type power switch arms have 50 Hz and 60 Hz components. The FDT is used to decouple the 50 Hz and 60 Hz components. The salient feature of the proposed SFC is that only one power electronic converter stage is used since the functions of the AC-DC and DC-AC power conversions are integrated into the TMPC. Therefore, the proposed SFC can simplify both the power circuit and the control circuit. In order to verify the functions of the proposed SFC, a hardware prototype is established. Experimental results verify that the performance of the proposed SFC is as expected.

• 전기학회논문지
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• 제63권3호
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• pp.358-366
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• 2014

This paper proposes a quasi Z-source AC-AC converter with the low DC voltage distribution capability operating as a power electronic transformer. The proposed system has configuration that the input terminals of two quasi Z-source AC-AC converters are connected in parallel, also their output terminal are connected in series. Simple control method of duty ratio was proposed for the in phase buck-boost AC voltage mode and the DC output voltage control. DSP based experiment and PSIM simulation were performed. As a result, the PSIM simulation results were same with the measured results. By controlling the duty ratio under the condition of 100 [${\Omega}$] load, quasi Z-source AC-AC converter could buck and boost the AC output voltage in phase with the AC input voltage, and the same time, the constant DC voltage could be output without affecting the AC output characteristics. And, the DC output voltage 48[V] was constantly controlled in dynamic state in case while the load is suddenly changed ($50[\Omega]{\rightarrow}100[\Omega]$). From the above result, we could know that the quasi Z-source AC-AC converter can act as a power electronic transformer with a low DC voltage distribution capability.

• 전력전자학회논문지
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• 제16권5호
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• pp.415-429
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• 2011

본 연구에서는 출력이 직렬 연결된 단상 quasi Z-소스 AC-AC 컨버터를 제안하였다. 제안된 시스템은 단상quasi Z-소스 AC-AC 컨버터 2대의 입력 단을 병렬로 연결하고 출력 단을 직렬로 연결한 구조로 되어 있으며, 역상 모드와 동상 모드 별 전류 흐름과 출력전압의 형성 과정을 나타내었다. DSP로 제어되는 실험 시스템을 제작하여 PSIM시뮬레이션 결과와 비교 분석하였다. 그 결과 각 모드별로 듀티 비를 제어하여 원하는 출력 전압을 벅-부스트 할 수 있었다. 컨버터 1대가 단독으로 운전한 경우에 비하여, 각각의 모드에 대하여 부하 저항의 증가에 따른컨버터 효율과 입력 역률을 제안된 방법에 의하여 개선할 수 있었다. 또한 역상 모드의 경우, 일정 부하에서 컨버터의 효율과 입력 역률을 각각 10[%]와 35[%]정도 개선하였으며, 특히 부하 저항이 변동하는 과도상태에서도 일정한 출력 전압을 유지할 수 있었다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 전력전자학술대회 논문집
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• pp.435-436
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• 2016

본 논문에서는 3상 Quasi Z-소스 AC/AC 전력변환기를 제안한다. 제안된 전력변환기는 3대의 단상 Quasi Z-소스 AC/AC 컨버터로 구성되어 있으며, 간단한 듀티 비 제어만으로도 동상 및 역상의 벅-부스트 출력 전압의 발생이 가능하다. 제안된 방식은 PSIM 시뮬레이션을 통하여 타당성을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.166-169
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• 2003

In this paper, a PWM Buck-Boost AC-AC converter for improvement of power quality of custom power is presented. The PWM Buck-Boost AC-AC converter is modelled by using circuit DQ transformation whereby the design guideline is obtained. Based on the analysis, the converter system is implemented with the design criteria and the experimental results show the validity of modelling and analysis.