• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권10호
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• pp.683-692
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• 2000

A new primary-side-assisted zero-voltage and zero-current switching full bridge DC-DC converter with transformer isolation is proposed. The auxiliary circuit adopted to assist ZCS for the leading leg is composed of only one small transformer and two diodes. It has a simple and robust structure, and load current control capability even in short circuit conditions. Possibility of magnetic saturation due to asymmetricity of circuits or transient phenomena is greatly reduced, which is a very attractive feature in DC/DC converters with transformer isolation. The power rating of the auxiliary transformer is about 10% of that of the main transformer. Operation of a 12.5KW prototype designed for welding application was verified by experiments.

• 한국자기학회지
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• 제9권1호
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• pp.55-63
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• 1999

AC 전원선로에서 발생하는 수 kHz에서 수십 MHz에 이르는 광대역의 주파수특성을 가진 전원노이즈는 전기, 전자, 통신장비의 정상적인 동작에 많은 장해요소가 되고 있으며 이들 전도성 노이즈를 억제하기 위한 기기로 기존에는 써어지 억제기와 필터가 적용되어 왔다. 그러나, 이러한 기존의 노이즈 대책기기는 전력 공급선과 노이즈 피해회로 상호간의 전기적인 절연 분리가 원천적으로 불가능하므로 전도성 노이즈 중에서 가장 큰 피해를 끼치는 공통모드 노이즈 억제성능이 지극히 제한적이다. 따라서 본 논문에서는 전원회로의 공통모드 및 정상모드 노이즈 억제에 사용 가능한 차폐절연변압기에 대한 모의 등가회로를 제안하였으며, 계산과 실험을 통해 그 성능을 비교 해석함으로써 모의 해석의 유효성을 입증하였다. 또한 차폐절연변압기의 설계 방법을 제시하였으며, 제작된 3kVA급 시작품과 비 차폐된 절연변압기의 노이즈 성능을 비교함으로써 전도성 노이즈 억제성능의 우수성을 검증하였다.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2009년도 추계학술발표대회 논문집
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• pp.371-376
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• 2009

The Power Conditioning System is Power Transfer System which make array DC current to the Grid sinusoidal current. These are Low Frequency Transformer Inverter Type, High Frequency Transformer Inverter Type and Transformer-less Type. Low Frequency Transformer Type has a Excellent Isolation property, but doesn't have competitiveness in Size and Cost. Also High Frequency Transformer Type has a good Isolation property but there are many steps in Power transfer Switching. Nowadays, Transformer-less Type inverter change a transformer to DC/DC Converter which is small and cost effective. In this paper shown the DC/DC Converter Transformer-less Type multi-string inverter design and simulation. The Control Algorithm will be introduced and Simulation was accomplished.

• 전력전자학회논문지
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• 제21권5호
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• pp.434-441
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• 2016

This paper deals with transformer turns ratio design with the consideration of loss minimization in isolated bidirectional DC-DC converter. Generally, the rms value of current, magnitude of current at switching instance, and duty ratio of a converter vary according to the turns ratio of an isolation transformer in the converter under the same voltages and output power level. Therefore, the transformer turns ratio has an effect on the total loss in a converter. The switching and conduction losses of IGBTs and MOSFETs consisting of dual-active bridge converter are analyzed, and iron and copper losses in an isolation transformer and inductor are calculated. Total losses are calculated and measured in cases of four different transformer turns ratios through simulation and experiment with 3-kW converter, and an optimum turns ratio that provides minimum losses is found. The usefulness of the proposed transformer turns ratio design approach is verified through simulation and experimental results.

• Journal of Power Electronics
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• 제15권6호
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• pp.1468-1479
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• 2015

Renewable energy resources such as wind and photovoltaic power generation systems demand a high step-up DC-DC converters to convert the low voltage to commercial grid voltage. However, the high step-up converter using a transformer has limitations of high voltage stresses of switches and diodes when the transformer winding ratio increases. Accordingly, conventional studies have been applied to series-connect multioutput converters such as forward-flyback and switched-capacitor flyback to reduce the transformer winding ratio. This paper proposes new single-ended converter topologies of an isolation type and a non-isolation type to improve power efficiency, cost-effectiveness, and output ripple. The first proposal is an isolation-type charge-pump switched-capacitor flyback converter that includes an extreme-ratio isolation switched-capacitor cell with a chargepump circuit. It reduces the transformer winding number and the output ripple, and further improves power efficiency without any cost increase. The next proposal is a non-isolation charge-pump switched-capacitor-flyback tapped-inductor boost converter, which adds a charge-pump-connected flyback circuit to the conventional switched-capacitor boost converter to improve the power efficiency and to reduce the efficiency degradation from the input variation. In this paper, the operation principle of the proposed scheme is presented with the experimental results of the 100 W DC-DC converter for verification.

• 전기학회논문지
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• 제66권4호
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• pp.636-642
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• 2017

Recently, new power devices, SiC and GaN FETs, are commercialized. They are expected to change power electronics environments. They will raise operating frequencies of power electronic equipments. Accordingly, design method will be changed greatly. In this paper, an 1 MHz resonant converter with fully compensated coreless isolation transformer is proposed, where the primary voltage is proportional to the secondary current and the primary current to the secondary voltage. 30 W prototype is constructed and tested, and its usefulness is verified.

• Journal of Power Electronics
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• 제2권2호
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• pp.112-123
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• 2002

This paper presents a novel prototype of the utility AC power interfaced soft-switching sinewave pulse modulated inverter using the high-frequency flyback for the small scale distributed renewable energy power conditioner. The proposed cricuit with a high-frequency isolation link has a funtion of electrical isolation, which is more cost-effective and reliable for the small-scale distributed renwal energy utilization system from a safety point of riew. The discontinuous conduction mode(DCM) operation of the high-frequency flyback transformer is adopted to establish a simple and low-cost circuit configuration and control scheme. For the simplicity, the circuit operating principle is described on the basis of the modified conventional full bridge inverter, whitch is the typical conventional high-frequency full-bridge inverter employing the high requency flyback transformer to eanble the effictive function of the electrical isolation. Than, the new circuit topology of the unility-interfaced soft-switching sinewave pulse modulated inverter using IGBTs is proposed. The proposed cricuit topology is additionally composed of the auxiliary power regenerating snubber cricuits, which are also mathematically analyzed for the parameter desigen settings. Finally, the performance of the propose inverter is evaluated on the basis of computer-aid simulation. It is noted that the sinewave pulse modulated output current of the inverter is synchronous to the AC main voltage.

• 전기학회논문지
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• 제56권6호
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• pp.1055-1063
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• 2007

This paper introduces an optimal design technique for a 250-watt isolation transformer using an optimization method, dynamic encoding algorithm for searches (DEAS). Although the optimal design technique for transformers dates back to 1970s and various optimization methods have been developed so far, literature concerning global optimization for transformer core design is rarely found against its importance. In this paper, core configuration of the isolation transformer whose performance is computed by complex mathematical steps is optimized with DEAS. The optimization result confirms that DEAS can be successfully employed to transformer core design for various performance specifications only by adjusting weight factors in cost function.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.917-920
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• 2005

This paper introduces an optimal design technique for a 250-watt isolation transformer using a recently developed optimization method, dynamic encoding algorithm for searches(DRAS). Although the optimal design technique for transformers dates back to 1970s and local optimization is often undertaken using FEM nowadays, literature concerning global optimization of transformer cores is rarely found against its importance. In this paper, a small isolation transformer is used as a model to be optimized with application of DEAS to corresponding mathematical description. The optimization result confirms that DEAS can be successfully employed to design transformer cores for various design specifications only by changing cost functions.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제51권2호
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• pp.85-91
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• 2002

A novel multi-section power divider configuration is Proposed to obtain wide-band frequency performance up to microwave frequency region. Design procedures for the proposed microwave broadband power divider are composed of a Planar multi-section three-Ports hybrid and a waveguide transformer design procedures. The multi∼section power divider is based on design theory of the optimum quarter- wave transformer Furthermore, in order to obtain the broadband isolation performance between the two adjacent output ports, the odd mode equivalent circuit should be matched by using the lossy element such as resistor. The derived design formula for calculating these odd mode∼matching elements is based on the singly terminated filter design theory. The waveguide transformer section is designed to suppress the propagation of the higher order modes such as waveguide modes due to employing the metallic electric wall. Simulation and experiment show excellent performance of multi section power divider.