• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.654-664
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• 2017

This paper proposed an unified dual-phase-shift (UDPS) control for dual active bridge (DAB) converters in order to improve efficiency for a wide output power range. Different operating modes of UDPS are characterized with respect to the reactive current distribution. The proposed UDPS has the same output power capability with conventional phase-shift (CPS) method. Furthermore, its implementation is simple since only the change of the leading phase-shift direction is required for different operating power range. The proposed UDPS control can minimize both the inductor rms current and the circulating reactive current for various voltage conversion ratios and load conditions. The optimal phase-shift pairs for two bridges of DAB converter are derived with respect to the comprehensive reactive power loss model, including the reactive components delivered from the load and back to the source. Simulation and experimental results are illustrated and explained with details. The effectiveness of the proposed method is verified in terms of reactive power losses minimization and efficiency improvement.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.385-386
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• 2020

최근, 에너지저장장치를 활용하여 태양광-ESS 하이브리드 시스템이 도입되고 있다. 태양광-ESS 하이브리드 시스템은 구성방식에 따라 다양한 전력변환장치를 활용한다. 그중 DAB 컨버터는 절연형이며, 양방향 전력전달이 가능하므로 스위칭 기법, 토폴로지 개발 등 연구가 활발히 진행되고 있다. 본 논문에서는 태양광-ESS 하이브리드 시스템에 적용되는 대표적인 벅-부스트 컨버터와 DAB 컨버터에 대해 리뷰한다.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.439-440
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• 2017

본 논문에서는 지능형 반도체 변압기를 구성하는 Dual Active Bridge (DAB) 컨버터와 계통 연계형 인버터와의 연결에 따른 임피던스 영향을 분석하기 위해 컨버터의 입력 임피던스와 인버터의 출력 임피던스 각각에 대한 전달함수를 분석하고자 한다. 이를 통해 인버터와 컨버터 간의 임피던스 영향을 이론 분석과 모의 시험을 통해 확인하고, 제어기의 설계 방향을 제안하고자 한다.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.207-209
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• 2019

This paper proposes a grid-tied photovoltaic (PV) system, consisting of Voltage-fed dual-active-bridge (DAB) dc-dc converter with single phase inverter. The proposed converter allows a small dc-link capacitor, so that system reliability can be improved by replacing electrolytic capacitors with film capacitors. The double line frequency free maximum power point tracking (MPPT) is also realized in the proposed converter by using Ripple Correlation method. First of all, to eliminate the double line frequency ripple which influence the reduction of DC source capacitance, control is developed. Then, a designing of Current control in DQ frame is analyzed and to fulfill the international harmonics standards such as IEEE 519 and P1547, $3^{rd}$ harmonic in the grid is directly compensated by the feedforward terms generated by the PR controller with the grid current in stationary frame to achieve desire Total Harmonic Distortion (THD). 5-kW PV converter and inverter module with a small dc-link film capacitor was built in the laboratory with the proposed control and MPPT algorithm. Experimental results are given to validate the converter performance.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.336-344
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• 2017

This paper presents the three-port DC-DC converter modeling and controller design procedure, which is part of the solid-state transformer (SST) to interface medium voltage AC grid to bipolar DC distribution network. Due to the high primary side DC link voltage, the proposed converter employs the three-level neutral point clamped (NPC) topology at the primary side and 2-two level half bridge circuits for each DC distribution network. For the proposed converter particular structure, this paper conducts modeling the three winding transformer and the power transfer between each port. A decoupling method is adopted to simplify the power transfer model. The voltage controller design procedure is presented. In addition, the output current sharing controller is employed for current balancing between the parallel-connected secondary output ports. The proposed circuit and controller performance are verified by experimental results using a 30 kW prototype SST system.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.6
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• pp.507-514
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• 2022

This study proposes an optimal design process for a high-frequency transformer that has a large leakage inductance for dual-active-bridge converters. Notably, conventional design processes have large errors in designing leakage transformers because mathematically modeling the leakage inductance of such transformers is difficult. In this work, the geometric parameters of a shell-type transformer are identified, and finite element analysis(FEA) simulation is performed to determine the magnetization inductance, leakage inductance, and copper loss of various shapes of shell-type transformers. Regression models for magnetization and leakage inductances and copper loss are established using the simulation results and the machine learning technique. In addition, to improve the regression models' performance, the regression models are tuned by adding featured parameters that consider the physical characteristics of the transformer. With the regression models, optimal high-frequency transformer designs and the Pareto front (in terms of volume and loss) are determined using NSGA-II. In the Pareto front, a desirable optimal design is selected and verified by FEA simulation and experimentation. The simulated and measured leakage inductances of the selected design match well, and this result shows the validity of the proposed design process.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.245-246
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• 2016

본 논문에서는 지능형 반도체 변압기를 구성하는 양방향 DC-DC Dual Active Brldge(DAB) 컨버터의 소신호 모델과 전달함수의 분석을 통해 컨버터의 안정도와 동작 특성을 파악하고, 이를 통해 동 특성 및 정상상태의 안정성을 향상시킬 수 있는 제어기 설계 방안을 제안한다.

• Journal of Power Electronics
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• v.19 no.2
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• pp.431-442
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• 2019

This paper proposes a unified high-frequency bipolar buck-boost (UHFBB) control strategy for a dual-active-bridge (DAB), which is derived from the classical buck and boost DC/DC converter. It can achieve optimized current stress of the switches and soft switching in wider range. The UHFBB control strategy includes multi-control-variables, which can be achieved according to an algorithm derived from an accurate mathematical model. The design method for the parameters, such as the transformer turns ratio and the inductance, are shown. The current stress of the switches is analyzed for selecting an optimal inductor. The analysis is verified by the experimental results within a 500W prototype.

• Journal of IKEEE
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• v.23 no.3
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• pp.994-1002
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• 2019

In this paper, we propose the development of a power conversion system for electric power take-off (e-PTO) of agricultural electric vehicles. Most e-PTOs use commercial power $220V_{AC}$. A bidirectional power conversion system having a two-stage structure consisting of a DC-DC converter and a DC-AC inverter for supplying a high output voltage using a low battery voltage of an agricultural electric vehicle is suitable. we propose a power conversion system consisting of the one-stage dual active bridge (DAB) converter and the two-stage bidirectional full bridge inverter. In addition, we propose a soft start algorithm for reducing the inrush current generated by the link capacitor charging during the initial operation. A 3kW prototype system and its corresponding algorithms have been implemented to verify its effectiveness through experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.150-157
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• 2021

Nowadays, a DC microgrid that can link various distributed power sources is gaining much attention. Accordingly, research on fault situations, such as line-to-line and line-to-ground faults of the DC microgrid, has been conducted to improve grid reliability. However, the blackout of an AC system and the oscillation of a DC bus voltage have not been reported or have not been sufficiently verified by previous research. In this study, a 20 kW DC microgrid testbed using a power HIL simulation technique is proposed. This testbed can simulate various fault conditions without any additional grid facilities and dangerous experiments. It includes the blackout of the DC microgrid caused by the AC utility grid's blackout, a drastic load increment, and the DC bus voltage oscillation caused by the LCL filter of the voltage source converter. The effectiveness of the proposed testbed is verified by using Opal-RT's OP5707 real-time simulator with a 3 kW prototype three-port dual-active-bridge converter.