• Journal of Electrical Engineering and Technology
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• 제11권3호
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• pp.629-638
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• 2016

This paper proposes a State-of-Charge (SOC) balancing control of Battery Power Modules (BPMs) for a modularized battery for Electric Vehicles (EVs) without additional balancing circuits. The BPMs are substituted with the single converter in EVs located between the battery and the inverter. The BPM is composed of a two-phase interleaved boost converter with battery modules. The discharge current of each battery module can be controlled individually by using the BPM to achieve a balanced state as well as increased utilization of the battery capacity. Also, an SOC balancing method is proposed to reduce the equalization time, which satisfies the regulation of a constant DC-link voltage and a demand of the output power. The proposed system and the SOC balancing method are verified through simulation and experiment.

• 한국산학기술학회논문지
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• 제21권3호
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• pp.585-593
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• 2020

현재까지 총 29건의 전기저장장치의 화재가 발생되었는데, 이 중 22건이 신재생에너지 연계용이며, 완전충전 이후, 운전대기 상태인 휴지기간 동안에 계절과 무관하게 화재사고가 발생되었다. 이것은 병렬로 연결된 셀들의 SOC 상태가 서로 다른 경우, 의도하지 않게 SOC가 높은 셀에서 낮은 셀로 전류가 이동하는 셀프에너지 밸런싱 현상으로, 일부 셀이 과충전되어 열폭주로 인한 화재의 원인으로 평가되고 있다. 따라서, 본 논문에서는 전기저장장치의 셀프에너지 밸런싱을 방지하는 새로운 BMS의 회로구성과 운용 알고리즘 그리고 SOC 평가알고리즘을 제안한다. 제안한 알고리즘과 구현한 BMS를 바탕으로 리튬이온전지의 열화 특성과 열화 및 정상 셀 간의 셀프에너지 밸런싱 특성을 분석한 결과, 정상 셀 대비 열화 셀의 방전 용량 비율은 91.75[%]이며, 열화율이 8.25[%]임을 알 수 있었고, SOC가 높은 정상 셀에서 SOC 낮은 열화 셀로 전류가 이동하는 셀프에너지 밸런싱 현상이 발생함을 확인하였다. 또한, 셀프에너지 밸런싱 전류가 과도하게 높아지는 경우, BMS가 확실하게 셀들의 병렬연결을 분리하여, 리튬이온전지의 안전성을 향상시킬 수 있어, 본 논문에서 제안한 BMS의 유용성을 확인하였다.

• 전기학회논문지
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• 제66권2호
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• pp.292-299
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• 2017

In this paper, multiple ESS(Energy Storage System) control strategy for microgrids is presented. Installation of ESS becomes mandatory when microgrids are used to supply high quality power to the loads. The one of main functions of the ESS is to maintain power balance. However ESS has limitation of its capacity and instantaneous injecting power. Power allocation method based on SOC(State Of Charge) of each ESS is proposed. P-Q control is employed as the basic control strategy for the distributed ESSs. By using the proposed method, the coefficients in the conventional P-Q control method are modified. The ESSs with higher SOC inject more active power, while those with lower SOC inject less, leading to more balanced SOC levels among the ESSs. The proposed method is demonstrated by simulation using PSCAD/EMTDC.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.29-38
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• 2017

This paper presents a study on the state-of-charge (SOC) reference based active cell balancing in real-time. The optimal references of SOC are determined by using the proposed active cell balancing system with the bidirectional DC/DC converters via the dual active bridge (DAB) type. Then, the energies between cells can be balanced by the power flow control of DAB based bidirectional DC/DC converters. That is, it provides the effective management of battery by transferring energy from the strong cell to the weak one until the cell voltages are equalized to the same level and therefore improving the additional charging capacity of battery. In particular, the cell aging of battery and power loss caused from energy transfer are considered. The performances of proposed active cell balancing system are evaluated by an electromagnetic transient program (EMTP) simulation. Then, the experimental prototype is implemented in hardware to verify the usefulness of proposed system.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2018년도 전력전자학술대회
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• pp.156-158
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• 2018

The inconsistencies between paralleled battery cells are becoming more considerable issue in high capacity battery applications like electric vehicles. Due to differences in state-of-charge (SOC) and internal resistance within individual cells in parallel, charging or discharging current is not appropriately balanced to each cell in terms of SOC, which may shorten the lifetime or sometimes cause safety issues. In this paper, an intelligent cell-balancing algorithm is proposed to overcome the inconsistency issue especially for paralleled battery cells. In this scheme, SOC information collected in the sub-BMS module is sent to the main-BMS module, where the number of parallel cells to be connected to DC bus is continuously updated based on the suggested SOC comparison rule. To verify the method, operation of the algorithm on 4 paralleled battery cells are simulated on Matlab/Simulink. The simulation result shows that the SOCs of paralleled cells are evenly redistributed. It is expected that the proposed algorithm provides high reliable and prolong the life cycle and working capacity of the battery pack.

• Journal of Power Electronics
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• 제17권6호
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• pp.1625-1636
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• 2017

A power electronic transformer (PET) based on the cascaded H-bridge (CHB) and the isolated bidirectional DC/DC converter (IBDC) is capable of accommodating a large scale battery energy storage system (BESS) in the medium-voltage grid, and is referred to as a power electronic transformer based battery energy storage system (PET-BESS). This paper investigates the PET-BESS and proposes a coordinative control strategy for it. In the proposed method, the CHB controls the power flow and the battery state-of-charge (SOC) balancing, while the IBDC maintains the dc-link voltages with feedforward implementation of the power reference and the switch status of the CHB. State-feedback and linear quadratic Riccati (LQR) methods have been adopted in the CHB to control the grid current, active power and reactive power. A hybrid PWM modulating method is utilized to achieve SOC balancing, where battery SOC sorting is involved. The feedforward path of the power reference and the CHB switch status substantially reduces the dc-link voltage fluctuations under dynamic power variations. The effectiveness of the proposed control has been verified both by simulation and experimental results. The performance of the PET-BESS under bidirectional power flow has been improved, and the battery SOC values have been adjusted to converge.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 추계학술대회 논문집
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• pp.33-34
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• 2016

This paper presents a load sharing method based on the low bandwidth communication (LBC) applied to a DC microgrid in order to balance the state of charge (SOC) of the battery units connected in parallel to the common bus. In this method, SOC of each battery unit is transferred to each other through LBC to calculate average SOC value. After that, droop coefficients of battery units are adjusted according to the difference between SOC of each unit and average SOC value of all batteries in the system. The proposed method can effectively balance the SOC of battery units in charging and discharging duration with a simple low bandwidth communication system.

• 한국태양에너지학회 논문집
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• 제24권2호
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• pp.1-7
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• 2004

In this paper, the new improved method for photovoltaic system was studied available for a lighting load by measuring the state of charge of lead-acid batteries. Photovoltaic systems has been evaluated as one of the most new and renewable energy and especially, the Stand-Alone Photovoltaic system has been used to a street light, a road sign light, an air caution light, an emergency call. Many Stand-Alone PV system are installed by a group. Although the pre-installation cost of PV system is high and it has not been operated due to the absence of optimal management standards. In this paper, it is proposed a new operating method by the measurement of lead-acid battery's SOC with a Ah balancing.

• 전기학회논문지
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• 제64권4호
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• pp.616-622
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• 2015

A microgrid which is composed of distributed generation systems, energy storage systems and loads is operated in the grid-connected mode and in the islanded mode. Especially, in the islanded mode, a microgrid should maintain frequency in the allowed range. The frequency is decided by a balance between power supply and power demand. In general, the frequency is controlled by using battery energy storage systems (BESSs) in the microgrid. Especially, droop control is applied to controlling BESSs in the microgrid. Meanwhile, over-charging and deep-discharging of BESS in operation and control cause life-shortening of batteries. In this paper, a fuzzy droop control is proposed to change droop gains adaptively by considering state of charge (SOC) of BESSs to improve the life cycle of the battery. The proposed fuzzy droop control adjusts droop gains based on SOC of BESSs in real time. In other to show the performance of the proposed fuzzy droop control, simulation based on Matlab/Simulink is performed. In addition, comparison of the convention droop control and the proposed fuzzy droop control is also performed.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 추계학술대회
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• pp.97-98
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• 2017

본 논문에서는 Full-bridge 서브모듈로 구성된Delta 구조 MMC를 기반으로 하는 BESS의 SOC 균등제어 기법에 대하여 기술하고 있다. Full-bridge로 구성된 서브모듈의 직류단에는 배터리가 연계되어있다. 배터리는 그 모델에 따라 고유의 전압특성 곡선을 갖기에 SOC 제어를 통한 배터리 출력전압의 균등제어가 필요하다. 본 논문에서는 Delta 구조 MMC BESS의 영상분 전류주입과 개별 배터리의 SOC 차를 이용한 SOC 균등제어 기법을 제안하였다. 그리고 PSCAD/EMTDC를 통하여 제안하는 기법을 시뮬레이션으로 검증하였다.