배터리 에너지 저장 장치의 충전 요소에 대한 전압 평형화 연구

Abstract

본 논문은 배터리 에너지 저장 장치의 충전 요소를 충전, 방전시키는 양방향 DC-DC 컨버터와 이 충방전 과정에 의해 발생하게 되는 전압 불평형을 해결하기 위한 전하 균일 장치를 제안한다. 단일 전하 균일 장치의 균일화 속도를 향상시키기 위해 새로운 스위칭 방법을 제안한다. 제안된 스위칭 방법은 균일화 전하가 과 충전된 배터리 셀에서 충전이 부족한 셀로 바로 이동하기 때문에 빠른 균일화가 가능하다. 또한 배터리 셀 전압을 측정하지 않고 동작할 수 있기 때문에, 기존 스위칭 방법보다 시스템 크기와 가격을 줄일 수 있지만 배터리 스트링이 길어질 경우 하나의 다권선 변압기에 많은 수의 배터리 셀을 연결해야 하는 실행상의 문제점을 지니게 된다. 이러한 문제를 해결하기 위해 단일 전하 균일 장치의 새로운 스위칭 방법과 회로 구성에 근거하여 모듈 전하 균일 장치를 제안한다. 모듈로 구성되어 있기 때문에 유연한 균일 장치 설계, 낮은 전압 스트레스, 빠른 시간에 충전 요소의 균일화 등 장점을 갖는다. 또한 모듈 사이에 추가적인 장치들을 사용하지 않고 다권선 변압기의 자화 에너지를 이용하여 모듈 균일화를 달성하기 때문에 모듈화와 관련된 크기, 가격, 손실로부터 영향을 받지 않는다. 하드 스위칭 방식을 사용하는 기존 양방향 DC-DC 컨버터의 문제를 해결하기 위해 새로운 양방향 DC-DC 컨버터를 제안한다. 공진 셀을 이용하여 컨버터의 주 스위치 전압 및 전류의 스트레스 증가 없이 영 전압 스위칭을 수행하기 때문에, 스위칭 손실과 EMI 노이즈가 저감된다. 또한 제안된 컨버터는 단일 공진 인덕터를 사용하기 때문에, 구성이 간단하고 크기와 무게를 줄일 수 있는 장점을 갖는다. 이론적 동작을 확인하고 성능을 평가하기 위해서, 두 개의 모듈로 구성된 전하 균일 장치와 1kW 급 양방향 DC-DC 컨버터에 대한 실험을 수행하여 검증한다. |This paper proposes the bidirectional dc-dc converter, which charges and discharges charge units of battery energy storage system, and charge equalizers to solve the voltage unbalancing caused by charge and discharge process. A novel switching method is proposed to improve equalization speed of the single charge equalizer using the multi-winding transformer (SCEMT). Since the proposed switching method directly transfers the electric charges from the overcharged battery cells to the undercharged battery cells, it is possible to achieve fast equalization than with the conventional switching method. Furthermore, the SCEMT can reduce the system size and cost because voltage sensing circuits are not required for each battery cell. However, the SCEMT is difficult to apply into a long series-connected battery string because it suffers from the problems related to the implementation of multiple-winding in a single transformer. To overcome these difficulties, a novel module charge equalizer (MCE) based on the proposed switching method and configuration of the SCEMT is proposed. Due to the modularization, the MCE have many advantages, such as flexible equalizer design, low voltage stress for the devices, and high-speed equalization. Furthermore, instead of using additional components between modules, since the proposed MCE utilizes the magnetizing energy of the multi-winding transformer for equalization between modules, it does not suffer from the size, cost, and loss that are related to the modularization. A novel bidirectional dc-dc converter is proposed to overcome problems of the conventional bidirectional dc-dc converter using hard-switching. To achieve zero-voltage-switching (ZVS) for the main switches without increasing their voltage and current stresses, the proposed bidirectional dc-dc converter utilizes a resonant cell. Due to the single resonant inductor, the proposed bidirectional dc-dc converter has the advantages of simple implementation and reduced size. These new features of the proposed bidirectional dc-dc converter provide higher efficiency and lower EMI noise than the conventional bidirectional dc-dc converter. In order to verify the theoretical operation and evaluate the performance, the experiment is performed with the two-module charge equalizer prototype and 1kW rated bidirectional dc-dc converter prototype.; This paper proposes the bidirectional dc-dc converter, which charges and discharges charge units of battery energy storage system, and charge equalizers to solve the voltage unbalancing caused by charge and discharge process. A novel switching method is proposed to improve equalization speed of the single charge equalizer using the multi-winding transformer (SCEMT). Since the proposed switching method directly transfers the electric charges from the overcharged battery cells to the undercharged battery cells, it is possible to achieve fast equalization than with the conventional switching method. Furthermore, the SCEMT can reduce the system size and cost because voltage sensing circuits are not required for each battery cell. However, the SCEMT is difficult to apply into a long series-connected battery string because it suffers from the problems related to the implementation of multiple-winding in a single transformer. To overcome these difficulties, a novel module charge equalizer (MCE) based on the proposed switching method and configuration of the SCEMT is proposed. Due to the modularization, the MCE have many advantages, such as flexible equalizer design, low voltage stress for the devices, and high-speed equalization. Furthermore, instead of using additional components between modules, since the proposed MCE utilizes the magnetizing energy of the multi-winding transformer for equalization between modules, it does not suffer from the size, cost, and loss that are related to the modularization. A novel bidirectional dc-dc converter is proposed to overcome problems of the conventional bidirectional dc-dc converter using hard-switching. To achieve zero-voltage-switching (ZVS) for the main switches without increasing their voltage and current stresses, the proposed bidirectional dc-dc converter utilizes a resonant cell. Due to the single resonant inductor, the proposed bidirectional dc-dc converter has the advantages of simple implementation and reduced size. These new features of the proposed bidirectional dc-dc converter provide higher efficiency and lower EMI noise than the conventional bidirectional dc-dc converter. In order to verify the theoretical operation and evaluate the performance, the experiment is performed with the two-module charge equalizer prototype and 1kW rated bidirectional dc-dc converter prototype.