Integration of Lithium Batteries to Improve Reliability and Power Density of WBG-based Medium Voltage Direct Current Converters

新兴的宽带隙半导体（WBG）通过提高开关频率和降低损耗，为显著改善电力电子变换器的性能提供了机会。然而，即使使用快频率WBG开关，所需的直流电容器仍然很大且易受伤害。这是因为直流电容器的尺寸主要是根据低频电压纹波。大约三分之一的变换器故障是由直流电容器故障引起的，并且通常超过一半的功率变换器的尺寸被直流电容器所占据，例如模块化多级变换器（MMC）中的功率模块。这个及时提出的项目是通过将高性能紧凑型锂电池集成到电源转换器中来减少直流电容器。集成电池可用于多种用途，包括提供电网辅助服务，提高了该解决方案的经济可行性。人们普遍认为，未来的电力系统将由电力电子转换器主导，因此这项研究有望为锂电池开辟一个巨大的新市场。该项目将重点关注连接到中压交流电网（11-132kV）的电池集成交流-直流转换器。由于系统的可控性，中压交直流变流器有望在未来配电网中得到广泛应用。苏格兰的一项研究估计，只有在苏格兰，如果集热器和连接电路连接到中压直流，就有可能减少17亿英镑的成本。拟议的项目是基于角直流项目，该项目由苏格兰电力能源网络（SPEN）开发，用于演示直流电路运行的第一个点对点MVDC链路（30兆瓦，54千伏）。卡迪夫大学是Angle-DC项目的唯一学术合作伙伴。具体而言，该项目将(1)量化将电池集成到MVDC转换器中的效益；(2)考虑效率、功率密度和可靠性，开发先进的MVDC转换器拓扑结构和控制策略，以集成电池；(3)制定电池和MVDC转换器安全运行的协调保护策略；(4)通过分布式账本技术协调系统动态，提供辅助服务。该研究将在实验室规模的实验平台上进行验证，该实验平台已在卡迪夫建立，与角直流项目中的MVDC转换器相比，具有相同的拓扑结构，但功率额定值降低。

The emerging wide bandgap semiconductors (WBG) offer an opportunity to significantly improve the performance of power electronics converters by increasing switching frequency and reducing losses. However, the required DC capacitors stay large and vulnerable even if fast-frequency WBG switches are used. This is because DC capacitors are sized mainly according to low-frequency voltage ripple. About one third of converter failures are caused by failed DC capacitors and it is often that more than half the size of power converters is occupied by DC capacitors, e.g., power modules in Modular Multi-level Converters (MMC).This timely project is proposed to reduce DC capacitors by integrating high performance compact Lithium batteries into power converters. The integrated batteries can be used in a multi-functional way including to provide electric grid ancillary services, which improves the economic viability of such solution. It is accepted wisdom that future power systems will be dominated by power electronics converters, so the proposed study is expected to address a large new market for Lithium batteries.The project will focus on battery-integrated AC-DC converters connected to Medium Voltage AC grid (11-132kV). Medium Voltage AC-DC (MVDC) converters are expected to be widely adopted in future distribution networks for system controllability. A study in Scotland has estimated a reduction of £1.7bn in the costs of the collector and connection circuits would be possible only in Scotland if they were connected to Medium Voltage DC. The proposed project is based on the Angle-DC project, which is being developed by Scottish Power Energy Networks (SPEN) to demonstrate the first point-to-point MVDC link (30 MW, 54 kV) for operation of a DC circuit. Cardiff University is the only academic partner of the Angle-DC project.In detail, the project will (1) quantify benefits of integrating batteries into MVDC converters; (2) develop advanced MVDC converter topologies and control strategies to integrate batteries, considering efficiency, power density and reliability; (3) develop co-ordinated protection strategies of batteries and MVDC converters for safe operation; (4) co-ordinate system dynamics through distributed ledger technologies to provide ancillary services. The research will be verified on a lab-scale experimental platform, which has been established at Cardiff and has the same topology but down-scaled power ratings compared to the MVDC converters in the Angle-DC project.