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，为显著提高电力电子转换器的性能提供了机会。然而，即使使用快速WBG开关，所需的直流电容器仍然很大且容易受到攻击。这是因为直流电容器的大小主要根据低频电压纹波来确定。大约三分之一的变流器故障是由故障的直流电容器引起的，通常一半以上的功率变流器的尺寸被直流电容占据，例如模块化多电平变流器(MMC)中的功率模块。集成电池可以多功能使用，包括提供电网辅助服务，这提高了这种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，因此拟议的研究有望解决锂电池的一个巨大的新市场。该项目将专注于连接到中压交流电网(11-132kv)的电池集成AC-DC转换器。由于系统的可控性，中压AC-DC(MVDC)变流器有望在未来的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，集电极和连接电路的成本才有可能降低17亿GB，前提是它们连接到中压直流。拟议的项目基于由苏格兰电力能源网络公司(SPEN)开发的Angel-DC项目，该项目演示了第一条用于直流电路运行的点对点MVDC链路(30兆瓦，54千伏)。加的夫大学是Angel-DC项目的唯一学术合作伙伴。具体来说，该项目将(1)量化将电池集成到MVDC转换器中的好处；(2)开发先进的MVDC转换器拓扑和控制策略，以集成电池，考虑效率、功率密度和可靠性；(3)制定电池和MVDC转换器的协调保护策略，以确保安全运行；(4)通过分布式分类帐技术协调系统动态，以提供辅助服务。这项研究将在加的夫建立的实验室规模实验平台上进行验证，该平台与Angel-DC项目中的MVDC转换器具有相同的拓扑结构，但额定功率较小。

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.