基于MMC的中压直流配电网稳定控制与故障穿越方法研究

Modular Multilevel Converter Based Medium Voltage DC Distribution Network (MMC-MVDC) presents clear advantages such as power flow controllability, high quality of power supply, flexible access to distributed generation, quick response and so on. With these advantages, MMC-MVDC provides a feasible choice for smart grid and energy internet. However, the stability control and fault ride through capabilities are the two key technology bottlenecks for the application of MMC-MVDC. In this context, for the weak damping and low inertia characteristics of MMC-MVDC, small-stability analysis model of MMC-MVDC is developed. Based on which the influence mechanisms of control parameters and key equipment parameters on the small-stability of MMC-MVDC are revealed, so as to solve voltage oscillation and voltage instability caused by multiple converters connection. Based on small-stability analysis of MMC-MVDC, the droop coefficient online setting strategy based on fast communication and the adaptive droop control strategy are proposed, so as to solve the voltage surge/fluctuation problems caused by power fluctuation and multi operation modes switching, achieving security and stable operation of MMC-MVDC. Besides, the DC faults ride through methods are studied to solve the short-term shutdown problem caused by DC faults, achieving reliable and continuous operation of MMC-MVDC under DC faults. Finally, the dynamic simulation experimental platform of MMC-MVDC is built to verify and correct the above theory and key strategies. The research will break through the stable and reliable continuous operation bottleneck of MMC-MVDC, so as to promote the engineering application and development of MMC-MVDC.

基于模块化多电平换流器的中压直流配电网（MMC-MVDC）具备潮流可控、供电质量高、分布式电源灵活友好接入等优良性能，适应智能电网的发展需求。然而，稳定控制和故障穿越能力是限制其推广应用的两大技术瓶颈。首先，本项目针对多换流器并网MMC-MVDC呈现弱阻尼、低惯性的特点，研究MMC-MVDC小扰动稳定数学模型，揭示控制参数对小扰动稳定的影响机理。以此为基础，针对功率波动、多运行方式切换引起的电压冲击及波动等问题，研究基于通讯的下垂系数在线整定和自适应下垂控制方法，保障MMC-MVDC的安全稳定运行。然后，研究故障限流器、直流断路器动作特性及匹配原则，结合小扰动稳定机理，研究MMC-MVDC故障穿越方法，保障其在直流故障下可靠连续运行。最后，搭建直流配电网实时数模混合仿真平台，对上述理论进行验证和反馈校正。本项目研究成果将突破安全稳定、可靠连续运行技术瓶颈，推进MMC-MVDC的工程应用。

在能源革命，“碳达峰、碳中和”，新型电力系统的背景下，新能源发展前景巨大。然而，新能源天然具有强随机性和间歇性的特点，直接接入交流配电网会对电能质量产生很大的影响。常见的分布式电源主要有光伏电池、燃料电池、风力发电和燃气轮机等，这些电源产生的电能均为直流电或可通过简单整流后变为直流电，所以将分布式电源接入直流母线不仅能够节省大量换流环节及损耗，而且直流母线可以作为缓冲环节降低分布式电源功率波动带来的负面影响, 满足分布式电源灵活、高渗透率接入的需求。在此背景下，基于MMC的中压直流配电网（MMC-MVDC）是具备良好的发展前景和应用需求。然而，稳定控制和故障穿越能力是限制MMC-MVDC推广应用的两大技术瓶颈。本项目提出适用于MMC-MVDC小扰动稳定分析的模型，准确描述MMC-MVDC的动态响应特性，揭示控制参数和关键设备参数对MMC-MVDC小扰动稳定的影响机理，以解决多换流器并网引起的直流电压振荡、电压失稳等问题，为稳定控制和故障穿越提供理论基础。提出鲁棒性高、抗扰能力强的MMC-MVDC下垂系数、下垂工作点自适应变化的下垂控制方法，提出了“调控一体”控制方法、等负载率主从控制方法，以解决间歇性分布式电源和随机性负荷功率波动、多运行方式切换引起的直流电压冲击及波动等问题，实现MMC-MVDC的安全稳定运行。提出了一种适用于柔性直流电网的直流侧故障穿越通用原理，在此基础上，提出了MMC-MVDC故障穿越方法，以解决MMC-MVDC短时停运问题，通过协调换流器、混合式直流断路器和故障限流器快速隔离故障，实现MMC-MVDC可靠连续运行。项目成果对解决MMC-MVDC安全稳定可靠运行难题提供了技术支撑，有益于推动MMC-MVDC的发展和工程落地，推动新能源的发展，推进“双碳”进程，具有重要的科学意义和工程实践价值。