水下高压直流微网是实现长期、连续、实时、原位观测的海底观测网或其它水下大型直流供电系统的关键基础。随着越来越多的科学研究热点转向海洋，水下高压直流微网将在未来扮演着重要角色，其中，接地故障的诊断与隔离是保证其能够长期可靠运行的关键。本项目针对水下高压直流微网接地故障的效应机理、诊断理论和隔离方法开展相关理论研究。首先，对水下直流微网的构成元素进行分解并分别研究，提出合适的建模方法，并建立微网的系统模型，为故障机理、诊断及隔离提供理论分析基础；然后根据模型研究并获得接地故障对系统稳态和动态特性的影响机理；接着在故障的效应分析结果上开展故障诊断和定位理论及方法研究；为了能够可靠地隔离已定位的故障，提出了一种高可靠性的主动式故障隔离方法；最终，建立完整的水下高压直流微网接地故障机理、诊断与隔离的理论及实现方法，为我国建设海底观测网或者水下直流供电系统奠定理论基础。

Underwater High Voltage Direct Current (U-HVDC) micro grid is the fundament of seafloor observation network that enables long-term, continual, real-time and in-situ observation, or the realization of other large-scale underwater DC powered system. It is becoming an important role in ocean science research with the continuous increase of science interests on ocean, and its Ground Fault (GF) detection and isolation is a key factor for ensuring its system reliability. In this project, research on the theory and method of detection and isolation of GF at U-HVDC micro grid are carried out. Firstly, the elements of the underwater micro grid are decomposed and studied individually. Proper model for each element is proposed, in turn the system model of the whole U-HVDC micro grid is built, which will be the foundation of the following theoretical analysis such as GF effect and detection. Then, the mechanism of fault effect such as the system’s steady and dynamic response with the presence of GF is studied and concluded. Based on the analysis result of GF effect, the GF detection theory and locating methods are proposed and validated; In order to isolate the located fault reliably, a high reliable active fault isolation method is proposed and validated as well. Finally, the effect mechanism, detection theory and isolation method of the GF at U-HVDC micro grid are concluded, which will provide essential theory and realization method for constructing domestic seafloor observation network or other underwater DC powered system.