Research On Fault Analysis And Multi-Layer Collaborative Protection Schemes For Microgrids

The microgrid is composed of distributed generations,loads,energy storage devices and protective control systems.It is an independent distribution system,which can be controlled,protected and managed autonomously.The power supplied by microgrids is flexible,reliable and high quality.However,due to the large number of distributed generations and the flexible operation modes of microgrids,the traditional distribution network protection is difficult to meet the reliability and stability requirements.Based on the topological structure and operational characteristics of microgrids,this paper divides the fault of microgrids into the fault of key equipment and the fault of lines,establishes the fault handling mechanism of key equipment,and analyzes the fault characteristics of microgrids.On this basis,the operation and regulation manipulating scheme and the multi-layer collaborative inverse-time protection scheme are proposed.The work in the dissertation is shown as follows:(1)For the fault of key equipment,a completed fault handling specification is analyzed and formulated.Some of the anomalies of the equipment cannot be quickly eliminated by the relay protection device,and it needs to rely on the operation and maintenance of microgrids.According to the theoretical analysis and simulation verification,the output characteristics of the distributed generation under different control modes are studied for different types of line faults.(2)This paper presents an operation and regulation manipulating scheme and develops its application.The research establishes a standardized,reasonable and practical manipulating scheme.The scheme focuses on three kinds of microgrids’ manipulations,i.e.key equipment switching,operation mode switching and black start.Based on the combination of the presented scheme,the field data and monitoring screen,an operation and regulation manipulating simulation platform for microgrids is developed.This simulation platform is deployed to the microgrid of an island in Zhejiang Province.(3)This paper proposes a multi-layer collaborative inverse-time protection scheme.According to the diffusion of fault effects,the scheme divides the protection area into the core layer,the regional layer and the system layer.It puts forward an inverse-time differential current(ITDC)protection based on the positive sequence current phasor,and designs a multi-layer cooperative protection algorithm.Besides,to reduce the influence of the non-periodic components on the calculation of phasor,an improved algorithm for phasor calculation is proposed.The simulation model is established in PSCAD/EMTDC,and the effectiveness and reliability of the protection scheme is verified by results.The field application and simulation results show that the operation and regulation manipulating scheme can effectively deal with the key equipment faults of microgrids,and the multi-layer collaborative inverse-time protection scheme can effectively deal with the line faults.They all have good prospects for application.