Research On Microgrid Protection Based On Distributed Decision

In recent years,people pay more and more attention to environmental protection and research on new clean energy and renewable energy,and then push forward the development of distributed power rapidly in power system.EHV long-distance transmission technology has brought many benefits for the power system.But with the economic development,power consumers are increasingly demanding on the reliability of power supply,centralized long-distance power transmission can no longer meet the power requirements.The distributed generator access can be flexible and decentralized to supply for the local load.The advantage is significant.However,the operational characteristics of distributed generators also bring many problems to the stability of the system.Micro-grid is a reasonable and effective solution to the access problem of distributed power.Micro-grid's small energy management system is able to coordinate and manage distributed power supplies in a more decentralized way,reducing the impact and impact of distributed power supply on the system and facilitating the full utilization of clean energy.Micro-grids can operate in parallel,by the large system to balance the power,stabilize voltage and frequency of the micro-grid;it can also be operated in island with distributed power supply directly to the load.As the micro-grid becomes a hot research topic in power system,the protection of micro-grid also becomes an urgent problem to be solved.Due to the unique operation modes of the micro-grid,the protection methods of the traditional distribution network are no longer suitable for the use of the micro-grid.Reliable and efficient protection method of micro-grid is one of the hot points in power system research.In this paper,classify them by reading and analyzing a large number of literatures on the protection methods of micro-grids,aiming at the existing protection methods of micro-grids,according to the applicable scope of protection by.They are respectively:the protection methods applied to the grid-connected operation of the microgrid,the protection methods applied to the islanding operation of the microgrid and the protection methods applied to both two operation modes at the same time.The first two protection methods belong to the protection methods that need the island monitoring.The micro-grid needs the island detection device to identify current operation mode of the micro-grid first,and then switch to appropriate protection device to protect micro-grid.The last one belongs to the micro-grid protection method that does not need islanding monitoring device and it is suitable for various situations of micro-grid.This facilitates the analysis of the advantages and disadvantages of various protections and then facilitates the improvement of methods.Then establish a micro-grid model with inverter distributed power supply.Through the establishment of inverter and control model,build in photovoltaic,wind power,gas turbine inverter power supply,and analyze the distributed power output characteristics and fault characteristics.Then based on the typical structure of microgrid,a simulation model is established to analyze the fault characteristics of microgrids in different operating states in detail laying the foundation for proposing the new protection methods.Through the detailed analysis of the change of electrical quantity and fault characteristics under the grid-connected and island operation states of microgrid,this paper finds out the logical relationship between adjacent lines.By using this relationship,combining over-current protection.wide area protection and distributed decision-making propose a distributed protection method for micro-grid grid-connected operation state based on the STU.And use the simulation model to verify its reliability and feasibility.Then the analogy with the traditional current protection method and the new protection method the traditional under-voltage protection is improved and a new distributed protection method under the microgrid in island is proposed.At present,as the smart grid develops rapidly it can acquire,process,transmit,and make decisions on the information through the intelligent terminal and the communication system so as to quickly determine and isolate the faulty area.However,the distribution structure of distribution network is becoming more obvious.Distributed protection has become a hot spot and trend in micro-grid protection.Therefore.a set of MAS protection system is proposed in this paper.Based on the protection system,a set of protection method applies for various operation conditions of microgrid without islanding monitoring is proposed.Layered MAS system:Device layer-Executive layer-Coordination layer.Each agent has its own functions and responsibilities.The executing agent simplifies,processes and calculates a large amount of electrical quantity information provided by the device agent to obtain a local logic signal,and then,in combination with the corresponding logic signal of the agent executing in the same layer,judges and diagnoses the fault quickly and accurately according to the prescribed criterion isolation.The method takes into account a variety of information,and can determine the fault under various operating conditions of the microgrid.The method also disperses the protection decision-making power to each executive agent without synchronizing sampling and reducing the requirements for the channel.At last,the rationality and reliability of the proposed new protection scheme are verified by PSCAD simulation.