Key Technologies For The Application Of IEC 61850 To Distributed Controls In Smart Distribution Grids

With the development of national economy,the requirements about power service quality increase significantly from customers and the distribution network plays a more crucial role in improving the reliability of power supply.While the Distributed Energy Resources(DERs)are integrated into the utility grid with an increasing proportion,the distribution network evolves from the traditional unidirectional power flow,to a newer paradigm where the power flows bi-directionally.The fluctuation and intermittent characteristics of DER's output result in a considerable uncertainty of power flow and impact the voltage profile in distribution network.So,the increasing reliability requirements and DER integrations cause new challenges to relay protection and control in the distribution network.Under this circumstance,new control methods have been researched and it turns out that the distributed architecture is a favorable solution to above issues,which incorporates more actors and utilizes the peer-to-peer communication to execute more flexible and advanced control functions.The traditional centralized architecture is becoming less popular to apply control applications because it uses one single decision-making component to process all the data and cannot adapt well to the dynamic topology changes in distribution network.The distributed controls,for instance,the distributed Fault Location,Isolation and Service Restoration(FLISR)scheme can generally reduce the service restoration time from several hours to a few minutes or even less,and can improve the system reliability effectively.Therefore,it is widely favored by the power utilities and attracts much attention of researchers as a promising method.Currently,there are some on-going and finished researches on distributed controls of smart distribution grid,but some key technologies are still to be solved including the aspects of system interoperability,the "Plug and Play" of Intelligent Electronic Device(IED),and adaptability to dynamic topology changes of distribution grids.This thesis extends the DEC 61580 standard's information modelling,commnunication service mapping and configuration philosophy to enhance the interoperability and "Plug and Play" capability of IEDs for Distribution Automation System(DAS).And topology processing methods are presented for IEDs to recognize the realtime topology information autonomously,which enable the distributed controls to automatically adapt to topology changes of distribution grid.The main contributions and innovations of this thesis are summarized as follows:(1)The standardization system and information modelling principle of IEC 61850 are summarized and the application foundation of IEC 61850 is analyzed on background of distributed controls in DAS.It draws a conclusion that both the centralized and distributed control architectures can benefit from the IEC 61850's information model,communication service mapping and System Configuration Language(SCL).Because the object-oriented inform model and SCL description specification are core means to realize the system interoperability and "Plug and Play"capability of IEDs.(2)New Logical Node(LN)classes are modelled where the automatic fault section location(AFSL),fault section isolation(AFSI),service restoration controller(ASRC)LNs are proposed for the distributed FLISR functions and the DER islanding management(DISM)LN is proposed to manage the DER's islanding situations mainly concerned with the Direct Transfer Trip(DTT)protection.All these LNs include the data objects to describe the complicated data flows between distributed function blocks.It also presents the communication service mapping based on the communication mode and realtime performance requirements when exchanging the data in distributed controls.These new LN classes extend the IEC 61850 semantic space as well as data models to cover the domain of DAS and its distributed control applications.Moreover,the modelling metohd is versatile and provides a reference mode for IEC 61850-based information modelling of other distributed applications.(3)Special requirements of the DAS configuration are analyzed consisting of the system boundary of a configuration project,the topology configuration for distributed applications,and the automatic identification and configuration process for IEDs.The SCL schema is extended with elements of Process,Line and other equipment type codes which are able to describe the distribution network topology and functional specification.The planned contents are allocated into a new format of the Configured IED Description(CID)file to facilitate the distributed applications,which contains the descriptions of primary topology,communication system,data models and data flow.Based on the proposed SCL schema,a registry service is designed to assist the automatic identification and configuration of IEDs when they are remotely installed into a DAS.By combining the LN classes and data flow description element "ExtRef"in SCL,this thesie puts forward a method for the dynamic setting of communication data flow between distributed IEDs.These configuration methods provide an IEC 61850 standardized description specification about the information models and communication behaviors to improve the system interoperability required by distributed controls.(4)Applying the proposed IEC61850 configuration information,this thesis presents two autonomous topology processing methods for IEDs' distributed controls.One methoed is based on a loop circuit area and the other is based on a neighborhood area.With these methods,the loop circuit area is modelled as an undirected graph and is expressed by an adjacency list.Then,the Breadth First Search(BFS)is used to detect the connected topology area within the graph and Depth First Search(DFS)is used to find out the routing path between vertexes.In detail,the method based on neighborhood area divides the whole graph into subparts according to the definition of each IED's neighborhood area.It uses the neighbor-to-neighbor communications to fulfill topology processing in a distributed manner.So,it just needs a minor topology configuration and can make convenience for "Plug and Play" of IEDs as well as the system configuration management.It operates more flexiblely and adapts better to the networks which are deployed with a sophisticated distributed functions.It shows an acceptable realtime performance as well.(5)Tests are carried out on a simulated system of active distribution network.The proposed IEC 61850 information models and configuration methods are put into effect.SCL-based configuration files are analyzed and verify the IED's automatic registry and configuration process.Then,the DTT protection is selected as the test case to check the neighborhood-area-based topology processing method.Test results show that the DTT protection can operate correctly in multiple cases of topology reconfiguration and faulty points.Therefore,the distributed topology processing method is able to recognize the topology in realtime and is available to set the data flow links dynamicly for distributed applications.That is,it makes the distribued control applications autonomously adapt to the dynamic topology changes in distribution grid.Conclusively,the extension of IEC61850 standard to distributed controls in DAS can essentially solve the interoperability and "Plug and Play" integration issues,which contributes to the data interactions of distributed controls and reduces the configuration complexity of DAS.The topology processing methods based on IEC 61850 configurations enable the IEDs to autonomously recognize the topology in realtime and adapt to the dynamic topology changes in distribution grids,which facilitate the distributed controls to operate in a more flexible and autonomous way.Therefore,the research results have practical significances to facilitate the distributed controls by improving the interoperability of DAS,and contribute to the development of smart distribution grid.