Research On Real-time And Reliability Guarantee Of Communication Services In Smart Grid

Smart grid is a heterogeneous network integrated with multiple network communication technologies.Meanwhile,it carries various communication services.How to ensure the realtime performance and reliability of key services is an urgent problem to be solved.The openness and interactivity of power grid are enhanced with the development of smart grid in China.And the real-time performance and reliability of communication is further decreased.Regional interconnection of smart grid has become an inevitable trend.Once power outage occurs,it will not only cause power outage losses,but also affect the national economy and society.Therefore,it is significant to conduct research on the real-time performance and reliability of communication services in smart grid.Intelligent substation and wide-area protection system are key communication scenarios of the smart grid.It is necessary to analyze the real-time and reliability requirements of communication services and establish corresponding security measures.The communication system of intelligent substation is build based on IEC 61850.Due to the early proposal of IEC 61850,it cannot well guide the reliable operation of intelligent substations.The service priority specified in IEC 61850 needs to be improved,because it cannot guarantee the real-time performance of key services in intelligent substations under extreme security threats.Due to the long distance,multiple nodes,large capability and complex structure of communication in wide-area protection system,the traditional point-to-point method cannot satisfy its demand.Therefore,the power wide-area protection system has developed into the networked communication.The transformation of communication mode has brought about a series of new problems.Communication mode of exchange network based on TCP/IP has been widely used.While network congestion occurs in the wide-area protection system,the delay of the message based on TCP protocol will increase dramatically.The delay will have a profound impact on safety and stable operation of the power system.Although the UDP protocol has good real-time performance,it cannot guarantee the reliability of the message,a better solution is urgently needed.Therefore,the communication requirements of intelligent substation and wide-area protection system are researched in this paper.The real-time guarantee scheme and reliability evaluation method are proposed respectively to ensure the safety and stable operation of smart grid.The specific work is as follows.1)In order to guarantee the service quality of key services of intelligent substation,the priority classification method adopted by IEC61850 standard is improved,and a more reasonable and detailed priority classification method is proposed.The priority of the intelligent substation service is analyzed according to the three factors of information transmission delay requirement,grid urgency and information volume,and the priority is determined.According o IEEE802.1Q,this paper assigns different levels of priority from 1 to 7 according to the real-time requirements of the intelligent substation service.When the intelligent substation communication network is disturbed or attacked,the burst data flow in the network may cause congestion.The new priority classification method gives higher-level priority values to key businesses,ensuring reliable and reliable delivery of critical services in real time.According to the SPQ scheduling algorithm adopted by the current intelligent substation,after dividing the multi-level priority in the intelligent substation,the real-time demand of the lower priority service cannot be considered.Based on the WRR scheduling theory,and the strict priority mechanism of SPQ algorithm,an improved algorithm PWRR is proposed.The PWRR algorithm can not only guarantee the transmission speed of high-latency demand services,but also take the real-time requirements of other services into account,reduce the impact between various service flows,and meet the service quality requirements of multiple service transmissions in intelligent substations.2)Using the method of information physical fusion system,the reliability evaluation of intelligent substation is studied.By considering the reliability factors in the system and information system and the interaction between them,the intelligent substation power system side is analyzed.Based on the interaction of information network system,a method of quantitative analysis of interaction effects is proposed to obtain the reliability index of intelligent substation in which the primary physical system and the information network system are integrated.On this basis,the Monte Carlo simulation method is used to evaluate the reliability of the intelligent substation,and the D2-1 intelligent substation is used as an example to analyze the results.The evaluation results are in line with the actual situation.At the same time,the Monte Carlo simulation method and the analytical method are combined to get a new method of reliability assessment.3)According to the communication characteristics of the wide area protection system and aiming at the problem of TCP cannot guarantee real-time and UDP cannot guarantee reliability,a UDP transmission scheme based on the mechanism of combining error correction,error detection,and retransmission for application messages is proposed.This scheme can provide low delay and reliable transmission service for applications.An original BCH code is selected as the error correction coding algorithm considering the complexity of the algorithms,and a coding grouping method is designed.An experiment to verify the grouping method is also presented.We conduct theoretical analysis and simulations to verify the real-time of a message after employing the error correction mechanism.To provide reliability under the condition of having burst errors and packet loss,the mechanisms of error detection in the application layer and frame retransmission are further designed,and their real-time performance is analyzed.The analysis reveals that the increased delays are nearly negligible when exploring the mechanisms designed in this study of error correction,error detection,and retransmission.Moreover,this paper presents a comprehensive application algorithm of the scheme and analyzes its reliability.The result shows that the reliability provided by the proposed scheme is higher than the other UDP transmission scheme.Finally,the correctness of the proposed method is verified by programming experiments.4)Based on the communication equipment of wide area protection system and the reliability of information flow,considering the impact of network quality of service such as information flow loss and delay,this paper studies the communication service type and communication path of wide-area protection system.Considering the reliability of communication equipment and information flow comprehensively,this paper establishes the overall reliability model of the wide area protection system.On the base of the above,this paper proposes the multi-service reliability evaluation method of wide area protection system and obtains the key communication nodes for improving reliability.Through the wide area protection system of IEEE14 node power system,the key communication node examples of multi-service are given,which provides a basis for improving the reliability of the wide area protection system.