Theories And Methods For Load Emergency Control Of Cyber Physical Power Systems

With the development of smart grid technology,large number of sensing devices,communication,computing and electrical power equipment are connected through the power grid and communication network to form a multi-dimensional heterogeneous complex system with the integration capabilities of real-time sensing,dynamic control and information services,which is cyber physical power systems(CPPS).Under the environment of CPPS,the acquisition and utilization of multiple wide-area information brings data support for power system analysis and control,but also introduces the risk of communication network failure.In this paper,funded by the National Natural Science Foundation(Theories and Methods for Load Preventive and Emergency Control of Cyber Physical Power Systems,51577030),focused on the frequency stability issues after large disturbance in power system,an in-depth study of theories and methods for load emergency control of CPPS is carried out.The main work content and innovation of this paper are as follow:taking CPPS as the research object,the interaction mechanism between power system and communication system is explored through the power communication services;focused on the specific load emergency control services,with consideration of both utilization of wide-area information and risk of communication failure,the frequency prediction method and emergency control strategy meeting the requirements of online application are proposed;a co-simulation method to support the studies in CPPS is put forward.The specific works are as follow:With the analysis of composition structure in CPPS,the fact that the power system and communication system are interacted through communication services is indicated,and a vulnerability assessment framework to assess the impact of communication system failures on wide-area electric power system operation is proposed.The original research contributions of this paper are that:1)both latency and interruption faults are considered probabilistically to assess the reliability of communication services;2)a multi-level analytic hierarchy process structure is adopted to quantify different impacts of communication services;3)the communication network failure is quantified as the contribution of components to services failure,which is used to illustrate the weakest section of the whole network.A case study of integrated power and communication systems is used to demonstrate the usefulness of the proposed framework.The proposed method can be used to evaluate the vulnerability of communication systems for electric power grids in both static and dynamic states.Taking the load emergency control supporting the frequency stability of power system as the research object,studies of frequency prediction and control strategy are carried out.In this paper,we try to find out the balance between the accuracy and computing speed of the algorithm based on the incompatibility of model or artificial intelligence-based fast prediction method in real-time application.The physical model-based simplified method can remain the connection between physical parameters,but the accuracy is limited;while the artificial intelligence method cannot consider the model connection of original data,and require samples of high quality.Thus,an extreme learning machine method integrated with system frequency response model is proposed to predict the frequency with the consideration of the observability of power nodes.In terms of control strategy,based on the wide-area load emergency control network,an algorithm of using the fast response capability of interruptible load to support the frequency of power grid is proposed.With utilization of the accurate prediction result and the improved sample acquisition method,a precise load shedding strategy is put forward.Then based on the capacity of power nodes and the corresponding communication path parameters,the emergency control capability index of power load nodes is calculated,which is used to dispatch the load shedding requirement.The proposed method can ensure the minimum cost of load shedding and the execution reliability.The event-driven discrete characteristic of communication system and the time continuous characteristic of power system make the researches in power and communication combined system more complex.Simplification of either system’s model should be processed during simulation using single simulation tool,which will bring negative impacts on the accuracy and practicability of the research results.The hybrid simulation platform,which can be used to analyse complex dynamic performance of power and communication combined system,has therefore become the research hotspot in recent years.To summarize the research findings in this field,unified simulation methods,non-real time simulation methods and real time simulation methods are discussed respectively.Simulation tools,system architecture and data synchronization problem are reviewed and analysed in detail,and the time synchronization problem is indicated as the key issue in hybrid simulation research.A new time synchronization method based on state cache is proposed to provide idea for further research.Based on power system simulation tool OPAL-RT and communication simulation tool OPNET,a real-time co-simulation platform for power CPS is proposed with originally developed data transmission interface and conversion module,which can simulate the dynamic characteristics of system precisely with high speed.A case study of load control system demonstrates the reasonability and validity of the platform.