Application Of Networked Control System In Power System

Security control for modern large power grids is a complicated problem with no perfect solution for the time being—the 8.14 blackout that occurred in North America in 2003 substantiated the difficulty to solve the problem. It has been listed as one of the nine pioneer fields of new technology in the journal of Technical Review of America. The control systems used in power system, such as power system emergency control, EMS/SCADA, or voltage and reactive power control, power system protection, and substation automation, all work independently and communicate by peer to peer via private network. In that case, introducing NCS technology to power system will provide a novel solution to the problem of large system security control. Our study, funded by National Science Foundation of China, aims to deal with this problem, especially such aspects as network performance effect on control performance, hydroturbine generating unit, AGC, TCSC and power system integrative information transmission.Firstly, this paper describes the fundamentals of the theory of NCS, including the model, node driven mode, time delay, task schedule and network schedule problems. The upper threshold of time delay in NCS is then presented by means of the network calculus theory, and the idea of using well developed real-time schedule algorithm in NCS is put forward. Based on the proposed NCS theory, some problems in power system NCS are analyzed, including integrative information transmission, impact of time delay on the controlled system, information security, multi-rate sampling, and synchronized sampling, and then the effective solutions to the problems are given.Secondly, in order to study the network performance effects on NCS, the networked excitation system is studied and simulated with networked control simulation tool True time toolbox. The issues of task schedule, network schedule, node driven mode and communication network type in power system excitation system are then addressed. The results of simulation analysis validate that dynamic schedule EDF algorithm can guarantee the performance of networked excitation system in task schedule and network schedule, that event driven mode can perfectly avoid vacant sampling problem in NCS, and that the Ethernet with high band and priority mechanism can guarantee the performance of the NCS based excitation system.Furthermore, a networked AGC model is proposed based on the time-delay dynamic system theory. The time delay dependent stability cretia and the time delay independent stability cretia are compared. As the latter is more conservative and strict in engineering application, a robust controller designed with the former cretia is proposed. The digital simulation of networked AGC demonstrates that the controller designed with the time delay dependent stability cretia has lower conserativity and better performance.The networked based hydroturbine generation unit and its realization are also dealt with in this paper. The uncertain model of time delay is built by the multiplicative perturbations model, and the robust control structure of networked hydroturbine generating unit is thereby deduced; then a controller with both robust stability and performance robustness is designed. The simulation of frequency and load perturbation indicate thatμcontroller has superior control effect than H∞controller and conventional PID controller.Next, the wide-area measuring system (WAMS) based on TCSC networked control strategy is presented. In order to transform the TCSC model with time delay to the conventional model without time delay, the augmented status is introduced. The controller design is based on the discrete sliding mode control theory so as to meet the demand of engineering application. A feasible improvement approach solution is also proposed to overcome the chattering problem. In addition, a single machine to infinite bus system is studied through digital simulations to demonstrate the comprehensive applications of the proposed strategy.Finally, after analyzing the conventional IP QoS model, an integrated information transmission mode based on MPLS is proposed with the characteristics of information transmission in power system in consideration. The results of network simulation indicate that MPLS + DiffServ network has better performance than DiffServ network alone in the power information congestion control, and that it guarantees the time delay and communication reliability of real time control information transmission.