Sampled-data-based Load Frequency Control For Power Systems With Open Communication Networks In Loop

A clean,low-carbon,safe and efficient energy system has become the direction of the energy development reform in China.Building a new generation of power system is a key step to realize energy reform.The new generation of power system is an intelligent power system with a highly cyber-physical integration,and an open communication network is the basic framework to realize its main function.Load frequency control(LFC)employs the open communication network for measurement signals collection and control signals distribution.However,the usage of the open communication network may bring challenges of the time delay and bandwidth limitation of communication network,as well as network security to the LFC system.In addition,the practical LFC system is a sampled-data control system,and the update of control signal has a large period.Therefore,for the power systems with open communication network in loop,this dissertation fully considers the possible problems of transmission delay,communication bandwidth and denial-of-service(Do S)attack of communication network as well as some practical problems in LFC,and investigates in-depth the design of LFC scheme.The research contents are summarized as follows:(1)For ideal sampling control network environment and the reduction of the overall inertia of power system caused by large-scale wind power grid connection,a discrete and fast state-feedback LFC scheme is proposed.Firstly,based on the sampled-data control theory,an LFC system model is established.Next,based on the Lyapunov direct method,the stability criterion of the LFC system considering sampling is proposed.Then,the exponential decay rate is introduced to guide the design of LFC with fast frequency response performance.Finally,the simulation tests are carried out based on the LFC system of one-area,traditional two-area with wind power grid connection and deregulated three-area with wind power grid connection.Test results show that the proposed control scheme can guarantee the stable operation of the LFC system in a large control signal renewal period and provide a fast frequency response.(2)For sampling control network environment with transmission delay,a robust proportional-integral LFC scheme is proposed to solve the problem of parameter uncertainty and enhanced volatility in power system after renewable energy sources are connected to the grid.Firstly,based on the sampled-data control theory,a proportional-integral LFC model considering transmission delay and sampling is established.Under this model,the stability criterion of LFC system considering sampling and transmission time delay is proposed based on the Lyapunov direct method.Then,parameter uncertainty and H_?robust performance evaluation conditions are proposed to guide robust LFC design.Finally,the simulation tests are carried out based on a one-area LFC system and a three-area LFC system with renewable energy sources.Test results verify that the proposed control scheme can guarantee the stable operation of the LFC system and alleviate the influences of the uncertainty of transmission delay,sampling and system parameters and the fluctuation of renewable energy sources output.(3)For the periodic sampling control network environment with communication bandwidth limitation,an adjustable event-triggered LFC scheme oriented to control performance standards is proposed to solve the problem of communication burden and computation burden.First,the event-triggered communication strategy is introduced into the LFC,and an event-triggered LFC model considering the transmission time delay and periodic sampling is established.Under this model,based on the Lyapunov direct method,the stability criterion of the event-triggered LFC system considering the transmission delay,periodic sampling and threshold parameters is proposed,and the initial parameters of the proposed control scheme are designed.Then,based on the control performance standards,a dynamic adjustment scheme is proposed to adjust the threshold parameters of the event-triggered LFC system.Finally,simulation tests are carried out based on IEEE 9-bus test system and IEEE 39-bus test system.Test results verify that the proposed control scheme can reduce the communication burden and computation burden and meet the requirements of frequency control performance standards in LFC system.(4)For the aperiodic sampling control with communication bandwidth limitation,a fuzzy adjustable event triggering LFC scheme based on control performance standards is proposed to reduce the communication burden,computational burden and the generating unit wear and tear.First,the fuzzy control is introduced into the event-triggered LFC system,and the fuzzy event-triggered LFC system based on the control performance standards is established.Then,based on the Lyapunov direct method,the stability criterion of the fuzzy event-triggered LFC system considering the transmission delay,aperiodic sampling,fuzzy gain and threshold parameter is proposed.In addition,based on the stability criterion,a threshold parameter dynamic adjustment scheme is proposed to adjust the triggering conditions of the event-triggered LFC system for frequency control performance standards.Finally,simulation tests are carried out based on a one-area LFC system and an IEEE 39-bus test system.Test results verify that the proposed control scheme can reduce the communication burden and computation burden and meet the requirements of frequency control performance standards in LFC system.(5)Aiming at the problem of packet loss caused by Do S attack in periodic sampling control network environment,a resilient LFC scheme based on switching system is proposed.First,the Do S attack duration is set as the switching signal,and a switched LFC system model considering Do S attacks is established.Then,the stability criterion of the LFC system considering the duration and frequency of Do S attacks is proposed.Given the duration of Do S attacks and the frequency of attacks,a resilient proportional-integral-type controller is designed to resist Do S attacks.In addition,a dual-loop communication network is equipped in the LFC system to improve the reliability and resilience of the LFC scheme.Finally,the simulation tests are carried out based on traditional and deregulated three-area LFC system.The test results verify that the proposed control scheme can resist Do S attack to a certain extent and ensure the stable operation of LFC system.On the basis of the above research contents,the future research of LFC system is prospected from renewable energy sources'participation in frequency regulation of power system and the conservatism of DOS attack quantification.