Investigation Of Load Frequency Control Under New Circumstances

Load frequency control(LFC),also known as automatic generation control,achieves the stability of power system frequency and tie-line power,and serves as the basis of power system operation and control.In the past decades,significant improvement has be achieved from both theoretical study and engineering practise.Nevertheless,under the new circumstances of modern power systems,LFC begins to face new challenges,which includes: 1)active power allocation scheme design considering the adjustment cost in the background of power markets;2)robustness of LFC scheme considering the aggravation of uncertainty caused by increased active power disturbance;3)LFC reliablity considering cyber security.To solve these problems,under the sponsorship of National Natural Science Foundation of China and State Grid Corporation of China,this dissertation specifically investigates allocation scheme considering both adjustment cost and control performance,active disturbance rejection-based LFC scheme,vulnerability assessment of LFC system cyber security and defense scheme.The main work of the dissertation is summarized as follows:1.To solve the coordination problem in the situation where multiple units participate in frequency regulation,the differences of adjustment cost and control performance among different units are analyzed,based on which an optimal allocation scheme considering both of adjustment cost and control performance is proposed.Firstly,models of units are established,and basic criteria are used to evaluate the frequency control performance of different units.Objective functions reflecting adjustment cost and control performance are presented,and simulation-based optimization model is then constructed.Eventually,the second generation non-dominated sorting genetic algorithm(NSGA-II)is used to calculate Pareto solutions,based on which the optimal allocation scheme is obtained according to different operating scenarios.2.To attenuate the influence of uncertain active disturbance upon system active power balance,a novel active disturbance rejection-based composite feedback and feedforward LFC scheme is proposed.Firstly,LFC control model is deduced.Based on the measurability of system states,three types of disturbance(state)observer,which correspond to the situations where all the states are unmeasurable,partial states are unmeasurable and all the states are measurable,are designed.Then,by the aid of the observer information,attenuation scheme is given by removing the disturbance term in the controlled output channel(area control error,ACE),such that system frequency and tie-line power stability are guaranteed.3.To quantify the influence of cyber attack upon specific components of LFC system,assessment system for vulnerability of LFC system cyber security is presented.Firstly,two types of attack strategy are addressed,and attack scenarios using these two attack strategies are established.By quantifying the attack influences in respect to different attack scenarios,the assessment system is obtained.Finally,classifier-based attack detection scheme is addressed to alleviate the attack influence.4.To analyze the behavior of attackers and design more pointed defense scheme,from the perspective of the attacker,coordinated attack and detection schemes are designed.Two types of attack strategy,including false data injection and load manipulation attack,are discussed.In the meantime,three attack objectives including maximal system frequency deviation,maximal generation deviation and minimal attack cost,are addressed.Based on the objectives and strategies,coordinated attack models are constructed,and optimal attack sequences are calculated.Finally,a threshold-based detection scheme is presented to attenuate the attack influence.