Research On Load Frequency Fault Tolerant Control Methods For Power Systems

The load frequency control schemes of power systems have been widely used.However,due to the influence of various interference factors,the stability of power systems is often difficult to ensure accurately.When failures,load changes,parameter uncertainties and other factors are imposed on the power systems,effective control schemes are urgently needed to maintain the normal operation of the systems.Based on the robust control theory,this paper combines the definition of Lyapunov stability,linear matrix inequality technique,prescribed performance function and other contents to study the load frequency fault-tolerant control methods in one-area and multi-area power systems.The main research contents are as follows:(1)The problem of load frequency control in one-area power system based on failure distribution is studied.Firstly,according to the distribution characteristics of failures,a novel random failure model is proposed.By constructing Lyapunov function,a sufficient condition is obtained to ensure the stability of the power system.Due to the existence of coupling terms,the conventional method of variable replacement cannot be used.By transforming problem of processing coupling terms into a W-problem,a method of designing failure-distribution-dependent load frequency fault-tolerant controller is proposed.Through Matlab simulation experiments,the diagrams of overall distribution and trend of partial failure with two different probability conditions are obtained,as well as the system state trajectories under these two probabilities.The final trend of each state component towards zero indicates that the designed fault-tolerant controller can maintain stability of the system.(2)The problem of load frequency non-fragile fault-tolerant control for multi-area interconnected power systems with actuator failures is studied.Considering the exchange power of tie-lines between various regions,combining multiple time delays,actuator failures and other problems,the stochastic failure model of multi-area interconnected power systems is reestablished.Considering additive perturbation and multiplicative perturbation of controller gain,corresponding load frequency non-fragile fault-tolerant controllers are designed,respectively.Taking three-area power systems as the simulation object,the probability distribution of partial failure in each region with two types of perturbations and the trajectories of each state component in each region of the system are obtained,demonstrating the effectiveness of the designed non-fragile fault-tolerant controller and the advantages of the controller designed based on additive perturbation.By comparing the comparison scheme,the significance of the designed controllers are further explained.(3)The problem of load frequency fault-tolerant control with prescribed performance for fault multi-area interconnected power systems is studied.Firstly,the prescribed performance constrained conditions of load frequency control are given,and the constrained conditions are incorporated into the design process of load frequency fault-tolerant control by Taylor expansion.The auxiliary matrices are introduced and the method of variable substitution is adopted to obtain sufficient conditions for designing load frequency fault-tolerant controller under constrained condition,so that the closed-loop system can satisfy the prescribed performance constrained conditions while working stably under the situation that failures exist.In Matlab simulation,the frequency deviation satisfies different performance constraints in each region and the state response of each region ultimately tends to zero.From this,we can realize that the designed controller maintains the system’s stability while meeting the prescribed performance constraints.