Active Disturbance Rejection Control Of Multivariable Systems

There are a large number of multivariable systems in the thermal process.Because of the coupling between variables,the control of multivariable is more complicated than that in single variable system.For multivariable systems with small coupling,the controller can be designed using the controller design method of the single variable system by selecting the appropriate matching relationship between variables,so that the good control performance can be obtained.For multivariable systems with a large coupling,how to deal with the coupling between input and output variables is a difficulty when designing controller.The putting forward of effective relative gain can ease the coupling problem in multivariable systems,the relative gain array and relative frequency array of multivariable system reflect the change in the current loop when the other loop is closed.Based on the relative arrays,the approximate model of equivalent transfer function can be obtained.But the approximate model usually has model error.In order to remedy this defect,a controller with strong adaptability and robustness should be selected.As a new control technology independent of the precise model of the controlled object,active disturbance rejection controller(ADRC)estimates the external disturbance and model uncertainty by the extended state observer and compensates it by the control law,which effectively reduces the dependence on the precise model.This article puts forward a method to obtain equivalent transfer function by calculating effective relative gain array.Based on the approximate model,ADRC controller is designed,making full use of the strength ADRC to solve coupling,parameter perturbation,complicated multivariable system controller parameter tuning problem.Then an ADRC scheme for two-input-two-output system is proposed.By inputting the control quantity of the two loops into the extended state observer at the same time,the model information is fully utilized to achieve better control performance.For circulating fluidized bed boiler combustion system,the ADRC controller is designed based on the above two methods.Compared with other existing control strategies,the effectiveness of the two methods is verified from the aspects of tracking and disturbance rejection.For the load frequency control(LFC)in power system,the ADRC controller is designed based on the proposed two methods,and the control performance of the scheme is verified in the three area LFC system,and good control performance is achieved.