Analysis,Design And Tuning Of Linear Active Disturbance Rejection Control

Active disturbance rejection control(ADRC)has gradually attracted attention due to its spontaneous estimation and suppression ability of "total disturbance".At the same time,its successful application in the industrial field shows its wide application prospects,but its theoretical research needs to be further strengthened.Starting from the subject of Linear ADRC(LADRC)design,analysis and parameter tuning,this paper studies the parameter tuning problems of second-order LADRC and modified ADRC for time-delay systems,and the analysis of modified ADRC based on internal model control(IMC)and the EF-ADRC based power system load frequency control(LFC)problems.The main research results are summarized as follows:1)For LADRC,the parameters can be tuned via the bandwidths of the ESO and the feedback control,thus an LADRC can be regarded as a fixed-structured controller with several parameters to tune,just like a PID controller.The tuning rule of the second-order LADRC is proposed,with the aim to minimize the load disturbance attenuation performance in the integral of time square error sense,under the constraint of a specified robustness measure for the first-order processes with deadtime(FOPDT).The validity of the tuning rule is verified by testing for a variety of benchmark systems and the gravity drained tanks case.2)The tuning rules are obtained by integral time absolute error optimization with robustness constraints for two modified ADRCs based on the FOPDT.They are denoted as delayed designed ADRC(DD-ADRC)and Smith predictor based ADRC(SP-ADRC),respectively.A unified parameters tuning method should be developed to improve the performance and broaden the applications.3)The two-degree-of-freedom internal model control(TDF-IMC)is used to analyze two model-assisted modified ADRCs(MADRCs),which are SP-MADRC and predictor observer based ADRC(PO-MADRC).It is simply interpreted and tuned through the equivalent TDF-IMC by using the delay-free part of the system and time-delay sysytem itself as the nominal model for the IMC design and selecting the bandwidths of feedback control and ESO for MADRC as the inverse of the time constants of the setpoint filter and the disturbance-rejection filter in IMC,respectively.In this way,the two controllers can not only achieve structural equivalence,but also consistent control performance.4)An estimated flatness-based ADRC(EF-ADRC)is proposed for the LFC of power systems.Different from the traditional ADRC design,the selections of the order and the gains of the flatness-based ADRC controller are based on the flatness output,which is a linear combination of the system states,rather than the nominal integral cascade model.In addition,an extra ESO is adopted to estimate the system states and the unknown external disturbance.The former is used to replace the actual system states in the flat output,and the latter is used in trajectory planning of the estimated flat output to achieve the unbiased tracking.The proposed method is also extended to a four-areas system,and the simulation results show that the proposed method can achieve satisfactory performance.More importantly,The proposed EF-ADRC provides a general method for the systems with unmeasured flat output.