Active Disturbance Rejection Control Based On The Effective Open-loop Transfer Function Method

Due to the interactions between input and output variables, designing a controller for each loop independently using well established control methods for single-input/single-output (SISO) systems cannot be easily extended to multi-input/ multi-output (MIMO) systems. Although this problem has been widely attacked and some success has been achieved, the design and implementation of controllers for multivariable systems is still a challenge. The introduction of effective open-loop transfer function (EOTF) can successfully decompose MIMO systems into a number of equivalent independent single loops, which also provides a new idea to solve the above problem. However, this equivalent process is inevitable presence of model error, so a better adaptability and robustness controller is needed.In this paper, a decentralized active disturbance rejection control (ADRC) design method based on EOTF for MIMO interactive processes is proposed. The interaction effects for a particular loop from all other closed loops are directly incorporated into, and then, the individual controller of each single loop can be designed directly and independently. ADRC controller is independent on accurate mathematical model, so it can effectively reduce the accuracy requirements during the equivalent process, effectively avoids the problem of repeatedly adjust parameters.Secondly, simulations on two thermal processes like circulating fluidized bed boiler and boiler-turbine coordinate control system are illustrated for demonstrating the validity of the proposed control schemes. These two systems respectively represent two typical multivariable control problems. In the former one has strong coupling between variables, and the latter dynamic characteristic vary widely between subsystems. Compared with the multi-objective optimization algorithm scheme, the proposed method can reach good control effect, reflects excellent disturbance rejection and decoupling ability.Finally, the proposed ADRC scheme is also used to improve the disturbance rejection performance in power system. Take into account the interactions, and then use the concept of EOTF to convert the load frequency control (LFC) system into several equivalent independent single loops, ADRC can treat various uncertain factors as a disturbance and compensate it. Simulations on two area LFC system and three area LFC system have achieved frequency deviation control and get a good decoupling effect.