Active Disturbance Rejection Control With Input Constraints

Control input constraints are very common in industrial process, however, conventional controller design methods usually assume that the actuator dynamics is linear. Therefore, when there are rate and/or amplitude constraints in the actuator, the output signal of the actuator is not consistent with the output signal of the controller, which leads to reduced control performance, even system instability. Active disturbance rejection control (ADRC), which is a simple and effective control technique, has been developed rapidly in recent years. Just like other control methods, the control performance of an ADRC is influenced by the control input constraints. This thesis will study the compensation methods for ADRC with control input constraints, and try to solve the practical problem in the application of ADRC.Two compensation schemes are proposed in this thesis where there are magnitude and/or rate limits in the actuator for the linear active disturbance rejection controller (LADRC). In the first scheme, magnitude and rate limits with the same magnitudes as the actuator magnitude and rate limits are added to the input of the extended state observer (ESO). The idea is to introduce more detailed information of the system to the ESO, which can make the ADRC damp the error between the controller output and actuator output as soon as possible. In the second scheme, the error between the controller output and actuator output is considered as a new disturbance signal, which is added to the ESO to estimate, so that the ADRC can eliminate the error. Simulation study is carried on with these two methods for a first order plus dead time process with actuator saturation limit, and the results show that both two compensation methods for LADRC can achieve good control performance.Generation rate constraints (GRC) is an actual problem existing in the power system load frequency control. GRC, which occurs in the internal system rather than directly arises from the actuator, is not same as the magnitude and/or rate limit problem of the actuator. Therefore, the two schemes proposed above cannot be applied to this problem directly. An anti-GRC compensation scheme for LADRC is proposed in this thesis. The scheme is applied to the load frequency control for a single-area power system with generation rate constraints for simulation study. The results show that the proposed scheme has good compensation capacity, and that the proposed scheme is effective.