Approximation of linear active disturbance rejection control with PID control

Linear active disturbance rejection control (LADRC) is a new type of control method which combines modern control theory with PID control. It was shown that PID can be converted into LADRC in the literature, however, whether LADRC could be approximated with PID, and how the approximation is, is still unknown. This paper first shows that the integral function of LADRC is actually included in the estimation and compensation of the total disturbance, and further illustrates the relationship between second order LADRC and PID. According to the different order of LADRC, the strategy of practical PID + nth-order lead/lag compensator is proposed to approximate the LADRC. Simulation examples show that the second-order and third-order LADRCs have similar performance in disturbance rejection with the approximated PID respectively, but higher-order LADRC is better than the approximated PID. Therefore, LADRC is an extension of traditional PID and has a better application prospect in industrial process control. © 2020, Editorial Department of Control Theory & Applications South China University of Technology. All right reserved.