On External Disturbance Rejection of Linear ADRC

Active disturbance rejection control (ADRC) is a quickly developing practical control technology while its ability to reject external disturbance is necessary to investigate deeply. Focusing on the simple case that the plant is an exactly known second order plant, this paper investigates the external disturbance rejection of linear ADRC. It reveals a separation diagram, in which the external disturbance goes into the output via a bandpass filter. That is the reason why linear ADRC can reject both low-frequency and high-frequency external disturbance.