Date of Award


Degree Type



Electrical and Computer Engineering

First Advisor

Gao, Zhiqiang

Subject Headings

Automatic control, Process control, Stability, active disturbance rejection control stability margin design closed-loop damping infinite radius Nyquist plot enforced plant root locus


In this thesis, the impact of the disturbance rejecter concept and the enforced plant has been explored. In order for the active disturbance rejection controller (ADRC) to provide a reasonable alternative to the industry standard PID controller, it is necessary to develop tuning procedures capable of providing adequate performance with reasonable stability margins. A focus should be placed upon the disturbance rejecter, as it is the heart and soul of ADRC. In this thesis, transfer function analysis of the enforced plant has been performed to connect ADRC with the tools from classical control. The relationship between the gain parameter and observer bandwidth is studied to understand why higher bandwidths are attainable with smaller gains. A root locus technique demonstrates how the enforced plant poles change with observer bandwidth. The Nyquist stability criterion is used to offer tuning methods that satisfy gain and phase margins and ensures a transient that satisfies a given damping requirement. A technique is offered to display the infinite radius encirclements of the Nyquist plot within a finite graph. Analysis is performed on why the controlled response is typically slower than desired and how to correct it