  To support the adoption of active disturbance rejection control (ADRC) in
industrial practice, this article aims at improving both understanding and
implementation of ADRC using traditional means, in particular via transfer
functions and a frequency-domain view. Firstly, to enable an immediate
comparability with existing classical control solutions, a realizable transfer
function implementation of continous-time linear ADRC is introduced. Secondly,
a frequency-domain analysis of ADRC components, performance, parameter
sensitivity, and tuning method is performed. Finally, an exact implementation
of discrete-time ADRC using transfer functions is introduced for the first
time, with special emphasis on practical aspects such as computational
efficiency, low parameter footprint, and windup protection.
