Active Disturbance Rejection Control

Lumping model error and external disturbances into one ‘total disturbance,’ estimating it in real time, and canceling it out.

Active disturbance rejection control was developed by Chinese scholar Jingqing Han in the 1990s and introduced systematically in English in his 2009 paper ‘From PID to Active Disturbance Rejection Control.’ Rather than pursuing an accurate model, it needs only the system's order and a rough estimate of the control gain b₀; it lumps unmodeled dynamics, parameter changes, and external forces into a single ‘total disturbance’ f, treats that as an extra state, and estimates it in real time with an extended state observer (ESO, an algorithm that estimates internal states from inputs and outputs), then subtracts it from the control signal: u = (u₀ − f̂) / b₀. After cancellation, the plant behaves approximately like a chain of integrators, which a simple PD can then control well. The original version also includes a tracking differentiator and nonlinear feedback; the more commonly used linear ADRC only needs the observer bandwidth and controller bandwidth tuned, a bandwidth-based tuning approach that traces to Zhiqiang Gao's 2003 work. It resembles disturbance-observer approaches, though those usually need a nominal model; unlike adaptive control, it doesn't estimate specific parameters.

ExampleWhen a joint motor's load or friction changes with temperature, PID often needs retuning; ADRC instead folds all such changes into the total disturbance for the ESO to estimate and compensate, and the linear version mainly needs just two parameters tuned — observer bandwidth ω_o and controller bandwidth ω_c.

Also called

ADRC, Linear ADRC, LADRC, Extended State Observer Control

Related

Proportional-Integral-Derivative Control · Disturbance Observer · State Observer · Robust Control · Adaptive Control

Sources

Wikipedia: Active disturbance rejection control
Han J. From PID to Active Disturbance Rejection Control. IEEE Transactions on Industrial Electronics, 2009
Herbst G. Transfer Function Analysis and Implementation of Active Disturbance Rejection Control (arXiv:2011.01044)