Performance, robustness and noise amplification trade-offs in Disturbance Observer Control design

Abstract

In this work, we propose a Disturbance Observer (DOB) with a low pass filter with a single tuning parameter. The DOB can be added to a standard PI controller that is assumed to be controlling the system. Our DOB design can be applied to delayed and non-minimum phase systems and is decoupled from the PI control design. We analyse the impact of the DOB filter time constant in disturbance rejection performance, closed loop robustness and measurement noise amplification. The case of First Order plus Time Delay has been studied leading to a set of figures that highlight the trade-offs between those factors and can guide the designer. For arbitrary systems we propose simple rules and instructions for tuning the single parameter of the DOB, taking into account the trade-off between performance, robustness and noise amplification. Finally, we test our proposal experimentally in a real two-tank system setup.