Disturbance Observers for Second-order Lag Systems Designed without Explicitly Using the Disturbance Generating Model

In this letter, a disturbance observer (DOB) which can asymptotically estimate a step or sinusoidal disturbance by the full-order state observer with only the model parameters for second-order lag systems is studied. The basic idea is to obtain both the observer and the feedback gain matrices which can assign zeros on the imaginary axis and poles in the complex left half-plane of the closed-loop transfer function from the disturbance to the disturbance estimation error. Compared with the traditional DOB, the proposed DOB can generate an observer with a lower order.