Periodic disturbance cancellation by using dual-input describing function (DIDF) method

The issue of rejecting periodic disturbances arises in various applications dealing with rotating machinery. A new method using DIDF (dual-input describing function) is presented for the rejection of periodic disturbances with uncertain frequency. This can be added to an existing feedback control system without altering the closed-loop system stability. The objective is to design a nonlinear compensator to secure specified oscillation amplitude and frequency which are the same as disturbances. We suggest two procedures to determine coefficients for DIDF´s synthesis. The structure of the proposed DIDF is so simple that we can easily synthesize. A number of computer simulations were carried out to demonstrate the salient feature of the proposed DIDF compared to the conventional ones (that is, adaptive algorithms).