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).