Nonlinear steady-state tracking and disturbance rejection with application to power systems

Multi-input, multi-output nonlinear systems with unmeasurable disturbances are considered. Assuming that both the reference signal and the disturbance take constant values or are slowly time-varying, nonlinear static feedback is designed so that, in steady state, the output is equal to the corresponding reference signal, regardless of what the disturbance is. It is shown that, under certain conditions, in steady state, the system output tracks the constant (or slowly time-varying) reference input while rejecting the constant (or slowly time-varying) disturbance. It is also shown that the tracking error can be made arbitrarily small if the reference input and the disturbance are sufficiently slowly time-varying. This method is applied to an infinite-bus, single-machine power generator system