Control of nonlinear systems using filtered high-gain observer

This paper gives a special design of output feedback controller using low-pass filtering high-gain observer for a class of nonlinear systems where nonlinearities satisfy a semiglobal Lipschitz condition. The presence of high-gain observer in the adaptive law delivers a good property of disturbance rejection at the cost of peaking phenomenon as well as reduced robustness. The insertion of low-pass filter at the input signals overcomes the peaking phenomenon and makes the high-gain observer robust to uncertainties in modeling the nonlinear functions. In this way, the proposed technique guarantees that the output feedback controller stabilizes the system and achieves good tracking when the observer gain is sufficiently high. The simulation results demonstrate the high efficiency of our novel design which ensures good tracking for given command with guaranteed robustness.