Nowadays considerable amount of researches belongs to the sliding mode observers (SMOs) since they have good characteristics such as fast estimation, robustness to the uncertainties. But their sensitivity to the measurement noise degrades their quality. In this thesis, SMOs are analyzed from point of view of relay feedback systems. That is, based on the new structure, the relation between frequency of oscillations and accuracy or effecting from measurement noise are analyzed and discussed. Hence this thesis is based on three stages of design. In the first stage, it shows that by appropriate design of a compensator in the frequency domain, estimation of SMO becomes less affected from the measurement noise. However this design results some estimation errors. In the second stage of design, using another compensator, accuracy of SMOs is increased, but it results increasing of sensitivity of SMOs to the measurement noise. At the final stage of design, designing two different compensators, both increasing of accuracy and decreasing of sensitivity to the measurement noise are added to the SMOs. Simulations show the acceptable performance of proposed method, compared to the conventional SMOs.
Keywords: sliding mode observers, nonlinear system, relay feedback, frequency of oscillation, linear compensator.