  The extended state observer (ESO) plays an important role in the design of
feedback control for nonlinear systems. However, its high-gain nature creates a
challenge in engineering practice in cases where the output measurement is
corrupted by non-negligible, high-frequency noise. The presence of such noise
puts a constraint on how high the observer gains can be, which forces a
trade-off between fast convergence of state estimates and quality of control
task realization. In this work, a new observer design is proposed to improve
the estimation performance in the presence of noise. In particular, a unique
cascade combination of ESOs is developed, which is capable of fast and accurate
signals reconstruction, while avoiding over-amplification of the measurement
noise. The effectiveness of the introduced observer structure is verified here
while working as a part of an active disturbance rejection control (ADRC)
scheme. The conducted numerical validation and theoretical analysis of the new
observer structure show improvement over standard solution in terms of noise
attenuation.
