In this paper,the extended state observer (ESO) is brought into the frequency domain to show to what degree it forces the plant to behave like cascaded integrators and what can be done to improve the performance when the ESO is bandwidth limited.In particular,a root locus technique is used to show how the poles of the modified plant change as the ESO bandwidth increases.Based on the insight obtained,three correction techniques are explored to improve the system performance for those applications with a low ESO bandwidth.With these proposed techniques,the closed-loop system bandwidth is no longer as severely constrained by the ESO bandwidth as in the original ADRC.
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