REDUCED ORDER EXTENDED STATE OBSERVER WITHOUT OUTPUT DERIVATIVE IN ADRC

Abstract

As an observer based method; the ESO in ADRC introduces more phase lag when the observer order becomes higher. The key detriment of phase lag is the reduction of loop stability. A way to decrease the phase lag is to employ a RESO. Nevertheless, the underlying disadvantage of this approach is that RESO computation depends on output derivative. To overcome this problem, the derivative of the output is usually approximated from the difference of two neighbouring output sample values. However, this approach is not convenient for two raisons. First, the use of simple differences to derive the output is another source of phase lag. Second, observers are particularly sensitive to noise and derivative gains amplify noise increasing the sensitivity of the RESO. In this work, it is employed a method to obtain a RESO that does not depend on the output derivative. It is also developed the reduced order version of the GESO.