Construction of reduced state observers for systems with affine disturbances

The object of study is linear single-channel systems with affine parametric and external disturbances, presented in the so-called triangular form "input-output". The relative degree in control is equal to the dimension of the state vector and does not change upon transition to the canonical form "input-output" under the assumption of smoothness of external disturbances. It is known that for such systems, only by measuring the output variable, it is possible to construct an observer of mixed variables and restore linear combinations of state variables and external influences with a given accuracy. The estimates obtained are sufficient for the synthesis of dynamic feedback, which provides tracking of the output variable of a given signal. The paper considers an important practical case when, for a certain set of sensors, the output (adjustable) variable is not measured. It is necessary to design a reduced state observer for its evaluation in order to proceed to the construction of a mixed variables observer. First, motivating examples of second-order systems with different dimensions and different channels of action of external disturbances are considered. It is shown that when measuring both state variables with the help of piecewise linear corrective actions of the state observer, it is possible to restore external disturbances by their influence on the system (i.e., without using a dynamic disturbance generator). Conditions are formulated under which this principle can also be used in a system with external disturbances and incomplete measurements to restore an unmeasured state variable. The results obtained are extended to finite-dimensional single-channel systems of arbitrary order with affine disturbances, in which the output variable is not measured. The conditions of existence and the method of synthesis of a reduced observer with a piecewise-linear corrective action, which gives an estimate of the output variable, are formalized. The developed approach does not require the identification of external disturbances and solves the problem of observing the output variable with any given accuracy.