Influence of transfer function zeros on controller parameters

The paper is devoted to the influence of transfer function zeros on state feedback controller parameters. Nowadays, during the modal control system design process, the most attention is paid to the analysis of transfer function poles. If transfer function zeros are located closely to the poles, the control object tends to singularity, when the influence of the input control signals to the output signals becomes weaker. This fact leads to the designing of state-space controllers with extremely high values of control coefficients. Available methods for selecting the desired poles of closed loop systems are represented by the following variants: quantitative evaluation of the controllability and observability of object models and object model reduction. These methods have some disadvantages: dependence on the state-space representation of the control object model, ignoring some parts and characteristics of the control object model. In this paper, to analyze the state feedback controller parameters the invariant of the state-space representation characteristic is used – catalecticant (Hankel) matrix. As a result, it was found that control coefficients of the state feedback controller are inversely proportional to the determinant of the catalecticant matrix of the control object, and the determinant of the catalecticant matrix is equal to the resultant of transfer function polynomials. A method of converting the block diagram of the control object model using the residues of the transfer function was suggested. As a result of the conversion, poles, which cause high values of control coefficients, are isolated as a multiplicative uncertainty in the object model structure. The robust control theory can be used for control system designing with such organization of the control object.