Root-locus method for systems with transport lag

A method is presented for the construction of the root-locus of feedback control systems containing transport lag or distributed lag. The method utilizes an extension of the generalized parameter-plane representation of the system characteristic equation as developed by Siljak. The technique is primarily graphical and can be applied to high or low-order feedback control systems. An example is given in which the root-locus of a linear feedback control system containing transport lag is constructed. In this example the system gain is chosen as the parameter with respect to which the first two root-loci of the system are constructed. Construction of the remaining infinite number of root-loci can easily be accomplished if necessary. An advantage of this method is that a new root-locus is easily constructed from the system parameter-plane curves for a change in value of one of the system parameters.