The Effects of Modelling Strategies on Responses of Inventory Models

This paper describes methods to model inventories from the APVIOBPCS family. It aims to examine the limits of modelling approaches within control-theoretic models using the Simulink package. Discrete and continuous time models were considered together with a finite pipeline delay and the Forrester exponential delay, in continuous and sampled data representation. The main effect of using a finite delay is to deepen the stock-out and increase the required order rate compared with the same response observed with an exponential form delay. Total time for recovery is similar with all models. The discrete performances are close to the continuous representation for a smaller review period. Results presented here illustrate that the various forms of control-theoretic models present similar step response results irrespective of simulation technique used provided they have the same delay type. However, the gains required for minimum cost are substantially different for each delay form and modelling technique used.