Control of Production-Inventory systems of perennial crop seeds

Abstract

Production planning and inventory control are essential for the logistic performance of breeding companies. In this paper, we discuss such a system for perennial crop seeds in which production during multiple years and a number of growth cycles before production starts are characteristic. Large variations in yield and demand are typical and could easily lead to shortages or excess in seed stock. Both are costly phenomena. For these reasons, production planning as currently done by seed breeders without much technical support is extremely challenging. This paper describes and models the seed production process of a breeding company and examines its impact on inventory levels. The approach involves developing a time-discrete model parameterised with historical data. Subsequently, three control schemes are formulated: a classical feedback–feedforward PID controller, a feedback–feedforward PID controller with a Smith Predictor and a Model Predictive Control scheme. The goal of this paper is to present and validate a novel seed production–inventory model. Only aged plants are destroyed after a fixed number of production cycles. The ordering of new plants is the input control variable. The model represents the multi-year seed production of perennial crop seeds and expands upon the dead-time delay model, which typically does not account for production level uncertainty in production–inventory systems. The parameters of the model create a general approach; for both annual and perennial crop seeds.