Optimal Pump Scheduling: Representation and Multiple Objectives

This paper considers the pump scheduling problem using a multi-objective approach and several alternative representations to a candidate solution. Despite the practical importance of the optimisation of pump scheduling for water distribution networks (WDN), most of the published algorithms restrict themselves to a single objective, i.e., minimise the cost of pumping. Multiple objectives and alternative representations will be the key factors when deciding to apply optimisation algorithms for the real-world operation of WDN. The present work considers a bi-objective problem, where the objectives are: minimise the cost of pumping and maximise the minimum stop time. Solutions to pump scheduling problem are, usually, encoded using a binary string showing the state (on/off) of each pump during each time interval. In this paper a new representation to pump scheduling, based on time controlled triggers, is presented. This representation is capable of restricting the number of pump switches to a specified maximum. Different representations are compared by examining advantages and disadvantages of these methods through empirical experimentation