Coordinated control of relay feedback control systems for electrical power cost reduction

A study was undertaken to determine if coordinated control could be used to reduce the peak electrical demand for a group of cycling controllers. In this study, a bank of six aluminum furnaces was modeled and studied with a computer simulation. In this simulation, random disturbances in weight were used to simulate adding and removing aluminum from the furnaces. Three coordinated control algorithms were developed and simulated. These algorithms included a fixed and floating maximum number of units on at a time and a scheme in which adjacent units shared a duty cycle. Electrical cost savings from these algorithms was from 15 to 30%, depending on operating conditions.

Two proposed methods of implementing coordinated control are a digital controller and a simple system of relays and switches. The simpler implementation provides the quicker return on investment and an easy way to test the coordinated control concept. The digital control system is more expensive but offers the advantage of being a development system in which different algorithm variations can be implemented and tested. Success in this application should provide an incentive for considering coordinated control in other applications.