Retrofit of a Hot Rolling Mill Plant with Three-Level Active Front End Drives

This paper analyzes the advantages of a selective retrofit of the drives in a hot rolling mill plant. More specifically, three cycloconverter-based drives of the finishing rolling mill in the plant are proposed to be replaced by back-to-back converters, thus enabling an efficient management of the active and reactive power flows and improving the control of harmonic emissions. Three-level converters are utilized due to the high rated power and voltage of the roller motors. The retrofit is aimed to achieve the control of reactive power flows, active power losses and voltage stability at the coupling point, as well as the reduction of harmonics, the possibility of regenerative braking and the decrease of unscheduled shutdowns in the event of passive filtering trips. The study is based on real plant measurements, simulation tests and results from an experimental platform built at scale.