A Multimicroprocessor-Based Fully Digital AC Drive System for Rolling Mills

Theoretical considerations are given for a control scheme to decrease voltage disturbances in a cycloconverter-fed ac drive system, using a form of the vector control concept. The theory has been applied to a multimicroprocessor-based fully digital 72-arm cycloconverter-fed 5000-kW squirrel-cage induction motor drive control system. For speed and position sensors, a high-resolution sine encoder which generates a 15 000-sine wave/r has been developed to achieve high-performance speed regulation, particularly at ultra-low speeds. The factory test results compare far more favorably than those attainable using dc drives. They reveal that the ac drive system is suited to practical applications in main drives for rolling mills, including tandem cold mills.