Design and control of digital DC drives in steel rolling mills

This paper presents new technology of DC Drive mill system in modern steel manufacturing industry. The presented system consists of ac-to-dc PWM converters for both armature and field to drive 700KWseparately excited DC motor and every motor is controlled by two DC Drives one for armature and another is for filed. All the algorithms are implemented by PLC's and microprocessor system for the digital control of double loop dc drive machinery system. To get the better transient response than conventional, PI controllers are used. The total power factor of the industry with harmonics is greater than 98%. To achieve system above the base speed, field weakening method is used. Since 1991, it has been operating with high efficiency at Rasthriya Ispat Nigam Limited, Visakhapatnam steel plant (RINL-VSP) in Andhra Pradesh state, India.