A new approach to advanced cold mill drive systems

This report describes an advanced 1000 kVA AC cold mill drive systems in a modern steel manufacturing facility. The presented systems consist of an AC-to-DC PWM power converter and two PWM inverters to drive each 700 kW induction motor, and all algorithms are implemented using a TMS 320C40 digital signal processor (DSP) system that provides high computing power by employing a high level of parallel processing. The displacement power factor of the input line current is always unity and total power factor including harmonics is higher than 98%. The common DC link voltage is regulated within 1% of its rated value regardless of input voltage fluctuation and output load transient. The system achieves 1:5 field weakening control range. The available speed control bandwidth of the motor is about 60 Hz and torque bandwidth is about 350 Hz. Since July 1997, it has been operating with full capacity at Pohang steel mill company (Posco) in Kwang-yang, Korea.