Driving System Incorporating Vector Control Inverter for Large-Scale Paper Machine

The sectional drive of paper machines by squirrel-cage induction motors, a dream for many years of drive system engineers, has now been realized. A large-scale printing paper machine, with a 220-in wire width and 2600-ft/min speed, driven by 31 brushless ac motors, including squirrel-cage induction motors, has been in commercial operation for more than one and a half years with excellent performance. In this machine, squirrel-cage induction motors are applied to drive a wire part, a press part, and other parts whose capacity range is 400-750 hp. These motors are powered by current source inverters equipped with newly developed vector control technology. By applying this technology to the paper machine drive system, draw control accuracy of better than 0.02 percent was obtained. Torque sharing control between two induction motors which drive a wire turning roll and a couch roll was realized, and tension control at the calendar part was also realized. Other innovative techniques were also utilized to reduce torque ripple and escape torque resonance between the machine rolls and the motors. This system not only drastically reduces the maintenance work of dc motors but is also often more economical, higher in efficiency, smaller in physical size, and more rigid and resistant to a poor environment. After the success of this paper machine, these technologies are being diversified and applied to all industries, including the iron and steel, film, and the rubber and plastics industries, where conventional dc motors are widely used.