Performance Comparison of Fixed-Speed and DFIM-based Speed-Elastic Shredder Drive Concepts

Conventional shredder drives are operated in fixed- speed mode as the drive motor is directly coupled to the supplying power grid. Due to the discontinuous characteristic of the process, this leads to a severe load fuctuations in the drive train as well as at the grid interface. Investigations show, that the shredding process does not necessarily need a constant speed of the process machine, but allows speed variations in a quite wide range around the nominal operating point. In this paper the performance of the traditional fixed-speed drive configuration is evaluated and compared to an innovative concept, that allows a speed-flexible operation by using a Doubly Fed Induction Machine (DFIM) and, thereby, significantly reduces the strain of the drive train components as well as fluctuations in the drawn electrical power. In contrast to the grid-coupled Motor, the proposed speed-elastic proportional control is not able to adequately dampen torsionally oscillations in the drive train alone, so an additional damping controller is proposed. The performance of the drive concepts is compared based on a operational strength analysis using relevant process data.