Comparison of multi-motor synchronization techniques

Multi-motor applications has become a very attractive field in industrial applications replacing the traditional mechanical coupling. Applications can be found in paper machines, offset printing, textiles, differential drives, to name some examples. Multi-motor techniques are used where matched speed during acceleration, deceleration and changes in load requires "truly" speed and angle synchronization between at least two axes. Several synchronization techniques has bee developed in order to fulfill those necessities, in this work the master-slave, cross coupling technique, bi-axial cross-coupled control method, electronic (virtual) line-shafting and the relative coupling strategy are compared for different industrial applications. Practical results in a two 1.5 kW induction machine test ring are presented, showing advantages and limitation of those techniques during different load conditions. The work reported in this paper makes use of a V/Hz motor control scheme, but conclusions drawn can be applied to any motor control technique. Parallel research is on going, results are reported on future publications.