Perhaps equally important for some applications, it gives zero long term position offset as well as zero speed offset.
Just as the regulation of power line frequency seeks not just to maintain frequency but to produce the target number of cycles in every 24 hour (or shorter) period to maintain clock accuracy.
I don't want to get too far off topic here but paper making is quite an interesting VSD application/challenge. The endless web. Various technologies have been used throughout the decades but now, most use VFDs for the main power.
A little background on the application if I may. A typical newsprint machine may have 15 main drives, sections as they are called. The basic process hasn't changed much in decades. This goes from about a 2% suspension of cellulose fibre in water at the wet end which has little tensile strength to the finished product at the dry end - paper as most of us know it.
The challenge for the drives designer is to achieve and maintain constant speed ratios between the sections. Draw. At the wet end, it is about 1% or so. The difference over, say the last four sections, is typically 0.25% - in total. Most VFDs I've been involved with for this use encoders - 2048 or 4096.
It is not the most technically challenging except maybe, when you consider the powers involved. On the last one I did the drive supply transformer capacity was 4MVA comprising two 2MVA 12-pulse transformers. And that's sort of middle of the road for modern machines.
, didn't look any further back.)
