There are multiple components in a motor control system.
There are VSD, there are motors, and there are mechanical gears, such as reduction box. When we are looking at the solution to improve efficiency, there is high value in integrated, proven solution.
High efficiency motors:
We need to use high efficiency motor, with the recent changes in motor code, IE5 "Ultra-Premium Efficiency" motors are introduced. The parts we need to understand is that they may perhaps no longer the induction motor we are customed to, they may be PMSM (Permanent Magnet Synchronous Motor), maybe SynRM (synchronous reluctance motors). They cannot be run by DOL or Soft-starters anymore, and to run them in open-loop motor control, it is not guaranteed in the mechanical performance, torque response, nor on the actual efficiency achieved. Hence it is important to seek proven solution, usually via the same vendor, where they can provide verfied solution and guarantee.
VSDs:
The VSDs have efficiency, usually between 95% - 98%. Note low harmonic and AFE (active front end) drives tend to have less efficiency, due to the fact they have more IGBTs switching in operation.
There are newer technologies, such as SIC (Silicon Carbide) MOSFET semiconductors, they will have much smaller heat load. They are growing, however the market is not there yet. There are also some hybrid design, such as Inovance, they have traditional IGBT with SIC diodes, to reduce the switching losses. Hence improve the efficiency, and is able to reach a higher switching frequency.
Mechnical parts, such as reduction gear:
If we can get rid of them, why not. The motors nowadays when controlled by VSD, they can work in much wider frequency spectrum, typically VSD allow 0-599HZ output, while typical motor is rated at 50Hz. The accuracy of the mechnical speed has become better with larger speed span. The high pole number PMSMs can provide very good torque in very low speed and frequency range, allowing perfect performance, without sacrificing efficiency. The future lies with Direct drive application with VSDs.
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