There are currently three different types of VFD designs on the market. In theory, the main difference between these VFDs is the type of rectification they convert from AC power to DC power.
The most common centrifugal load applications for using frequency converters are pumps, fans and compressors. The most common constant torque load applications using VFDs are positive displacement pumps, gear pumps, reciprocating pumps, conveyors, extruders, extruder cutters, mixers and reciprocating compressors. The main considerations when choosing a VFD are:
VFD has many basic uses as a special process control that is not common in other types of shift control. When energy saving is the primary goal, VFD is best suited for centrifugal loads. Due to its flexibility in automatic process control systems, VFDs are also often used for constant torque loads. VFDs are very sensitive to applications, so you must thoroughly analyze application compatibility before choosing a VFD.