ATO Inc

There are two basic types of VFDs: the original scalar control type and the newer vector control type. ATO.com offers 1/2hp to 300hp in low prices, including single phase input to three phase output VFDs from 1/2hp to 7.5hp. The scalar control is open-loop using a voltage-frequency ratio and although it provides great speed regulation, ~0.5%, it does not have a fast response nor is it very precise. The vector control can be open- or closed-loop and uses current control of two vectors, torque and magnetizing