This is from wikipedia's article about Variable-Frequency Drive [snip] Controller: Variable frequency drive controllers are solid state electronic power conversion devices. The usual design first converts AC input power to DC intermediate power using a rectifier or converter bridge. The rectifier is usually a three-phase, full-wave diode bridge. The DC intermediate power is then converted to quasi-sinusoidal AC power using an inverter switching circuit. The inverter circuit is probably the most important section of the VFD, changing DC energy into three channels of AC energy that can be used by an AC motor. [/snip] I wonder what's the point of doing such a thing? Why not leave the AC current as it originally is? Is is purely a way to regulate the current?