[PDF] Why Use Variable Frequency Drive? - paddockindustries Simply put, a VFD is a power conversion device. The VFD converts a basic fixed-frequency, fixed voltage sine-wave power (line power) to a variable- frequency, variable-voltage output used to control speed of induction motors. A basic block diagram of this process is depicted in Fig. Electrical Drives – Classification of AC Drives & VFD Block Diagram of an AC Electric Drive. The electric motor is the core component of an electrical drive that converts electrical energy (directed by power processor) into mechanical energy (that drives the load). The motor can be DC motor or AC motor depends on the type of load.