VSD Principle of Operation

Although there are different types of electronic VSDs, they are all similar in design and consist of four basic components:

Rectifier — the rectifier changes the incoming alternating current (AC) supply to direct current (DC). The type of rectifier used can vary depending on the type of performance required from the drive. The rectifier design will influence the extent of the harmonic content present in the incoming supply. It can also control the direction of power flow.

Intermediate circuit — the rectified DC supply is then conditioned in the intermediate circuit, normally by a combination of inductors and capacitors. Over 98% of drives currently in the marketplace use a fixed–voltage DC link.

Inverter — the inverter converts the rectified and conditioned DC back into an AC supply of variable voltage and frequency. This is normally done with a semiconductor switch.

Control unit — the control unit gives and receives signals to the rectifier, the intermediate circuit and the inverter to correctly operate the equipment.