Variable Frequency Drive (VFD)

 

For many years, the major challenge to some motor-driven applications was the inability to control their speed. However, the advent of reliable power electronics made it possible to control the speed of motors using variable-frequency drivers.

VFDs are widely used in many applications nowadays. The main reason is that they have greater functionality and operation capabilities compared to conventional motor drives when starting a motor.

The working of VFD is based on the control of frequency and voltage simultaneously through a PWM inverter, it is used to control the speed of AC motor-driven applications. In addition, variable frequency drives offer protections like phase, under, and overvoltage protection.

Components of VFD

To understand the working principle of a variable frequency driver, it is important to know what it is composed of. In other words, you need to know what leads the currents passing through a VFD of a 3-phase motor, for instance, to be changed from AC to DC and then back to AC again.

VFD comprises three main sections: Rectifier, Filters, and Inverter.

1. Rectifier: The first stage of VFD. It converts AC power fed from the mains to DC power. It mainly utilizes diodes that are connected in parallel to convert AC power into DC.
2. Filter: A capacitor that is used to smooth the rectified DC power.
3. Inverter: Transistors (IGBTs) used to work to be switched on and off rapidly to create a pulse-width modulation which creates an AC-like wave that will allow the VFD to control the speed of the motor.