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WHAT IS VFD AND ITS PRINCIPLE, WHY VFD IS USED
It is also called adjustable speed drive and frequency inverter.
It is used to control AC motor speed and torque by varying input voltage and frequency of incoming supply. Used in Electro mechanical system.
WHY WE USE VFD?
Many AC motors use fixed speed for operation for constant output required in industries but some applications need variable speed functions in motors and precise motion of motors required like paper winding machine and conveyor belt for production unit. VFDs are mainly used to control the operation of AC Motors.
PRINCIPLE AND OPERATION OF VFDs
The basic functionality and principal of VFD is to convert fixed frequency electrical supply into variable frequency and voltage that is given to the motor with corresponding change in motor speed and torque.It produces constant ratio of voltage to frequency for producing torque by regulating the voltage. in proportion to the frequency regulation. It gives only 1-2 percent loss due to heat dissipating caused by high frequency electrical signal switching.
The circuit diagram and block diagram is shown below
Circuit diagram of VFD
Block diagram of VFD
COMPONENTS IN VFD
The following components are used in the VFD.
Rectifier is the simple circuitry of electronics devices that converts the incoming alternating voltage to direct current (DC supply). Different designs can be used of rectifier for VFD operation. It can also control the direction of power flow. This DC Power has voltage ripples so next we have to smoothing the voltage.
INTERMEDIAT CIRCUIT or DC LINK
Intermediate circuit consists of inductors and filter capacitors circuits. This step performs voltage smoothing.
The inverter again change the rectified and DC Conditioned output to alternating voltage (AC). At the inverter’s end output, the PWM (Pulse Width Modulation) technique is used with help of special types of transistors like IGBT (Insulated gate bipolar junction transistors) to get high frequency pulse width modulated signal with effective voltage.
How this technique works?
The answer is simple the IGBT circuitry turns ON and OFF at high frequency with duration of on-time or width of pulse, controller to approximate sinusoidal waveform.
As name describes, it controls all the operations of VFD like rectification, intermediate circuit and invert to get correct output. It contains the processor which governs overall operation.
DIFFERENT PULSE VFDs
IMPORTANCE OF VFD
As in technology advancement now more power microprocessor based VFDs are coming which is cost effective and reliable. In industrial market, VFDs save energy by controlling centrifugal pumps, motors and fans etc.
If you use VFDs technically and professionally, 25 to 35 percent energy can be saved. Only need to evaluate complete evaluation industrial package for power savings.
Furthermore, it makes sure reduction of motor starter and exerts less stress on motor windings and bearings.
BENEFITS OF VFDs
It helps to save energy and more reliable performance which increase profit margins. Many complex industrial processes could be run smoothly by adjusting the speed and torque of motors. In this case VFDs take the signals from controller like PLC (Programmable logic controller) or tachometer. (Manual Adjusting of VFD for speed is also possible but it depends upon application)
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