Explain variable frequency drive

variable frequency drive

VFD is stand for Variable Frequency Drive, It is an electronic gadget, this gadget is to use for control RPM of different kind of electrical motors like a single-phase or three-phase motors also. This gadget is the ability to performing the task is to control the required rpm, like reduce or increase the speed (rpm) of the motor.

In other words, adjust increase or decrease the frequency that result is directly affect the (RPM) of the motor.
VDF is only used in AC motors only.
And can be used in small to the large motor also
VFD is to perform without effect the torque, impedance and magnetic flux.

The basic concept of how to control the speed

The speed of the AC motor is inversely proportional to its number of stator poles and directly proportional to the supply voltage’s (frequency). Therefore the speed of the motor either depends on a number of stator poles and the second method changed the frequency with the help (VFD).
The number of stator poles is fixed to every motor and cannot be changed.
And another concept (VFD) we can change and varying the frequency with the help of (VFD) that can be effect the (RPM) speed of the motor.

Advantage of VDF

As VFD usage in HVAC applications has redoubled, fans, pumps, air handlers, and chillers can benefit from speed control. Variable frequency drives provide the following advantages:

• energy savings
• low motor starting current
• reduction of thermal and mechanical stresses on motors and belts throughout starts
• simple installation
• high power factor
• lower KVA

Comparison of  VFD vs Starter Types

Starter Type                            Starting Current (% of FLA)
VFD                                                    100%
Wye-Delta Starter                              200-275%
Solid State Soft Starter                     200%
Autotransformer Starter                   400-500%
Part Winding Starter                        400-500%
Across the Line Starter                    600-800%


Motor speed (rpm) is dependent upon frequency.

Varying the frequency output of the VFD controls motor speed:

Speed (rpm) = frequency (hertz) x a hundred and twenty / no.of poles

Example:
2-pole motor at different frequencies

3600 rev = sixty hertz x a hundred and twenty / 2 = 3600 rev

3000 rev = fifty hertz x a hundred and twenty / 2 = 3000 rev

2400 rev = forty hertz x a hundred and twenty / 2 = 2400 rev


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