1

VARIABLE FREQUENCY DRIVE

Made by:VANSHIKA JINDALB.TECH III YEAR (EEE)

2

CONTENTS

1. What is VFD-INTRODUCTION2. Electrical motor facts3. Affinity laws4. VFD fundamentals and working 5. Energy saved by motor using VFD6. Applications8. Advantages9. Disadvantages10. References

3

INTRODUCTION• A Variable Frequency Drive (VFD) is a type of controller

that drives an electric motor by varying the frequency and voltage supplied to the electric motor.

• Also called as variable speed drive, adjustable speed drive, adjustable frequency drive, or an AC drive.

4

ELECTRIC MOTOR FACTS• Electric motors account for more than two-thirds of all energy

used in industry.

• 63% of the energy consumed is linked to air & liquid flow (HVAC)

5

AFFINITY LAWS1) Flow is proportional to speed,(in pumps)2) Pressure is proportional to the square of speed, (fans)3)Horsepower is proportional to the cube of speed. (motors)

6

ENERGY SAVINGSReducing speed by 20 percent requires only 50 percent of

the power and 50% savings

PERCENT SPEED

FREQUENCY(HERTZ)

PECENT SAVINGS

100% 50 0%90% 44 27%80% 38 49%70% 32 66%60% 26 78%50% 20 88%40% 14 94%

7

VFD FUNDAMENTALS

50 Hz Power

Electrical Energy

ABB

Variable Frequency

To Motor

VFD

RECTIFIER(AC - DC)

INVERTER(DC - AC)

AC DC AC

VFD

Variable Frequency50 Hz

A variable frequency drive converts incoming 50 Hz utility power into DC, then converts to a simulated variable voltage, variable frequency output

The basic components of VFD are: 1. Rectifier 2. DC Bus 3. Inverter

8

WORKING OF VFD

• First, the Converter (usually a diode rectifier) converts three-phase AC power to DC power.

• Next, the DC Bus stores and filters the DC power in a large bank of capacitors.

• Last, the Inverter (usually a set of six IGBTs) switches or inverts the DC power in a Pulse Width Modulated (PWM) AC waveform to the motor.

MotorL1

L2

L3

C

L

Input Converter(Diode Bridge)

Output Inverter(IGBT’s)

DC Bus(Filter)+

_+_

+

_

+

_

+ +

_ _

9

RECTIFIER• Basic Building blocks of rectification• Diodes (Uncontrolled)

Gate Pulse

Conduction after

Gate Pulse

THYRISTOR

Controlled output voltage

10

1. THREE PHASE RECTIFIERS OR CONVERTERS

D1 D3 D5

D4 D6 D2

11

2. DC BUS• Conversion of AC into DC is not a perfect process.

There are Ripples’• How to eliminate the ripples?

Filters-The capacitor which absorbs the ac ripple and delivers a smooth dc voltage. so capacitor is used as a filter.

3. INVERTER ACTION• Filtered output from DC bus is sent to inverter in VFD• Switching DC voltage ON and OFF will make it AC• The output from the VFD is a “rectangular” wave form.

VFD’s do not produce a sinusoidal output

12

RECTIFIER

PositiveDC Bus

NegativeDC Bus

+

-

INVERTER

CONVERTING DC INTO AC

13

RECTIFIER

PositiveDC Bus

NegativeDC Bus

+

-

INVERTER

14

RECTIFIER

PositiveDC Bus

NegativeDC Bus

+

-

INVERTER

15

RECTIFIER

PositiveDC Bus

NegativeDC Bus

+

-

INVERTER

16

RECTIFIER

PositiveDC Bus

NegativeDC Bus

+

-

INVERTER

17

RECTIFIER

+

-

INVERTER

PositiveDC Bus

NegativeDC Bus

How Often You Switch From PositivePulses To Negative Pulses DeterminesThe Frequency Of The Waveform

Frequency

Volta

ge

SPEED OF MOTOR:Synchronous Speed = 120 x frequency

no. of motor poles

18

1. Used in Air compressors, refrigeration compressors, vacuum pumps, and high-pressure blowers.

2. Convert ventilation, and air conditioning (HVAC) systems to variable air volume (VAV) systems

3. Used in wind turbines and other small hydroelectric generation projects that will be connected to the power grid.

4. Acts as a inverter in power grid

APPLICATIONS

19

1. Significant energy and cost savings by control and regulation of

1. Motors2. Motor-driven centrifugal pumps, 3. Fans and blowers

2. Protection from overload currents

3. Safe Acceleration.

ADVANTAGES OF VFD

20

1. Harmonic content: deviation of waveform from pure sinusoidal shape.1. Line Reactors: Protect the drive from sudden

disturbances.2. Bearing damage: Pulse width modulated voltage

induces bursts of shaft currents results in bearing damage.1. Shaft grounding through carbon brushes.2. Insulated bearings are used

DISADVANTAGES

21

REFERENCES• Mr. Aung Zaw Latt, Dr. Ni Ni Win. “Variable Speed Drive of Single

Phase Induction Motor Using Frequency Control Method” 2009 International Conference on Education Technology and Computer

• Auzani Jidin, Jurifa Mat Lazi, Abd Rahim Abdullah, Fazlli Patkar, Aida Fazliana Abd Kadir, Mohd Ariff Mat Hanafiah. “Speed Drive Based on Torque-Slip Characteristic of the Single Phase Induction Motor” IEEE PEDS 2005

• B.L. Theraja, A.K. Theraja, “A Textbook of Electrical Technology” Published by S.Chand

• Gopal K. Dubey, “Fundamentals of Electrical Drives” Second Edition, published by Narosa Publishing Houses

• Specification of Variable Frequency Drive Systems to Meet the New IEEE 519 Standard.

• A Novel Output Filter Topology to Reduce Motor Overvoltage.• http://literature.rockwellautomation.com/idc/groups/literature/

documents/ar/7000-ar002_-en-p.pdf

22

s

23

THANK YOU