ravi vfd final2007

8/8/2019 RAVI VFD FINAL2007

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MOTORSMOTORS MOTORSMOTORS

TRACTION

AGRICULTURE

PROCESS INDUSTRY

DOMESTICS (HOUSES)

MEDICAL LABS

AVIATIONS

AUTOMOBILE S

A CA C A C A C

MOTORSMOTORS MOTORSMOTORS

D CD C D CD C

A CA C A C A C

D CD C D CD C

Etc

Etc

Etc

Etc

Etc


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WE KNOW THAT MOTOR ROTATES AT SOME SPEED

WE CANT LET THE MOTOR TO RUN AS PER ITSWISH

IT HAS TO RUN AT SOME SPEED AS PER OUR REQUIREMENT & NECESSITY & TO ACHIEVE

SOME PURPOSE

WHEN THERE IS REQUIREMENT & NECESSITY & PURPOSE

THE TERM CONTROL COMES TO PICTURE


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POLES

VOLTAGE

RESITANCE

FREQUENCY


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Variable-frequencydrive (VFD) :is a system for controlling the rotational speed of

an AC electric motor by controlling the frequency of the electrical power supplied

to the motor.

Variable-frequency drives are also known as

Adjustable-frequencydrives (AFD)

Variable-speed drives (VSD)

Inverter drives.

VVVFD (variablevoltagevariablefrequency drives.)

VFD Applications:

Ventilations systems for large buildings,

Motors for Blowers & Fans ,

Pumps, Conveyor, Machine tool drives , Tractions, Lifts etc


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Operating principle: ( SPEED CONTROL)

The synchronous speed of an AC motor is determined by the frequency of the AC

supply and the number of poles in the stator winding, according to the relation:

Where

f = AC power frequency (hertz)p = Number of poles

s = slip.


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BLOCK DIAGRAM OF VFD CONTROL FREQUENCY CHANGER:

1. Rectifier-Inverter type

2. Cycloconverter


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1. Rectifier

2. Soft Charge Circuit

3. Inverter

4. Pulse Width Modulation

5. Control & Regulation Section

Parts and Operations of a Drive

ACTUAL PANEL ENERGY SAVINGS V / HZ RATIO DRAWBACKS


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The 3-phase AC voltage goes into the rectifier section which is made up

of a group of gated diodes (silicon rectifiers or SCRs).

The D1 & D2 convert L1 power to DC

D3 & D4 convert L2 power to DC

D5 & D6 convert L3 power to DC

In this type of circuit, the DC voltage is 1.35 times the AC line voltage.

If 240 Vac is coming in, 324 Vdc can be obtained.

Rectifier

BACK


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On larger drives, (22 450kW or 30 600Hp), inrush current

will be 3 to 8 times so there is a necessity to restrict this

inrush current , if not it will damage VFD circuit or linefuses would be blown every time the VFD s operated.

Hence soft charge circuit is used to power up the drive , &

the inrush of current is restricted .

The soft charge circuit on some of the VFDs has a resistors

to limit starting current & to vary the charging time of the

capacitors.

This current resistor even has its own safety, a thermal

switch, which shorts out if the current rush is too high in thesoft charge circuit & blows the fuses on the soft charge

circuit preventing the drive from starting.

Operation

Initially SCRs in the main rectifier section remain off.

Rectifier section in the soft charge circuit starts applying

DC power through the current resistors charging up the

capacitors in the DC Link.

When these capacitors are charged to the DC voltage of

minimum value, the control section starts the firing of the

SCRs in the main rectifier.

Soft Charge Circuit

BACK


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This section takes the DC voltage from the

intermediate section and, with the help of the

control section, fires each set of IGBT (or other

semi conductor device) and provides AC out put

to the motor terminals U,V and W.

Firing of the IGBTs provides Pulse Width

Modulation (PWM) .

For any drive larger than 18.5kW (25Hp),

master coils are provided to smooth the

waveform going to the motor.

The smoother the waveform the less heat isgenerated at the motor and the longer the

motor lasts.

Inverter

This PWM frequency can vary from 3.5KHz to 15 kHz, which

means it is audible.

It is also known as the CarrierFrequency, which isVariable

by mostVFD manufacturers.

A low carrier frequency can have an annoying noise, but a

higher carrier frequency generates more heat in the drive

and motor.

If the carrier frequency noise is too loud particularly with

supply fans, LC filters can be placed between the VFD andmotor and the noise stops at this filter.


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OutputOutput

FrequencyFrequencyBase FrequencyBase Frequency

6060

OutputOutput

VoltageVoltage

Hz30

460460

230

115

15 900

Volts/Hertz Ratio

BACK

CONTROL

SINCE AIR GAP FLUX V

f


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ENERGY SAVINGS ( WITH CONCERNED APPLICATION )

Motor-driven centrifugal pumps, fans and blowers offer the most dramatic energy-saving opportunities .

Blowers operate for extended periods at a reduced load.

Since they are notalwaysoperatingattheirfullload the amount of energy you can save by reducing the current

to them as well as the amount of stress release on your motor is enormous and results in an energy efficient and

longer lasting system.


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ENERGY SAVINGS ( WITH CONCERNED APPLICATION )

% flow


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Airflow Volume

(percent of

maximum)

Daily Operating

Time (hours)

Energy ConsumedUsing a

Damper(kWh/year

)

Energy Consumed

Using a

VFD(kWh/year)

Difference inEnergy

Consumption

(kWh/year)

50% 2 18 500 4 800 13 700

60% 3 29 300 9 800 19 500

70% 6 61 700 26 800 34 900

80% 6 63 300 35 900 27 400

90% 4 44 200 32 600 11 600

100% 3 34 200 35 200 1 000

Total 24 251 200 145 100 106 100

CASE STUDY ENERGY SAVINGS

BYPASS VFD

BACK


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BACK


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BACK

CONSTANT RATIO SAVES ENERGY IF NOT MOTOR

CURRENT WILL BE UNSTABLE & TORQUE CAN DIMINSH &

MOTOR MAY GET DAMAGED


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ADVANTAGES OF VFDs

1. Energy saving

2. Better system control

3. Reduced maintenance

4. Higher efficiency

5. Easy retrofit

6. Remote mounting

7. Simple control

8. Bypass capability

DISADVANTAGE OF VFDs

1. At full load operation energy saved is nill

2. Need by pass circuit at full load

3. Not possible to control dc drives

4. VFDs are bit costly

5. Drive circuits needs additional protection circuits

due to initial current


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CONCLUSION

In addition to energy savings and better process control, VFDs can provide other benefits:

A VFD may be used for control of process temperature, pressure or flow without the

use of a separate controller.

Maintenance costs can be lower, since lower operating speeds result in longer life for

bearings and motors.

Accurate Speed Regulation


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REFERENCESS

[1] A variable-frequency three-phase induction motor drive system by Brian A.

Welchko and. Thomas A. Lipo, fellow, IEEE, IEEE transactions on industry

applications,vol.37, no.6, november/december20011739.

[2] www.en.wikipedia.org/wiki/Wikipedia

[3] Electrical technology by A K Thereja and B L Thereja

[4] Advance Electric Drives by Bimal K Bose


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ravi vfd final2007

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