Submitted by

T.VANI SANTHOSHI – 09W91A0252

CH.ASHWINI - 09W91A0217

V.PRIYANKA GOUD – 09W91A0256

D.BASAVESHWAR – 07W91A0208

E.RAVI RAJA - 08W91A0239

Under the guidance of

M.Spandana,M.tech

Asst.Prof, EEE department

Malla Reddy Institute of Engineering and Technology

VARIABLE FREQUENCY DRIVES

A variable-frequency drive (VFD) is a type of adjustable-speed drive 

It is used in electro-mechanical drive systems to control AC motor speed and torque  by varying motor input frequency and voltage.

INTRODUCTION

• Systems employed for

motion control are called

drives and may employ

any of the prime movers

such as diesel or petrol

engines ,electric motors,

for supplying mechanical

energy for motion control .

• Drives employing

electrical motors are

known as electrical drives.

ELECTRICAL DRIVES

There are two types of electrical drives mainly

1. DC Drives

2. AC Drives

• DC drives are dc motor control systems

• AC drives are AC motor speed control systems

TYPES OF ELECTRICAL DRIVES

It controls the rotational speed of an AC motor by controlling the frequency of electrical power supplied to motor.

It’s a specific type of adjustable speed drive

What is a VFD

Danfoss Danfoss = First company to = First company to mass produce a.c. variable frequency drives (VFD)mass produce a.c. variable frequency drives (VFD)

EVOLUTION OF VFD

2003 2007

199819931988198319731968

A variable frequency drive generally consists of following:

Ac motor

Main controller assembly

Operator interface

DESCRIPTION OF VFD

It is usually a 3 – phase induction motor.

An AC motor is an electric motor driven by an alternating current.

The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet.

AC MOTOR

It is a solid state power electronic conversion device. It consists of three main parts

Bridge rectifier

DC link

Inverter

MAIN CONTROLLER ASSEMBLY

It converts AC input power to DC intermediate power using a rectifier or converter.

BRIDGE CONTROLLED RECTIFIER

DC intermediate power is then converted to quasi sinusoidal AC power using inverter switching circuit

DC LINK

It changes DC energy into three channels of AC energy that can be used by AC motor

BASIC INVERTER

The operator interface often includes an alphanumeric display and/or indication lights and meters to provide information about the operation of the drive.

A serial communications port is also often available to allow the VFD to be configured, adjusted, monitored and controlled using a computer

OPERATOR INTERFACE

CIRCUIT DIAGRAM OF VFD

WORKING OF VFD

AC motor characteristics require the applied voltage to be proportionally adjusted whenever frequency is changed in order to deliver the rated torque

BLOCK DIAGRAM OF VFD

There are many methods of control for frequency in variable frequency drives

Among them PWM is mostly used because of its own advantages.

METHODS OF CONTROL

Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches.

PULSE WIDTH MODULATION

VFD’s use their output devices (IGBTs, Transistors, thyristors) only as switches.

They can be classified as

Voltage source inverter fed drives i.e. constant voltage

Current source inverter fed drives i.e. constant current

TYPES OF VFD OF VFD

• Constant voltage converter : intermediate DC link voltage remains constant during each output cycle

• Constant current drives : large inductor is placed between the input rectifier and the output bridge, so the current delivered is nearly constant

CONSTANT CURRENT AND VOLTAGES DRIVES

Cooling of the motor is usually not good in low speed range

.When frequency reaches zero, motor is shut off.

The motor shall require a load reactor and filters if the pump leads from the VFD exceed certain conditions

FACTORS AFFECTING SPEED CONTROL

ENERGY SAVINGS

Example : vfd for centrifugal pumpFlow is proportional to speedPower varies to the cube of the

speed change20% reduction in speed

= 50% reduction in energy

50% reduction in speed

= 80% reduction in energy

VFD controllers designed to operate at 111v volts to 690v are often classified as low voltage units.

Typically designed for use with motor rated to deliver 0.2 k.watts up to several mega watts.

Medium voltage VFD controllers are designed to operate at 2400/4162 volts (60hz), 3000 volts(50 hz )

VFD RATINGS

• VFDs are frequently used to control motors for: Fans, Pumps, Compressors

Mills.

• Oil & Gas, petroleum, petro chemistry: oil transfer pumps, compressors,

pumps, etc.

• Mining: mortar pumps, fans, etc.

• Water and waste water: water supply pump, etc.

APPLICATIONS

Hence variable frequency drives are mainly used because of the following reasons:

• Stable and reliable performance

• Saves energy and therefore reduces energy costs

• Isolated control signal provided by fibre optics between Power cell and Controller

CONCLUSION

QUERIES ???

THANK YOU