Variable Frequency Drive

Shaishav Parmar (110010741010) 2nd SEM – ME (SPC)ADIT, New

V.V.Nagar

Outline

Introduction

Objective

Basic of VFDBlocks.

Function &Operation

PWMprinciple

Interfacing with DSP controller

Advantages

Disadvantages

Applications

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Introduction VFD’s adjust the speed of a driven shaft to a predetermined

speed often this is done via an automatic speed selection process.

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These automatic processors often use referencesignals

generated by other devices, drives, controllers, limiters etc.

VFD’s can control speeds to within 0.1% tolerance and are the control system of choice in many speed control applications.

Convert line voltage & frequency to controllable values andapply to motors.

Intro………

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provide continuous control,

matching motor speed to the specific demands of thework being performed.

Also called VSD or VAD

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Objective

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The main objective of the VFD is to vary the speed of the motor while providing the closest approximation to a sine wave for current (while pulsing DC voltage to the motor).

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Basic of VFD

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1. AC Line input section

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AC Line input section

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The voltage on an alternating current (ac) power supply rises and falls in the pattern of a sine wave.

Voltage is +ve , Current in one direction

Voltage is -ve , Current in oppositedirection

Results in large amount of energy.

2. Input Rectifier Section

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Rectifier output

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Input Rectifier Section

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convert incoming ac power into directcurrent (dc) power.

Two rectifiers are use for each singlephase.

Generally three phase rectifier is use tohandle large power in industries

3. DC bus Section

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DC bus Section

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It contains capacitors to accept powerfrom the rectifier,

store it, and later deliver that powerthrough the inverter section.

Sometimes we use chokes with capacitormainly to reduce

1)harmonic noise (interference) &2)temporary loss of power.

4. Invertor Section

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Inverter

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Inverter section using PWM

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Inverter

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The inverter contains transistors that deliver power to the motor. The “Insulated Gate Bipolar Transistor” (IGBT) is a common choice in modern VFDs.

Higher Switching capacity

current Uses PWM technique tosimulate sinewave into desired frequency

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Basic principle of PWM

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Commonly used technique forcontrollingpower to electrical devices.

The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load ON and OFF at a fast pace.

The longer the switch is ON compared to the OFF periods, the higher the power supplied to the load is.

PWM

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PDELIVERED = PSUPPLIED x Duty Cycle

Duty Cycle = ON time / Total Period of Pulse

PWM waveform

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Basic Interfacing block of motor with LF2407 using VFD inverter

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Advantages

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It can control speeds to within 0.1% tolerance Energy savings Reduction of thermal and mechanical

Stresses onmotors

simple installation because smaller in size Lower Power consumption Soft starting during belts starts Fast & Precise response Precise speed and torque control High reliability and availability Low audible noise

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Disadvantages

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Produces “noise” due to PWM that can interfere withother susceptible circuits.

Reflected Wave Voltages.

EMI both reflected and conducted.

circuit Noise can lead to drive overcurrent,

malfunction, and motor bearingfailures.

Need to keep cable runs short to limit “noise”

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Perform for various application

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Variable-torque control to drive a fan orpumpunder light head.

Constant-torque control to drive a pumporcompressor or other equipment against higher head.

Constant horsepower to drive a machine tool, suchas a lathe or milling machine.control for

precisein rolling steel orcontrol ofcalendaring

positionplastic

Motion needed sheeting.

Applications

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Marine – propulsion, powergeneration,dynamic positioning, and work vessel systems.

Oil & Gas – control systems for pumps, gas and diesel engines, compressors,turbines, boilers, conveyers.

Environmental – in waste water, potable water, pollution control, pumping,desalination, ozone regeneration.

Industrial – Paper Mills, Cement Plants,MiningControls, Car Plants, Steel Mill

References

1.Electronics measurements & instrumentation by A.K Sahney

2.www://en.wikipedia.org/w/index.php?title=Variable_frequency_drive&oldid

3.www.delta.com.tw/product/em/drive/ac_motor/ac_motor_main.asp

4.www.danfoss.com/North.../VFD-101+for+HVAC+Market.html

5.www.irc.wisc.edu/file.php?id=266

6.www.us.sbt.siemens.com/HVP/.../SED2DriveBasics.pps - United States 22-Jun-

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