Acdrive Basics

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AC Drives Basics


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Course content

Topics covered in this section -

AC Drive (Variable Frequency Drive) subsystems

Rectifier,

Inverter,

Motor,

Control Interface,

Cable

Software tools, Efficiency, Applications of AC Drives(VFD)


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Variable Frequency Drive ( VFD ):

An adjustable frequency AC drive converts an input lineconstant voltage and frequency to an adjustable voltageand frequency output .

Normally speed and current control are provided.

More sophisticated drives also provide torque control.


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Main components of AC Drive :

Equipment Operation

M3

Line

Line Supply

Unit

Inverter

Unit

Motor

Line voltage

Rectification

Smoothing

Inversion

Motor

Waveform

DC bus,

capacitorand choke

Functional principle of the drive system


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Output waveform of AC Drive


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Variable Frequency Drive ( VFD )Panel:

Plus: CONTROL TRAFO,CONTROL FUSES, METERS,PUSH BUTTONS, INDICATIONS,CABLES,AUX. CONTACTORS ETC.

I/P SWITCH& FUSE(OPTIONAL)

I/P CONTACTOR(OPTIONAL)

SEMICONFUSE

DOL BYPASS CONTACTOR(OPTIONAL)

FREQ. CONVERTERMODULE

O/P CONTACTOR

dU/dTFILTER(OPTIONAL)

3 PHASESC IM

3 PHASESUPPLY


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AC Drive Technology

AC Drive Types

Current Source Invertors (CSI)

Constant current principle Large inductor in DC link

Types

Six Step

Voltage Source Invertors (VSI)

Constant voltage principle

Large capacitor in DC link

Types

Six Step (Variable Voltage)

Pulse Width Modulated (PWM)

Our Focus


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AC Drive Control principles

AC Drive Control Principles

Scalar (simple constant volts per hertz i.e. V / f )

Vector (field oriented)

Sensorless Vector

Direct Torque Control (ABB exclusive)


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AC Drives Control principles

Flux vector control can calculate torquecontrol only at 1-3 ms intervals.A modulator is needed to calculate

switching timesControl response is around 10 ms

Flux vector control

Direct Torque Control DTC

DTC can calculate torque control at 0.025ms intervals

Each switching is directly activated bytorque controlControl response is around 1 ms


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AC Drives

AC Drive Capabilities:

Controllable Speed

Controllable Acceleration / Deceleration

Electronic Reversing

Current Limiting

Torque Limiting Intelligent Process Interfacing

Integral Process Control Possible

Multiple Motors Possible

Bypass Possible

Programmable Settings


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AC Drives

AC Drive Performance Advantages:

Accurate Speed Regulation

Dynamic Speed Response

High Process Efficiency

High Input Power Factor

Low Operating Cost


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Application Types

Constant Torque Applications

Torque

TorqueHP

100

50

%Torque

& HP

% Speed

50 100(Base)

150

Constant Torque (CT)

Constant Power (CP)


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Constant torque applications

Example: Positive DisplacementPumps,Conveyors,Mixers,Extruders, Cranes,etc.

Features

High starting torque

Intermitent overloads

Typical kW Range - 0.12 to 2800

Typical Speed Range - 10 to 100%

Speed Controlled with Coast to Stop/ Regeneration /braking

Chopper

Typical Speed Regulation is 1 to 5%

Acceleration Time From 2 to 90 Seconds

Breakaway Torque From 150% to 225%


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Application Types

Constant Power (CP)

HP100

50

%Torque& HP

% Speed

100(Base)

150

Torque

200

HP


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Application Types

Example: Winders (Center Driven)

Speed is Slow

LowTorque Required

Speed is High

Speed is Low

High Torque Required


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Application Types

Variable Torque (VT)

Torque (square)

Flow

100

50

%Torque,Flow,

& HP

% Speed

50 100(Base)

HP (cube)


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Application Types

Example: Centrifugal Fan

Move Air or Other Gaseous Materials

Typical kW Range >2.2 to 3000kW Speed Range From 25 to 100%

Coast To Stop

Speed Controlled With 3 to 5% Speed Regulation Acceleration From 2 to 90 Seconds

StartingTorque From 50 to 100%

No overload requriments


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Application Types

Example: Centrifugal Pump

Move Air or Other Gaseous Materials

Typical kW Range >2.2 to 3000kW Speed Range From 25 to 100%

Coast To Stop

Speed Controlled With 3 to 5% Speed Regulation Acceleration From 2 to 90 Seconds

StartingTorque From 50 to 100%

No overload requriments


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Application Types

Fan Operation

100

50

% Flow

50

125

100 150

%Pressure

SystemCurve

FanCurve

OperatingPoint


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Application Types

Power Requirements For All Types

%InputPower

Volume Control Methods : Outlet Dampers: Inlet Guide Vanes

: Variable Frequency Drives


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Energy saving - Example

Throttling by a valve

Parallel running of Pumps

Variable speed control of the pump

On-off control of the pump

By-passing by a valve


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Relative Power consumption

Software tools - FanSave, PumpSave


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Control Accuracy & Regulation

Speed Regulation Simple Scalar 1% to 3%

Scalar with Slip Compensation 0.5% to 1%

Vector with Encoder 0.01%

Direct Torque Control (DTC) 0.1% to 0.5%

DTC with Encoder 0.01%

Speed Response Simple Scalar 3 %s

Scalar with Slip Compensation 3 %s

Vector with Encoder 0.3 %s

Direct Torque Control (DTC) 0.4 %s

DTC with Encoder 0.1 %s


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Application Issues

Other

Drive Efficiency 98%

Power Factor 0.97 (displacement)

Current Harmonics 35% to 45% THD(network dependent)


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Rectifier Configurations

Current Waveforms

12-pulse Rectifier

~3

6-pulse Rectifier

3~

24-pulse Rectifier

3~

3~

12-pulse Rectifier


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Thyristor bridge in motoring

We study how U+ (DC) voltage is developed.

Thyristors are controlled to diode mode( Fully fired ) so the bridgealways selects the highest of AC voltages (U,V,W) for U+

Anyway line inductance L slows down the transfer of current fromphase to phase. This transfer is called commutation.

U

V

W

U+

U-

E L


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Thyristor bridge in generating

In generating mode the DC bridge is supporting the current so if theAC voltage disappears, the current will grow high.

A Thyristor cannot be turned of by control, so it will continue

conducting and the current will increase until the the fuses interruptthe current.

U

V

W

U+

U-


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Improving commutation

Risk for problems can be reduced by higher AC voltage. This givesmore margin for commutation. The alternatives:

The infeed transformer can be selected to give e.g. 20 % higher

voltage. There can be an autotransformer in the converter boosting the

generating bridge voltage by 20 %

UVW

U+

U-

U+

U-M


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Braking to resistor

braking chopper

braking resistor

CH

Net

mechanical

energyelectricalenergy

motor converterline rectifiermotor asgenerator

M

3


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ACS 600 Power Plates

Basic construction

P1 P2 P3


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Power Plate connections, single inverters

P1 P2 P3

R4 - R7

U

P1 P2 P3 P1 P2 P3 P1 P2 P3

R8, R9

V W

P1 P2 P3 P1 P2 P3 P1 P2 P3

Phase module

P1 P2 P3 P1 P2 P3 P1 P2 P3

Phase module

P1 P2 P3 P1 P2 P3 P1 P2 P3

Phase moduleR12i

U

U

U

V

V

V

W

W

W

P1 P2 P3 P1 P2 P3

R10i, R11i

P1 P2 P3 P1 P2 P3P1 P2 P3 P1 P2 P3


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Power Plate connections, parallel inverters

P1 P2 P3 P1 P2 P3 P1 P2 P3

R8, R9

P1 P2 P3 P1 P2 P3 P1 P2 P3

R8, R9

2 x R8,R9

U

U V W

V W

P1P2P3P1P2P3P1P2P3 P1P2P3P1P2P3P1P2P3P1P2P3P1P2P3P1P2P3

R12i


R12i


R12i


R12i4 x R12i


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Control Cards - Example

C l C d E l


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Control Cards - Example


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MultiDrive

DSU = Diode Supply Unit TSU = Thyristor Supply Unit

ISU = IGBT Supply Unit DBU = Dynamic Braking Unit

ACU = Control Unit ICU = Main Switch

Effi i


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Efficiency


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AC motor general benefits

Robust and simple construction

=>High reliabilityClosed structure

=>Protected against harshenvironment

=>Saves cost of additionalclean air cooling system

No brushes or sliprings in themotor

=>Minimal maintenanceHigh efficiency

=>Substantial energysavings


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Motor Torque Speed curve

0

1

2

1 2

motor mode

generator mode

Tmax

nominal torque

TORQUE

SPEED

Typical torque/speed curve of a cage induction motor

M T S d i h F C


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Motor Torque Speed curve with Freq.. Conv.

T

n

Torque curves of a cage induction motor fed byfrequency converter

Motor efficiency Typical (DOL)


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Motor efficiency - Typical (DOL)

Motor losses


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Motor losses

Li h i


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Line harmonics

Cabling


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Cabling

Recommended cable types


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Recommended cable types

Fieldbus


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Definition of a Fieldbus

Fieldbus

Fieldbus


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Fieldbus System

Fieldbus

HMIHMI

System Bus

PROFIBUS-PAPROFIBUS-DP

Ethernet, TCP/IP Backbone

Operation

level

Control

level

Devicelevel

Software tools


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Software tools

Supporting the lifecycle of drives

DriveSize - Advanced dimensioningtool for drivesDriveBuilder - Configuration tool

producing cabinet dimensions andline drawingsDriveWindow - Comprehensive

set of features forcommissioning, maintenance andtraining

DriveLink - Communication interfacebetween Windows-based monitoringsoftwares and ABB drivesDriveSupport - Clear, concise servicetool for ABB drives

AC drives are the most eco efficient products we know of


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AC drives are the most eco-efficient products we know of

During the past ten years, ABB AC Drives have been reducingenergy consumption in pumps and fans by about 46 TWh every year.

This corresponds to 38 million tons less CO2 emissions per year.

0 1000 2000 3000 4000 5000 6000 7000 8000

GWh

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999


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Acdrive Basics

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