AC Drive Technology

7/29/2019 AC Drive Technology

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Copyright 2007 Rockwell Automation, Inc. All rights reserved.

TORQUE ControlTechnologies

Copyright 2005 Rockwell Automation, Inc. All rights reserved


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Diode rectifier converts AC line voltage to fixed voltage DC.

DC voltage is filtered to reduce current ripple from rectification. Inverter changes fixed voltage DC to adjustable PWM AC voltage.

Diode rectifier converts AC line voltage to fixed voltage DC.

DC voltage is filtered to reduce current ripple from rectification. Inverter changes fixed voltage DC to adjustable PWM AC voltage.

Power Diagram


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What we Have at output to control

1) Voltage,

2) Torque Current IT,

3) Flux Current Iq and

4) Angle between voltage and Current.

5) Motor Thermal Condition


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Motor Control Technologies

ConveyorMixer

Extruder

Volts / HertzSensorless

Vector

Field

Oriented

Speed Regulator Speed Regulator Torque RegulatorSpeed Regulator

Current LimitAdvanced

Current Limit

High Bandwidth

Current Regulator

Converting

Flux

Vector

Speed Regulator Torque Regulator

Current Regulator

based on

Estimated Values

Converting

Parameter Selectable (Application Based)


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takes a speed reference and varies Voltage and Frequency

Volts/Hertz Control

The drive monitors total current - no current resolver, Cannotdistinguish between Id from Iq (Torque Capability limited)

Current Limit monitorsmotor current and altersfrequency command

Slip Compensation alters frequencyreference during load changes


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Maximum Voltage

MaximumFrequency

Frequency

Voltage

Motor NP Voltage

Motor NPFrequency

RunBoost

00

Fan Pump Volts/Hertz Variable Torque


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Volts/Hertz Control

To increase starting torque, V/Hz Drives use Voltage Boost to ovTo increase starting torque, V/Hz Drives use Voltage Boost to overer--flux theflux the

motor to increase starting torquemotor to increase starting torque

OutputOutputFrequencyFrequencyBase FrequencyBase Frequency60

OutputOutput

VoltageVoltage

Hz

30

460

248

138

15 90

Ratio @ 460VAC

= 7.67 V/Hz +

% BOOST

0

VoltageVoltage

BoostBoost

Voltage Boost over prolonged operating periods may result in oveVoltage Boost over prolonged operating periods may result in overheating of the motors insulation systemrheating of the motors insulation system

and result in damage or premature failure.and result in damage or premature failure.

CAUTION: Motor Insulation Life is decreased by 50% for every 10C above the insulations temperaturecapacityCAUTION: Motor Insulation Life is decreased by 50% for every 10C above the insulations temperaturecapacity


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Volts/Hertz Control

Notice that the ability of the drive to maintain high torque outputat low speeds drops off significantly below 3 Hz


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Volts/Hertz Control

Can not keep the shaft speed at desired level when subjected to shock loads.

However Drives with slip compensation feature correct for extra load but the dynamicsare somewhat limited.

Shock Load


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There are a couple of key things to point out.

First, the ability of the drive to maintain high torque output at low speeds drops off significantly

below 3 Hz.

This is a normal characteristic of a Volts/Hertz drive and is one of the reasons that the

operating speed range for Volts/Hertz drives is typically around 20:1.

Second, you can see as the load is increased, the motor speed drops off (due to slip). Using

Compensation can help.

Thirdly, the maximum Torque that can be had is 150 to 160% only.

Volts/Hertz Control


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Vector Definition ? To know the direction as well as magnitude of a certain quantity

Vector Drive Definition

The ability to independently identify and control the flux and torqueproducing components of current in a motor for the purpose ofaccurate torque and power control.

ITotal

= (IReal

) 2 + (IReactive

) 2


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Ia = Torque Producing Current (Armature Current)If = Flux Producing Current (Field Current)

DC

IaIa If

Z Z

DC

Ia

If

Load 1

Load 2

=a*sin (d)

DC Motor Model

T = K X

X Ia X Sin (d)d = 900


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Iq = Torque Producing CurrentId = Flux Producing CurrentIs = Total Stator Current

AC

Is

IdIq

Z

ZZ

AC

Id

Iq

Load 1

Load 2

Is

Is

= K Id * Iq * sin(d)

T = K X X Ia X Sin (d)d = Varies

AC Motor Model

d


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ConveyorMixer

Extruder


VectorField

Oriented

Speed Regulator Speed Regulator Torque RegulatorSpeed Regulator


Current Limit

High Bandwidth

Current Regulator

Converting

Flux

Vector


Current Regulator

based on

Estimated Values

Converting


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Sensorless Vector Control

Ability to sense the torque current and keep flux current constant through

out the operation.Produces Tmax/Amps of motor Current keeping Flux Current Constant


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Improved control technique by providing both a magnitude and anglebetween the voltage and current. Current out of phase with voltage is fluxcurrent. Current in phase is torque producing current.

V/Hz drives only control the magnitude.

Vangle controls the amount of total motor current that goes into motor flux,enabled by the Torque Current Estimator.

By controlling flux current, any additional current goes to producing torque,and we get better torque per amp (avoids underfluxing and overfluxing).


The Torque Current Estimator block determines the percent of current that

is in phase with the voltage, providing an approximate torque current.


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High Starting (Maximum) Torque about 250%

By controlling flux, low speed operation and torque control is improved over the

standard V/Hz drive


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Shock Load

Better Dynamic Response to shock loads


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ConveyorMixer

Extruder


VectorField

Oriented

Speed Regulator Speed Regulator

Torque Regulator

Speed Regulator


Current Limit

High Bandwidth

Current Regulator

Converting

Flux

Vector


Current Regulator

based on

Estimated Values

Converting


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Voltage Feedback

Flux Vector Control w/ Feedback

Uses Speed & Current Regulator ,

Has a Current Resolver that separates Torque and Flux CurrentsAuto - tuning is a must


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Flux Vector Control w/o Feedback


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2

1

Torque

Speed (Hz)1 2 5 10 20 30 40 50 60

Flux Vector Control Torque Vs Speed

Much better response at low speeds 2Hz Torque is greater than 150%


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Shock Loads

Shock load dynamic Response much faster

Encoder FOC

Load Removed

Sensorless FOC

Load Removed

FOC,

FV & SV

Load applied

V/HzLoad

Applied

0.9

0.875

0.85

0.825

0 1 2 3 4 5

Time (seconds)

PerUnitQu

antities


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COMPARING AC DRIVE PERFORMANCECOMPARING AC DRIVE PERFORMANCE


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Starting into

rotating loads

V/Hz SVC FVC

Better G ood Best

FVC operation is best since the position and velocity of therotor is known and restarting is immediate.

V/Hz being a soft speed regulator is very forgiving forrestarting into loads with high inertia.

SVC may be more difficult to implement due to limitations bymanufacturer. Processor & algorithm dependent.

FVC operation is best since the position and velocity of theFVC operation is best since the position and velocity of the

rotor is known and restarting is immediate.rotor is known and restarting is immediate.

V/Hz being a soft speed regulator is very forgiving forV/Hz being a soft speed regulator is very forgiving for

restarting into loads with high inertia.restarting into loads with high inertia.

SVC may be more difficult to implement due to limitations bySVC may be more difficult to implement due to limitations by

manufacturer. Processor & algorithm dependent.manufacturer. Processor & algorithm dependent.

Control Selection


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V/Hz operation inheriently controls multiple motors. SVC or FVC operation with multiple motors is only possible

when motor shafts are mechanically locked together andassumptions are made about total motor current values.

V/Hz operation inheriently controls multiple motors.V/Hz operation inheriently controls multiple motors.

SVC or FVC operation with multiple motors is only possibleSVC or FVC operation with multiple motors is only possible

when motor shafts are mechanically locked together andwhen motor shafts are mechanically locked together and

assumptions are made about total motor current values.assumptions are made about total motor current values.

Multi-motor

Operation fromone drive V/Hz SVC FVC

BestNot

RecommendedNot

Recommended

Control Selection


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V/Hz is typically good for up to 10:1 Constant Torque.

SVC is typically good for up to 40:1 Constant Torque.

FVC is typically good for up to 1,000:1 which includescontinuous operation at Zero Speed.

V/Hz is typically good for up to 10:1 Constant Torque.V/Hz is typically good for up to 10:1 Constant Torque.

SVC is typically good for up to 40:1 Constant Torque.SVC is typically good for up to 40:1 Constant Torque.

FVC is typically good for up to 1,000:1 which includesFVC is typically good for up to 1,000:1 which includes

continuous operation at Zero Speed.continuous operation at Zero Speed.

Constant

Torque Range V/Hz SVC FVC

Good Better Best

Control Selection


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V/Hz has no quantifiable response time or bandwidth.

Typical SVC specifications may state 100 Radians/second.

Typical FVC specifications may state 1,000 Radian/second.

V/Hz has no quantifiable response time or bandwidth.V/Hz has no quantifiable response time or bandwidth.

Typical SVC specifications may state 100 Radians/second.Typical SVC specifications may state 100 Radians/second.

Typical FVC specifications may state 1,000 Radian/second.Typical FVC specifications may state 1,000 Radian/second.

Dynamic

Response V/Hz SVC FVC

Good Better Best

Notuning AdjustableGains for tuning AdjustableGains for tuning

Control Selection


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What is ?

Force Technologyis Allen-Bradleys version ofField ORiented

Control

Field Oriented Control is the First AC Motor Control Technology

That Can Truly Obtain DC Like Dynamic PerformanceForce Technologyhas been developed over a 10 year period and is independent of the

hardware platform. In other words, as new hardware technologies are developed ForceTechnologywill continue to improve.

Allen-Bradley has 9 patents on the basic technology and continues to be a leader inField Oriented Control technology.


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FORCE-FIELD ORIENTED CONTROL

Excellent Technology to produce as high as 400% Maximum torqueProduces 100% torque at zero speed Key for Hoist Application


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FORCE-FIELD ORIENTED CONTROL W/OFeedback


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FORCE-FIELD ORIENTED CONTROL

FORCE-FIELD ORIENTED CONTROL Torque Vs Speed

Excellent response at low speeds At 1Hz Torque is greater than 250%


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FORCE - FIELD ORIENTED CONTROL

Shock load dynamic Response is Excellent

Encoder FOC

Load Removed

Sensorless FOC

Load Removed

FOC,

FV & SV

Load applied

V/HzLoad

Applied

0.9

0.875

0.85

0.825

0 1 2 3 4 5

Time (seconds)

PerUnitQuantities


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Advantages of Over DC

Higher Bandwidth on Current Regulator

Quicker Reaction to Shock Loads

Reduced Motor Maintenance - AC Motor MTBF 5 Times Longer than DC- AC Motor

Cost to Repair One Fourth of DC

AC Motor Lower Rotor Inertia

AC Motor Adaptable to Harsh Environments


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Performance Comparison with Encoder

FORCETechnology

TypicalVector

Digital DCDrive

Speed Control

Speed Regulation +/-0.001% +/-0.05% +/-0.001%

Dynamic Response 100 Rad 15 Rad 100 Rad

Speed Range 1000:1 100:1 1000:1

Torque Control

Regulation, No RTD +/-2% +/-20% +/-5%

Dynamic Response 2500 Rad 300 Rad 950 Rad


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Performance & Benefits for

1000 to 1 Speed Range

Full Torque at Zero Speed

0.001% Speed Regulation

2% Torque Regulation


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Applications For

Extruder

High Starting Torque

Up to 400% w/ Proper

Sizing

Material Handling

Low Speed Performance

Creep / Idle Speeds Metals

Precise Speed Control

Casters / Process Lines /

Slitters Precise Torque Control

Load Share / Tension

Leveling

Crane/Hoist

Full Torque at Zero Speed

Continuously

Torque Proving Circuits

Fast Response / Torque

Switchable Speed / Torque

Web Handling

Precise Line Speed Control

Precise Torque Control

Draw / Load Share

Tension Control

Winder Control

Dia Comp / Taper Tension


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Vector Vs Field Oriented Control

Vector Control

Acknowledges that motor current is the vector sum of the torque and flux currentsand uses this information to provide better control of motor speed/torque.

Field Oriented Control The ability to independently control the flux and torque in a motor for the purpose of

accurate torque and power control.


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Documents

AC Drive Technology