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8/9/2019 DTC_ABB_R3_BW

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Direct Torque ControlInduction Motor Vector Control Without an Encoder

Freq. Ref. V/f

Ratio

AC

Motor

Scalar Frequency Control

PWM

Modulator

V

f

SpeedControl

TorqueControl

ACMotor

T

Flux Vector Control

VectorControl

PWMModulator

V

f

SpeedControl

TorqueControl

ACMotor

Direct Torque Control

HysteresisControl

SpeedControl

TorqueControl

DCMotor

T

DC Drive

Evolution

of Drive

ControlTechniques

What

makes DTC

different?


2/10

Comparisons of Control TypesContro l Type Torque

Contro l

Flux

Contro l

Res po nse A dv an tag es Dis adv an tag es

DC Drive Direct Direct High High accuracy

Good torque response

Simple

Motor maintenance

Motor cost

Encoder required for high accuracy

Scalar Frequency

Control

None None Low No encoder

Simple

Low accuracy

Poor torque response

Flux Vector Control Indirect Direct High High accuracy

Good torque response

Encoder always required

Direct Torque

Control

Direct Direct High No encoder

Moderate accuracy

Excellent torque response

Encoder required for high accuracy

Integration of DTC into ABB DrivesWhere do we use it?

n ACS 600 family

Standard product line, 7 years experiencen ACS 600 Multidrive

Systems configuration

Common DC bus

Expanded communication

n ACS 1000 / ACS 6000 Medium voltage

n ACS 800


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DTC Advantages and Features

Why should we use it?

n Encoder not needed for many applications

n Excellent torque performance

Minimize process disturbances

Elimination of resonance problems

n Quiet operation

n Broad application coverage

Combining Theory and Technology

Field

Oriented

Control

Direct Self

Control

DSP

and ASIC

Technology

Direct

Torque

Control


4/10

Basic Direct Torque Control Scheme

Adaptive

Motor

Model

AC

Motor

Torque Ref

Flux Ref

Torque

Status

Flux

Status

Torque Comparator

Flux Comparator

Hysteresis Control ASIC

Optimal

Switching

Logic

S1, S2,

S3

Inverter

Current

DC Link Voltage

Switch Postions

Actual

Flux

Actual

Torque

Actual Speed

Actual Frequency

Hysteresis

Window

DSP

Complete Direct Torque Control Drive

Speed

Control

Torque Ref

Control

DirectTorqueControl

(see Fig. 2)

Flux Ref

Control

Switching

Frequency

Control

AC

Motor

Current

DC LinkVoltage

Switch

Postions

S1,

S2, S3

TorqueRef

Flux Ref

Actual Speed

Hysteresis

WindowActual

Frequency

Flux Level

Torq(Spd)Ref

Absolute Torque Ref

SpeedRef

Inverter


5/10

Slow Reversing

Time (s)

%

-60

-40

-20

0

20

40

60

80

100

0 5 10 15 20 25 30 35 40 45

750 r m

-750 r m

Shaft Torque

S haf t s e ed

Slow reversing with constant torque load (80%).

Measured shaft torque and speed. No encoder.Slow

Reversing

Optimal Starting

High starting torque

up to 200 % of motornominal torque

superior performance

for applications like

extruders and cranes

Automatic start

immediate start on

a rotating pump or

fan motor

no restart delay

Torque

Speed

t

t

Torque

Speed

t

t

DTC PWM


6/10

Excellent Torque Control

Torque:

PWM

DTC

Torque step rise time

No encoder required for accurate

torque control

Full torque at zero speed

Direct control of torque

no nuisance trips

DTC

Flux vector

Open loop PWM

< 5 msec.

10 to 20 msec.

> 100 msec.

Torque Response

-20

0

20

40

60

80

100

1 2 3 4 5 6 7

Time (ms)

%

Estimated air-gap torque

70 % torque reference step at 25 Hz. No encoder.

Torque

Response


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Unbeatable Speed ControlPWM

no encoder

DC drive

with encoder

DTC

no encoder

DTC

with encoder

PWM

with encoder

Static speed error

Dynamic speed error

1 to 3 %

3 %sec.

0.01 %

0.3 %sec.

0.01 %

0.3 %sec.

0.1 to 0.5 %

0.4 %sec.

0.01 %

0.1 %sec.

0 1000 2000 3000 4000 5000

100

150

200

0

500

Torque

(Nm)

Speed

(rpm)

Time (msec.)

Torque

Speed

Typical Torque and Speed Performance Data

DC Drive with

Encoder

Scalar

Frequency

Contro l

Flux Vector

Contro l

(with Encoder)

Direct Torque

Contro l

Direct Torque

Contro l with

Encoder

Torque Control

Linearity +/- 3 % +/- 12 % +/- 4 % +/- 4 % +/- 3 %

Repeatability NA +/- 4 % +/- 1 % +/- 1 % +/- 1 %

Response Time 10 ... 20 ms 150 ms 10 ... 20 ms 1 ... 2 ms 1 ... 5 ms

Speed Control

Static Accuracy +/- 0.01 % +/- 1 ... 3 % +/- 0.01 % +/- 0.1 ... 0.3 % +/- 0.01 %

Dynamic Accuracy 0.3 %s 3 %s 0.3 %s 0.4 %s 0.1 %s


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Implementation of Special Features

n Flux Optimization

n Flux Braking

n Automatic (Flying) Start

n Quiet Operation

n Power Loss Ride Through

Low Audible Noise

No high-pitch

audible whine,due to just-in-time switching

Low motor noise,

due to sophisticated flux

optimization

Low-noise fans0 5 10 15 20 25

0

20

40

60

80

Frequency (kHz)

Typical motor noise spectrum

DTC

PWM

Noise

level

(dB)


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Power Loss Ride Through

Fast response to mains side

interruptions

Controlled operation

during power loss

0 5 10 15 20 25

TM

fOUT

UMIN

UDC

Time (sec.)U

DC = DC voltage

UMIN = DC voltage minimum limit

fOUT

= output frequency (proportional to speed)

TM = motor torque

The DTC Solution

What do we get?

n Reduced encoder countn Fast torque response

n High starting torque

n Special features

n Broad application coverage


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Direct Torque ControlInduction Motor Vector Control Without an Encoder

Direct Torque Control

Questions ???

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