introduction to variable speed drives · pdf fileintroduction to variable speed drives pekik...

1

Introduction to Variable Speed Drives

Pekik Argo DahonoElectrical Energy Conversion Research Laboratory

Institute of Technology Bandung

Why Electric Drives

• Electric drives are available in any power.

• They cover a wide range of torque and speed.

• Adaptable to almost any operating conditions.

• Electric drives are operable instantaneously.

• High efficiency.

• Easily controllable.

• Can be operated in all four quadrants.

• Can be built in a variety of designs.

2Variable Speed Drives

2

Limitations of Electric Drives

• The dependence on a continuous power

supply causes problems with vehicle

propulsion.

• Due to the magnetic saturation, electric

motors are likely to have a lower power-to-

weight ratio than high pressure hydraulic

drives.


Why we need variable speed drives

• Some industrial process need variable speed

drives (robots, machine tools, conveyors,

etc.)

• Some industrial machines will be more

efficient if driven by a variable speed drive

(pumps, blowers, fans, etc.)

• Vehicle propulsion system.


3

Energy flow and typical losses


Energy Team


4

Energy Team


Pumping System

• Variable –flow variable-pressure

• Constant-flow variable-pressure

• Variable-flow constant-pressure


5

Pump Characteristics

( )3

221121

3

Speed Power Pump

(kWh)Energy Pump

(kW)Power Pump

)()/( (kW)Power Pump

∝

×−×=−

×××=

××=

××=

tHQHQkEE

tHQk

HQk

mheadhmFlowk

RPM2

RPM1

FLOW2

FLOW1∝

2

2

RPM2

RPM1

PRESSURE2

PRESSURE1∝


Pumping System with Valve Control

PUMP

MOTOR

STARTER

MOTORIZEDVALVE

SET-POINTCONTROLLER

SENSOR

FLOW

REFERENCE


6

Pumping System with VSD

PUMP

MOTORSENSOR

FLOW

REFERENCE

CONTROLLER

SET-POINTCONTROLLER


Variable-flow variable-pressure

Pumping System

200 400 600 800 1000 1200 1400 1600 1800

0

0

40

80

120

160

200

240

Tota

l H

ea

d (

FT

)

Flow (GPM)

40 50 6070 75

8078

30

100% SPEED

84% Speed

operating

Point

Valve Losses

Throttled Operating

Point

Throttled

System

Curve

Unthrottled

System Curve

Pump Output =

Power

Head (Ft.) x Flow (GPM) x Specific Gravity

3960


7

Energy input for variable-flow

variable-pressure pump

20

10

30

40

50

60

70

80

0

500 700 900 1100 1300 1500 1700

FLOW (GPM)

INP

UT

KW

ADJUSTABLE SPEED

OPERATION WITH

ENERGY EFFICIENT MOTOR

VALVE OPERATION

WITH STANDARD

EFFICIENTMOTOR


Constant-flow variable-pressure

200 400 600 800 1000 1200 1400 1600 1800

60

0

40

80

120

160

200

240

TO

TA

L H

EA

D

(FT

.)

FLOW (GPM)

40 50 60 70 75

8078

30

20

100

140

180

220

CONSTANT FLOW

100% SPEED

PUMP POWER OUTPUT =

HEAD x FLOW x SPECIFIC GRAVITY

3960

VALVE LOSSES

REDUCED SPEED

OPERATING POINT

CONSTANT SPEED

THROTTLED OPERATING POINT


8

Constant-flow variable-pressure

20

10

30

40

50

60

70

0

100 120 140 160 180 200 220 HEAD (FT.)

INP

UT

KW

ADJUSTABLE SPEED

OPERATION WITH

ENERGY EFFICIENT MOTOR

VALVE OPERATION WITH

STANDARD EFFICIENT MOTOR


Variable-flow constant-pressure

PUMPMOTOR

STARTER

MOTORIZED

VALVE

SET-POINT

CONTROLLER

SENSOR

MAIN

VALVES

PRESSURE

REFERENCE

CONSTANT


9


PUMP

MOTORSENSOR

CONSTANT

PRESSURE

REFERENCE

CONTROLLER

SET-POINT

CONTROLLER

MAIN

VALVES



200 400 600 800 1000 1200 1400 1600 1800

60

0

40

80

120

160

200

240

TO

TA

L H

EA

D

(FT

.)

FLOW (GPM)

40 50 6070 75

8078

30

20

100

140

180

220

CONSTANT SPEEDOPERATING POINT

CONSTANT PRESSURECONTROL LINE

TOTAL FLOW

SYSTEM CURVE

BYPASS PARTIALLY

OPEN

MAIN SYSTEM CURVE #2

MAINSYSTEM CURVE #1

BYPASS CLOSEDSYSTEM

VALVES OPEN

MAINFLOWMAINFLOW

BYPASSFLOWBYPASSFLOW

CLOSING SYSTEM VALVES

OPENING BYPASS VALVE

SYSTEM CURVE #1

SYSTEM CURVE #2


10


200 400 600 800 1000 1200 1400 1600 1800

60

0

40

80

120

160

200

240

TO

TA

L H

EA

D

(FT

.)

FLOW (GPM)

REDUCED SPEED

OPERATING POINT

20

100

140

180

220 CONSTANT SPEEDOPERATING POINT

100% SPEED

PUMP OUTPUT POWER =HEAD x FLOW x SPECIFIC GRAVITY

3960

40 50 6070 75

8078

30

90% SPEED

BYPASS

FLOW

BYPASS

LOSSES

MAIN

FLOW

TOTAL

FLOW



20

10

30

40

50

60

70

0

FLOW (GPM)

INP

UT

KW

ADJUSTABLE SPEED

OPERATION WITHENERGY EFFICIENT MOTOR

BYPASS OPERATION WITHSTANDARD EFFICIENT MOTOR

500 700 900 1100 1300 1500 1700

80


11

Comparison of two pumping systems


Two-Stages Pumping System


12

Benefits

• High availability

• Fast and precise control

• Minimized energy consumption

• Reduced emission

• Minimized actuator equipment

• Soft starting

Variable Speed Drives 23

Power Consumption


13

Investment and Energy Costs

Variable Speed Drives 25Energy is calculating for 1300 kW motor and 3 years operation

Fans


14

Rotary screw air compressor


Lifts


15

Lift Energy Comparison


Mechanical Variable Speed Drives

Conveyor Belt LoadCentrifugal-Acting

In-Line Fluid CouplingFull-SpeedAC Motor


16

Mechanical Variable Speed DrivesV-Belt

Hand crank opens and closes sheave tomove belt up or down.

Beltridesup or

down basedon groove

setting

Available up to 100 kW


Mechanical Variable Speed Drives

MotorizedSpeed Changer

PIV Transmission BoxFull-Speed Input

Reduced-SpeedOutput

PrimeMover

Operator-ControllerPotentiometer forSpeed Selection

ACMotor


17

Conventional Variable Speed Drives

Full-Speed AC Motor

Full-Speed Shaft

Variable-SpeedShaft

Magnetic fieldfor Flux Control

FieldControl

Speed Potentiometer


Conventional Variable Speed DC Drives

source AC

φ3

Motor

G

Generator

Exciter

M

Motor

Load


18

Modern Variable Speed DC Drives

M

Motor

Load

source AC

ConverterQuadrant -Four

supply Field


Conventional Variable Speed AC Drives

• Pole changing

• Stator voltage control

• Rotor resistance control

• Slip-recovery drive system


19

Modern Variable Speed AC Drive System

Converter AC-ACsou

rce

A

C

φ3

supply AC

frequency-variable

voltage-Variable

Motor AC


Advantages of Variable Speed AC Drives

• Commutatorless and brushless

• High-power and high-speed

• Simple design and robust

• High-efficiency


20

Classifications of Variable Speed AC Drives

• Motor types : induction and synchronous

motors

• Power supplies : inverter, cycloconverter,

matrix converter.

• Inverter types : voltage source, current

source, square type, PWM.


Variable Voltage Inverter System

φ3

Motor AC

outv

source AC

rectifier

Controlled

inductor

Smoothing

capacitor

Smoothing

inverter

wave-Square

• DC voltage is variable and controlled by the rectifier.

• The output voltage of inverter is quasi square-wave.

• The output frequency is determined by the inverter.

• The output voltage is determined by the rectifier.

• An LC filter is required in the dc link.


21

PWM Inverter System

φ3

Motor AC

outv

source AC

rectifier

edUncontroll

capacitor

Smoothing

inverter PWM

• The dc voltage is constant. No controller is required by the rectifier.

• The inverter is controlled by pulse width modulation (PWM) technique.

• The output current is almost sinusoidal.

• The output voltage and frequency are controlled by the inverter.

• Only a dc capacitor is used as the filter in the dc link.


Current Source Inverter System

φ3

Motor AC

outi

source AC

rectifier

Controlled

inductor

Smoothing

inverter

wave-Square

• The dc link current is controlled by the rectifier.

• The inverter output current is quasi square-wave.

• The output current frequency is controlled by the inverter.

• The magnitude of the output current is controlled by the rectifier.

• Only an inductor is used as the filter in the dc link.


22

Six-Pulse CSI System


Twelve-Pulse CSI System


23

PWM CSI System


Cycloconverter System

source AC

Motor AC

• No dc link.

• The output voltage magnitude and frequency are controlled

by the cycloconverter.

• The output frequency is less than the ac supply frequency.


24

Load Commutated Inverter System

φ3

Motor

sSynchronou AC

outi

source AC

rectifier

Controlled

inductor

Smoothing

inverter

commutated Load

• The dc link current is controlled by the inverter.

• The output current waveform is quasi square-wave.

• The thyristors of inverter are commutated by the help of load voltage.

• The inverter frequency is determined by the motor speed.


Large LCI System


25

Slip Recovery Induction Drivemotorinduction

rotor Wound

RectifierInverter

sou

rce

A

C

• Converter rating is smaller than motor rating

• Only subsynchronous operation is possible

• Wound rotor motor is required


VSD with Unity Power Factor Rectifier

dC

boostL

inCinL

IM

• Input current waveform is almost sinusoidal and

unity power factor

• Insensitive to input voltage variation

• Applicable up to 100 kW


26

VSD with PWM Rectifier

dC

source AC

IM

rectifier PWM inverter PWM

• Power flow is bidirectional

• Input current waveform is almost sinusoidal

• Input power factor is adjustable

• Insensitive to input voltage variations


Matrix Converter

IM

⇒

sou

rce

A

C

• No dc link

• Output frequency is less than the input frequency

• Input current is almost sinusoidal

• Input power factor is adjustable


27

Additional Advantages of using VSD

• Soft starting (reducing system kVA requirement and lengthening rotating equipment life).

• Increased motor life

• Shortened compressor startup time

• Process ride through

• Increased speed range

• Extended operating range before surge line

• Suitable for automation

• Can be used to overpowering the equipment without endangering the motor


Medium Voltage ABB Drives


28

Toshiba System


VSD Price


29

Technical Barriers

• VSD may reduce the motor efficiency

• VSD draws nonsinusoidal input current

• VSD may induce overvoltage to motor winding when the cable is longer than 50 meters

• VSD may induce bearing currents

• VSD may overloading shunt capacitor in the supply system

• Special technicians, engineers, and operators may required


Motor efficiencies

00

80

85

90

95

25 50 75 100

% E

FF

ICIE

NC

Y

% FULL-LOAD TORQUE

100 HPENERGY EFFICIENT

MOTOR

100 HPSTANDARD EFFICIENT

MOTOR

60 HZ

60 HZ

30 HZ

60 HZ

60 HZ

30 HZ


30

Chances to save energy

• Are there motors that drive fans, pumps, or

compressors which are modulated by dampers or

valve?

• Are there motor using speed control devices?

• Is there machinery that can be operated at other

than its current speed?

• For the motors identified by the above three

questions, what is the duty cycle and load profile?


Power Line Considerations


31





32



Implementation cost factors

• How will the VSD improve quality?

• What costs associated with existing motor drive inefficiencies?

• What are the costs of maintaining existing equipment? Are they obsolete and in need of replacement?

• Do other problems of equipment reliability cause production delays and higher production costs? How can they be eliminated by VSDs with self-diagnostic features?

• Is there opportunity to create additional space by removing large mechanical equipment with the installation of VSD?

• Can plant noise be reduced by using VSD?

• What shutdown arrangements are required to provide time to install a VSD?


33

Factors that influence first cost

• Rectifier and inverter type

• Harmonic effects

• Isolation requirements

• Control specifications

• Special requirements

• Training requirements


Thank You

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