High Power Drives

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PROF.V.T.RANGANATHAN

HIGH POWER DRIVES

Prof.V.T.Ranganathan

Dept. of Electrical EngineeringIndian Institute of Science


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Medium Voltage Drives:Motor voltages: 2.3kV,

3.3kV,4.16kV, 6.3kV, 6.9kV

Requirements:Availability: 99.9%

Efficiency: > 97%Input PF: > 0.98 at all speeds

On The Fly Start: YESRegeneration:Not always needed


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Desirable:Easy to install, minimum cabling

Possibility of locating transformeroutside converter room

Retrofit on existing normal

motors

No limit on cable length to motor


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MV Drive Configurations:

InductionMotor

SynchronousMotor

SlipRingMotor

VSI CSI CSI LCI

Cyclo

Converter

CSI(Kramer)Scherbius

VSI


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APPLICATION TYPES

SLOW RESPONSE FAST RESPONSE

FANSPUMPSCOMPRESSORS

CRANESHOISTSWINDERSCOILERSROLLING MILLSPAPER MILLS


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Induction Motor Drives:From 0.5 MW up to 5MW

Synchronous Motor Drives:From 3 MW up to 100MW

Slip Ring Induction Motors:From 0.1MW to 10s of MW


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Information from ABB website


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DEVICES USED IN DIFFERENT CONFIGURATIONS

VSIs ------ IGBTs ----- up to 6.5Kv, 600Amore commonly 3.3kV,800/900A

IGCTs ------ up to 5.5kV, 900A

LCIs -------- SCRs ------ up to 4.5kV,3000A


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IGBT Vs IGCT

EasierHardSeries

connection

Smaller forsimilar

rating

Higher forhigh

voltage

ratings

Voltagedrop

ComplexEasierGate drive

HigherLower(


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Two Level Inverter Configuration


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Ton

Tc/2

Vp

Vref

Vdc__2

-Vdc__2

SINE-TRIANGLE PWM FOR 2-LEVEL INVERTERS


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Max. IGBT voltage rating: 3300V

Max. DC Bus : 2200V

Max. Motor L_L Voltage:1700V (sq. wave)1300V (PWM)

IGBT current /module :400A

RMS Current of :150A

O/P KVA rating/module : 275KVA (for 1100V)

For higher KVA, modules have to be paralleled.


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Motors of 1MW and above:Designed at higher voltages

KV: 1.5 2.2 3.3 4.2DC Bus: 2.0 3.0 4.5 5.8

Such voltages require multiple devices in series.

Direct series connection of devices is difficult;also it leads to very high dv/dt stress on

motor windings.

Multistepped waveform of motor voltage preferred.

This leads to multilevel inverter configurations.


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Functional equivalent of three level inverter

Pole voltage can have three levels: +Vdc/2, 0, -Vdc/2

Motor line voltage will have 5 levels:

+Vdc, +Vdc/2, 0, -Vdc/2, -Vdc


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Waveforms of Pole Voltage and Line Voltage:


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THREE LEVEL DIODE CLAMPED INVERTER


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THREE LEVEL H-BRIDGE INVERTER


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Effect Of VSI Operation on Induction Motors

Nonsinusoidal voltages: lead to harmoniccurrents, torque pulsations. This problem is

tackled by resorting to pulsewidth modulation

Voltage steps applied to motor: this leads to

1) dv/dt stress on the motor insulation;

2) bearing currents;

3) overvoltage due to reflections when long cablesare used to connect motor to inverter.


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SOLUTION TO PROBLEMS DUE TO VSI OPERATION

MULTISTEP INVERTERS

OUTPUT FILTER BETWEENINVERTER AND MOTOR


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OTHER CONVERTERS FOR INDUCTION MOTOR DRIVES

A.CYCLOCONVERTERS

SIMPLE LINE COMMUTATED CIRCUIT

OUTPUT FREQUENCY LIMITED TO ABOUT 20Hz

LINE SIDE POWER FACTOR NOT GOOD

INPUT CURRENT DRAWN FROM LINE HAS COMPLEXWAVESHAPE

USED IN HIGH PERFORMANCE LOW SPEEDAPPLICATIONS SUCH AS ROLLING MILLS,CEMENT MILLS ETC.


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THREE PHASE CYCLOCONVERTER


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B. CURRENT SOURCE INVERTERS

RUGGED COMPARED TO VSI

REGENERATION INHERENT

TORQUE RESPONSE SLOW COMPARED TO VSI

LOW SPEED OPERATION REQUIRES PWM WHICHIS NOT EASY

OUTPUT CAPACITOR RESONATES WITH1. MOTOR LEAKAGE INDUCTANCE REQUIRING

ELIMINATION OFTHE RESONANCE FREQUENCYTHROUGH PWM

2. MOTOR MAGNETIZING INDUCTANCE, LIMITINGTHE HIGHEST FUNDAMENTAL FREQUENCY OFDRIVE OPERATION


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CSI DRIVE CONFIGURATION

MOTOR

GTOINVERTER

CHOKE

RECTIFIER

vrvi

id

CAPACITOR


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FEATURES OF SLIP RING MOTORS

CONNECTION CAN BE MADE TO ROTOR

ROTOR RESISTANCE CONTROL WAS USED

IN SOME EARLY APPLICATIONS E.G. WIND

TUNNELS, PUMPS ETC.

SUBSYNCHRONOUS CASCADE WAS THE

FIRST COMMERCIAL APPLICATION OF

ROTOR SIDE CONTROL


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SUBSYNCHRONOUS CASCADE

INVERTER

CHOKE

RECTIFIER


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FEATURES

CAN WORK ONLY AT SUBSYNCHRONOUSSPEEDS THIS IS SUFFICIENT FOR MANY

APPLICATIONS SUCH AS WATER PUMPING,FANS ETC.

TRANSFORMER REQUIRED TO IMPROVELINE SIDE DISPLACEMENT FACTOR


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FEATURES (contd.)

HARMONICS ARE INJECTED INTO THELINE

ROTOR CURRENT IS NOT SINUSOIDALLEADING TO TORQUE PULSATIONS


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FEATURES (contd.)

IT WAS RECOGNISED THAT IF ROTORSIDE CONVERTER COULD HANDLEBIDIRECTIONAL POWER FLOW,SUPERSYNCHRONOUS OPERATION ALSOWOULD BE POSSIBLE

CYCLOCONVERTERS WERE USED ONTHE ROTOR SIDE FOR INJECTINGCURRENT AT ANY REQUIRED PHASE AND

FREQUENCY


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FEATURES (contd.)

RESULTING DRIVE HAD THE DRAWBACKS

THAT LINE CURRENT WAS NOTSINUSOIDAL AND THE CIRCUIT WASCOMPLEX

TODAY, ROTOR CURRENT CAN BECONTROLLED BY CONNECTING VSIs INCASCADE


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GRID CONNECTED SLIP RING MACHINE

WITH ROTOR SIDE CONTROL

STEPDOWNTRAFO.

SLIP RINGINDUCTIONMOTORFEC + INVERTER RATED FOR SLIP POWER

PS

PR


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FEATURES

Variable speed constant frequency operation

Converter power rating is fraction of systempower

Operation below and above the synchronousspeed possible

Active and reactive power can be controlled in adecoupled manner


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OPERATING REGION OF GRID CONNECTEDSLIP RING MACHINE

WITH ROTOR SIDE CONTROL

speed

torque

1 p.u. 2 p.u.

1 p.u.

-1 p.u.

SUBSYNCHRONOUSMOTORING

SUBSYNCHRONOUSGENERATION

SUPERSYNCHRONOUSMOTORING

SUPERSYNCHRONOUSGENERATION

0 p.u.

S

InverterRating

= 1 p.u.


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DOUBLE INVERTER FED

SLIP RING INDUCTION MOTOR DRIVE

GRIDDIODE BRIDGE

OR

IGBT FRONT END

COMMON

DC BUS

STATOR SIDEINVERTER

ROTOR SIDEINVERTER

SLIP RINGMOTOR

PS PR


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Operating region of the drive

speed

torque

1 p.u-1 p.u-2 p.u 2 p.u

-1 p.u

1 p.u

Mode I

Mode IIMode III

Mode IV


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Important FeaturesImportant Features


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Proposed drive can extract 2p.u. power from 1p.u. motor

Motor can run at 2p.u. speed without field weakening

operation.

The drive is extremely rugged at very low speedincluding the zero speed operation without rotorencoder.

Controller depends very little on machine parameters

Negligible effect of temperature variation

Important FeaturesImportant Features


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Application AreasApplication Areas

Because of the following features:

Reliable sensorless operation even at very

low speedHigh speed with full torque operation

SUITABLE APPLICATION AREAS ARE:

ROLLING MILLS

CRANES AND HOISTS

HYBRID ELECTRIC BUS


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LCI DRIVE CONFIGURATION

SYNCH.MOTOR

INVERTER

CHOKE

RECTIFIER

vr

vi

id


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FEATURES

The rectifier works at line frequency

The inverter decides the motor frequency,which can be greater than the linefrequency also

The choke serves to isolate the two sides

Regeneration is possible by reversing theroles of the two converters


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The turn-off of the inverter thyristors is brought about

by the machine back emf; hence the nameLoad Commutated Inverter

The motor has to be operated at leading power factor for

this to be possibleAt low speeds

The back emf is not sufficient to turn off the thyristors

The dc link current has to be brought to zero byphasing back the rectifier; then the new pair ofconducting devices in the inverter have to be fired;

the dc link current then has to be brought up againThis mode of operation lasts until the output frequencyreaches about 5 Hz.

SCR BASED LOAD COMMUTATED CSI


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SCR BASED LOAD COMMUTATED CSI

WITH ACTIVE FILTER

FEATURES


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FEATURES

SCRs USED INSTEAD OF GTOs

GATE DRIVE MUCH SIMPLER

ACTIVE FILTER COMPENSATES MOTOR REACTIVE

POWER AND INJECTS CONTROLLED REACTIVE

POWER TO MANAGE THE COMMUTATION OF

THE SCRs


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VSI OF THE ACTIVE FILTER CAN ALSO STARTTHE MOTOR

NO NEED FOR PULSING THE DC LINK CURRENTAS IN LCI

ACTIVE FILTER ALSO COMPENSATESTHE HARMONICS OF THE CSI

MOTOR SEES SINUSOIDAL VOLTAGEAND CURRENT


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Experimental Results


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PROPOSED LCI FED SM DRIVE - CONFIGURATION


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Proposed LCI fed SM Drive - Advantages

Output machine current and therefore output machinevoltages are nearly sinusoidal.

Developed torque is smooth.

Machine power factor can be controlled.

Control is speed sensor-less.

Starting procedure is easier.

Can be added on as a retrofit to existing LCI drives


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NEW INDUCTION MACHINE CONFIGURATION

A new type ofinduction machine is proposed where torqueand flux component of current flow through two separatewindings, as in DC Machines and Synchronous machines.

Torque component of current comes from a load commutatedCSI built with SCRs, whose commutation is ensured bycontrol.

Flux component of current comes from a separate VSI whichswitches at lower switching frequency compared to active

filter.


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ACTIVE REACTIVE MACHINE DRIVE

INV1CSI

A1

B1

C1

(11kV)

REC1CSI

3-phSOURCE

3-PH TRANSFORMER

INV 3

VSI

ACT-REACTMACHINE

INV2VSI

LCFILTER

A2

B2

C2

(2.2 kV)

(2.2 kV)

TRANSFORMER

& RECTIFIER


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simulation results

Voltage & current response of winding 1

3.04 3.045 3.05 3.055 3.06 3.065 3.07 3.075 3.08 3.085 3.09

-15

-10

-5

0

5

10

15

Steady state response of winding 1 voltage and current

time(sec)

Vs1(1un

it=15Volt),Is1(1unit=1A)

Vs1

Is1


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CONCLUSION


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CONCLUSION

PRESENT MARKET IN HIGH POWER MEDIUM VOLTAGEDRIVES SHARED BWTEEN THREE LEVEL VSI DRIVES FORINDUCTION MOTORS AND CYCLOCONVERTER OR LCI

FOR SYNCHRONOUS MOTORS

NEW APPROACH OF HANDLING THE MAIN POWERTHROUGH SCR CIRCUITS AND THEREACTIVE/HARMONICPOWER THROUGH VSIs RESULTS IN SINUSOIDALMOTOR VOLTAGE AND CURRENT

HOLDS PROMISE FOR RETROFIT AS WELL ASNEW APPLICATIONS

High Power Drives

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