Assignment No2 f

8/7/2019 Assignment No2 f

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EE538EE538

ASSIGNMENT No:2ASSIGNMENT No:2Vector Controlled Induction MotorsVector Controlled Induction Motors

E/05/185 Lokugamage A.U.

E/05/295 SiriwardhanaA.S.L

E/05/298 Sooriyadasa S.M.D.P.K

E/05/321 Thrikawela M.M.E/05/341 WickramarathneW.J.C.

E/05/354 Wijesurendra K.P.N.U


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IntroductionIntroduction

controlled electrical drives has undergone rapid expansiondue mainly to the advantages of semiconductors in bothpower and signal electronics

This leads to AC drive control with ever lower powerdissipation hardware and ever more accurate control

structures. In vector control, speed and torque can be controlled by

controlling both the magnitude and the phase of each phasecurrent and voltage vectors

Control of current/voltage associated with field, hence thisstrategy is called field oriented controlled as well.

Two control strategies are filed orientation withcurrent control and field orientation with voltagecontrol (FOC)


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comparisoncomparisony Controlled strategies we have discussed such as inverter fed

IM, provided good steady state response but not in

transients (high current flow in transients which can damage

drive system)

y Deviation of air gap flux linkage in magnitude as well as in

phase, from their set values is the reason for this.

y other controllers utilized stator phase voltage/current

magnitude and frequency but not their instantaneous

phase, which deviate linkage flux from its set value.

Air gap flux

oscillation

Oscillation

of torque

Oscillation

of speedDamage to the system

Current

oscillations

Large stator currents

High rated equipments

required


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Comparison contnd..Comparison contnd.. Now its clear that for good dynamic characteristics control of

phase in above quantities is necessary which is addressed by

vector controlled system

In FOC both phase and magnitude of stator quantities are

controlled. Hence good dynamic performance

In FOC the ease of reaching constant reference (torque

component- IE and flux component of the stator current- IF)

Independent control of torque and flux is possible as dc drives

handling system limitations and achieve higher power conversion

efficiency compared to other techniques Suitable for high performance application such as servos, process

drives, metal rolling mills etc.


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Field Orientation with Current ControlField Orientation with Current Control

y In IM current in rotor which generate torque should begenerated by induction.

Figure 1.a Figure 1.b Figure 2.a Figure 2.b

I1 generates ] then apply I2 , since linked flux of rotor bars is changed it

induces I3 (refer vector diagram) to neutralize this (Fleming law+ lense law)

How ever due to induced I3 requires a field change (current caring conductorin a field) vector diagram changes as figure 2.b after certain time.

If rotor is assumed to be locked, then stator is rotates such that field and I1again parallel and again orientation is restored as figure 4.a

In reality stator is stationary and rotating vector is formed by rotating current

IE & IF (figure 5)

I1

I2 I3 ]

I1

I2

I3

]

I1

I2 I3

I1

I2 I3

]

J


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FOC with current control contnd..FOC with current control contnd..I1

I2

I3

I3

]

I2

J

Figure 4.a Figure 4.b

I2

IE

IF

I1

I

IE

I2

J

IF

Figure 5.aFigure 5.b

IE=I1cosJ- I2sinJtorque component IF=I1sinJ+ I2cosJflux

component)

Above relationship is obtained using vector rotor

(VR) which rotates current vector by the angle of field

I1

I2

sinJ cosJ

+

+

+

-

In puts to VR are set point values I1*

& I2* and field angle which is taken

from Hall generators which are at

deferent angles in air gapFigure 6


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FOC with current control contnd..FOC with current control contnd..

y Vector Analyzer (VA) converts angle (J) into sinJ & cosJ

y What actually VR does is transformation of current

vector I from field oriented coordinate system to stator

oriented coordinate system. Refer figure 7

y Output of VR fed in to variable current static controllerU to obtain IE and IF (vector multiplier)

I1

I2

CosJ sinJ

SinJ + cosJ U

IE*

IF*

IE

IF

Figure 7


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Application of vector rotor for fieldApplication of vector rotor for field

orientation in an IMorientation in an IMy This gives separate access to the field current andseparate access to torque producing current

y Thus it is possible to operate an IM in same manner as a

separately excited dc motor with current control

J

U

VA

IE

IFIF*

VR

I1*

I2*

IE*

sinJ cosJ


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Field orientation with voltage controlField orientation with voltage control

Open loop Control

To achieve the field orientation,

It is necessary to determine voltage

positioning values UE and UF

correspond to the current reference

values I and I

This relationship can be obtained in two steps

cosJ

U

VA

IE

IFIF*

VR 1

I1*

I2*

IE*

sinJ


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Step 1

Voltage vector U] in the field coordinate system is formed from the

current vector U] I

and I

U] vector contains,

Vectors for the resistive & inductive voltage drops of the

current

Vector for the back emf of the motor

This relationship is established in a computation circuit E

To do this, E needs information from the motor and contains a

simulation of the structure of the motor


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Step 2

U]

is transformed to Us* (Stator coordinate system)

Use Us* = D] U]

This transformation is done by the VR1

Result (UE and UF

) is then fed to the static convertor as

manipulated variables

Motor resistance is varying with the operating temperature

Thus, current at the stator deviates from the reference values I and I

The operating temperature of the motor cannot generally be taken in to

account in the computational circuit

There fore, Closed loop system is required


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Closed loop control

At steady state, components ofI] remain constant

And I] can be obtained by measurement of the stator oriented

current vectorIs and subsequent transformation of the field coordinate

system,

I] =D-1]Is

I] =D]Is

VA2

cosJ

U

VA

IE

IFIF*

VR 1

I1*

I2*

IE*

sinJ


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This transformation is done by VR2

Since actual I] is known error can be calculated

Then error is fed to integrator type controller (PI)

Hence required current can be maintained even

though the operating temperature is varying

Closed loop control Ctd


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This model along with the

Clark and Park

transformations can be used

as a alternative method for

deriving a time independentcoordinate system.

Below procedure can be

used to derive the time

independent coordinatesystem.

Isd and Iaq are the two

current vectors which are

important.

A Mathematical Model for

Coordinate Transformation

IM

Motor


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A Mathematical Model, cont Space Vector definition and projection

The (a ,b ,c)->( ,) projection (Clarketransformation)

The ( ,)->(d ,q) projection (Park

transformation)


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referencesreferences

y EE538 course note -: Siemens review

y Electric Motor Drives by R. Krishnan

y Field Orientated Control of 3-Phase AC-

Motors, Literature Number:

BPRA073:Texas Instruments Europe

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Assignment No2 f