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EE8412Advanced AC Drive Systems

Topic 6 Field Oriented control (FOC)

Source: ABB

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Lecture Topics

• Field Orientation• General Block Diagram of FOC• Direct Field Oriented Control• Direct FOC with Current Controlled VSI• Indirect Field Oriented Control

EE8412 Advanced AC Drive Systems

Field Oriented Control (FOC)

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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• Classification of Field Orientation

Topic 6 Field Oriented Control

Field OrientationEE8412

• Rotor flux orientation• Stator flux orientation• Air-gap flux orientation

Focus on rotor flux orientationIt is relatively simple and widely used

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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• Torque Production in DC Motors

Topic 6 Field Oriented Control

Field OrientationEE8412

afae iKT λ=

Te – electromagnetic torqueKa - armature constantλf - flux produced by field circuitia - armature current

• λf = const → Te is proportional to ia

• Flux λf and ia can be controlled independently → highdynamic performance.

(1)

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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5

eω

eω

rω

rθslθ

fθ

dsi

qsi

rλr

sir

• Rotor Flux Orientation

Topic 6 Field Oriented Control

Field OrientationEE8412

Rotor flux orientation is achieved by aligning the d-axis of the synchronous reference frame with the rotor flux vector λr

0=qrλrdr λλ = and (2)

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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• Electromagnetic Torque

Topic 6 Field Oriented Control

Field OrientationEE8412

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

−

−

−

=

)(2

3

)(2

3

)(2

3

qrdsdrqsr

m

qrdsdrqsm

qsdsdsqs

e

iiL

PL

iiiiPL

iiP

T

λλ

λλ

(3)

(2) → (3): qsrTqsdrTe iKiKT λλ == (4)

• With rotor field orientation, the torque expression in (4) forthe induction motor is similar to that of a dc motor in (1).

• Keep flux λr constant, Te is proportional to iqs

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Field OrientationEE8412

• ids – flux-producing component ← kept at the rated value

• iqs – torque-producing component ← controlled independently

• Flux and Torque Producing Components

eω

eω

rω

rθslθ

fθ

dsi

qsi

rλr

sir

eω

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Field OrientationEE8412

• Rotor Flux Angle θf

eω

eω

rω

rθslθdsi

qsi

rλr

sir

eω

θf

θf - rotor flux angle

θr - rotor angle

θsl - slip angleslrf θθθ +=

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Field OrientationEE8412

• General Block Diagram of FOC

rω

csbsas iii ,,

*eT

*rλ

fθ rλ eT

rω

*rω

csbsas vvv ,,

Rotor flux and torque are controlled independently → to achieve high dynamic performance

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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• Direct and Indirect FOC

• Direct FOCRotor flux angle θf is obtained by using flux-sensing devices embedded inside the motor or using measured motor terminal voltages and currents

• Indirect FOCRotor flux angle θf is obtained from detected rotor position angleθr and calculated slip angle θsl

θf = θr + θsl

Topic 6 Field Oriented Control

Field OrientationEE8412

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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• System Block Diagram

Topic 6 Field Oriented Control

Direct FOCEE8412

*dsv*qsv

csbsas iii ,,

*dsi*qsi

*rλ

*eT

fθ

rλ

dsi

qsi

fθ

** , bsas vv*csv

csbsas vvv ,,

Direct FOC - Rotor flux angle θf is obtained by measured motor terminal voltages and currents

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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sRsir

lsL

mir

mL

lrL rrj λωr

svr

rR rir

spλr

rpλr

• Rotor Flux Calculator

Topic 6 Field Oriented Control

Direct FOCEE8412

( )∫ −= dtiRv ssss

rrrλ

( )sssm

rsm

m

sssrr iL

LLiL

LiL

Lrrr

rrr

σλλ

λ −=+−

=

rs

m

LLL2

1−=σ

smrrr iLiLrrr

+=λ →

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Direct FOCEE8412

• Rotor Flux Calculator

( )

( )⎪⎪⎩

⎪⎪⎨

⎧

−=

−=

qssqsm

rqr

dssdsm

rdr

iLLL

iLLL

σλλ

σλλ

⎪⎪⎩

⎪⎪⎨

⎧

=

+=

−

dr

qrf

qrdrr

λλ

θ

λλλ

1

22

tan

Decomposing the rotor flux into the d- and q-axis components

from which the magnitude and angle of the rotor flux are

• FeaturesOnly use stator-side variables toCalculator rotor flux.

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Direct FOCEE8412

• Rotor Flux Calculator

eω

rω

fθ

dsiqsi

rλr

sir

qrλ

drλ

• Space vector diagram for rotor flux calculation• d- and q-axis currents and flux are ac variables

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Direct FOCEE8412

• Simulation Block Diagram for Rotor Flux Calculation

m

r

LL

x

y

drλ

qrλ rλ

fθdsλ

qsλ

dsv

qsvbsv

csv

asv

asibsi

csi

dsi

qsi sLσ

sR

sR

m

r

LL

xy1tan −

22 yx +

sLσ

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Direct FOC with Current-Controlled VSIEE8412

• System Block Diagram

*dsi*qsi

*rλ

*eT

fθ

rλ

qsi

fθ

×

** , bsas ii

eT

*csi

csbsas iii ,,

csbsas vvv ,,csbsas iii ,,

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Direct FOC with Current-Controlled VSIEE8412

• Current-Controlled VSI

dCdV

1S

2S

3S 5S

4S 6S

B

C

P

N

asi

bsi

csi

A

Hx

i∆

asi*asi

ANv

δ

ANv

δ*asi

asi

1t 2t 3t

i

dV

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Direct FOC with Current-Controlled VSIEE8412

• Simulation Results(rpm)rω

rω*rω

(rad)fr

θλ (Wb),

rλfθ

)(Aasi

m)(N ⋅e

T

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Indirect FOCEE8412

• System Block Diagram

( )dtslrf ∫ += ωωθ

VSI

PWMdq/abc

*dsv

abc/dq

*dsi*qsi M

rωslω

*rλ

*eT

Stationary Frame(ac signals)

Synchronous Frame(dc signals)

csbsas iii ,,

mL/1

dsi

qsi

Integrator

fθ

*rr

mLλτ fθ

sω

*qsv

rωTK/1

CurrentControllers

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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Topic 6 Field Oriented Control

Indirect FOCEE8412

• Slip Frequency Calculation

qsrr

msl i

Lλτ

ω =

Refer to Chapter 14 for detailed derivations

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4

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EE8412 Advanced AC Drive Systems

Topic 6Field Oriented Control (FOC)

Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley-IEEE Press, 2006, ISBN: 0-471-73171-4