vector control (field oriented control, direct torque control) · 2 of field oriented control (foc)...

1

„Vector Control(Field Oriented Control, Direct Torque Control)“

Referents:Prof. Dr.‐Ing. Ralph Kennel

([email protected])Technische Universität München

Arcisstraße 2180333 München

Germany

2

of Field Oriented Control (FOC)

as well as Direct Torque Control (DTC)

is to operate AC machines/motors

directly by the physical law of Lorentz force

(that means, the torque is produced

by an electrical current in a magnetic field)

magnetic field

and armature current (for torque production)

are controlled separately and independently

The General Idea

3

Force Production in Synchronous Machines

… in principle the magnetic conditions in a synchronous machines are equal… to DC machines

B

If

B

4

… even in high speed condition the mechanical motion is so slowthat Maxwell‘s equations can be applied in the same way

(there is no energy radiation – there is no Displacement Current)

B

If

B

Force Production in Synchronous Machines

11

voltage and frequency are irrelevant

for this type of control

… under this assumption

any AC machine/motor

behaves like a DC motor

The General Idea

12

constanttorque

constantpower

Torque and Power Characteristics of Electrical Machines

13

constanttorque

constantpower

base speedrange

field weakeningrange

Torque and Power Characteristics of Electrical Machines

14

Referents:Prof. Dr.‐Ing. Hans‐Georg Herzog

([email protected])Prof. Dr.‐Ing. Ralph Kennel



Germany

characteristic


15

(Linear) Control Loop

controllercontrolling

elementcontrolled

system

control error e(t)

advantages of (linear) control loops

• well accepted compromise between stability and dynamics

• simple optimization procedures (step response …)

• acceptable robustness against parameter variations

• (limited) implicit linearization auf non-linear components

16

Step Responses

overshoot

compromise

lower dynamics

17

Cascade Structure

- --

Drehzahl-regelung

Drehmoment-/StromRegelung

M3~

i

Lageregelung

Lagegeber

Tacho

Kommutierungssignale

s*

s

n* i*

n

position controllerspeed

controller

torque/currentcontroller

commutation signals

tacho generator

position encoder

servomotor

cascaded control with 3 control loops

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… controls the magnetic fieldby a current (Ampère’s law) in d-direction and

… and the torqueby a quadrature (armature) current in q-direction

the position of the magnetic field is neededto perform FOC

this can be obtained by a position sensoror so-called “sensorless control”

Field Oriented Control (FOC)

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-

Feldschwächung

- -

-

M-Regler Strom-Regler

Feld-Regler

Ma-schinen-modell

ej

e-j

e-j

M3~

i

u

Encoder

n* i*q

i*d*

for asynchronousmachines

field weakening field controller

speedcontroller

currentcontrollers

machine

model

for synchronousmachines

Field Oriented Control (FOC)

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Field Oriented Control

20

• Rotor flux orientation

• PI-controllers

• Cascaded structure

• Limitation in the dynamic response

• Average voltage control

*

sdi

*

sqi

sdi

sqi

*

sdv

*

sqv

dq

abc

*

sv

*

sv

*v*

bv

*

cv

1S

2S

3S

s

r

*

r

*w

w

PI

wPI

diPI

qiPI

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… controls the magnetic field

by the stator voltage (Faraday’s law)

… and the torque

by the stator current (Lorentz force)

DTC does not need a position/speed sensor

unless position or speed have to be controlled

Direct Torque Control (DTC)

22

22

*ww

*T

T *

Direct Torque Control

• Stator flux and torque tontrol

• Hysteresis controllers

• No current regulation

• No modulator

• Switching table

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23

• magnetic flux is integral of stator voltage

• magnetic flux moves in direction of stator voltage

3v

3v

s k

s k 1s k

1s k

Results DTC: Stator flux distortion

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• Stator flux path control

• Current waveform

• Number of commutations

• Direct Self Control (DSC)

Results DTC: Torque and flux hysteresis bands

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increasing

25

25

• Tn=20[Nm],w=1000[RPM]

Final Compariosn: Steady state

0.9 0.92 0.94 0.96 0.98 10

10

20

30

Tor

que

[Nm

]

0.9 0.92 0.94 0.96 0.98 10

10

20

30

Tor

que

[Nm

]

0.9 0.92 0.94 0.96 0.98 10

10

20

30

Tor

que

[Nm

]

0.9 0.92 0.94 0.96 0.98 10

10

20

30

Time [s]

Tor

que

[Nm

]

FOC

DTC

PTCk1

PTCk2

26

26

0.9 0.92 0.94 0.96 0.98 1-30

-15

0

15

30

Am

plitu

de [

A]

0.9 0.92 0.94 0.96 0.98 1-30

-15

0

15

30

Am

plitu

de [

A]

0.9 0.92 0.94 0.96 0.98 1-30

-15

0

15

30

Am

plitu

de [

A]

0.9 0.92 0.94 0.96 0.98 1-30

-15

0

15

30

Time [s]

Am

plitu

de [

A]

• Tn=20[Nm],w=1000[RPM]

FOC

DTC

PTCk1

PTCk2

THD

2%

9.5%

6%

3.5%


27

27

0.9 0.92 0.94 0.96 0.98 1-400

-200

0

200

400

Vol

tage

[V

]

0.9 0.92 0.94 0.96 0.98 1-400

-200

0

200

400

Vol

tage

[V

]

0.9 0.92 0.94 0.96 0.98 1-400

-200

0

200

400

Vol

tage

[V

]

0.9 0.92 0.94 0.96 0.98 1-400

-200

0

200

400

Time [s]

Vol

tage

[V

]

• Tn=20[Nm],w=1000[RPM]

FOC

DTC

PTCk1

PTCk2


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0.69 0.7 0.71 0.72 0.73-5

0

5

10

15

20

Time [s]

Torq

ue [N

m]

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• Torque reference step of 15 [Nm]

Final comparison: Torque response

FOC

DTC

FOC

DTC

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29

• Flux reference step of 0.19 [Wb]

0.4 0.45 0.5 0.55 0.6 0.65 0.70.65

0.7

0.75

0.8

0.85

Time [s]

Flux

[Wb]

FOCDTC

Final comparison: Stator flux response

30

30

• Stator current behavior

FOC DTC

Final comparison: Stator flux response

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31

• High starting current

Final comparison: Starting without limitation

0 0.1 0.2 0.3-70

-35

0

35

70

Am

plitu

de [

A]

0 0.1 0.2 0.3-70

-35

0

35

70

Am

plitu

de [

A]

0 0.1 0.2 0.3-70

-35

0

35

70

Am

plitu

de [

A]

0 0.1 0.2 0.3-70

-35

0

35

70

Time [s]

Am

plitu

de [

A]

FOC

DTC

PTCk1

PTCk2

-37.8 [A]

-62.4 [A]

65 [A]

64.3 [A]

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32

• Stator flux

FOC DTC

Final comparison: Starting without limitation

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33

• Limited stator current

0 0.1 0.2 0.3-40

-20

0

20

40

Am

plitu

de [

A]

0 0.1 0.2 0.3-40

-20

0

20

40

Am

plitu

de [

A]

0 0.1 0.2 0.3-40

-20

0

20

40

Am

plitu

de [

A]

0 0.1 0.2 0.3-40

-20

0

20

40

Time [s]

Am

plitu

de [

A]

FOC

DTC

PTCk1

PTCk2

Final comparison: Starting with current limitation

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• Stator flux

FOC DTC

Final comparison: Starting with current limitation

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any AC drive under FOC (or DTC) behaveslike a synchronous drive

or a DC motor with speed/position control

… under speed control a real speed is kept constantaccording to the speed reference

under any load until maximum torque… when exceeding maximum torque

the drive is not stopping at standstill (breakdown),but reducing speedas long as the required torque can be provided

characteristicAC machine with speed control

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an electrical machine with inverter supply

and speed control

always provides

the characteristic of a synchronous machine

… independant on the type

of the respective electrical machine


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speed

torq

ue

motor operationPel > 0

Pmech< 0

generator operationPel < 0

Pmech> 0

… variations of supply voltageresult in a shift of the characteristic … but vertically only

… variations of supply frequencyresult in a shift of the characteristic horizontally

load characteristic

operation point

… that is exactly, what speed control performswhen speed reference varys


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speed

torq

ue

motor operationPel > 0

Pmech< 0

generator operationPel < 0

Pmech> 0

… here the characteristicsare arbitrary definitions as well

… the transition frommotor to generator operation

or vice versavirtually happens „automatically“

… as soon asthe operation point changes

from the first quadrantto the fourth quadrant

(or vice versa)


39

source : SIEMENS

characteristic of (synchronous) drivewith speed control

thermal limitation

limitation by maximum stator voltage

limitation by maximum stator current

… unfortunately in most data sheetsthe 1. quadrant is presented only


40

Referents:Prof. Dr.‐Ing. Hans‐Georg Herzog

([email protected])Prof. Dr.‐Ing. Ralph Kennel



Germany

advantages in comparison to U/f Control


41

advantages of FOC or DTCin comparison to U/f Control

that FOC or DTC are feedback control schemes

U/f control is a feedforward control scheme

FOC and DTC can react on (torque) disturbances

– U/f control cannot

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DC SM ASM

Advantages

Disadvantages

- Simple control

- interior ventilation

simple to realize

- high protection standard

- small size

- maintenance free

- low inertia

- high torque

even at standstill

- high dynamics

- losses in the stator

- high protection standard

- maintenance free

- high overload capability

- low cost

- high torque

even at standstill

- high speed range

- low protection standard

- mechanical wear

(brushes, collector)

- current limitation

- standstill

(collector segments)

- high speed

(commutation)

- maximum terminal

voltage of 200 V

(transformer needed)

- losses in the rotor

(heat transfer via shaft)

- high cost

- limited speed range

- limited overload

capability

(demagnetizion)

- harmonic losses

mainly in the rotor

(heat transfer via shaft)

- high inertia

- field current needed

(losses, size,

bigger inverter)

- complex control

- Parameter depending

control

Comparison of Different Electrical Machines

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Thank You !!!

Any Questions ?

Prof. Dr.-Ing. Ralph Kennel

Technische Universität München

Electrical Drive Systems and Power Electronics

vector control (field oriented control, direct torque control) · 2 of field oriented control (foc)...

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