IMPROVING DIRECT TORQUE CONTROL USING MATRIX CONVERTERS Technical University of Catalonia....

IMPROVING IMPROVING DIRECT TORQUE CONTROL DIRECT TORQUE CONTROL

USING MATRIX CONVERTERSUSING MATRIX CONVERTERS

Technical University of Catalonia. Electronics Engineering Department. Colom 1, Terrassa 08222, Catalonia, Spain

University of Malta.Department of Electrical Power and Control Engineering.

Msida MSD 06, Malta

Research Student:

Carlos Ortega García

Home Supervisor:

Dr. Antoni Arias Pujol

Malta Supervisor:

Dr. Cedric Caruana

2

IndexIndex

Introduction

Matrix Converters.

Direct Torque Control.

Classical

Using Matrix Converters.

Sensorless Control of a DTC drive using hf injection

Conclusions.

3

IntroductionIntroduction

Matrix Converters (MC) Advanced circuit topology capable of generating AC-AC.

Load voltage with arbitrary amplitude and frequency, and

sinusoidal input/output waveforms.

Power Factor Correction (PFC).

No inductive or capacitive elements

are required, thus allowing a very

compact design.

A very good alternative to Voltage Source Inverters (VSI).

4

Direct Torque Control (DTC).

Simple and robust signal processing scheme. No coordinate transformation and no PWM generation are

needed. Quick and precise torque response. The torque and flux modulus values and sector of the flux are

needed. High torque ripple.


5

High Frequency Signal Injection.

Non Model-Based method. Avoids problems at low and zero speed due to the lack of

back-EMF. No dependence of machine parameters. Saliency required.


6

Main objectives:

Improve the Direct Torque Control, regarding torque ripple,

using small vectors of Matrix Converters.

Analysis of different High Frequency signal Injection

methods for sensorless Direct Torque Control.


7

A switch, Sij, i={A,B,C}, j={a,b,c} can

connect phase i of the input to phase j of the load.

Switches states characterized by:

closed is switch if 1

open is switch if 0

ij

ijij S

SS

A mathematical model of the MC can be derived:

Voltage equations: Current equations:

)(

)(

)(

)()()(

)()()(

)()()(

)(

)(

)(

tv

tv

tv

tStStS

tStStS

tStStS

tv

tv

tv

C

B

A

CcBcAc

CbBbAb

CaBaAa

cN

bN

aN

)(

)(

)(

)()()(

)()()(

)()()(

)(

)(

)(

ti

ti

ti

tStStS

tStStS

tStStS

ti

ti

ti

c

b

a

CcCbCa

BcBbBa

AcAbAa

C

B

A

V SBS Ab

S Ac

V SA

V SC

M

Lf

Lf

Lf

R f

Rf

Rf

S Aa

S Ba S Bb S Bc

S Cb S CcS Ca

Cf

Cf

Cf

Matrix ConverterInput Filter

ISB

ISA

I SC

I a I b I c

IB

IA

I C

VaN

VbN V cN

State of the ArtState of the Art

Matrix Converters

8

Since any output phase can be connected to any input phase, there are 27 possible switching configurations.

Applying Clark’s transformation to all switching states, it can be found that MC can generate:

18 active vectors, 6 rotating vectors, and 3 zero vectors.

Output line-to-neutral voltage vectors Input line current vectors

Matrix Converters

Sector

1

23

4

56

±1,±2,±3

±4,±5,±6

±7,±8,±9

a )

Sector

1

23

4

5 6

±2,±5,±8

±1,±4,±7±3,±6,±9

b)

State of the ArtState of the Art

9

Direct Torque ControlDirect Torque Control

Stator flux *s and torque T*

e

references are compared with the corresponding estimated values.

Both stator flux and torque errors, E and ETe, are processed by means

of hysteresis band comparators.

A proper VSI voltage vector is selected.

The flux vector reference and the hysteresis band tracks a circular trajectory, thus, the actual flux follows its reference within the hysteresis band in a zigzag path.

Look-up table

Flux and Torque Estimator

S

H

T e

T e*

S*

T e

S

E

H Te

E Te

Voltage Source Inverter

IA

IB

V o

S A

S B

S C

S(n)

M

S(1)

S(2)S(3)

S(4)

S(5) S(6)

V 3t1

V 4t2

V 3t3V 4t4

S

V 1

V 2V 3

V 4

V 5 V 6

1

23

4

5 6

a) b)

sin||||'2

3sr

sr

me LL

LpT

10

Direct Torque Control using Direct Torque Control using Matrix ConvertersMatrix Converters

Matrix converter generates a higher

number of output voltage vectors with

respect to a VSI.

Another variable, <sin >, is

introduced to control the input power

factor.

Keeping this variable close to zero,

unity power factor operation is

possible.

A new hysteresis comparator is introduced which controls this variable.

Classical DTC using Matrix Converters

Voltage VectorTable

MatrixConverter

Flux and TorqueEstimator

S

H

T e

T e*

S*

T e

S

IA

IB

V o

S(n)

S A

S B

S C

H

H Te

<sin >

E T e

E

< sin >estimator

M

Direct Torque Control for Induction Motors Using Matrix Converters (CPE-05)

11

A new torque hysteresis comparator will provide

four different levels instead of three to distinguish

between small and large positive and negative

torque errors.

E Te

H Te

H TeE Te

Large vectors will be used when large

torque error is detected.

When torque error is small, the small

voltage vector will be applied.

Zero vectors will be applied if small

torque error is detected and back EMF

imposes a variation in torque towards

its reference value.

The use of small vectors of Matrix Converters

Zero vector applied Low torque slope

Small vector applied Medium torque slope

±Upper torque band

±Lower torque band

Large vector applied High torque slope

±Upper torque band

±Lower torque band

a) b)


12

Torque ripple performance.Comparison between the classical use of MC in DTC and the proposed method.

Classical DTC using MC Proposed method

0.85 0.9 0.95 14

4.5

5

5.5

6

6.5

7

7.5

8

Time (s)

Tor

que

(Nm

)

0.85 0.9 0.95 14

4.5

5

5.5

6

6.5

7

7.5

8

Time (s)

Tor

que

(Nm

)


ref=100% rated speed and TL=100% rated torque.


13

Torque ripple performance.Comparison between the classical use of MC in DTC and the proposed method.


0 250 500 750 1000 1250 15000.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Speed (rpm)

rms

valu

e of

Te

ER

RO

R (

Nm

)

Classcal DTC using MCProposed method

The use of zero and large vectors in the classical method leads into an over/undershoot, more pronounced as the speed increases.

Small vectors are more effective keeping the torque within the its reference bands.


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Sensorless ControlSensorless Control

Saliency

gmax

gmin

r

(a)

(b)

gmaxgmin

Lm

r(elec)

Asymmetry in the machine. Magnetizing inductance variation. Asymmetry in the rotor Rotor Position.

t

tV

v

v

i

ii

si

si

cos

sin

tLtL

tLtL

LL

Vi

i

irsis

irsis

qsdsi

i

si

si

2sinsin

2coscos

15


frame rotating injection. Straightforward in vector

controlled drives. The carrier can be

superimposed to the voltage reference.

v ds*

iqs*

ids*

VoltageSourceInverter

iabc

i

PMSM

flux positionestimate

+

-

-

+

abc

e

++

+

+

dq

dq

PI

PI

ids

iqs

v qs*

vs*

vs*

vsi

vsi

i

i

i

tan -1e j2 ite -jiti i i i ipos

Synchronous filter

Band-pass filter

High-pass filter

2r

16


injection in a DTC drive. Flux and Torque processed errors, Hs and

HTe, converted directly to switching signals.

No voltage command => Difficult to inject. Injection directly modifying the vector

pattern imposed by the DTC switching table.

V 4 V 5 V 4 V 6Vn

Vn

Vn+

1

Vn+

1

x K x K

T z

T i

Voltage VectorTable

Stator Fluxand

TorqueEstimator

S

H

T e

T e*

S* E

H Te

E Te

VoltageSourceInverter

iabc

i

S A

S B

S C

S(n)

PMSMInjectionalgorithm

VSI+

PMSM hf Model

abc/

i i

VSI+

FundamentalEstimator

Synchronousfilter

i f

+

-

-

-

-

+

+

+

High bandwidth of hysteresis controllers. Difficult to inject outside of this bandwidth. Decoupling of fundamental and hf currents is necessary

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injection in a DTC drive.

Steady state at 375 rpm Speed reversal.

Comparison between real and estimated position

0 0.05 0.1 0.15 0.2-4

-2

0

2

4

Time (s)

Mod

el b

ased

an

gle

esti

mat

e (r

ad)

0 0.05 0.1 0.15 0.2-4

-2

0

2

4

Time (s)

Inje

ctio

n m

etho

d

angl

e es

tim

ate

(rad

)

0 0.1 0.2 0.3 0.4 0.5 0.6-4

-2

0

2

4

Time (s)

Mod

el b

ased

an

gle

esti

mat

e (r

ad)

0 0.1 0.2 0.3 0.4 0.5 0.6-4

-2

0

2

4

Time (s)

Inje

ctio

n m

etho

d

angl

e es

tim

ate

(rad

)

18

Conclusions Conclusions

Advantages of Matrix Converters over the traditional VSI has

been combined with the advantages of the DTC scheme.

The use of small vectors of the MC has been investigated.

High frequency injection in a DTC drive has been presented.

19

Thank you.

IMPROVING DIRECT TORQUE CONTROL USING MATRIX CONVERTERS Technical University of Catalonia....

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