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IMPROVING
DIRECT TORQUE CONTROLUSING 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 Garca
Home Supervisor:
Dr. Antoni Arias Pujol
Malta Supervisor:
Dr. Cedric Caruana
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Index
Introduction
Matrix Converters.
Direct Torque Control.
Classical
Using Matrix Converters.
Sensorless Control of a DTC drive using hf injection
Conclusions.
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Introduction
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).
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Direct Torque Control (DTC).
Simple and robust signal processing scheme.
No coordinate transformation and no PWM generation areneeded.
Quick and precise torque response.
The torque and flux modulus values and sector of the flux are
needed.
High torque ripple.
Introduction
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High Frequency Signal Injection.
Non Model-Based method.
Avoids problems at low and zero speed due to the lack ofback-EMF.
No dependence of machine parameters.
Saliency required.
Introduction
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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.
Introduction
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A switch, Sij, i={A,B,C},j={a,b,c} can
connect phase i of the input to phasej
of the load.
Switches states characterized by:
closedisswitchif1
openisswitchif0
ij
ij
ijS
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
VSB
SAb
SAc
VSA
VSC
M
Lf
Lf
Lf
Rf
Rf
Rf
SAa
SBa
SBb
SBc
SCb
SCc
SCa
Cf
Cf
Cf
Matrix ConverterInput Filter
ISB
ISA
ISC
Ia
Ib
Ic
IB
IA
IC
VaN
VbN
VcN
State of the Art
Matrix Converters
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Since any output phase can be connected to any input phase, there are 27
possible switching configurations.
Applying Clarks 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
2
3
4
5
6
1,2,3
4,
5,
6
7,8
,9
a)
Sector
1
23
4
5 6
2,
5,
8
1,4,73,6
,9
b)
State of the Art
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Direct Torque Control
Stator flux y*sand torque T*e
references are compared with the
corresponding estimated values.
Both stator flux and torque errors,
EyandETe, are processed by meansof hysteresis band comparators.
A proper VSI voltage vector is
selected.
The flux vector reference and thehysteresis 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
yS
Hy
Te
Te*
yS*
Te
yS
Ey
HTe
ETe
Voltage Source Invert er
IA
IB
Vo
SA
SB
SC
S(n)
M
S(1)
S(2)S(3)
S(4)
S(5) S(6)
V3t
1
V4t
2
V3t3V
4
t4
yS
V1
V2
V3
V4
V5
V6
y1
y2
y3
y4
y5
y6
a) b)
yy sin||||'2
3sr
sr
me
LL
LpT
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Direct Torque Control using
Matrix Converters
Matrix converter generates a higher
number of output voltage vectors
with respect to a VSI.
Another variable, , 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 Torque
Estimator
yS
Hf
Te
Te*
yS*
Te
yS
IA
IB
Vo
S(n)
SA
SB
SC
Hy
HTe
ETe
Ey
estimator
M
Direct Torque Control for Induction Motors Using Matrix Converters (CPE-05)
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A new torque hysteresis comparator will provide
four different levels instead of three to distinguish
between small and large positive and negative
torque errors.
ETe
HTe
HTe
ETe
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 vecto r applied Medium torque slope
Upper to rque band
Lower torque band
Large vector applied High torque slope
Upper torque band
Lower torque band
a) b)
Direct Torque Control using
Matrix Converters
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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)
Torque
(Nm)
0.85 0.9 0.95 14
4.5
5
5.5
6
6.5
7
7.5
8
Time (s)
Torque
(Nm)
The use of small vectors of Matrix Converters
wref=100% rated speed and TL=100% rated torque.
Direct Torque Control using
Matrix Converters
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Torque ripple performance.
Comparison between the classical use of MC in DTC and the proposed method.
The use of small vectors of Matrix Converters
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)
rmsvalueofTe
ERROR(Nm)
Classcal DTC using MC
Proposed 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.
Direct Torque Control using
Matrix Converters
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Sensorless Control
Saliency
a
b
gmaxgminqr
q
(a)
(b)
gmaxgmin
Lm
qr(elec)
Asymmetry in the machine.
Magnetizing inductance variation.
Asymmetry in the rotor Rotor Position.
t
tV
v
v
i
ii
si
si
w
w
b
a
cos
sin
tLtL
tLtL
LL
V
i
i
irsis
irsis
qsdsi
i
si
si
wqw
wqw
wb
a
2sinsin
2coscos
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Sensorless Control
ab frame rotating injection.
Straightforward in vector
controlled drives.
The carrier can be
superimposed to the
voltage reference.
vds
*
iqs
*
ids
*
Voltage
Source
Inverteriabc
iab
PMSM
flux position
estimate
+
-
-
+
abcab
qe
++
+
+
dq
ab
dq
ab
PI
PI
ids
iqs
vqs
*
vas
*
vbs
*
vasi
vbsi
iab
wi
wi
tan-1ej2wite-jwitiab
iiab
iipos
Synchronous filter
Band-pass
filterHigh-pass
filter
2qr
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Sensorless Control
ab injection in a DTC drive.
Flux and Torque processed
errors, Hys 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.
V4
V5
V4
V6V
n
Vn
Vn+1
Vn+1
xK xK
Tz
Ti
Voltage VectorTable
Stator Fluxand
TorqueEstimator
yS
Hy
Te
Te*
yS
* Ey
HTe
ETe
VoltageSource
Inverteriabc
iab
SA
SB
SC
S(n)
PMSMInjectionalgorithm
VSI
+PMSM
hfModel
abc/ab
iiab
VSI+
FundamentalEstimator
Synchronousfilter
ifab
+
-
-
-
-
+
+
+
High bandwidth of hysteresis controllers.
Difficult to inject outside of this bandwidth.
Decoupling of fundamental and hfcurrents is necessary
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Sensorless Control
ab 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)
Modelbased
angleestimate(rad)
0 0.05 0.1 0.15 0.2-4
-2
0
2
4
Time (s)
Injectionmethod
angleestimate(rad)
0 0.1 0.2 0.3 0.4 0.5 0.6-4
-2
0
2
4
Time (s)
Modelbased
angleestimate(rad)
0 0.1 0.2 0.3 0.4 0.5 0.6-4
-2
0
2
4
Time (s)
Injectionmethod
angleestimate(rad)
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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.
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Thank you.
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