DTC-IM drive with 5-level hybrid cascaded h-bridge
inverter
Didarul Islam, C.M.F.S. Reza
Power Electronics and Renewable Energh Research Lab
Department of Electrical Engineering, Faculty of
Engineering University of Malaya
Kuala Lumpur, Malaysia
didarul0101@gmail.com
Abstract—Due to control simplicity and easy
applicability DTC has become popular and adopted in
many industrial applications. But it still suffers from a few
drawbacks like- comparatively large torque ripple in a low
speed range and its performance is highly depended on
speed of the motor and hysteresis bands of torque and flux
ripple. To address these problems, this paper represents a
direct torque control (DTC) strategy for induction motor
(IM), utilizing hybrid cascaded H-bridge multilevel
inverter (HMLI) extending the idea of basic two level DTC
proposed by Takahashi. Simulation results shows that the
DTC drive performance has been considerably improved
in terms of lower torque and flux ripple and less THD.
These have been evaluated by simulation and compared
with the basic DTC developed by Takahashi and other
DTC proposed to date.
Key words: DTC, Multilevel inverter, Induction motor, VSI.
I.
INTRODUCTION
Direct torque control (DTC) induction motor drive is
becoming more popular day by day due to its fast dynamic
response and robustness to the variation of the machine
parameters without using the current controller [1-4]. It is
evident that the high torque ripple problems allied with the
basic DTC system can be reduced by efficiently increasing the
output resolution of the inverter. In literature, many methods
has already been introduced to address this problem such as
zero state modulation [5], space vector modulation (SVM) [6]
and the application of multilevel inverter [7]. These modified
schemes generally provide better performance in terms of
torque and flux smoothing with added switching losses and
power circuit complexity.
Modified switching table with a four level hysteresis
controller for flux and torque has been proposed to improve the
DTC-IM drive performance [8]. The torque ripple problem
comes with the hysteresis controller and look-up based
switching signal generator has been deal with the inclusion of
PI controller and the SVM inverter [9]. The SVM-DTC drive
imitate the advantage of basic DTC with the torque and flux
ripples minimization afforded by the SVM strategies, but it
c
978-1-4799-4315-9/14/$31.00 2014
IEEE
Prof. Dr. Saad Mekhilef
Power Electronics and Renewable Energh Research Lab
Department of Electrical Engineering, Faculty of
Engineering University of Malaya
Kuala Lumpur, Malaysia
saad@um.edu.my
needs powerful processor and runs at higher switching
frequency.
In other study proposed for DTC control scheme fed by
multilevel inverter utilizing the mathematical equations for
SVM and predictive control strategy for selecting the voltage
vector rather than look-up table. Significant improvement of
flux ripple as well as torque ripple has been found. But the uses
of mathematically complex equation, however, requires high
power computational processor particularly if the voltage levels
are high [10, 11]. For this drawback some researcher preferred
to use look-up table based switching signal generation [2] .
Advantage of these approaches is simplicity yet good dynamic
response. But these approaches are somewhat limited to three
level neutral point clamp (NPC) multilevel inverter. The other
version of this type is flying capacitor (FC) inverter [12], which
is also limited to three levels. In this paper, a 5-level hybrid
cascaded H-bridge multilevel inverter is used with lookup table
based DTC drive.
However, the application of multilevel inverter, which is the
main focus of this work, increases the number of voltage
vectors utilized to regulate the torque and flux. Three main
multilevel inverter topology has been found in industrial
application; flying capacitors (FC), cascaded H-bridge (CHB)
and neutral point clamped (NPC) [13]. Simple design and
modular structure of cascaded H-bridge multilevel inverter has
the inherent advantages among these inverter topologies. This
topology is suitable for asymmetrical multilevel inverter
implementation. Supplying different value of dc voltage to
different cascaded cell higher number of levels can be achieved
for an inverter circuit. With “c” H-bridge cells in each arm,
maximum possible number of levels by an inverter is 3c and it
can be generated when the dc supply voltages of the cascaded
cells are chosen by ratio three [14].
In the following section, concept of multilevel inverter is
introduced. Section-III graphically illustrates the voltage
vectors and inverter state; followed by a brief description of
DTC with five level inverter in section-IV. Sections V describe
the simulation result of proposed DTC and following section
concludes the paper.
332
II.
CASCADED H-BRIDGE MLI
Cascaded H-bridged cell is one of the basic MLI.
Advantage of this structure is its modular structure where the
inverter contains small identical cell. But it requires high
number of isolated DC supply. k-cell in each arm of inverter
has (2k+1) voltage level and it needs 3k isolated DC supply. In
the proposed method high voltage stage is replaced with
slandered six switch topology thus it reduces the total number
of DC supple by 2. As a result required number of dc supply
becomes 3k-2.
Structure of the five level cascaded hybrid bridge multilevel
inverter (CHBMI) introduced in this paper has been shown in
Figure 1. High voltage main stage is consisting of conventional
six switch inverter each of its phases is connected in series with
H-bridge medium voltage stage. High voltage stage is supplied
by only one dc supply whereas medium voltage stage is
supplied by 3 isolated dc supply. Medium voltage supply is
identical with those of asymmetrical MLI but owing to the
lower voltage levels cost of the stage is much lower compared
to main high voltage stage. As a result significant reduction of
dc supply cost can be achieved by this topology [5].
To determine the output voltage levels of used topology in
Figure 1, any output phase (A, B or C) voltage with respect to
negative terminal of main stage is considered. Therefore output
voltage levels varies in between (3+1)Vs=4Vs to (0-1)Vs = 1Vs with uniform stepping of Vs. Thus it forms a 5-level
inviter.
Figure 1: 5-level cascaded H-bridge multilevel inverter feeding
induction motor.
III.
VOLTAGE VECTORS AND INVERTER STATES
Switching variable of the MLI represented by ሾୟୠୡ ǡ ୟୠୡ ሿ
where X is (0 or 1) whereas Y is (-1, 0 and +1). States of the
high and medium stages are determined by ୟୠୡ and ୟୠୡ
respectively. Output voltage vector can be calculated using
following equation (1) where ୟୠ ǡ ୠୡ ǡ ୡୟ represent line to line
voltage and ୟ୬ ǡ ୠ୬ ǡ ୡ୬ represent phase voltage.
ୟ െ ୠ
ୟ െ ୠ
ୟୠ
൥ୠୡ ൩ ൌ ͵• ൥ ୠ െ ୡ ൩ ൅ • ൥ୠ െ ୡ ൩
ୡୟ
ୡ െ ୟ
ୡ െ ୟ
(1)
Phase voltages of the Y-connected load is represented by
the following equation (2)
˜ୟ୬
ୟୠ െ ୡୟ
ʹ െͳെͳ ͵ୟ ൅ ୟ
ଵ
୚
൥˜ୠ୬ ൩ ൌ ൥ୠୡ െ ୟୠ ൩ ൌ ౩ ൥െͳ ʹ െͳ൩ ൥͵ ୠ ൅ ୠ ൩
ଷ
ଷ
˜ୡ୬
ୡୟ െ ୠୡ
െͳെͳ ʹ ͵ୡ ൅ ୡ
(2)
The voltage vector realized by Park’s transformation is
given in (3)
ͳ
˜ୢ
ቂ˜ ቃ ൌ ቎
୯
Ͳ
െ ͳൗʹ
ξ͵ൗ
ʹ
െ ͳൗʹ
˜ୟ୬
˜
቏൥ ୠ୬ ൩
െξ͵ൗ
ʹ ˜ୡ୬
(3)
Substituting (2) into (3) gives
ͳ
˜ୢ
ቂ˜ ቃ ൌ ୱ ቎
୯
Ͳ
െ ͳൗʹ
ξ͵ൗ
ʹ
െ ͳൗʹ
͵ୟ ൅ ୟ
቏ ൥͵ୠ ൅ ୠ ൩
െξ͵ൗ
ʹ ͵ୡ ൅ ୡ
(4)
Equation (4) can be used to generate any voltage vector
from any inverter switching state. Voltage vector diagram for 5
levels inverter can be drawn by superposition of individual
stage vector diagram. First vector diagram of the two-level
inverter main stage has been drawn. Then on each tip of the
vectors one complete vector diagram of the three-level medium
stage voltage vector has been supper imposed. The final vector
diagram is shown in Figure 2
.
Figure 2: 5-level inverter voltage vector diagram.
There are 53 phase voltage combination is possible for 5level inverter with ሺ െ ͳሻ ൅ ͳ ൌ ͸ͳ unique voltage vector.
Number of the inverter levels is represented by ‘’. It gives
2014 IEEE 9th Conference on Industrial Electronics and Applications (ICIEA)
333
more degree of choice to select the desired voltage vector for
control purpose. Voltage vector produced by a 5-level CHBMI
is shown in Figure 2 on d-q plane. Each vector has been drawn
along with its switching state. For medium stage first two digits
represent phase ‘A’ upper switch S1 and S3. Similarly next two
digits stand for phase ‘B’ and last two digits for phase ‘C’. For
high state, first digits stand for phase ‘A’ and goes respectively
for other two phase.
IV.
DTC WITH ASYMMETRIC 5-LEVEL MLI
Configuration of the basic DTC proposed by Takahashi and
Noguchi [4] is illustrated in figure 4. In these method measured
terminal voltage are utilized to estimate the instantaneous value
of the flux and torque and thereby an optimal switching vector
is selected to directly control the torque. However, the only
drawback for this control is the staggered motion of the rotor
due to the use of voltage vector fed by VSI. But this 3 level VSI
is limited to offer few number of voltage vectors irrespective to
the torque demand. There by same voltage vector is selected for
large and small torque and the flux error. Option of selecting
the voltage vector can be greatly enhanced by 5-level
asymmetrical MLI.
A. Vector Selection Strategy for the Proposed DTC
Torque can be controlled by retaining the stator flux
constant and speeding up the rotation of the flux linkage as
quickly as possible. Amplitude and rotation of the stator flux
can be maintained constant by selecting proper inverter voltage
vectors. Inverter voltage vector can be defined as:
˜ୱ ൌ ˜ୟ୬ ൅ ˜ୠ୬ ‡୨ሺଶȀଷሻ஠ ൅ ˜ୡ୬ ‡୨ሺସȀଷሻ஠
˜ୱ ൌ ሾͳ ‡୨ሺଶȀଷሻ஠ ‡୨ሺସȀଷሻ஠ ሿሾ˜ୟ୬ ˜ୠ୬ ˜ୡ୬ ሿ୘
(5.a)
(5.b)
Using equation (2) and after algebraic manipulation it
becomes as follows:
˜ୱ ൌ
୚౩
ଷ
ͳ
୘
୨ሺଶȀଷሻ஠ ൩
൥‡
‡୨ሺସȀଷሻ஠
ʹ െͳെͳ ͵ୟ ൅ ୟ
൥െͳ ʹ െͳ൩ ൥͵ୠ ൅ ୠ ൩
െͳെͳ ʹ ͵ୡ ൅ ୡ
(5.c)
When the stator winding is fed by an inverter as shown in
Figure 1, voltage˜ୟ୬ can be determined by the state of the
switches (S1, S2, S3 and S4) of medium stage phase and high
stage switches (S13 and S14). Similarly the voltage ˜ୠ୬ and ˜ୡ୬
can be determined from the state of their respective switches.
Phase ‘A’ of medium stage full bridge consists of switches S1,
S2, S3 and S4 and connected to dc voltage Vs. Main stage of
the inverter is a conventional six switch (S13…S16) inverter
and supplied by 3Vs. Each arm of the six switch inverter is
cascaded with corresponding phase of the medium stage.
Switching state and output voltage of phase ‘A’ of this topology
has been shown in Table 1. State of S2, S4 and S14 has been
skipped as they are always complimentary to S1, S3 and S13
respectively to avoid short-circuit of dc source. For phase ‘B’
and ‘C’ similar switching table can be presented.
TABLE 1: SWITCHING TABLE OF PHASE ‘A’
Figure 3: Basic DTC block diagram
As then number of available voltage vector is high, it offers
more degree of freedom to select proper voltage vector to
regulated torque and flux. Thus the dynamic behavior of torque
and flux is improved. Figure 4 shows the block diagram of
proposed DTC scheme.
S13
0
0
0
0
1
1
1
1
S1
0
1
0
1
0
1
0
1
S3
0
0
1
1
0
0
1
1
Xa
0
1
-1
0
0
1
-1
0
Ya
0
0
0
0
1
1
1
1
Output
0
Vs
-Vs
0
3Vs
4Vs
2Vs
3Vs
Equation (5.c) has been expressed in terms of switching
variable Xa, Xb….Yc. However, these variables can be further
represented as function of switching state as follows:
ୟ ሺଵଷ ሻ ‫ א‬ሼͲǡͳሽ ֜ ୟ ሺଵଷ ሻ ൌ ଵଷ
ୟ ሺଵ ǡ ଷ ሻ ‫ א‬ሼെͳǡ Ͳǡͳሽ ֜ ୟ ሺଵ ǡ ଷ ሻ ൌ ଵ െ ଷ
Where ୒ ‫ א‬ሼͲǡͳሽ
Therefore equation (5.c) can be represent as
Figure 4: Block diagram of proposed DTC scheme.
334
˜ୱ ሺଵ ǡ ଷ ǥ ଵ଻ ሻ ൌ
୘
ͳ
ʹ െͳെͳ ͵ଵଷ ൅ ଵ െ ଷ
୚౩
൥‡୨ሺଶȀଷሻ஠ ൩ ൥െͳ ʹ െͳ൩ ൥ ͵ଵହ ൅ ହ െ ଻ ൩
ଷ
െͳെͳ ʹ ͵ଵ଻ ൅ ଽ െ ଵଵ
‡୨ሺସȀଷሻ஠
2014 IEEE 9th Conference on Industrial Electronics and Applications (ICIEA)
(6)
Using equation (6) any voltage vector can be calculated if
the switching states are known. Combined switching vector
along with their switching state has already been shown in
Figure 2.
However, to select the desired voltage vector it has been
labeled as shown in
Figure 5 and thereby a look up table has been constructed.
Figure 5 is the representing only one sector. It shows that that
the vector 8 can be achieved by three different switching states.
This redundancy actually opens up a scope to optimize the
switching frequency of main stage and switching losses.
However to optimize the switching losses a technique proposed
[15] has been adopted
to its reference value. Both error signals have been processed
through its respective hysteresis controller to generate the index
of 3D look-up table consist of 61 possible voltage vector. For
flux hysteresis 5% of the nominal flux is taken as the hysteresis
band whereas for torque hysteresis 10% of the nominal torque
has been taken as the torque hysteresis band.
Using the above indexes generated by the hysteresis
comparator along with sector number a predefined voltage
vector is selected. Following statute has been used to select
voltage vector for a given sector. A pictorial explanation has
been shown in Figure (shaded triangle, sector 1 and odd
sector).
For a positive torque demand vector situated above the
sector boundary (shaded triangle) has been used and for
negative vectors below the sector boundary has been selected.
Each group of vector connected by thick lines represents a
particular flux demand.
The higher the absolute value of the torque the far the vector
goes from the sector boundary (creating the higher load angle).
e.g. 38<39<40<41
For higher flux demand vector with higher amplitude has
been selected. e.g. 41-40-39-39,60-59-58-57 for maximum
positive flux and 11-10-2-0-6-16-15 for zero flux whereas 4544-43-23,33-55-54-53 for maximum negative.
01 10 00
0
10
10
00
01 10 00
01
0
00
1
0
10
1
00
00
10
01
1
01 10 00
0
01
0
00
1
00
1
00
0
01 10 00
00
0
60
11
0
110
1
00
0
10
00
35
10
1
0
17
1
00
01
00
0
00
1
01
1
00
16
10
01
0
00
0
00
0
10 01 00
36
37
00 0010
0
01 10 00
00
10
10
00
0
10
0
59
00 00 01
00
10
01
00
10
0
1
00 00 01
10
0
00
1
00 00 01
33
00 001058
00
01
0
00
1
55
34
00
54
11
0
00
0
0
10
1
00
53
00
0
10
01 10 00
0
10
00
01 10 00
0
00
1
1
00
0
00
1
00 00 01
1
00
0
10
10
1
01
00 00 01
0
10
00 00 01
0
00
1
1
00
1
1
00
10
0
0
00
00
1
00
38
19
0
0
10
0
56
10 01 00
For any sector, estimated flux has been compared with its
nominal value and flux error ሺȲୣ୰୰ ሻ is determined. In similar
way torque error ሺୣ୰୰ ሻ signal has been generated by comparing
11
7
18
10 01 00
Where Ȳ୶ and Ȳ୷ are the real and imaginary component of
estimated flux respectively. Ʌis the angle of rotating flux in d-q
plane.
20
00
0
1
00
32
0
10
0
(7.b)
39
0
01
00
00
0
6
1
10
10 01 00
01
00 0010
0
00
00
0
൅ ͳʹǤͷሻ െ ͳͷ୭ ൐ ߠ ൐ െͳͺͲ୭
21
10
0
10
10
0
5
15
31
10
൅ ͲǤͷሻ െ ͳͷ୭ ൑ Ʌ ൏ ͳͺͲ୭
8
0
01
0
01
10
00
10
0
01
1 001
00 0010
0
00
0
14
52
0
2
1
00
40
00
0
01
9
0
10
00
0
01
10
30
10
4
00 0010
00
3
01
00 0010
00
0
41
22
10 01 00
13
23
11
0
00
0
0
1
00
29
51
11
42
10
0
0
01
28
00
0
10 01 00
50
24
00 0010
12
01
0
01
00 00 01
0
10
00
43
0
01
00
00
0
ଷ଴
10
0
஘
49
10 01 00
ሺ
஘
ଷ଴
27
0
10
ሺ
(7.a)
48
0
00
ሻ
44
25
26
0
ൌቐ
ஏ౮
45
47
00
Ʌ ൌ ƒ”…–ƒሺ
ஏ౯
46
10
0
B. Flux and Torque Control Strategy
With several choices in hand to select the desired voltage
vector, a proper selection scheme must be adopted to achieve
the desired dynamic torque response and to keep the switching
loss as low as possible. It has been mentioned in previous
section, 5-level inverter offers 61 useable voltage vectors.
Therefore the d-q plane of the voltage vector is subdivided into
12 sectors with 30o of each started from -15o. Empirical rules
has been used and investigation shows that a 4 level torque
hysteresis along with 8 level torque hysteresis utilize the
highest number of available voltage vector in d-q plane. Sector
has been calculated using following set of equation.
A similar strategy can be drawn for even sector with the
above procedure.
10
01
Figure 5: a. labeled vector diagram of proposed MLI b. Zoomed
version of shaded triangle
00
.
00
01
10
57
Figure 6: vector selection of sector -1 (Shaded Triangle (150 to +150))
V.
RESULT AND DISCUSSION
Simulation has been done using MATLAB/Simulink..
Sampling time has been kept limited for real time
implementation in future. Same parameter for both
conventional and proposed DTC scheme has been used.
2014 IEEE 9th Conference on Industrial Electronics and Applications (ICIEA)
335
Bandwidth of the stator flux controller has been set to ±5%
of the reference stator flux which is ±0.1Wb, whereas a
hysteresis band of ±0.9Nm has been set for the torque
controller. For the proposed multilevel version of the DTC, flux
and torque hysteresis controller has been sub-divided according
to figure 7(a) and 7(b) respectively.
(a)
(d)
(b)
(e)
Index
4
3
2
1
(c)
0
(f)
T
0
Ͳ1
Ͳ2
Ͳ3
(b)
Figure 8: Simulation result based on proposed MLI based
DTC
Ͳ4
Figure 7: Simulation result based on proposed MLI based
DTC
(a)
(d)
The dc-bus voltage has been selected to 400 Vdc for the
case of basic DTC and for its multilevel counterpart the main
stage dc-bus voltage has been kept to 300 Vdc whereas medium
stage is one third of its main stage.
(b)
(e)
Figure 8 represent the steady state character of the IM
controlled under the proposed DTC scheme. The mechanical
speed has been kept to Ÿ=50 rad/s and Tl=1 Nm .load torque
has been applied. Stator phase-A voltage and phase-B voltage
has been separately shown in figure 8(a) and 8(b) for clarity.
Stator 3-phase current has been shown in figure 8(c) where
figure 8(d), 8(e) and 8(f) representing the sector selection and
flux ripple and the electromagnetic torque respectively. A
comparison between 8(e) with respect 8(d) highlight the
demagnetizing effect that appears repetitively at the beginning
of each even sector which then over compensated in the next
sector. As a result of that small spike appeared with an interval
of two sectors.
(c)
(f)
Figure 9: Simulation result based on basic DTC scheme
(a)
Figure 9(a)-(b), 9(c), 9(d), 9(e), 9(f) consecutively represent
the phase voltage, phase current, sector succession, flux ripple
and torque ripple when basic DTC scheme is applied. From
Figure 8, it is evident that the proposed system outperforms in
terms of flux and torque ripple to its counterpart of
conventional DTC scheme shown in Figure 9.
Selection of the voltage vector in the proposed DTC scheme
solely depends on the torque error and flux error. These means
the gradient of the torque ripple (or flux) depend on the
magnitude error of the torque ripple (or flux). Therefore the
probability of overextend outside the hysteresis band for the
torque is reduced.
336
2014 IEEE 9th Conference on Industrial Electronics and Applications (ICIEA)
(b)
1.83
Figure 10: THD analysis of proposed DTC at speed 500rpm
2
[2]
82%
2.6%
14.2%
61%
0.71
70%
0.34
1
0.5
[1]
1.12
1.5
REFERENCE
0
Torque
Flux
DTC MLI
DTC Basic
THD
% Reduction
[3]
[4]
[5]
[6]
Figure 11: Quantitative result in terms of torque (N-m) and
flux (Wb) ripple and percentage THD of stator current.
[7]
Figure 9(f) shows the torque response of conventional DTC
using six switch inverter. The torque ripple band in this case is
about 1.12 N-m. Figure 8(f) is the proposed MLI version of
DTC. In this instant the torque ripple is 0.34 N-m. Therefore
using this topology and control about 70% torque ripple has
been reduced. In both case the load torque and speed demand
has been kept same.
[8]
FFT analysis of the stator current for both proposed DTC
and convention DTC has been performed and shown in figure
10(a) and 10(b) respectively. A comparative study in terms of
torque (N-m), flux (Wb) and THD (%) has been shown in
figure 11 and found that a significant improvement has been
achieved in all the parameters.
[9]
[10]
[11]
[12]
I.
CONCLUSION
In this paper a DTC scheme utilizing 5 levels cascaded Hbridge MLI has been proposed. Thanks to 61 suitable voltage
vector combination inherently generated by the MLI which
facilitate the control strategy of proposed DTC scheme.
Conception of basic DTC scheme has been modified and
extended for five levels inverter. Multilevel torque and flux
hysteresis controller has been designed by simply dividing the
Clarke plane into twelve equal sectors. Simulation based study
revealed that the steady state performance of the IM has been
improved noticeably. These performances are now subjected to
the experimental validation along with a comprehensive
comparison with the other existence established methods
[13]
[14]
[15]
Ahmed M, El Badsi B, Bouzidi B. DTC Scheme for a Four-Switch
Inverter Fed Induction Motor Emulating the Six-Switch Inverter
Operation. 2013;
Alloui H, Berkani A, Rezine H. A three level NPC inverter with neutral
point voltage balancing for induction motors Direct Torque Control. In:
International Conference on Electrical Machines (ICEM) 6-8 Sept.
2010; Rome: ICEM. pp. 1-6
Baader U, Depenbrock M, Gierse G. Direct self control (DSC) of
inverter-fed induction machine: a basis for speed control without speed
measurement. IEEE Transactions on Industry Applications 1992;
28:581-8.
Takahashi I, Noguchi T. A new quick-response and high-efficiency
control strategy of an induction motor. IEEE Transactions on Industry
Applications 1986; IA-22:820-7.
Abdul Kadir MN, Mekhilef S, Ping HW. Voltage vector control of a
hybrid three-stage 18-level inverter by vector decomposition. Power
Electronics, IET 2010; 3:601-11.
Habetler TG, Profumo F, Pastorelli M, Tolbert LM. Direct torque
control of induction machines using space vector modulation. IEEE
Transactions on Industry Applications 1992; 28:1045-53.
del Toro X, Jayne M, Witting P, Arias A, Romeral J. Direct torque
control of an induction motor using a three-level inverter and fuzzy
logic. In: International Symposium on Industrial Electronics; 4-7 May
2004; Unknown: IEEE. pp. 923-7
Quindere KEB, Ruppert EF, de Oliveira MEF. Direct torque control of
permanent magnet synchronous motor drive with a three-level inverter.
In: 37th IEEE Power Electronics Specialists Conference; 18-22 June
2006; Jeju: IEEE. pp. 1-6
Tang L, Zhong L, Rahman MF, Hu Y. A novel direct torque control for
interior permanent-magnet synchronous machine drive with low ripple
in torque and flux-a speed-sensorless approach. IEEE Transactions on
Industry Applications 2003; 39:1748-56.
Khoucha F, Lagoun SM, Marouani K, Kheloui A, El Hachemi
Benbouzid M. Hybrid Cascaded H-Bridge Multilevel-Inverter
Induction-Motor-Drive Direct Torque Control for Automotive
Applications. IEEE Transactions on Industrial Electronics 2010;
57:892-9.
Lee KB, Huh SH, Yoo JY, Blaabjerg F. Performance improvement of
DTC for induction motor-fed by three-level inverter with an uncertainty
observer using RBFN. IEEE Transactions on Energy Conversion 2005;
20:276-83.
Escalante MF, Vannier JC, Arzande A. Flying capacitor multilevel
inverters and DTC motor drive applications. IEEE Transactions on
Industrial Electronics 2002; 49:809-15.
Rodriguez J, Lai J-S, Peng FZ. Multilevel inverters: a survey of
topologies, controls, and applications. Industrial Electronics, IEEE
Transactions on 2002; 49:724-38.
Martins CA, Roboam X, Meynard TA, Carvalho AS. Switching
frequency imposition and ripple reduction in DTC drives by using a
multilevel converter. IEEE Transactions on Power Electronics 2002;
17:286-97.
Kadir MNA, Hussien ZF. Asymmetrical Multilevel Inverter: Maximum
Resolution for H-Bridge Topology. In: Power Electronics and Drives
Systems, 2005 PEDS 2005 International Conference on; 0-0 0; pp.
1068-71
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