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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
The Direct Torque Control of Induction Motor
by using Matrix Converters
Ch.Manohar, T.Abhiram (Asst.Prof), Dr.K.Sumanth (Prof&HOD)

Abstract— In this paper a new control method of matrix
converter is proposed which uses the combined advantages of
matrix converter with the direct torque control (DTC) of
induction motors. The simulation results are carried out for
different speeds and loads of an induction motor and the total
harmonic distortions for the specified loads and speeds are
discussed.
Index Terms—AC-AC power conversion , induction motor
drives , torque control.
and the flux leading to different switching strategies. Each
strategy affects the drive behavior in terms of torque and
current ripple, switching frequency, and two- or four-quadrant
operation capability [15]–[17]. In [18], a speed-dependent
switching strategy has been proposed in order to achieve fast
torque response in a wide speed range. In this paper a new
control method of matrix converter is proposed which uses
the combined advantages of matrix converter with the direct
torque control of induction motors.
I. INTRODUCTION
Three phase matrix converters have received considerable
attention in recent years because they may become a good
alternative to voltage-source inverter pulse width-modulation
(VSI-PWM) converters [1]–[6].The advantages with the
matrix converters are they provides bidirectional power flow,
sinusoidal input/output waveforms, and controllable input
power factor..Matrix converters are in compact size due to the
absence of dc link capacitor which also tends to reduce the
cost of the equipment. There are two approaches which are
used widely in controlling methods. The first one is based on
transfer function analysis and has been proposed in [1]. The
second one is based on space-vector modulation (SVM)
technique which has some advantages, such as immediate
comprehension of the required commutation processes,
simplified control algorithm, and maximum voltage transfer
ratio without adding third harmonic components [5], [7]–[9].
The direct torque control (DTC) technique for induction
motors was initially proposed as DTC [10] or direct
self-control [11], then the method was generalized to
current-source-inverter-fed induction motors and to VSI-fed
and current-source-inverter-fed synchronous machines [12].
The main advantages of DTC are robust and fast torque
response, no requirements for coordinate transformation, no
requirements for PWM pulse generation and current
regulators. In [13] and [14], a control scheme for induction
motors based on DTC has been analyzed, but the rotor flux is
assumed as reference, instead of stator flux, in order to
achieve the highest pull-out torque. Using a VSI, different
vector selection criteria can be employed to control the torque
Manuscript received Oct 15, 2011.
Ch.Manohar, Electrical Power Engineering, Sreenidhi Institute of
Science
and
Technology
.,(e-mail:[email protected]).
Hyderabad,India, 9676190870 T.Abhiram(Asst.Prof), Electrical and
Electronics Engineering,Hyderabad,India, 9866307221., (e-mail:
[email protected]).
Fig. 1. Schematic representation of a matrix converter.
II. DIRECT TORQUE CONTROL BY MATRIX CONVERTER
A. Matrix Converter Theory
In three-phase/three-phase matrix converters, the nine
bidirectional switches allow any output phase to be connected
to any input phase as schematically represented in Fig. 1.
There are 27 possible switching configurations; among these,
only 21 can be usefully employed in the DTC algorithm.
These configurations are summarized in Table I. The first 18
switching configurations (named) have the common feature of
connecting two output phases to the same input phase. The
corresponding output line-to-neutral voltage vector and input
line current vector , have fixed directions, as represented in
Figs. 2 and 3, and will be named “active configurations.” The
magnitude of these vectors depends upon the instantaneous
values of the input line-to-neutral voltages and output line
currents respectively as shown in Table I. Three switching
configurations determine zero input current and output
voltage vectors and will be named “zero configurations.”
have the three output phases connected to a different input
Dr.K.Sumanth(Prof&HOD), Electrical Power Engineering, Sreenidhi
Institute of Science and Technoloy, Hyderabad, India, 9948316222.,
(e-mail: [email protected])
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
phase. In this case, the output voltage and input current
vectors have variable direction and cannot be usefully used. It
should be noted that the voltage vectors produced by a matrix
converter can be utilized using the SVM technique to
synthesize the instantaneous voltage vector required by
field-oriented control of induction motors [5]–[9].
B. Basic DTC Principles
In principle, the DTC is a hysteresis stator flux and torque
control that directly selects one of the six nonzero and two
zero voltage vectors generated by a VSI (Fig. 4), in order to
maintain the estimated stator flux and torque within the
hysteresis bands. In particular, the stator flux is controlled by
a two-level hysteresis comparator, whereas the torque by a
three-level hysteresis comparator, as shown in Figs. 5 and 6,
respectively. On the basis of the hysteresis comparator
outputs and the stator flux sector number, the most opportune
VSI voltage vector is selected at each sampling period,
according to the switching table given in Table II.
As an example, considering the stator flux vector lying in
sector 1 ,the voltage vectors V2 and V6 can be selected in
order to increase the flux while V3 and V5 can be applied to
decrease the flux. Among these, V2 and V3 determine a
torque increase, while V5 and V6 a torque decrease. The
zero-voltage vectors are selected when the output of the
torque comparator is zero, irrespective of the stator flux
condition. Using the switching table given in Table II, it is
possible to implement DTC schemes having good
performance.
TABLE I
SWITCHING CONFIGURATIONS USED IN THE PROPOSED
CONTROL SCHEME
Fig. 3. Input line current vector configurations.
Fig. 4. VSI output line-to-neutral voltage vectors and corresponding stator
flux variations in a period ∆t.
Fig. 5. Flux hysteresis comparator.
C. DTC Principles Using Matrix Converters
Fig. 2. Output line-to-neutral voltage vector configurations.
From the previous considerations, it appears that the matrix
converter generates a higher number of output voltage vectors
with respect to VSI. This feature can be utilized to keep under
control a further variable in addition to stator flux and torque.
In the proposed control method, the average value of the sine
of the displacement angle Ѱi between the input line-to-neutral
voltage vector and the corresponding input line current vector
has been chosen as a third variable. In principle, the proposed
control technique of the matrix converter selects, at each
sampling period, the proper switching configuration, which
allows the compensation of instantaneous errors in flux
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
magnitude, and torque, under the constraint of unity input
power factor. This last requirement of the input side of the
matrix converter is intrinsically satisfied if the average value
of sin(Ѱi) maintained close to zero. The hysteresis regulator
shown in Fig. 7 directly controls this variable. The average
value of sin(Ѱi) obtained by applying a low-pass filter to its
instantaneous value. The criteria utilized to implement the
switching table for the matrix converter can be explained
referring to an example. We can assume that V1 is the VSI
output voltage vector selected by the DTC algorithm in a
given switching period. From Figs. 2 and 4 and from Table I it
appears that in order to generate a voltage vector similar to V1
one of the matrix converter switching configurations
±1,±2,±3 must be chosen. The magnitude and the direction of
the corresponding output voltage vectors depend on the input
line-to-neutral voltage vector. Among the six vectors, those
having the same direction of and the maximum magnitude are
considered. If the input line-to-neutral voltage vector lies in
sector 1 then the switching configurations, which can be
utilized, are +1 and -3. Both these switching configurations
satisfy the torque and flux requirements. As can be noted from
Table I and Fig. 3, these configurations determine input
current vectors lying on the directions adjacent to sectors 1
and 4. Then, if the average value of sin(Ѱi) has to be
decreased, the switching configuration- 3 has to be applied.
On the contrary, if the average value of sin(Ѱi) has to be
increased, the switching configuration +1 has to be applied.
The switching table based on these principles is shown in
Table III. The first column contains the voltage vectors
selected by the basic DTC scheme to keep the stator flux and
torque within the limits of the corresponding hysteresis bands.
The other six columns are related to the sector in which the
input line-to-neutral voltage vector is lying. Depending on the
output value Cᵩ of the hysteresis comparator, the left or the
right sub column has to be used in selecting the switching
configuration of the matrix converter. When a zero-voltage
vector is required from Table II, the zero configuration of the
matrix converter, which minimize the number of
commutations, is selected. A schematic diagram of the
proposed drive system is represented in Fig. 8. The reference
values of torque and stator flux are compared with the
estimated values. The output of the hysteresis comparators,
together with the numbers of the sectors of the stator flux
vector and input line-to neutral voltage vector, are the input to
the switching configuration selection algorithm (Tables II and
III). In the lower part of the diagram are shown the estimators
of electromagnetic torque, stator flux, and average value of
sin(Ѱi). These estimators require the knowledge of input and
output voltages and currents. However, only the input
voltages and output currents are measured, while the other
quantities are calculated on the basis of the switching states of
the matrix converter.
Fig. 6. Torque hysteresis comparator.
TABLE II
BASIC DTC SWITCHING TABLE
Fig. 7. Hysteresis comparator of the average value of sin(Ѱi ).
TABLE III
MATRIX CONVERTER SWITCHING TABLE
Fig. 8. Block diagram of the DTC scheme with matrix converter.
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Fig 13..Electro magnetic Torque at speed 1000 rpm and load at
25Nm
Fig 9.simulation diagram of matrix converter using DTC
Fig 14. Stator Current at speed 1730 rpm and load at 15 Nm
III .SIMULATION RESULTS
Fig 15.Electro magnetic torque at speed 1730 rpm and load at
15Nm
Fig 10.Electro magnetic torque at speed 100 rpm and load at 20Nm
Fig 16.Total Harmonic Distortion for the input voltages at
speed 100 rpm and load at 20 Nm
Fig 11.Stator Current at speed 100 rpm and load at 20 Nm
Fig 12. Stator Current at speed 1000 rpm and load at 25 Nm
Fig 17.Total Harmonic Distortion for the input voltages at
speed 1000 rpm and load at 25 Nm
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
[16]
[17]
[18]
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Fig 17.Total Harmonic Distortion for the input voltages at speed
1730 rpm and load at 15 Nm
IV. CONCLUSION
In this paper, a new induction motor drive scheme has been
proposed in which a matrix converter is employed in driving
an induction motor using the DTC technique.
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[1]
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