MODIFIED DIRECT TORQUE CONTROL FOR BLDC MOTOR DRIVES

International Journal of Control Theory and Computer Modeling (IJCTCM) Vol.6, No.3, July 2016
DOI : 10.5121/ijctcm.2016.6301 1
MODIFIED DIRECT TORQUE CONTROL FOR BLDC
MOTOR DRIVES
Fatih Korkmaz, smail Topaloğlu and Hayati Mamur
Department of Electric-Electronic Engineering, Çankırı Karatekin University,
Uluyazı Kampüsü, Çankırı, Turkey
ABSTRACT
In this paper, a new adaptive reference based approach to direct torque control (DTC) method has been
proposed for brushless direct current (BLDC) motor drives. Conventional DTC method uses two main
reference parameters as: flux and torque. A main difference from the conventional method of it was that
only one reference parameter (speed) was used to control the BLDC motor and the second control
parameter (flux) was obtained from speed error through the proposed control algorithm. Thus, the DTC
performance has been especially improved on systems which need variable speed and torque during
operation, like electric vehicles. The dynamic models of the BLDC and the DTC method have been created
on Matlab/Simulink. The proposed method has been confirmed and verified by the dynamic simulations on
different working conditions. The simulation studies showed that the proposed method reduced remarkably
the speed and the torque ripples when compared the conventional DTC method. Moreover, the proposed
method has also very simple structure to apply the conventional DTC and its extra computational load to
the controller is almost zero.
KEYWORDS
Brushless machines, Direct torque control, Vector control, Torque control
1. INTRODUCTION
The BLDC motors are in our life for many years in computers, robotics, aerospace applications etc.
In recent years, the BLDC motors applications have became more popular in industrial and daily
utilization, like CNC machine tools, servo systems, home appliances, and electric vehicles. The
main reasons of the increasing on popularity of the BLDC motors, in other words, main advantages
of the BLDC motors, can be listed as follows[1-4]:
• High efficiencies
• High power densities
• High starting torque
• Wide speed ranges
• Linear torque and speed characteristics
• Low maintenance and works in any condition
The BLDC motors not only have advantages of conventional DC motors but also have advantages
of AC motors as can be seen from the list. Because, they have the AC motor mechanical structures
–no brushes or collectors–while they have the DC motors electrical characteristic.[5]
The DTC method was developed by Takahashi in the middle of the 1980s, for three phase induction
motors. The DTC method converts three phase parameters of the motor (three phase voltage and
currents) to two phase independent vector components with Clarke transformation; thus, it proposes
control of every component separately, like conventional DC motors. Although, it was developed
for the induction motors, it has been applied many other motor types like permanent magnet AC
motors, BLDC motors, switched reluctance motors, linear motors[6-7].

2
In literature, many kind of BLDC motor drive methods can be found. In [8], artificial neural
networks based method was used in modeling of BLDC to get the maximum power consumption.
Very simple and effective three-level neutral point clamped inverter was proposed to drive axial
flux BLDC motors, in [9]. Field Programmable Gate Array (FPGA) based BLDC motor driver with
using digital pulse-width modulation (PWM) is presented in [10]. In addition, several different
methods, which based of the DTC, were studied in BLDC drivers. Reference [11] proposes the
DTC method for matrix converter fed BLDC motor. The DTC of BLDC motor method using with
four-switch inverter in constant torque region was proposed in [12].
In this paper, a new approach to the DTC method has been proposed for small scale electric vehicles
that work in variable speed and torque conditions, naturally. In the proposed method, optimum
stator flux reference value was obtained by PI controller with usage of the speed error. The dynamic
model of the proposed method was developed with Matlab/Simulink. The dynamic simulations
were performed and results were presented to illustrate the validity of the proposed method.
2. DIRECT TORQUE CONTROL OF BLDC
The BLDC motor has three phase stator windings with permanent magnet rotor and electrical model
of the motor that connected with PWM inverter, is given in Fig. 1[13].
Voltage equations of the motor can be obtained by the following equation;
൥
Vୟ
Vୠ
Vୡ
൩ = ൥
R 0 0
0 R 0
0 0 R
൩ ൥
iୟ
iୠ
iୡ
൩ + ൥
L 0 0
0 L 0
0 0 L
൩
ୢ
ୢ୲
൥
iୟ
iୠ
iୡ
൩ + ൥
eୟ
eୠ
eୡ
൩ (1)
Where Vୟ, Vୠ, Vୡ are phase voltages, R is phase resistance, L is phase inductance, iୟ, iୠ, iୡ are phase
currents and eୟ, eୠ, eୡ are back EMFs.
Figure 1. Electrical Model of the Motor that Connected with PWM Inverter
The mechanical moment equation of the motor given by the following equation;
Tୣ = T୐ + Bω୫ + j
ୢωౣ
ୢ୲
(2)
Tୣ and T୐ describes generated electromagnetic torque and load torque, respectively. B is the friction
coefficient, j is the inertia and ω୫ is the angular velocity of rotor[14].
The DTC method needs to transformation of the three phase motor parameters to two phases. In this
transformation, electrical parameters of the motor (voltages, currents, back emf) should to be
transformed to stationary reference frame and it can also be named as α − β transformation or
Clarke transformation in many sources. The Clarke transformation matrix is given (3).

3
൤
fα
fβ
൨ =
ଶ
ଷ
቎
1 −
ଵ
ଶ
−
ଵ
ଶ
0
√ଷ
ଶ
−
√ଷ
ଶ
቏ ൥
fୟ
fୠ
fୡ
൩ (3)
Where, fα, fβ are α − β components of motor parameters, and fୟ, fୠ, fୡ are the abc frame
components [15].
With the transforming of the three phase parameters of the motor, α − β components of the phase
voltages can be written as:
vୱα = Rୱiୱα + Lୱ
ୢ୧౩α
ୢ୲
+ eα (4)
vୱβ = Rୱiୱβ + Lୱ
ୢ୧౩β
ୢ୲
+ eβ (5)
Where vୱα, vୱβ are the stator voltages, iୱα, iୱβ are the stator currents and eα, eβ are back emf in the
α − β referance frame.
In the DTC scheme, stator flux components are obtained from α − β components of the measured
stator voltages and currents as given below [16]:
λୱα = ‫׬‬ሺvୱα − Rୱiୱαሻdt (6)
λୱβ = ‫׬‬൫vୱβ − Rୱiୱβ൯dt (7)
The magnitude of the flux can be calculated with;
λ = ටλୱα
ଶ
+ λୱβ
ଶ
(8)
and position of the stator flux vector can be calculated with;
θ = arctan
λ౩β
λ౩α
(9)
The calculation of the electromagnetic torque of the BLDC motor in α − β reference frame is given
below;
Tୣ =
ଷ୮
ସ
ቂ
ୢλ౨α
ୢθ౛
iୱα +
ୢλ౨β
ୢθ౛
iୱβቃ (10)
Where λ୰α and λ୰β are the α − β components of the rotor flux vector, p is the number of the poles
and θୣ is electrical angle of the rotor.
The α − β components of the rotor flux vector can be obtained as:
λ୰α = λୱα − Lୱiୱα (11)
λ୰β = λୱβ − Lୱiୱβ (12)
The different forms of the rotor flux α − β components can also be obtained from the following
equations;

International Journal of Control Theory a
ୢλ౨α
ୢθ౛
=
ୢλ౨α
ୢ୲
ୢ୲
ୢθ
ୢλ౨β
ୢθ౛
=
ୢλ౨β
ୢ୲
ୢ୲
ୢθ
It means, electromagnetic torque can be
Tୣ =
ଷ୮
ସ
ቂ
ୣα
ω౛
iୱ
The six active voltage vector, PWM inverter switching states and stator voltage vector sectors are
shown in Figure 2. Inverter switching look
Figure 2. PWM
Table
onal Journal of Control Theory and Computer Modeling (IJCTCM) Vol.6, No.3, July 2016
ୢ୲
θ౛
=
ଵ
ω౛
ୢλ౨α
ୢ୲
=
ୣα
ω౛
(13)
ୢ୲
θ౛
=
ଵ
ω౛
ୢλ౨β
ୢ୲
=
ୣβ
ω౛
(14)
, electromagnetic torque can be written with in another form as:
ቂ ୱα +
ୣβ
ω౛
iୱβቃ (15)
. Inverter switching look-up table is also given in Table 1.
PWM Inverter Switching States and Stator Voltage Vector Sectors
able 1. Inverter Switching Look-Up Table
Vol.6, No.3, July 2016
4
nd Stator Voltage Vector Sectors

5
Figure 3. The Conventional DTC Block Diagram
In the conventional DTC (C-DTC) method, control algorithms works with two separate reference
values as torque (or speed) and flux references. Because, in idea of the DTC, stator flux vector has
two components (α − β components) and they can be controlled independently from each other.
One of them controls flux, while the other one controls torque. In generally, flux reference is kept
constant and the speed control of the motor can be achieved by setting up the torque reference
value. This approach is very appropriate for constant torque-variable speed applications. The
conventional DTC block diagram is given in Figure 3.
3. ADAPTIVE FLUX BASED METHOD
In variable torque and variable speed applications, like small electric vehicles, keeping the flux
constant causes high torque and speed ripples. A new approach was designed and investigated in
this paper to overcome this problem. In the proposed approach, a new PI controller was used to
determine optimum flux reference value according the motor speed. So, two different PI controllers
were used in proposed DTC (P-DTC) method. One of the PI controllers calculates reference torque
and the other one calculates reference flux with use of the speed error. The proposed DTC Simulink
block diagram was given in Figure 4.
In dynamic simulations, the BLDC motor was performed under two different working conditions.
The parameters of the blocks and the motor that used in dynamic simulations were given in
appendix. Total simulation time was 1 sec. for all conditions. The sampling time was 10 µs.
The motor load constant (5Nm) and the speed reference was changed 500 rpm to 1500 rpm at 1.
sec. in first working condition. The speed and the torque responses of the motor were given in Fig. 5
and Fig. 6, respectively.

Figure
Figure 5. Overview to Speed Responses
Figure 6. Zoomed-View to Speed Responses of t
ure 4. The Proposed DTC Simulink Block Diagram
o Speed Responses of the BLDC in Variable Speed-Constant Load
View to Speed Responses of the BLDC in Variable Speed-Constant Load
6
Constant Load
Constant Load

Figure 7. Torque
It can be seen in Figure 5–7. that, the BLDC motor speed and torque responses were improved with
the P-DTC method. The torque and speed ripples reduced remarkably with the P
especially in high speed reference values. In
were almost same with both methods.
Figure 8. Overview to Speed Responses of t
Figure 9. Zoomed- View to Speed Responses of t
Torque Responses of the BLDC in Variable Speed-Constant Load
that, the BLDC motor speed and torque responses were improved with
DTC method. The torque and speed ripples reduced remarkably with the P-
especially in high speed reference values. In 500 rpm speed reference, the motor dynamic behaviors
ere almost same with both methods.
to Speed Responses of the BLDC in Variable Torque-Constant Speed
View to Speed Responses of the BLDC in Variable Torque-Constant Speed
7
Constant Load
that, the BLDC motor speed and torque responses were improved with
-DTC method
00 rpm speed reference, the motor dynamic behaviors
Constant Speed
Constant Speed

Figure 10. Torque
In the second test, the motor was simulated at constant speed reference (2000 rpm) and the torque
reference was changed to 0 Nm to 5 Nm at
were given in Figure 8–10, respectively
After the second test studies, which t
torque curves were showed that the motor
variable torque conditions. The C
reference. But with the P-DTC method
The dynamic simulations proved
method. Moreover, the computational times of the both system were compared during the tests and
it must be pointed out that the P
DTC. So, it can be said that, the proposed method has n
can applicable on BLDC motor driven electric vehicles.
4. CONCLUSIONS
In recent years, BLDC motors have been used many industrial applications and it has gain great
popularity between electric motors. On the other hand, the DTC is well
control method not only for induction motors but also many other motor types. This
a new perspective to the conventional
BLDC motors which considered
variable speed and torque conditions with single reference in
method was modified with the adding of second PI controller that produces optimum flux reference.
In order to test the validity and
been performed under different working conditions and results were presented.
results showed that the proposed method reduced remarkably the speed and the torque ripples when
compared conventional DTC method. The proposed method
the conventional DTC and its extra computational load to the contro
APPENDIX
The parameters of the blocks and the motor that used in dynamic simulations are
400V, stator phase resistance, Rs (ohm) = 0.45, stator phase inductance Ls (H) = 8.5e
hysteresis band limits = ±0.005, torque hysteresis band limits = ±0.02, stator flux reference = 0.32
weber, sampling time 10 µsec.
Torque Responses of the BLDC in Variable Torque-Constant Speed
Nm to 5 Nm at 1. sec. The speed and the torque responses of
, respectively.
After the second test studies, which the torque reference value was changed, the speed and the
that the motor performance was also improved in constant speed
que conditions. The C-DTC method had much torque peaks especially in
method, the motor had very small peaks for both torque references.
d that the P-DTC method can be a good alternative to the
Moreover, the computational times of the both system were compared during the tests and
P-DTC method had almost same computational time with the
DTC. So, it can be said that, the proposed method has not extra load on controller structu
motor driven electric vehicles.
, BLDC motors have been used many industrial applications and it has gain great
popularity between electric motors. On the other hand, the DTC is well-known high performance
control method not only for induction motors but also many other motor types. This paper presents
conventional DTC method. The proposed DTC method applied
BLDC motors which considered drives small size electric vehicles. These vehicles works in
variable speed and torque conditions with single reference input: speed. The conventional DTC
modified with the adding of second PI controller that produces optimum flux reference.
validity and applicability of the proposed method, dynamic simulations
nt working conditions and results were presented. The simulations
compared conventional DTC method. The proposed method had also very simple structure to apply
the conventional DTC and its extra computational load to the controller was almost zero.
The parameters of the blocks and the motor that used in dynamic simulations are, DC bus voltage
400V, stator phase resistance, Rs (ohm) = 0.45, stator phase inductance Ls (H) = 8.5e
8
Constant Speed
. sec. The speed and the torque responses of the motor
, the speed and the
also improved in constant speed -
much torque peaks especially in 0 Nm torque
very small peaks for both torque references.
to the C-DTC
Moreover, the computational times of the both system were compared during the tests and
almost same computational time with the C-
ot extra load on controller structure and it
, BLDC motors have been used many industrial applications and it has gain great
known high performance
paper presents
DTC method. The proposed DTC method applied to the
. These vehicles works in
put: speed. The conventional DTC
modified with the adding of second PI controller that produces optimum flux reference.
applicability of the proposed method, dynamic simulations were
The simulations
also very simple structure to apply
almost zero.
, DC bus voltage
400V, stator phase resistance, Rs (ohm) = 0.45, stator phase inductance Ls (H) = 8.5e-3, flux

9
ACKNOWLEDGEMENTS
Thanks to Cankırı Karatekin University because of their valuable contributions to this paper.
This research was funded by a grant (No. MF050315B15) from the Research Council of Cankırı
Karatekin University. This research was performed in cooperation with the Institution.
REFERENCES
[1] C. Xia, Z. Li, and T. Shi, “A Control Strategy for Four-Switch Three-Phase Brushless DC Motor
Using Single Current Sensor”, Industrial Electronics, IEEE Transactions on , vol.56, no.6, pp. 2058–
2066, June 2009.
[2] Z. Xiaofeng, L. Zhengyu, "A new BLDC motor drives method based on BUCK converter for torque
ripple reduction,", Power Electronics and Motion Control Conference, 2006. IPEMC 2006. CES/IEEE
5th International , vol.2, no., pp.1–4, 14-16 Aug. 2006
[3] I. Topaloglu, F. Korkmaz, H. Mamur, R. Gurbuz, “Closed-Loop speed control of PM-BLDC motor
fed by six step inverter and effects of inertia changes for desktop CNC machine” Elektronika IR
Elektrotechnika, vol. 19, no 1, pp. 7–10, 2013.
[4] I. Tarimer, A. Akpunar, R. Gurbuz, “Design of a direct sliding gearless electrical motor for an
ergonomic electrical wheelchair”, Elektronika IR Elektrotechnika, no 3, pp. 75–80, 2008.
[5] F. Korkmaz “A New Approach to DTC Method For BLDC Motor Adjustable Speed Drives” The
Fourth International Conference on Instrumentation and Control Systems(CICS-2016), vol. 6, no 5,
pp-37–44, April 2016
[6] I. Takahashi and T. Noguchi , “A new quick-response and high efficiency control strategy of an
induction motor” IEEE Transactions on Industrial Applications, vol.I A-22 , no.5, pp. 820–827, 1986.
[7] F. Korkmaz, I. Topaloglu, R. Gurbuz, “Simulink model of vector controlled linear induction motor
with end effect for electromagnetic launcher system”, Elektronika IR Elektrotechnika, vol. 20, no 1,
pp. 29–32, 2014.
[8] M. Nizam, A. Mujianto, H. Triwaloyo, Inayati, "Modelling on BLDC motor performance using
artificial neural network (ANN)", Rural Information & Communication Technology and Electric-
Vehicle Technology (rICT & ICeV-T), 2013 Joint International Conference on , vol., no., pp.1–4, 26-
28 Nov. 2013.
[9] S. De, M. Rajne, S. Poosapati, C. Patel, K. Gopakumar, "Low-inductance axial flux BLDC motor
drive for more electric aircraft", Power Electronics, IET , vol.5, no.1, pp.124–133, January 2012.
[10] A. Tashakori, M. Hassanudeen, M. Ektesabi, "FPGA based controller drive of BLDC motor using
digital PWM technique", Power Electronics and Drive Systems (PEDS), 2015 IEEE 11th
International Conference on , vol., no., pp.658–662, 9-12 June 2015.
[11] R. Muthu, M.S. Kumaran, L.A. Rajaraman, P. Ganesh, P. Reddy, "Direct Torque Control of matrix
converter fed BLDC motor", Power Electronics (IICPE), 2014 IEEE 6th India International
Conference on , vol., no., pp.1–6, 8-10 Dec. 2014.
[12] S.B. Ozturk, W.C. Alexander, H.A. Toliyat, "Direct torque control of four-switch brushless DC Motor
with non-sinusoidal back-EMF", Power Electronics Specialists Conference, 2008. PESC 2008. IEEE ,
vol., no., pp.4730–4736, 15-19 June 2008.
[13] W.S. Im, W. Liu, J.M. Kim, "Sensorless control of 3-phase BLDC motors using DC current model",
Energy Conversion Congress and Exposition (ECCE), 2014 IEEE , vol., no., pp.4484–4490, 14-18
Sept. 2014.
[14] P.K. Girija, A. Prince, "Robustness evaluation of SMO in sensorless control of BLDC motor under
DTC scheme", Power Signals Control and Computations (EPSCICON), 2014 International
Conference on , vol., no., pp.1-6, 6-11 Jan. 2014.
[15] F. Korkmaz, I. Topaloglu, M.F. Cakir, R. Gurbuz, "Comparative performance evaluation of FOC and
DTC controlled PMSM drives", Power Engineering, Energy and Electrical Drives (POWERENG),
2013 Fourth International Conference on , vol., no., pp.705–708, 13-17 May 2013.
[16] F. Korkmaz, M.F. Cakir, Y. Korkmaz, I. Topaloglu, “Fuzzy based stator flux optimizer design for
direct torque control”, International Journal of Instrumentation and Control Systems (IJICS), vol.2,
no.4, pp. 41–49, October 2012.

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