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A Novel Digital Control Technique for
Brushless DC Motor Drives
Fernando Rodriguez, Student Member, IEEE, and Ali Emadi, Senior Member, IEEE
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 54, NO. 5, OCTOBER 2007
2365-2373
Adviser:Ming-Shyan Wang
Student:Wei-Cheng Huang
Student ID:MA020107
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Outline
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Abstract
Introduction
Novel Digital Control
Conduction -Angle Control
Current-Mode Control
Controller Design
Simulations
Conclusion
References
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Abstract

Brushless dc (BLDC) motor drives are continually gaining
popularity in motion control applications. Therefore,it is
necessary to have a low cost, but effective BLDC motor
speed/torque regulator.
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This paper introduces a novel concept for digital control of
trapezoidal BLDC motors. The digital controller was
implemented via two different methods, namely conductionangle control and current-mode control.
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Introduction
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This paper proposes a novel digital controller that treats the BLDC motor
drive like a digital system.
The BLDC system may only operate at a few predefined states that produce
constant predefined motor speeds. Speed regulation is achieved by
alternating states during operation,which makes the concept of the
controller extremely simple for design and implementation purposes.
This novel concept will help reduce the cost and complexity of the motor
control hardware. That, in turn, can boost the acceptance level of BLDC
motors for commercial mass production applications,successfully fulfilling
the promises of energy savings associatedwith adjustable speed drives.
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Novel Digital Control(1/2)
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Fig. 1. Proposed digital control.
1) If the actual motor speed is less than the commanded speed, then switch
or stay at state 2 ( W ).
2) If the actual motor speed is greater than the commanded speed, then
switch or stay at state 1 ( W ).
H

L
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Novel Digital Control(2/2)
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Fig. 2 Digital control actuation signal.
.
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Conduction -Angle Control
Fig. 3 Conduction-angle control state definitions.
.
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Current-Mode Control
Fig. 4. Current-mode control state definitions.
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Controller Design(1/6)
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Newton’s second law applied to rotary motion
T

d
dw(t )
 w(t )b  J
T L
dt
(1)
The solution to the differential equationgives the instantaneous
speed as a function of motor parametersand load conditions,
see

dw(t ) b
T
d TL
(2)
 w(t ) 
dt
J
J
T
T
w(t ) 
d
b
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L
T
T
 ( w(0) 
)e
b
d
L
( b ) t
J
(3)
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Controller Design(2/6)
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Understeady-state conditions and with the substitution of the
timeconstant into (3) yields (4)
T
T
w(t  )  w 
T
J
d
ss

(4)
L
m
The instantaneous torque sensitivity values kti , i = a, b, c are
approximatedby kt which is the peak to peak value of kti . The
current peak values are assumed to be constant since operation
is insteady state
T
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d
 k ta i a  k tb ib  k tc ic  k t I
(5)
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Controller Design(3/6)
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Equation (5) is substituted into (4) and solved for the
averagecurrent. The equation for the current is a function of
the desiredsteady-state rotor speed. It can be used to find the
necessarycurrent to produce ωL and ωH for a given load
I ( wss) 
1
(
k T
t
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J
w T
ss
L
)
(6)
m
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Controller Design(4/6)
Fig. 3 Conduction-angle control state definitions.
I (w  w
ss
H
) IH
I (w  w )  I
ss
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L
L
(7)
(8)
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Controller Design(5/6)
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The average current instate 1 must be equal to the integral
over the partial conductionangle as shown below.
 2 ,min
1


1


d


0
d

I L T   I H


 2 ,min 
 0

IH

I H  2 ,min

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 2 ,min
2 ,min
0

(9)
IL
IH
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Controller Design(6/6)
In summary, to implement the digital controller to any BLDC motor under a
constant load torque, the following procedureshould be followed.
1)Find the following motor parameters from the manufac-turer’s data sheet.
kt
Torque sensitivity constant.
b
Viscous friction constant.
J
Rotor moment of inertia.
τm Mechanical time constant.
2) Determine the desired operating speed and specify the load torque.
3) Choose ωH and ωL to cover the desired speed range.
4) Use (6) to determine the values of I H and I L , ( I H → CBmin and I L →
CBmax ).
5) Use (9) to determine the value of  2 , min (only necessary for conductionangle control).
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Simulations(1/8)
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1)Determine the conduction interval for all three phases.
2) Estimate the conduction interval duration (TC ).
3) Maintain the phase currents within the CB during the
conduction interval for all three phases.
4) Determine when  2, min is reached during a conduction
interval.
5) Choose the appropriate state to apply to the next conduction interval.
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Simulations(2/8)
Fig. 5. Counter stop and start indicators.
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Simulations(3/8)
Fig. 6. Instances of speed comparison for choosing state 1 or state 2.
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Simulations(4/8)
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Fig. 7.
Block diagram of proposed digital control implemented in PSIM.
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Simulations(5/8)
Fig. 8. Simulation results for a 0.3-N · m load (conduction-angle control). (a) Speed and current results for ω ∗ = 900 rpm with a 0.3 N · m
load. (b) Speed andcurrent results for ω ∗ = 1000 rpm with a 0.3 N · m load. (c) Speed and current results for ω ∗ = 1100 rpm with a 0.3
N · m load.
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Simulations(6/8)
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Fig. 9. Simulation results for a 0.3-N · m load (current-mode control). (a) Speed and current results for ω ∗ = 900 rpm with a 0.3 N ·
m load. (b) Speed and current results for ω ∗ = 1000 rpm with a 0.3 N · m load. (c) Speed and current results for ω ∗ = 1100 rpm
with a 0.3 N · m load.
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Simulations(7/8)
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Simulations(8/8)
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Fig. 10. Digital control Simulink model.
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Conclusion(1/5)
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Conclusion(2/5)
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Conclusion(3/5)
TABLE IV
SUMMARY OF EXPERIMENTAL RESULTS FOR 0.3-N · m LOAD
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Conclusion(4/5)
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The conduction angel control simulations and experimental
results were in accordance with one another. Speed
regulationfor all the commanded speeds were well within
acceptable limits.
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It is important tonote that all the measured speed ripples
included the inherent speed ripple associated with trapezoidal
BLDC motors. The inherent speed ripple is largely due to the
nonideal trapezoidal back EMF, which does not have perfectly
flat plateaus asassumed in the PSIM simulations.
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Conclusion(5/5)
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In conclusion, this paper has presented the initial investigation
and proof-of-concept for a new way of lookingat digital
control for BLDC motors.
Further development and modification of the state definitions
will allow for additional speed ripple reduction, making it
suitable for high-performance motor drive applications.
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References
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[1] C. W. Lu, “Torque controller for brushless DC motors,” IEEE Trans. Ind.
Electron., vol. 46, no. 2, pp. 471–473, Apr. 1999.
[2] P. Pillay and R. Krishnan, “Application characteristics of permanent magnet synchronous and brushless DC motors for servo drives,” IEEE Trans. Ind.
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[3] P. Pillay and R. Krishnan, “Modeling of permanent magnet motor drives,”
IEEE Trans. Ind. Electron., vol. 35, no. 4, pp. 537–541, Nov. 1988.
[4] J. U. Lee, J. Y. Yoo, and G. T. Park, “Current control of a PWM inverter
using sliding mode control and adaptive parameter estimation,” in Proc. IECON
20th Int. Conf., Sep. 1994, vol. 1, pp. 372–377.
[5] V. I. Utkin, “Sliding mode control design principles and applications to
electric drives,” IEEE Trans. Ind. Electron., vol. 40, no. 1, pp. 23–36, Feb. 1993.
[6] M. A. El-Sharkawi, Fundamentals of Electric Drives. Pacific Grove, CA:
Brooks/Cole, 2000, pp. 5–10.
[7] J. Chen and P.-C. Tang, “A sliding mode current control scheme for PWM
brushless DC motor drives,” IEEE Trans. Power Electron., vol. 14, no. 3, pp.
541–551, May 1999.
[8] H. C. Chen, M. S. Huang, C. M. Liaw, Y. C. Chang, P. Y. Yu, and J. M. Huang,
“Robust current control for brushless DC motors,” Proc. Inst. Electr. Eng.—
Electric Power Applications, vol. 147, no. 6, pp. 503– 512, Nov. 2000.
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References
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[9] F. Rodriguez and A. Emadi, “A novel digital control technique for brush- less
DC motor drives: Conduction-angle control,” in Proc. IEEE Int. Elect. Mach.
Drives Conf., May 2005, pp. 308–314.
[10] F. Rodriguez, P. Desai, and A. Emadi, “A novel digital control technique for
trapezoidal brush-less DC motor drives,” in Proc. Power Electron. Technol. Conf.,
Chicago, IL, Nov. 2004.
[11] A. A. Aboulnaga, P. C. Desai, F. Rodriguez, T. R. Cooke, and A. Emadi, “A
novel, low-cost, high-performance single-phase adjustable-speed mo- tor drive
using PM brush-less DC machine: IIT’s design for 2003 Future Energy
Challenge,” in Proc. 19th Annu. IEEE Appl. Power Electron. Conf., Anaheim,
CA, Feb. 2004, pp. 1595–1603.
[12] International Rectifier, IR2130/IR2132(J)(S) & (PbF) 3-phase bridge driver.
Data Sheet No. PD60019 Rev.P.
[13] dSPACE, Implementation Guide For Release 4.0: Real-Time Interface (RTI
and RTI-MP). Documentation Guide, Aug. 2003.
[14] dSPACE, Experiment Guide For Release 4.0: Control-Desk. Documentation Guide, Aug. 2003.
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Thank for your listening
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