Transactions on Engineering and Sciences
Vol. 2, Issue 7, July 2014
ISSN: 2347-1964 Online 2347-1875 Print
Implementation of Different Speed Control
Strategies of BLDC Motor
Vivek Kota1
1, 2&3
Vishnuvardhan Pasumarthi2
Yadithya Tangirala3
Dept. of EEE, Andhra Loyola Institute of Engineering & Technology, VJA, A.P.
Abstract: Brushless DC (BLDC) motors are one of the electrical drives that are rapidly gaining popularity,
due to their high efficiency, good dynamic response and low maintenance. In this paper a speed
controller has been designed by using two types of control strategies. First one addresses the PID
(Proportional Integral Derivative) controller and the second one addresses about the PI (Proportional
Integral) controller .The simulation results are carried out by using MATLAB/SIMULINK successfully
for closed loop operation of the three phase BLDC motor so that the motor runs very closed to the
reference speed. The performance parameters are compared for both control strategies for speed control
of BLDC motor drive. The results presented validate control strategies in improving the motor
performance.
I. INTRODUCTION
Conventional dc motors have many attractive properties such as high efficiency and linear torque speed
characteristics. The control of dc motors is also simple and does not require complex hardware. However,
the main drawback of the motor is the need of periodic maintenance. The brushes of the mechanical
commutators have other undesirable effects such as sparks, acoustic noise and carbon particles coming from
the brushes. Brushless dc motors can in many cases replace conventional dc motors. Brushed DC motors
develop a maximum torque when stationary, linearly decreasing as velocity increases. Some limitations of
brushed motors can be overcome by brushless motors; they include higher efficiency and a lower
susceptibility to mechanical wear.
A typical brushless motor has permanent magnets which rotate and a fixed armature, eliminating
problems associated with connecting current to the moving armature. An electronic controller replaces the
brush/commutators assembly of the brushed DC motor, which continually switches the phase to the
windings to keep the motor turning. The controller performs similar timed power distribution by using a
solid-state circuit rather than the brush/commutators system. The enhanced efficiency is greatest in the noload and low-load region of the motor's performance curve .Under high mechanical loads, brushless motors
and high-quality brushed motors are comparable in efficiency, environments and requirements in which
manufacturers use brushless-type DC motors include maintenance-free operation, high speeds, and
operation where sparking is hazardous (i.e. explosive environments) or could affect electronically sensitive
equipment.
II. PERMANENT MAGNET BRUSH-LESS DC MOTOR MODEL
BLDC motors are a kind of synchronous motor. This indicates the magnetic field produced by the stator
and the magnetic field produced by the rotor twirls at the same frequency. BLDC motors do not experience
the “slip” that is normally observed in induction motors. BLDC motor is built with a permanent magnet
rotor and wire wound stator poles. From the Fig 1, the Permanent magnet DC motors use mechanical
commutators and brushes to achieve the commutation. However, BLDC motors adopt Hall Effect sensors in
place of mechanical commutators and brushes. The stators of BLDC motors are the coils, and the rotors are
the permanent magnets. The stators develop the magnetic fields to make the rotor rotating. Hall Effect
sensors detect the rotor position as the commutating signals.
Figure 1: Bldc motor and controller diagram
A. Hall Effect sensor
Hall Effect Sensors are devices which are activated by an external magnetic field. We know that a
magnetic field has two important characteristics flux density, (B) and polarity (North and South Poles). The
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Techscripts
Transactions on Engineering and Sciences
Vol. 2, Issue 7, July 2014
ISSN: 2347-1964 Online 2347-1875 Print
output signal from a Hall Effect sensor is the function of magnetic field density around the device. When the
magnetic flux density around the sensor exceeds a certain pre-set threshold, the sensor detects it and
generates an output voltage called the Hall Voltage, VH.
Figure 2: Hall Effect Sensor
Hall Effect Sensors consist basically of a thin piece of rectangular p-type semiconductor material such as
gallium arsenide (GaAs), indium antimonide (InSb) or indium arsenide (InAs) passing a continuous current
through itself. When the device is placed within a magnetic field, the magnetic flux lines exert a force on the
semiconductor material which deflects the charge carriers, electrons and holes, to either side of the
semiconductor slab. This movement of charge carriers is a result of the magnetic force they experience
passing through the semiconductor material.
B. Speed torque characteristics
Figure 3: Speed- torque characteristics of bldc motor
This Figure shows an example of torque/speed characteristics. There are two torque parameters used to
define a BLDC motor, peak torque (TP) and rated torque (TR). During continuous operations, the motor can
be loaded up to the rated torque. As discussed earlier, in a BLDC motor, the torque remains constant for a
speed range up to the rated speed. The motor can be run up to the maximum speed, which can be up to
150% of the rated speed, but the torque starts dropping.
III. BLDC CONTROLLER
A. PI-Controller
PI controller will eliminate forced oscillations and steady state error resulting in operation of on-off
controller and P controller respectively. However, introducing integral mode has a negative effect on speed
of the response and overall stability of the system.
Thus, PI controller will not increase the speed of response. PI controllers are very often used in industry,
especially when speed of the response is not an issue. A controller is used when:
a) Fast response of the system is not required.
b) Large disturbances and noise are present during operation of the process
c) There is only one energy storage in process (capacitive or inductive)
B. PID – Controller
Figure 4: Controller model diagram of BLDC
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Techscripts
Transactions on Engineering and Sciences
Vol. 2, Issue 7, July 2014
ISSN: 2347-1964 Online 2347-1875 Print
The PID controller calculation algorithm involves three separate constant parameters, and is accordingly
sometimes called three-term control, the proportional, he integral and derivative values, denoted P, I, and D
respectively. These values can be interpreted in terms of time: P depends on the present error, I on the
accumulation of past errors, and D is a prediction of future errors, based on current rate of change. The
weighted sum of these three actions is used to adjust the process via a control element such as the position
of a control valve, a damper, or the power supplied to a heating element.
IV. SIMULINK ENVIRONMENT
The simulation for the BLDC motor is done by using different conventional controllers for controlling
Speed.
A. Case 1: BLDC motor with PI controller
Figure 5: Speed control of Bldc motor by PI controller
Figure 6: Rotor speed at Ki = 25 & Kp=0.015
Figure 7: stator emf’s at Ki=55 & Kp=0.015
Figure 8: stator current at Ki = 55 & Kp=0.015
B. Case 2: BLDC motor with PID controller
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Transactions on Engineering and Sciences
Vol. 2, Issue 7, July 2014
ISSN: 2347-1964 Online 2347-1875 Print
Figure 9: rotor speed at Ki = 25 , Kp=0.01 & Kd=0.25
Figure 10: stator emf’s at Ki = 25 , Kp=0.01 & Kd=0.25
Figure 11: stator current at Ki = 25, Kp=0.01 & Kd=0.25
V. CONCLUSION
The paper presents the closed loop speed controller for the BLDC motor drive. Two control strategies
namely PID control and PI control are presented for the drive. PI parameters are obtained as Kp =0.015,
Ki=55 .With PI controller, the peak overshoot of the speed response of the BLDC motor is reduced, rise time
tr=0.015sec, settling time ts= 0.045sec, peak time tp=0.02sec, Mp=5%. PID parameters are obtained as Kp
=0.01, Ki=25, Kd=0.25 .With PID controller, the peak overshoot of the speed response of the BLDC motor
Mp=6.25%, rise time tr=0.013sec, settling time ts=0.05sec, peak time tp=0.02sec. From the transients
parameters it is observed that PI controller gives fast response compared to PID controller. The PI controller
is better compared to PID controller as it possesses the disturbance rejection capability and can withstand to
load fluctuations.
REFERENCES
[1] V.Tipsuwanporn, W.Piyarat and C.Tarasantisuk, “Identification and control of brushless DC motors
using on-line trained artificial neural networks,” in Proc. Power Conversion Conf., pp. 1290-1294,
Apr.2002.
[2] Atef Saleh Othman Al-Mashak- beh“Proportional Integral and Derivative Control of Brushless DC
Motor” European Journal of Scientific esearchVol.35 No.2 (2009), pp.198- 203
[3] Microchip Technology, “Brushless DC (BLDC) motor fundamentals”, application Note, AN885, 2003.
[4] Gwo-Rueyyu and Rey-Chue Hwang “Optimal PID Speed Control of Brushless DC Motors Using LQR
approach” IEEE International Conference on systems
[5] C.Gencer and M.Gedikpinar “Modelling and Simulation of BLDCM using Matlab/Simulink” Journal of
Applied Sciences 6(3):688-691, 2006.
[6] Allan R. Hambley, “Electrical Engineering Principles and Application”, Prentice Hall,
New Jersey
1997.
[7] Rivera, D.E.skogestad, S.Morari M.IMC 4:PID controller design. Ind.Engchem.Processdes.Dev 1986,
25,252.
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