International Journal of Engineering Trends and Technology (IJETT) – Volume 21 Number 4 – March 2015
Implementation of Sensor less fault diagnosis and
control scheme for BLDC motor drive
S.Dhamodharan1, M.Daniel Pradeep2, L.Sanjay3, M. Senthamil selvan4
Assistant Professor, Dept.of.EEE, INFO Institute of Engineering, Coimbatore, India 1,2
UG Scholar Dept.of.EEE, INFO Institute of Engineering, Coimbatore, India 3,4
Abstract— The project aims to design and develop fault
tolerant control for BLDC motor drive. The fault diagnosis and
control schemes for induction motor drive were discussed by
many authors. But in BLDC motor, it is difficult to control the
drive arrangement. Because it needs the current position of the
rotor, it requires position sensors. Implementation of the
proposed fault tolerant control for BLDC will reduce such
drawbacks in the drive system. One leg and double leg switch
failures are considered in the proposed fault tolerant control
scheme. The proposed fault tolerant control for BLDC motor
drive is modeled and simulated using MATLAB. The
effectiveness of the control approach to the fault diagnosis
scheme is investigated and validated in hardware
implementation.
Index Terms— fault, back emf, zero crossing detection
I. INTRODUCTION
controller is used in the system for obtaining the desired
output. The control action is taken on the input with respect to
the output.
A motor drive system is usually sensitive to different kinds
of faults occurring at the front-end rectifier, or at the power
inverter or at the control subsystem. When one of these faults
occur the drive operation has to be stopped for a nonprogrammed maintenance schedule. The cost of this schedule
can be high and this justifies the development of fault- tolerant
motor drive systems. Fault diagnosis and monitoring are
modern ways to increase reliability, and they are possible
without installing extra hardware. The reliability improvement
of motor drives can be achieved by reliable and highperformance fault diagnosis schemes for these faults.
The proposed fault tolerant topology is shown in the below
figure:
Brushless DC(BLDC) motors are mostly used in many
applications due to its advantages namely high torque, high
efficiency, less control. When the faults of the drive system
occurs in industry it will lead to very high damage, therefore
the reliability of the system gets decreased. The proposed fault
tolerant control scheme will reduce such drawbacks i.e. it
improves reliability and efficiency. The fault control tasks are
1) Fault detection, Identification Drive systems are widely used
in applications such as pumps, fans, paper and textile mills.
Industrial drive applications are generally classified into
constant speed and variable speed drives. AC drives with a
constant frequency sinusoidal power supply have been used in
constant speed applications where as the DC drives are
preferred for variable speed drives. The advantages of AC
drives are reliable, easy to design, fast operation, good power
regulation.
Fig 1.Proposed fault tolerant drive
II.PROPOSED SYSTEM
The proposed method is based on the sensorless fault
tolerant control of bldc motor drive using back-emf sensing.
The two methods for sensing the back emf are comparing the
BEMF Voltage to Half the DC Bus Voltage and comparing the
BEMF voltage to motor neutral point. The selected back-emf
sensing method for the proposed system is comparing the
BEMF voltage to the motor neutral point. The open circuit
fault is only considered in the project. The fault control is
based on the zero crossing detection method. When the fault
occurs in one leg the pulses to the auxiliary leg is the same as
that of the pulses to the faulty leg. The proportional integral
ISSN: 2231-5381
This circuit is used for fault tolerant control of
sensorless control of BLDC motor. When the dc supply is
given to the circuit based on the conduction table the switch
conducts. If the fault occurs in the leg1 the pulses to the
switches Q1 and Q4 is given to the auxiliary switches and the
conduction is based on the table given. below. The triac
switches are used for isolating and bypassing the faulty leg to
the auxillary leg. If there is a fault occurring in one leg say
leg1, the bypass switch B2 is only, which makes the auxiliary
leg Q11 and Q21 are given the same pulse as that given for the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 21 Number 4 – March 2015
fault leg1. If there is fault occurring in two legs then the two
legs are replaced by the two auxiliary switches.
When one leg failure occurs the main circuit becomes as
shown in below figure:
Fig 4.Complete simulation model of proposed fault tolerant
drive
1
<= 0
Back EMF
Fig 2.One leg fault(A-B phase)
The above circuit is used when the fault has occurred in
only one leg the main circuit becomes as stated above. The
auxillary leg along with the bypass switch the circuit operates
as that of the normal motor. The back-emf is sensed using the
method of ZCD i.e. comparing back EMF voltage to the motor
neutral point method.
When the two legs are attaining faults the circuit will be
reduced as shown in below figure:
NOT
1
U
Compare
T o Zero
<= 0
NOT
2
V
Compare
T o Zero1
<= 0
NOT
3
W
Compare
T o Zero2
Fig 5.sub model for zero crossing detection
Fig 6.Sub model for fault tolerant switches or legs
Fig 3.Two leg fault(A-B phase)
The circuit above is used when the fault in the circuit
occurs in any of the two legs. Then those two faulty legs are
replaced by the two auxillary legs through the bypass switches
and their conduction is based on the conduction table. The
pulses to the auxillary switches are same as that of the pulses
given for the faulty legs. When there is a fault occurring in all
the three legs then the system is automatically made shut down
The simulation model given in the models are for the fault
tolerant sensorless control. The fault switches are made based
on the open circuit faults. The control sequences for the
inverter switches are designed and the phases of the rotor are
made 120º apart from each other. The back emf of the rotor are
found using the zero crossing detection methods. The function
is used for ensuring the positions of the rotor. The selector
block is used for the operation of the switches. The switching
table is used for giving the output pulse for the switches and
the speed of the brushless motor is controlled.
III.SIMULATION AND ITS RESULTS
The simulink model for the proposed fault tolerant control
topology is shown in the below figure
ISSN: 2231-5381
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International Journal of Engineering Trends and Technology (IJETT) – Volume 21 Number 4 – March 2015
used for driving the fault switch in the sensorless control. The
figure 10 shows the torque waveform of the proposed fault
tolerant topology.
For variable speed operation of the drive, the set
speed of the drive is varied. Due to changes in the set speed of
the drive the entire simulation results also gets varied. The
stator current and the back emf also vary during the changes in
the set speed. And the output speed of the motor or drive
attains its steady state according to the set speed.
Fig 7.output stator current
IV. CONCLUSION
Thus the proposed system is implemented in the matlab
simulink software package and the various results are obtained
for the BEMF sensing. The mosfet switch is kept open for a
particular period of time and thus the open circuit fault is
analyzed. Using zero crossing detector block in the simulink
the back emf of the motor is sensed. The rotor position signal is
sensed by using the values of the hall sensor method. The
output obtained from the sensorless method is inverted output
of the sensor.
Fig 8. back emf voltage
V. REFERENCES
Fig 9. rotor speed of BLDC drive
Fig 10.output torque of proposed fault tolerant drive
The output waveforms for the stator current, back emf
voltage, output torque of the sensorless fault tolerant control of
brushless motor is obtained. Due to the ripples there is some
deviations in the motor torque.
Figure 7 shows the output stator current of phase A voltage.
It shows the phase to phase stator currents of sensorless BLDC
motor drive. In the figure 8 shows the output back emf voltage.
It is the voltage from which the fault tolerant switch is
controlled. The figure 9 shows the output rotor speed of the
sensorless BLDC motor drive. The set speed to the speed
comparator and is compared with the output rotor speed and is
ISSN: 2231-5381
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