Sensorless Speed Control of Brushless DC Motor by MATLAB

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 09 Issue: 06 | Jun 2022 www.irjet.net p-ISSN: 2395-0072
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Sensorless Speed Control of Brushless DC Motor by MATLAB
Vinithaasri. S1, D. Sri Vidhya2
1M. E. Power Systems Engineering, K. S. Rangasamy College of Technology, Tiruchengode, Tamil Nadu - 637 215,
India.
2Associate Professor /EEE, K. S. Rangasamy College of Technology,Tiruchengode, Tamil Nadu - 637 215, India.
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Abstract - Sensorless BLDC motors are widely used in
household appliances, vehicles, aircraft, consumerelectronics,
medical devices, automated industrial equipment, and
instrumentation. Because of their design, these motors are
employed in a variety of industrial areas. Sensorless BLDC
motors are popular due to their increased efficiency,
reliability, power, acoustic noise, smaller size, lighter weight,
greater dynamic response, enhanced speed vs load torque,
wider speed range, and extended life. It offers a number of
advantages, including the elimination of the motor's neutral
voltage, a predetermined phase shift network, a low starting
speed, and a low cost. This study use MATLAB SIMULINK to
give a straightforward and dependable method for detecting
reverse emf zero-crossings for sensorless operation. An
abstract summarizes, in one paragraph (usually), the major
aspects of the entire paper in the following prescribed
sequence. The zero crossings of the reverse emf are projected
obliquely from the terminal voltages that are monitored in
relation to the dc negative pole, and thus approach never
involves any integration. Furthermore, when using line
voltages, neutral potential and common mode noise are no
longer needed. Through simulation, the efficiency of the
control strategy based on zero-crossing detection from
terminal voltage differences was studied.
Key Words: Sensorless operation, Zero Crossing
Detector, Reverse EMF,Speed control method,Brushless
DC Motor
1. INTRODUCTION
It has several advantages, including the eliminationofmotor
neutral voltage, a set phase shift circuit, a low beginning
speed, and inexpensive cost. Instead of brushes, this BLDC
motor is commutated electronically using power switches.
The voltage surges are caused by the remaining currentthat
is restricted when power switches produce armature
current. In the condition of sensorless BLDC motor driving,
commutation torque ripple has already been reduced.
Analysis, design, and implementation of a high-performance
sensorless method for BLDC motors are completed. BLDC
motors also referred to as PermanentMagnetDirectCurrent
Synchronous motors are still one of the motor types that
have grown in popularity in recent years, owing to their
superior features and performance. The BLDC motor, which
lacks position and speed sensors, has received a lot of
interest. Square wave control and sinusoidal currentcontrol
are the two most common BLDC motor control techniques.
To calculate the zero-crossing time of the reverse emf,
multiply the terminal voltage of the floating winding by the
motor's neutral point. Integration begins when the reverse
emf crosses zero and ends when the given threshold valueis
reached, resulting in immediate commutation. Frequency-
independent phase shifter for sensorless BLDC motor
control, capable of shifting the zero-crossing point of the
input signal with a defined phase delay. Jung and Ha have
developed an extended Kalman filter estimator for a
brushless dc motor to estimatespeedandrotorposition. The
rotor position is obtained indirectly by sensing the reverse
emf from one among the three motor terminal voltages of a
three-phase motor. The necessity to establish the right
values for the covariance matrix parameters, which
represent the errors in modeling and measurements, is a
barrier to using the extended Kalman filter technique for
rotor position estimation. Sensorless control techniques
based on the reverse emf's Zero Cross Point(ZCP)havebeen
widely employed in low-cost applications.Thezero-crossing
detector (ZCD) detects the ZCP of the reverse emf, and the
pulse is created by moving 30° fromtheZCP.WhentheBLDC
motor is at rest or at zero speed, the reverse emf cannot be
calculated using the ZCP technique.
As a result, a unique control is required for the smooth and
dependable sensorless control operation of BLDC motors.
Furthermore, the intricacies of sensorless motor starting
were not discussed. However, the direct commutation
instant detection approach suggested lacks the flexibility to
advance the commutation instant, which may be
implemented utilizing reverse emf zero-crossing detection
techniques. By measuring the motor terminal voltages, we
devised and constructed an integrated circuit enabling the
sensorless operation of a BLDC motor. Frequency
independent phase shifter for sensorless BLDC motor
control, capable of shifting the zero-crossing point of the
input signal with a defined phase delay. For speed and rotor
position estimation, an extended Kalman filter estimatorfor
a brushless dc motor has been created. commutationinstant
boosts torque generation, especially in high-speed BLDC
motor operating. The technique of zero-crossing detection
was utilized to start the BLDC machine successfully in
sensorless mode. The concept is developed in this paper to
present a simple running mode algorithm. In this paper, we
present a simple and reliable approach for detecting reverse
emf zero-crossings in sensorless operation using
MATLAB/SIMULINK, as well as hardware implementation
using DSP. DSP is required in hardware circuits to generate

the right moment for pulse production.Thezerocrossingsof
the reverse emf are approximated indirectly from the
terminal voltages measured concerning the dc negative
terminal, and no integration is required. Moreover, when
line voltages are employed, neutral potential and common
mode noise are no longer required. Along with this BLDC
motor model, the dynamic behavior of the motor, including
no-load, load, and load transients,hasbeeninvestigated.The
efficiency of the sensorlesscontrol detectionandlocalization
of zero-crossing via terminal voltage differences has been
studied using simulation.
1.1 Period of Normal Conduction
The terminal voltage waveform is substantially identical to
the reverse-EMF waveform. The terminal voltages, rather
than the reverse-EMFs, can be employed to detect the
commutation points of the BLDC motor in the proposed
sensorless control. As the rotor speed increases, so does the
phase lag's percentage contribution to the entire period. The
latency will disrupt the current alignment with the reverse-
EMF, causing major issues with high-speedcomputation.The
phase lag in commutation can induce substantial pulsing
torques in such drives, which can cause rotor speed
oscillations and excessive copper losses. The cut-off
frequency of the LPF is establishedat 2.5 kHz in thisresearch
by taking into account both the phase lag and the harmonic
dispersion of the reverse-EMF. The hysteresis comparator is
used to correct for the phase lag of the reverse-EMFs caused
by the LPF to establish the optimal inverter commutation
sequence based on rotor position. Furthermore, high-
frequency ripples in the terminal voltages can avoid
numerous output transitions.
1.2 Period of commutation
The traditional start-upprocedureshowscertainunforeseen
limitations that may affect the BLDC motor's performance.
To circumvent these constraints, a simple start-upapproach
is given that not only achieves the highest starting motor
torque but also controls the stator current. Unlike the usual
technique, which only excites two stator windings, the
suggested start-up scheme excites all triostatorwindings by
employing a specified starting voltage vector. The voltage
vector V3 is orthogonal to Vi and is positioned between
voltage vectors V1 and V2. It is selected as the next applied
voltage vector to maximize starting motor torque during
startup. It should be noticed that by varying the pulse width
of the switching devices, the amplitude of the stator current
for alignment of the rotor position may be simply modified.
Shows the three-phase current responsesoftheBLDCmotor
when the switch is turned on and the pulse widthsofthetwo
switches B- and C- are modulated at the same time. PWM
signal duty cycles when the switching period Ts is 100 μ
seconds. The size of the stator current can be readily
controlled by modifying the duty cycle, which can be
determined by taking the initial torque required at
alignment into account. According to the rotor position
before alignment, the motor may revolve in reverse during
alignment. However, because themaximumreverserotation
angle is just 90 mechanical degrees, it does not affect fuel
pump operation. After the rotor position has been aligned,
the start-up method is considered for accelerating the BLDC
motor from a standstill to a certainspeed,3000rpm,whichis
a minimum speed for the automobile fuel pump application.
Because the sensorless scheme does not start on itsown, the
motor must be started and brought to a particular speed
where the zero-crossing position of the reverse-EMFmaybe
detected.
2. Objective
The paper is to develop a sensorless brushless DC (BLDC)
motor control system. Sensorless techniques based on a
hysteresis comparison and apossible start-upmethodwitha
high beginning torque are proposed. The hysteresis
comparator compensates for the phase delay of the reverse
EMFs caused by alow-pass filter (LPF) while also preventing
numerousoutputtransitionscausedbynoiseorfluctuationin
the terminal voltages. The rotorpositionismaintainedatrest
for the greatest starting torque without the need for an extra
sensor or any motor parameter information.
3. Proposed System
The proposed system consists of the voltagesourceinverter
receiving the direct current voltage. The voltage source
inverter is a three-phase voltage source inverter with a 120
degree mode of operation. It comprises three legs, each of
which contains two MOSFETs. In all, six MOSFETs are
employed in the voltage source inverter.MOSFETsareMetal
Oxide Semiconductor Field Effect Transistors. It is the
voltage control device's switching device. If we adjust the
Vgs (Gate Source Voltage), we get a sinusoidal pulse with
modulation signals. We can regulate the Vds (Drain Source
Voltage), which is the output voltage. Induced via changing
modulation. It is defined as the ratio of the reference signal
voltage to the carried signal voltage. In my application, the
reference signal is a three-phase sinusoidal signal with a
displacement of 120 degree and the carrier signal is a
triangular signal. The inverterwill supplypowertotheBLDC
motor by adjusting the modulation.

Fig -1: Block diagram of the sensorless brushless
dc motor
As a result of Faraday's law, reverse emf will be induced in
the stator winding. As a result, this return emf will be in the
opposite direction as the source voltage. So, if we can detect
this reverse emf, we can feed it into the hysteresis
comparator. However, the reverse emf form is trapezoidal
because of the motor's salient pole rotor. We can't readily
distinguish "0" and "1" in this trapezoidal reverse emf. As a
result, the reverse emf provided to the LPF will beconverted
from trapezoidal to sinusoidal. This is passed on to the
hysteresis comparator. The hysteresis comparator is the
difference between the upper and lower values. It is an
alternating current motor with a stator similar to a three-
phase induction motor. The rotor is comprised of a
permanent magnet with four poles (projected Pole) It lacks
rotor winding, mechanical commutator, and brushes, yet its
speed-torque constant is similar to that of a DC shunt motor.
This is referred to as a BLDC motor. To provide power to the
motor stator winding, an electronic commutator (voltage
source) inverter is employed.
4. SENSORLESS BLDC MOTOR SIMULATION
The voltage source inverter receives the input DC voltage
and converts it to AC voltage. To generate the reverse emf, a
sinusoidal V/F control PWM approachisappliedtotheBLDC
motor, causing the motor to start asaninductionmotor.This
emf is detected using a voltage sensor, and the voltage is
passed to the hysteresis comparator. The hysteresis
comparator determines which winding should be energized
first; this comparator compares the EMFs of two phases and
generates PWM pulses; these pulses are fed to the inverter,
and the inverter supplies voltage to the motor; however, the
voltage sensor produces trapezoidal reverse emf, and when
this trapezoidal reverse emf is fed to the low pass filter, it
produces sinusoidal reverse emf. The hysteresis current
controller compares the actual motorcurrentandreferences
current waveforms; the difference is output as PWM pulses
by the current controller. The voltage source inverter
receives this pulse.
Fig -2: Simulation of Sensorless BLDC Motor
Table -1: Sample Table format
Parameters
Motor rating 1.5Hp
Rated torque 2.5N-m
Type of motor BLDC Motor
Supply voltage 420V
Rated speed 4630rpm
Rated current 5A
The inverter will supply voltage to the motor, reducing
stator current. Sensorless control is achieved by the use of a
hysteresis comparator approach, which includes LPFs for
suppressing high switching frequency ripples, hysteresis
comparators for creating three-phase commutation signals,
and a gating signals generator for generating six Pulses.
When detecting the three-phase terminal voltages, each one
is fed into an LPF to reduce the high switching frequency
fluctuation or noise. Because the BLDC motor only has two
phases activated at any given moment,theback-EMFmaybe
determined from its terminal voltage in the duration of an
open phase (60°). The only variation between the reverse-
EMF and its terminal voltage throughout the two-phase
conduction period (120°) is a statorimpedancevoltagedrop,
which may be negligible when compared to the DC voltage
source. The sensorless method inverter will supply voltage
to the motor, reducing stator current. Sensorless control is
achieved by the use of a hysteresis comparator approach,
which includes LPFs for suppressing high switching
frequency ripples,hysteresiscomparatorsforcreatingthree-
phase commutation signals, and a gating signals generator
for generating six Pulses. When detecting the three-phase
terminal voltages, each one is fed into an LPF to reduce the
high switching frequency fluctuation or noise. Because the
BLDC motor only has two phases activated at any given
moment, the back-EMF may be determinedfromitsterminal

voltage in the duration of an open phase (60°). The only
variation between the reverse-EMF and its terminal voltage
throughout the two-phase conduction period (120°) is a
stator impedance voltage drop, which may be negligible
when compared to the DC voltage source. The sensorless
method is simulated in MATLAB/SIMULINK in fig. 2.
5. Results and Discussion
In the proposed system, the simulated
graph of BLDC current and Back Emf shows that initially
the motor start from negative value of -2A and after
steadily attains its peak current of 2.5A for the time of
0.005s. The total amplitude of the current is 5A and its
time period for 1 cycle is 0.02 seconds. In the BLDC Back
EMF, amplitude of the Back EMF is 100v for the time
period of 0.005s and 0.02s for full cycle has shown in the
fig.3.
Fig -3: BLDC Current and reverse EMF
In the motor speed waveform, the initial speed of BLDC
motor is 500 rpm at time t = 0 and the final speed is rated
to 2000 rpm at time t=4.25s has shown in fig.4.
Fig -4: Motor Speed
In the torque waveform, the initial minimum value is -
38.7205 N-m and the maximum value is 40.27 N-m. The
constant peak value of torque is 2.5 N-m and minimum
constant value is 1.32 N-m has shown in fig. 5.
Fig -2 Torque Waveform
From the rotor angle waveform, the rotor angle starts rising
from the time of 3s and it gets reached upto 1777.75 at the
time of 10s has shown in fig.8.
Fig -5: Rotor Angle Waveform
From the PWM pulse generator, the gate pulse if value 1
starts generated after the time period of 3s in fig.6.
Fig -6: Gate Pulse Waveform
The dc voltage is 283.329v at initially and it gets peak value
of 500v. A constant voltage is 214.5 after the time period of
4..3s has shown in fig.7.

Fig -7: DC Link Voltage
The voltage is compared by hysteresis comparator block
and their waveforms are shown in fig. 8 and 9.
Fig -8: Hysteresis Comparator 1
Fig -9: Hysteresis Comparator 2
5. Conclusion
This paper proposes a sensorlesscontrol basedona terminal
voltage hysteresis comparator and a potential start-up
approach with a high starting torque. By changing both the
resistance ratio and the output voltagelevel ofthehysteresis
comparator, the maximum commutation phase lag is
lowered from -13° to 3°. The commutation signal is almost
parallel to the back-EMF. High-frequency fluctuations in the
terminal voltage can prevent numerousoutputtransitionsat
a hysteresis comparator. The stator current ripples were
decreased by using the hysteresis current controller. The PI
controller is used to accomplish closed-loop speed control.
REFERENCES
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Sensorless Speed Control of Brushless DC Motor by MATLAB

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Sensorless Speed Control of Brushless DC Motor by MATLAB