Assignment for Advanced Energy Conversion Systems (42091)

Advanced Energy Conversion Systems (42091)
Assignment: 1 (part 1)
Submitted to
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Contents
1. Introduction:..................................................................................................................................3
2. Construction..................................................................................................................................3
3. Basic driving principle of BLDC...................................................................................................4
4. Basic analytical formulas for motor performance analysis............................................................8
5. Calculations of some steady-state performance...............................................................................10
6. A Simulink model of BLDC....................................................................................................12
7. Dynamic and steady-state performance...........................................................................................14
Summery.............................................................................................................................................15
References...........................................................................................................................................15
List of figures
Figure 1 Classification of BLDC motors based on direction of magnetic flux. (A) Radial-flux (inner
rotor), (B) radial-flux (outer rotor)........................................................................................................3
Figure 2 BLDC drive system.................................................................................................................4
Figure 3 sequence of triggering.............................................................................................................5
Figure 4 Waveforms..............................................................................................................................6
Figure 5 FOC control..............................................................................................................................7
Figure 6 Dynamic per phase equivalent circuit......................................................................................7
Figure 7 Steady state equivalent circuit.................................................................................................8
Figure 8 Simulation..............................................................................................................................11
Figure 9 speed and torque...................................................................................................................11
Figure 10 Machine and Control Parameters........................................................................................12
Figure 11(A) Speed curve.....................................................................................................................13
Figure 11(B) Phase Current…………………………………………………………………………………………………………… 13
Figure 11(C) Torque……………………………………………………………………………………………………………………… 13
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BASIC OF BLDC
(BRUSHLESS D.C MOTOR)
1. Introduction:
BLDC motor industry is world larges growing motor industry because it’s use and advantages
over other motors for industrial, automation, aerospace, consumer, medical and instrumental
small devices.
As name implies, BLDC motor is brushless motor and it have more upper hand than DC
motors few are discussed below:
1. Less maintenance requirement.
2. High efficiency.
3. Higher speed variation.
4. Long operation life.
5. Less noise.
In addition, the motor supply high torque in small size effectively, and this think justify in
operation in construction.
2. Construction
BLDC motor classified according to stator windings and motor design.
According to the stator winding:
Single-phase, two phase, three phase and multi-phase. The single-phase BLDC motor generally
used in low power applications, up to 10 W, such as small fans. This motor has simple driving
circuit, simple structure and low cost as well as low maintenance. However, the drawback of this
type of motor is that motors are unidirectional and there is no starting torque hence secondary
part, which is produce reluctance torque is necessary for start the motor.
Multi-phase BLDC motor has four phase or above four-phase. These types of motors are highly
reliable so majorly used in military and aerospace applications. The reliability is high compared to
low phase winding motors.
According to the motor design
Based on motor design, further classified in terms of direction of magnetic flux: radial flux type
and axial flux type.
In radial flux type of motor construction, the rotor magnetic flux crosses the air gap in a radial
direction. This type of motor can be either an outer rotor type or an inner rotor type as shown in
Figure 1 (A and B).
Inner rotor design has a lot of advantages than outer rotor design. Such as, higher heat dissipating
capacity, high torque to inertia ratio and low rotor inertia. However, motor produce high vibration
and noise.
Outer rotor design means the rotor is in cylindrical shape with a shaft where the bearings are
mounted. The rotor magnets rotate around the stator windings which located in the iron core of
the motor. It has high rotor inertia. Also, motor rotate at constant speed. These types of motor
used in cooling fans, washing machines and disk drives. The advantages over inner rotor design
that it produces less vibration and noise compared to inner rotor.
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Figure 1 Classification of BLDC motors based on direction of magnetic flux. (A) Radial-flux (inner rotor), (B)
radial-flux (outer rotor)
Same as in axial flux type, the rotor magnetic flux crosses the air gap in an axial
direction. In this design, a disc rotor with magnets whose flux is in an axial direction
rotates facing the stator. The major advantage of this type of motor is that it produces
constant speed with high rotor inertia.
3. Basic driving principle of BLDC
Using Hall effect sensor
BLDC motor works on the same principle as that brushed DC motor, i.e., the Lorentz law
of force which state that whenever a current carrying conductor placed in a magnetic field
it experiences a force and magnet will experience an equal and opposite force. BLDC
motor is to changes the phase windings according to the position of permanent magnet on
the rotor using sensors such as, hall effect sensors.
A two pole three phase star connected BLDC motor drive and three Hall effect sensors
are paced from each other by 120 electrical degrees as shown figure 2. The use of Hall
sensors are that it detects the magnetic field flux from the rotor magnets and provides the
rotor position in six sections. According to positions of rotor, a semiconductor bridge
provide input to winding accordingly sequence.
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Figure 2 BLDC drive system
The switching sequences of driving circuit for the six-step drive is shown in below
figures. Which is generally a three-phase inverter, used to pass current. As characteristic
of BLDC, it requires two windings are excited at same time while other left unexcited.
The Hall sensors feedback can be used to deciding which two windings should be
energized. These two energized windings produce the constant torque at each cycle.
The six-step drive's back-EMFs of the stator windings are illustrated in Figure 2 along
with the connection between the phase currents and the sensor signals. For this given
scenario, the active winding, i.e., an exited winding, is triggered in every 60 electrical
degrees of rotation of rotor. The exiting winding is also called as commutation winding.
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At the instant shown in the figure 3, When T1, T3 and T5 are in ON condition then a,
b and c windings are got positive voltage. While T2, T4 and T6 provides negative
voltage to the windings. Current directions and rotor movements direction shown in
figure 3.
Figure 4 illustrates the Different waveforms at different positions of Triggering
semiconductor devices.
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Figure 4 Waveforms
Using Sine wave control
The three-phase sine-wave voltage produced by sine wave control, such as SVPWM, PWM wave
techniques. Sine wave control is more "exquisite" because it has less torque ripple and current
harmonics than square wave control. However, compared to square-wave control, it has higher
performance requirements for the controller, meaning that motor efficiency cannot be increased.
FOC control
FOC control, which is comparable to an improved sine wave control, obtains vector control of the
magnetic field of the motor's stator by controlling the current vector. Because the FOC controller
controls the direction of the motor stator magnetic field, it can keep the motor stator magnetic field
and the rotor magnetic field at 90° all the time as shown in figure 5, achieving maximum torque
output at a certain current.
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Small torque ripple, high efficiency, low noise, and fast dynamic response are all benefits of FOC
control. There are some drawbacks of this control such as higher controlling performance required,
high cost.
4. Basic analytical formulas for motor performance analysis
The per phase equivalent circuit is shown in figure 6. Where λm is the flux linkage of stator winding
per phase due to the permanent magnet.
Figure 6 Dynamic per phase equivalent circuit
For steady state conditions, v and e are sinusoidal at frequency, the equivalent circuit becomes the one
shown in Figure 7.
Where X=ωL and V, I, E and λm are phasor with rms amplitude. The steady state equation is given as
below:
V = E + ( R + jωL ) I
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Figure 5 FOC control
Figure 7 Steady state equivalent circuit

Whenever Current I and Emf E are in phase then motor produces maximum mechanical power as well
as maximum torque to ampere ratio. Considering ideal situation, the electromagnetic output power is
determined by:
Pem = m |E| |I| = mω| λm | |I|
Where m is the number of phases.
The electromagnetic torque is:
where ωr = 2ω/p is the speed of rotor in Rad/s, and p is the number of
poles.
Hence, the practical shaft output torque is
Tload = Tem-Tlosses
If we remove the amplitude signs, then:
And rotor speed is:
Speed-Torque curve:
If assume ωL<<R and E and I in phase, then:
V=E+IR
Substituting E~ ωr and T~I,
And
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Efficiency:
The definition of efficiency is the ratio of output power and input power,
Where Pin =mVI, And Pout=Tload ωr.
5. Calculations of some steady-state performance
The given parameters of motor as given as below:
Number of pole pairs p=3
PM flux linkage ψf=0.1057 Wb
Stator resistance Rs=1.8 ohm
Stator phase self-inductance Ls =10 mH
Rated torque TN=4.5 Nm
Inertia: J=0.002 kg*m^2
DC bus voltage Udc=200 V
𝜽f=45° and 𝞱⍵=90°
(1) Motor in steady state condition:
h=2*𝛟max/(𝜽f+𝞱⍵)
h=2*0.1057/ (45°+90°)
after calculating above terms, we can get
h=0.089
(2) EMF
Emf = h*⍵
= h*(2𝝅f) where f= speed*poles/60
= 0.089(2*3.14*50)
Emf = 28.20
(3) Steady state torque
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If we consider ideal condition, then:
Ld≈Lq ; Id=0
Hence, Te≈ 3/2*p(𝛙pm*Isq)
After putting all values in above equation then we got,
Isq = 9.5
(4) In ideal condition, Ld≈Lq, La=0
Hence,
Ld=La+1.5(Laa0+Lg2)
Considering ideal condition,
Ld = 1.5*motor self inductance
=1.5*001
=15mH
(5) Full load Tmech =4.5Nm
Is= Tmech*⍵r/2*Emax ( Emax=h*p*⍵r )
Is= Tmech/2*h*p
=4.5/0.089*2*3 (for two phase)
= 8.36 A
For single phase, Is=2*8.36 = 16.70 A
(6) Half load Tmech=2.5Nm
Is= Tmech/2*h*p
Putting all data,
Is=4.65 A
For single phase, Is= 2*4.65 = 9.3 A
6. A Simulink model of BLDC
The simulation for BLDC control as shown as figure 8.
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Figure 8 Simulation
Speed and torque waveform shown as figure 9.
Figure 9 speed and torque
Machine and control parameter shown as figure 10.
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Figure 10 Machine and Control Parameters
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7. Dynamic and steady-state performance
The speed curve, torque, phase current waveform shown as below figures 11.
Figure 11(A) Speed curve
Figure 11(B) Phase current
Figure 11(C) Torque
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Summery
In conclusion we can observe that principle of BLDC motor is nearly similar of PMSM. However BLDC
required controller and sensor for sensing rotor positions. A calculations and result of simulations
proves that in ideal conditions, simulation results and calculated results are nearly equal.
References
[1] https://www.ato.com/control-methods-of-bldc-motor
[2] kim, S. (2017). Electric motor control : Dc, ac, and bldc motors. Elsevier Science &
Technology. Chapter 10.
[3] 48531 EMS – Chapter 12. Brushless DC Motors
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