Active Power Factor Correction Project - Mustafa`s E

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Assessment Cover Sheet
Complete and attach this cover sheet to your assessment before submitting
Assessment Title:
Active Power Factor Correction Project
Programme Title:
Bachelor of Engineering and Technology
Course No:
ENB6008
Course Title:
Power Electronics
Student Name:
Mustafa Isa Al-Ansari
Student ID:
201000754
Tutor:
John leek
Due Date: 10/1/2015
Supervisor: John leek
By submitting this assessment for marking, either electronically or as hard copy, I confirm the
following:




This assignment is my own work
Any information used has been properly referenced.
I understand that a copy of my work may be used for moderation.
I have kept a copy of this assignment
Do not write below this line. For Polytechnic use only.
Assessor:
Grade/Mark:
Comments:
Date of Marking:
Abstract
This document aims to identify a problem in AC to DC converter using bridge rectifier with smoothing
capacitor which gives bad power factor. Then come up with circuitry that solve/correct the power
factor, known as active power factor correction. firs off all, results will be obtained from AC to DC
converter using smoothing capacitor to confirm this method gives poor power factor. This is followed
by, identify, build and test new solution to this problem which is active power factor correction that is
used to modify the power factor, and make it unity or 0.99, also a brief discussion will be provided on
the operation of the circuit. Finally a comparison between the smoothing capacitor result, and active
power factor correction results will be made to confirm importance of having unity/ .99 power factor
Objectives










identify common method that is used to convert AC to DC that gives bad power factor
taking experimental results to confirm that power factor is poor
Taking simulation results to see whether the theory matches the simulation or not
indentifying the problems of having poor power factor
providing a solution/circuit to that problem, and decribe the concept of active power factor
correction
discussing the operation of the circuit, and how it will correct the power factor
identifying the components that will be used based on the calculations
taking results to confirm that the circuit is having unity power factor, plot some graph such as
efficiency , and voltage regulation
providing a brief discussion on the results obtained
compare the results before , and after correcting the power factor
Contents
Abstract ......................................................................................................................................................... 2
Objectives ..................................................................................................................................................... 2
Part A............................................................................................................................................................. 4
Introduction .............................................................................................................................................. 4
Results and experimental methodology ................................................................................................... 5
Simulation section ( Part A) ........................................................................................................................ 13
Conclusion ................................................................................................................................................... 14
Part B........................................................................................................................................................... 15
Introduction: ............................................................................................................................................... 15
Calculation of components ......................................................................................................................... 16
Calculate the limiting resistor for pin 8................................................................................................... 17
Inductors calculation............................................................................................................................... 17
The operation of the circuit .................................................................................................................... 17
Results ......................................................................................................................................................... 18
Input parameters .................................................................................................................................... 18
Output parameters. ................................................................................................................................ 19
Conclusion ................................................................................................................................................... 23
References .................................................................................................................................................. 25
Table of figures
Figure 1 Input Voltage and Current vs. Time for Bridge Rectifier Circuit ..................................................... 4
Figure 2 Full wave bridge rectifier with resistive load ................................................................................. 5
Figure 3 full wave bridge rectifier with smoothing capacitor ....................................................................... 9
Figure 4the capacitor is only charge in short period of time ...................................................................... 10
Figure 5 output of the smoothing capacitor ............................................................................................... 11
Figure 6 AC to DC converter ( rectifier uning smoothing capacitor)........................................................... 13
Figure 7 simulation result of the rectifier circuit at 10 ohms ..................................................................... 13
Figure 8 Active power factoe correction .................................................................................................... 15
Figure 9 Active power factor correction based on discontinuous mode.................................................... 18
Figure 10 voltage regulation graph ............................................................................................................. 19
Figure 11 efficiency plot.............................................................................................................................. 20
Figure 12 the voltage ,and the current of the bridge are in phase ............................................................. 21
Figure 13 output of the circuit PFC ............................................................................................................. 22
Figure 14 the switching frequency graph ................................................................................................... 23
Table of tables
Table 1 input parameters.............................................................................................................................. 6
Table 2 output parameters ........................................................................................................................... 8
Table 3 input parameter using full wave bridge rectifier with smoothing capacitor ................................. 10
Table 4 output parameters ......................................................................................................................... 11
Table 5 THD at different load ...................................................................................................................... 12
Table 6: Measured and calculated Power Factor. ...................................................................................... 12
Table 7 input parameter of the APFC ......................................................................................................... 18
Table 8 output parameter of the APFC ....................................................................................................... 19
Part A
Introduction
Power factor is defined as the ration of the real to the apparent power or the cos the angle between
these two factors. Power factor is presented in numeric form, and has range between 0-1. This range is
used to described represents the offset in time, or the delay, between voltage and the current. 1/ unity
power factor means that the current is completely in phase with the voltage. the disadanteges of having
low power factor are :


Higher current results in a greater voltage drop on the line
The higher current can push equipment closer to their rated capacities. Cables are rated based
on their current carrying capacity.
In addition, poor power factor can be occurred in system where no linear load are used within the
circuit. the non linear loads can draw non sinusoidal current on the load which means harmonic
distortion will be produced, and because of that it effect circuit nearby such as radio or telephone ( RFI).
Also non sinusoidal wave form can draw high current which may saturate the substation transformer
core.
In AC to DC converter, a smoothing capacitor is added to convert the full-wave rippled output of the
rectifier into a smooth DC output voltage. This method is considered as waste of energy because the
current that is drawn on the load is not completely in the phase with the voltage supply therefore,
power factor is poor. In this case having poor power factor is not because of the current being not in
phase with voltage, but because the capacitor is charged only when the output approaches (near)
the peak for a short period of time near the peak of the voltage waveform. In other word the
current is being drawn on the load is not sinusoidal waveform as shown below:
Figure 1 Input Voltage and Current vs. Time for Bridge Rectifier Circuit
The following section will prove this, and will discuss the problem in further:
Results and experimental methodology
A transformer was connected to the main to step down the voltage from 240 V rms to 24 v rms. then a
bridge rectifier was used with A 10 ohm resistor, and 25 ohms (10+15 in series). The following diagram
illustrates the connection between the components. This was done because the power factor value
needs to be confirmed for using purely resistive loads and to confirm that the power factor is 1 before
adding additional components to the circuit which is a smoothing capacitor that is added after the
bridge in order to smooth the output of the bridge.
Figure 2 Full wave bridge rectifier with resistive load
This was followed by measuring the following parameters





Input Voltage in volts
input current in amps
real power in watts
apparent power in VA
power factor
The above parameters were found using wattmeter, and table below represents the values of these
parameters at 10 ohms, and 25 ohms.
Table 1 input parameters
Load resistor
Input voltage
Ac secondary
10ohms
23.9 V
10ohms+15ohms 24.7V
In series
Input current
Ac secondary
(Amps)
2.3 A
1A
Input power
(real)
Input VA
P.F
54.5 Watt
24.4 Watt
54VA
24 VA
1
1
In pure resistive loads, all the power that enters the circuit is consumed by the load and this means that
the reactive power is the same as the real power. Thus the reactive(VAR) power is zero, so the
waveform of the current is in phase with the voltage supply which makes the power factor to be unity(as
the power factor is defined as the ratio of the active power to the apparent power). However, the table
above shows a slight difference between the apparent power, and the real power, and this is due to the
circuit being not purely resistive, as the wiring in the circuit has a small value of inductance which causes
very small difference between the two values (watts and VA).
The above figure shows that current is in phase with the voltage which means that power factor is unity,
and the THD (total harmonic distortion) is close to zero.
After that, the following parameters were measured

peak input voltage using scope

average DC voltage was measured using DMM by sitting it to VDC( to measure only the DC
component)

output voltage AC was measured using SCOPE in LabView launcher

Output power can be found either by placing the wattmeter after the bridge or by using the
formula of power (VRMS2 /Rload). note VRMS should be the experimental, the one on scope
Vrms value:
 =

√(2)
 =
 =

√(2)
32
at 10 ohms
=22.6 volt
√(2)
output power:
=
=
222
=51
10
 2

watt
Table 2 output parameters
Load resistor
Peak input
voltage (volts)
10ohms
32
10ohms+15ohms 34
In series
Average DC
voltage
21
22
Output
voltage AC
ripple
10v
10v
Output power
51 w
21 w
The table above show sthat the output power has been reduced; this is because of the power
dissipation in the diode.The peak input voltage reduces because the load resistor draws more current as
the resistance is increased and due to this, the voltage decreases as the current increases and this shows
that it agrees with the theory.
This was followed by placing a 10,000uf capacitor in parallel with the load to form an AC to DC
converter(and to smooth the output voltage of the bridge). The following figure illustrates the AC to DC
converter.
Figure 3 full wave bridge rectifier with smoothing capacitor
Before the bridge, a wattmeter was placed to measure the following the parameters :





Input Voltage in volts
input current in amps
real power in watts
reactive power in VA
power factor
Load resistor
Input voltage
Ac secondary
10ohms
23.3
10ohms+15ohms 24.8V
In series
Input current
Ac secondary
(Amps)
4.37 A
2.29 A
Input power
(real)
Input VA
P.F
79.1 Watt
40.5 Watt
102VA
56.66 VA
0.76
0.7
The table above shows that the input power is not equal to the input VA and this results in a low power
factor as shown in the table. The reason for the changing in input voltage is because the resistance
draws more current when it is reduced and this is clear from the table as the table shows that the
current drawn by the 10 ohm resistor is more than the 10+15 series resistor . Also it shows that that
power factor is less than unity, this is because current is non-sunosudial waveform, while the voltage is a
pure sine wave. Also, the figure below shows that the capacitor is only changed when the voltage of
input supply approaches to the peak, then the diode change in its state in to reverse bias mode , hence
the capacitor is not changed after the peak.
Figure 4the capacitor is only charge in short period of time
The following parameters were measured in this part of the project:

peak input voltage using scope

average DC voltage was measured using DMM by sitting it to VDC( to measure only the DC
component)

output voltage AC was measured using SCOPE in LabView launcher

output power can be found either by placing the wattmeter after the bridge or by using the
formula of power (VRMS2 /Rload). note VRMS should be the experimental, the one on scope
Table 3 input parameter using full wave bridge rectifier with smoothing capacitor
Load resistor
Peak input
voltage (volts)
10ohms
29
10ohms+15ohms 31
In series
Average DC
voltage
27
30
Output
voltage AC
ripple
2.1
1.3
Output power
48.4 w
21 w
ripple voltage formula
∆ =

2∗∗
Table 4 output parameters
Load resistor
Peak input
voltage (volts)
10ohms
2.9
10ohms+15ohms 1.24
In series
Figure 5 output of the smoothing capacitor
Ripple voltage
Pk-pk
Ripple voltage
pk-pk
RMS ripple
voltage
2.25
1.2
2.1
1.3
0.7V
0.33v
The current peak values:
10 ohm: 10.3 A
25 ohm: 4.5 A
The frequency of the ripple current : 100Hz.
this was followed by measuring THD ( total harmonic distortion), and then measure the power factor
using the following equation
 =  =
Table 5 THD at different load
Load resistor
THD %
10ohms
48
10ohms+15ohms 95
In series
Table 6: Measured and calculated Power Factor.
Load resistor
Measured PF
10 ohm
25 ohm
0.77
0.71
Calculated
PF
0.77
0.72
1
√1 +  2
Simulation section ( Part A)
This part aims to simulate the AC to DC circuit to compare it with the practical results
Figure 6 AC to DC converter ( rectifier uning smoothing capacitor)
Figure 7 simulation result of the rectifier circuit at 10 ohms
the simulation, and practical results shows the same behavious whena smoothing capacitor is used to
smooth the output of the bridge, which it produces a current pulses that is only happen when the
voltage of the input voltage reaches near the peak of the waveform. so the I supply is draw non
sinusoidal waveform
Conclusion
When the circuit consisted of only the resistive load (it was a purely resistive circuit), the
current was in phase with the voltage thus the power factor was unity which means that the
load consumes the whole input power and makes full use of it(the table above proves that VA is
the same as input power). When the smoothing capacitor is added in parallel with the resistive
load(AC to DC converter), the load does not consume the whole power because the capacitor is
charged only when the output approaches (near) the peak for a short period of time near the
peak of the voltage waveform. For the rest of the supply cycle, the diodes are reverse biased,
and no current flows from the supply. The current waveform consists of short pulses near the
voltage peak as shown in the following figure.
So using a smoothing capacitor to smooth the output of the bridge is a bad way to convert from
AC to DC because the supply current will not be the exact replica of the voltage supply because
the capacitor is only charged for a very short period of time, and this peak current will be very
high which will saturate the core of the substation transformer , disturb the functioning of all
the other components (it could even cause them to fail), and harmonics distortion ( radio
frequency interference) which affects the circuits nearby such as radio and mobile phone .Due
to the aforementioned problems, a technique called active power factor correction will be
discussed in the next part of the document that reduces the emissions of harmonic currents
into the AC supply , and improve the power factor of equipments.
Part B
Introduction:
This section will include a solution for part A problem which is using smoothing capacitor to
smooth the output of the bridge rectifier results a bad power factor ( between 0.6-0.7). The
way the power factor was corrected is by using boost converter topology (as it is shown in
figure 8), and it is known as Active power factor correction. The figure below illustrate an active
power factor correction. There are two modes used to accomplish active power factor
correction:
1. Continuous Conduction
Mode (CCM).
2. Discontinuous
Conduction Mode(DCM).
Figure 8 Active power factoe correction
CCM
DCM
Continuous mode typically suits SMPS power levels
greater than 300W. This is where the boost converter’s
MOSFET does not switch on when the boost inductor
is at zero current, instead the current in the energy
transfer inductor never reaches zero during the
switching cycle With this in mind, the voltage swing is
less than in discontinuous Less voltage swing also
reduces EMI and allows for a smaller input filter to be
used. Since the MOSFET is not being turned on when
the boost inductor’s current is at zero, a very fast
reverse recovery diode is required to keep losses to a
minimum.
In this mode ( discontinuous) the MOSFET turns on
when the current reaches zero, and turn off when
the current reaches the envelop of the output of
the bridge. this mode is used for Switch mode
power supplies that have maximum output level
of 300 watt or less
The active power factor correction circuit was based on the discontinuous conduction mode.
Both use boost converter topology but uses different power factor controller as they usea
different IC chip. The chip that was used is TDA 4862.
Calculation of components
Multin (Pin3)
1 + 2
 =  (
)
2
where:



V out = is the maximum peak voltage of the bridge rectifier 35 V with no load
Vin= the input voltage MULTIN. the voltage must not exceeds 4V, so 2 V was decided to be the
input voltage of chip
R1, and R2 will form a voltage divider netwerk R2 was assumed (10k)
So R1 =
1 + 10
35 = 2 (
)
10
17.5 = (
1 + 10
)
10
175 = 1 + 10
165 = 1
1 ≅ 170
There is no a resistor with value of 170 K. As a result, 160 K was used in series with 10 K resistor
Pin1 Vsense
1 + 2
 =  (
)
2
where:

V out = is the desired output voltage it should more than peak voltage of the bridge's output

Vin= is the value of the input voltage in pin1 it should be 2.5 because from inside it is connected
to a comparator, and V ref is 2.5, so to switch error amplifier on both Vref , and Vsense pin
should have the same value which is 2.5 V

R1, and R2 will form a voltage divider network R2 was assumed (10k)
So R1 =
40 = 2.5 (
1 + 10
)
10
1 + 10
16 = (
)
10
16000 = 1 + 10
150 = 1
Calculate the limiting resistor for pin 8
a capacitor was placed to limit the current to the voltage supply pin (8)
maximum current at pin 8 must be 70mA or lower( it was assumed to be 10 mA )
zener diode voltage :16V
pin 8 was supplied by the output of the circuit which is 40V.
8 =
 − 

8 =
40 − 16
10 ∗ 10−3
 = .  
Inductors calculation
The operation of the circuit
Figure 9 Active power factor correction based on discontinuous mode
Results
After building the circuit on a bread board, then it was tested to make sure that the circuit is actually
boosting even at the maximum power which 50 watt.
Input parameters
The table below will include the input values such as voltage, current,power, and power factor.The
values were measured using a watt meter.
Table 7 input parameter of the APFC
AC Voltage
secondary
(volts)
25.5
24.6
AC Current
secondary
(amps)
0.738
0.92
Input power
(watt)
Input VA
Power factor
Load(ohms)
18.1
22.7
18.1
22.6
1
1
100
79
24.3
24.3
24
23.9
23.5
1.1
1.1
1.54
1.8
2.6
26.7
27.7
36
42.8
59
26.8
27.8
37.2
43.3
60
1
1
0.99
0.98
0.98
69
66
50
44
30
Output parameters.
Table 8 output parameter of the APFC
Load
current
(Amps)
0.39
0.48
0.56
0.6
0.8
0.9
1.3
Ripple
voltage (VpVp)
2.8
3.4
4
4.2
5.1
6.5
7.6
Figure 10 voltage regulation graph
Ripple RMS
voltage
Output voltage (V)
Output power
Load(ohms)
1
1.2
1.4
1.5
1.8
2.3
2.7
40.6
40.4
40.5
40.3
40.3
40.2
39.6
16
20
23.2
24.3
32
37.5
50.7
100
79
69
66
50
44
30
This graph shows the output voltage versus output power it shows that the voltage drops at the
maximum load by 1V, and this is due to the number of the primary winding, few windings must be
removed to regulate the voltage, and make steady voltage.
Figure 11 efficiency plot
Figure 12 the voltage ,and the current of the bridge are in phase
Figure 13 output of the circuit PFC
Figure 14 the switching frequency graph
since the input voltage is in phase with the current supply then this mean that all the current is occurred
in the first component, the circuit above shows components after the 16Khz which is the switching
frequency. these complements may produce RFI. So usually in this circuit , as RFI circuit is added to
minimize the effect of RFI.
Conclusion
to conclude, a problem in AC to DC converter was identify in this document which is when a
smoothing capacitor is added in parallel with the resistive load(AC to DC converter), the load
does not consume the whole power because the capacitor is charged only when the output
approaches (near) the peak for a short period of time near the peak of the voltage waveform.
For the rest of the supply cycle, the diodes are reverse biased, and no current flows from the
supply. The current waveform consists of short pulses near the voltage peak. this non sinusoidal
waveform disturb the functioning of all the other components (it could even cause them to
fail), and harmonics distortion ( radio frequency interference) which affects the circuits nearby
such as radio and mobile phone . Also, if this technique is commonly used then this will saturate
the substation transformer because it produces high peak of current. Then this problem was
solved by using active power factor correction based on discontinuous mode that uses boost
converter to make the current in phase with voltage.
References
https://www.fairchildsemi.com/application-notes/AN/AN-42047.pdf
http://m.eet.com/media/1149503/24650-46463.pdf
http://www.infineon.com/dgdl/AN_TDA4862G.pdf?folderId=db3a304412b407950112b41804e124ae&fi
leId=db3a304412b407950112b418052524af
http://www.ospmag.com/files/pdf/whitepaper/Power-Factor-and-Input.pdf

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