an electrolytic capacitor-less led driver using harmonics … · 2016. 5. 19. · krunal h. patel1...
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IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 03, 2016 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 1012
An Electrolytic Capacitor-Less LED Driver using Harmonics Injection
Technique Krunal H. Patel1 Dhiren A. Luhar2 Prof. Chetan D. Upadhyay3
1,2M.E. Student 3Assistant Professor 1,2,3L.D. College of Engineering, Ahmedabad-380015
Abstract— An LED lighting system requires a driver for to
the power conversion from ac voltage to dc regulated current
output. The electrolytic capacitor is use in the LED driver.
But life of electrolytic capacitor is less then LED. Here we
use film capacitor instead of electrolytic capacitors. But it’s
Maximum capacitance per Unit volume is lower Then
electrolytic capacitor. The output current in above driver is
pulsating. In this paper we use harmonics injection
Technique for make output current constant.
Key words: Flyback Converter, Peak to Average Ratio,
Harmonics Injection Technique
I. INTRODUCTION
Nowadays LEDs are widely used in lighting area. These are
niche applications compared with general illumination. An
LED is a p-n junction semiconductor which emits light
spontaneously directly from an external electric field
(electroluminescence effect). Typical lifetimes are 25,000 to
50,000 hours, but heat and current settings can extend or
shorten this time significantly. An LED lighting system use
driver to handle the power conversion from ac voltage to dc
regulated current output. In driver large capacitance is
Require for balance the energy difference between the input
pulsating power and the output DC power delivered to the
LED load. Electrolytic capacitors are use for the energy
storage capacitor in LED lamps due to their high energy
density and low cost. The estimated lifespan of the LED
devices can last up to at least 50,000 hours but electrolytic
capacitors typically last only up to approximately 10,000
hours. The reliability of the electrolytic capacitors include
their sensitivity to their operating temperature, ripple current
and internal equivalent series resistance (ESR). [1] Table I
shows a comparison on the properties of three types of
capacitors. Properties compared at the ambient temperature
of 50oC, available range of values and maximum
capacitance per unit volume (μF/cm3) at the same voltage
rating. Among the three types of capacitors, electrolytic
capacitors give the highest value available in a single
package. The lifetime of the electrolytic capacitors will be
shortened by half if the operating temperature is increased
by 10oC. [2]
Capacitor Lifetime
(hours)
Available
Range
Maximum
capacitance
per Unit
volume
(µF/cm3)
Electrolytic <10000 1 µF-12 mF 200
Polyester
Film >100000 10 pF-80 µF 30
Ceramic >100000 10 pF-10 µF 5
Table 1: Comparison among several types of capacitors
Thus, for high ambient temperature, the lifetime of
the electrolytic capacitor becomes the critical factor that
determines the lifetime of the entire application. polyester
film capacitor and Ceramic capacitor are the best choice in
terms of the lifetime. But their capacitance per unit volume
and range are lesser then Electrolytic capacitor. So the
pulsating current brings flicker with twice the line
frequency[3]. The peak to average ration of output current
should be 1. Here we use harmonics injection Technique for
make output current constant and make this ratio near to 1.
We can set duty cycle of flyback converter for Harmonics
injection. In order to inject the third and fifth harmonics into
the input current, the function of the duty cycle in a half-line
cycle is derived.[5]
II. RELATIONSHIP BETWEEN VOLTAGE RIPPLE AND STORAGE
CAPACITANCE
Assume that the input power factor is unity. The input
voltage and input current is defined as Vin (t) = Vm sinωt [1]
Iin (t) = Im sin ωt [2]
The instantaneous input power can be derived as
Pin (t) = Vin (t) Iin (t) = (1 cos 2 )
2
m mV I t [3]
It can be obtained from (3) that the average input
power is
Pin 2
m mV I
[4]
Fig. 1: Key waveform of the converter (power factor =
unity)
Assume the efficiency of the converter is 100%. It
means that the average input power is equal to the output
power Po. These results in
Po 2
m mV I
[5]
It can be seen that when Pin > Po, CB is charged,
and VC increases, and when Pin < Po, CB is discharged, and
VC decreases.
Substitution of (5) into (3) yields
Pin (t) = Po (1 − cos 2ωt) [6]
From the (6) and Fig. 1, we can see that Pin is equal
to Po at Tline/8 and 3Tline/8. It can be seen that CB is charged
from Tline/8 to 3Tline/8, and VC increases. Consequently, VC
gets its minimum and maximum values at Tline/8 and
3Tline/8, respectively.
An Electrolytic Capacitor-Less LED Driver using Harmonics Injection Technique
(IJSRD/Vol. 4/Issue 03/2016/270)
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The energy charging CB from Tline/8 and 3Tline/8 is
line
line
3 /8
/8
[ ]
T
in
T
PoE P t Po dt
[7]
ΔE can also be expressed as
ΔE = 1
2
CB*(V 2Cmax− V 2Cmin) [8]
From (7) and (8), we have
CB =2 2
max min
2
* ( ) C C
Po
V V
=
max min
2
* *[( ) / 2] C C C
Po
V V V
[9]
From this equation we know that if ΔVC is
intentionally increased, the value of CB will be significantly
reduced.[4] Thus, film capacitors can be used instead of
electrolytic capacitors.
III. PEAK-TO-AVERAGE RATIO OF OUTPUT CURRENT
Fig.1 shows that the waveform of the output current follows
the shape of a sine square function. Its peak-to-average ratio
is 2. Therefore, it is necessary to reduce the peak-to-average
ratio of the output current to guarantee LED’s safety.[5]
A. Harmonics Injection Into Input Current to Reduce Peak-
to-Average Ratio of Output Current
The optimum output current for driving the LED is a pure dc
current, its peak-to-average ratio is 1. In such a situation, the
output power will be purely dc, and correspondingly, the
input power must be purely dc due to the absence of the
storage capacitor. So, the input current will be
( )( ) * sin
o o o
in
V V Ii t
Vin t Vm t
[10]
According to this the input current tends to infinity
at the zero-crossings of the input voltage. It is show in Fig.
2.
Fig. 2: Key waveform when Pin=Po
There is a conflict that if the input power factor is
unity, the peak-to-average ratio of the output current is 2,
and if the peak-to- average ratio of the output current is to
be reduced to 1, the input power factor will be zero.
Therefore, the trade-offs must be balanced. This is
achievable by injecting some odd harmonics into the input
current to reduce the peak-to-average ratio of the output
current, while maintaining the input power factor to be
higher than 0.9 as required by the regulation standards.
B. Relationship between Injected Third and Fifth
Harmonics and Peak-to-Average Ratio of Output Current
When both the third and fifth harmonics are injected, the
input current is derive by
iin1+3+5(t) = I (sin ωt + I*3 sin 3ωt + I*
5 sin 5ωt) [11]
And the corresponding output current io1+3+5 is
1 3 5
1 3 5
* *
3 5
( ) ( )( )
sin (sin sin 3 sin 5 )
in in
o
o
m
o
V t I ti t
V
V It t i t I t
V
[12]
The average value of io1+3+5 in a half-line cycle is
1 3 5 1 3 5
0
1( )
2
m
o o
o
V Ii i t
V
[13]
It can be seen from (13) that the average value of
io1+3+5 in a half-line cycle is determined by the fundamental
component of the input current and has nothing to do with
the injected Harmonics. From (12) and (13), the normalized
output current with the base of Io1+3+5 is derived as
* 1 3 5
1 3 5
1 3 5
2 * * * * 2 * 4
3 5 3 5 5
( )( )
2 sin [(1 3 5 ) 4( 5 ) sin 16 sin ]
o
o
o
i ti t
i
t I I I I t I t
[14]
Fig. 3: Waveform of i∗o1+3+5
As shown in Fig. 3, it is necessary to find the
turning points of i∗o1+3+5 by using (14). After that, calculate
the minimum peak-to-average ratio of the output current of
the three cases within the corresponding range of I∗3 and I*5.
Case I Case II Case I
I*3 0.465 0.44 0.389
I*5 0.135 0.092 0.087
Min(i∗o1+3+5|peak) 1.340 1.382 1.396
Table 2: Minimum peak to average ratio of the output
current and the corresponding I*3 and I*
5 in three case.
When we determine the range of I*3 and I*
5, the
input power factor should be ensured to be higher than 0.9.
From Table the minimum peak-to-average ratio is 1.34,
which occurs in case I.
IV. CALCULATION FOR FLYBACK CONVERTER
Fig. 4: Flyback converter
Electrolytic capacitor less flyback converter is shown in
Fig.4. Here L0 and C0 is high frequency harmonics filter in
the secondary side. The switching frequency is much higher
than the line frequency, the input voltage can be treated to
be constant in a switching period. Here switching frequency
is 200kHz and line frequency is 50Hz. The flyback
converter is designed in discontinuous current mode (DCM)
An Electrolytic Capacitor-Less LED Driver using Harmonics Injection Technique
(IJSRD/Vol. 4/Issue 03/2016/270)
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so that a high power factor is automatically achieved. Two
mode of operation.
A. Mode 1:
When the switch Q turns on, the primary current ip increases
linearly from zero, and it reaches the peak value when the
switch turns off. The peak and average value of ip in a
switching cycle are
sin( )
in y m L y
p pk
p s p s
v D V w t Di t
L f L f
[15]
2sin1
( ) ( )2 2
m L y
p av p pk y
p s
V w t Di t i t D
L f
[16]
From (16) and Fig. 4, it can be obtained that the
average input current in a switching cycle is 2
sin( )
2
m L y
in
p s
V w t Di t
L f
[17]
It can be seen from (17) that if Dy is kept constant
in a halfline cycle, the input current will be proportional to
the input voltage, and so, PFC can be automatically
achieved.
B. Mode 2:
When Q turns off, the secondary diode conducts, and the
energy stored in the primary side of the transformer is
transferred to the secondary side. The peak value of the
secondary current is then
sin( ) ( )
m L y
s pk p pk
p s
nV w t Di t ni t
L f
[18]
Thus, the secondary current ts is will decrease
linearly. The reset time tr for is to fall to zero is
0 0 0
sin sins s pk s m L y m L y
r
p s s
L i L nV w t D V w t Dt
V V L f nV f
[19]
The corresponding duty cycle is
0
sinm L yr
r
s
V w t DtD
T nV
[20]
In a switching cycle, the average value of the
secondary current can be expressed as 2 2 2
0
sin1( ) ( )
2 2
m L y
s av s pk r
p s
V w tDi t i t D
L V f
[21]
Fig. 5: waveforms of the primary and secondary currents of
flyback converter
Thus, the average value of output current in a half-
line cycle can be derived as 2 2
0
00
1( )
4
m y
s av L
p s
V DI i t d w t
L V f
[22]
According to (17), if the duty cycle is kept constant
at Dy 0, the fundamental component of the input current is 2
12
m y
p s
V DI
L f
[23]
If the third and fifth harmonics are injected into the
input current, substitution of (17) and (23) into (11), leads to 2
1 3 5
2
0 * *
3 5
sin ( )
2
(sin sin 3 sin 5 )2
m L y
p s
m y
L L L
p s
V w tD t
L f
V Dw t I w t I w t
L f
[24]
Equation (24) can be rewritten as
1 3 5
* 4 * * 2 * *
0 5 3 5 3 5
( )
16 sin (4 20 ) sin (1 3 5 )
y
y L L
D t
D I w t I I w t I I
[25]
Equation (25) means that we can vary the duty
cycle in a half-line cycle to inject the third and fifth
harmonics into iin . Substituting I∗3 = 0.465 and I∗ 5 = 0.135
into (25), the duty cycle is 4 2
1 3 5 0( ) 2 .16 sin 4.56 sin 3.07
y y L LD t D w t w t
[26]
The function of Dy1+3+5 is too complicated to be
implemented. The accuracy of (26) strongly depends on ωLt0
,For the sake of simplicity,(26) can be rewritten as
0( ) (1 sin )
y fit y LD t D a k w t
[27]
Where k is determines the input power factor and
ak determines the output power. k is find by the set power
factor to 0.9. and a is find by the take output current
constant.
Substitution of k=-0.61 and a=2.02, equation (27)
became
0( ) 2.02(1 0.61 sin )
y fit y LD t D w t
[28]
So the duty cycle can be easily implemented by
simply sampling the input voltage.
V. SIMULATION AND RESULTS
Data form the prefer paper. [5]
Parameters values
Input voltage Vin 198-264VAC/50Hz
Output voltage Vo 25VDC
Output current 0.35A
the transformer: n 3
Primary inductance: Lp 270μH
Primary filter capacitor Co 0.1 μF
Input filter inductance Lin 100μH
Output filter capacitor Co 0.47 μF
Output filter inductance Lo 30 μH
Table 1: Data form the prefer paper. [5]
A. Simulation Model (Harmonics Injection-Sine Block) In
Matlab
Fig. 6: Simulation Model using Sine Block
An Electrolytic Capacitor-Less LED Driver using Harmonics Injection Technique
(IJSRD/Vol. 4/Issue 03/2016/270)
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Fig. 7: input voltage and current using sine block
Fig. 8: output voltage and output current and secondary
current using sine block
B. Simulation Model (Function of Duty Cycle) in Matlab
Fig. 9: simulation model using duty cycle function
Fig. 10: input voltage and current using duty cycle function
Fig. 11: output voltage and output current and secondary
current using duty cycle function
VI. CONCLUSION
These papers represent the harmonics injection using
function of duty cycle. By injecting the third and fifth
harmonics into the input current the peak-to-average ratio of
the output current is reduced. In both simulation model with
direct sine block and duty cycle function the output and
input waveforms are similar.The experimental results
showed the effectiveness of the proposed electrolytic
capacitor-less ac–dc LED driver.
APPENDIX: LIST OF SYMBOLS
Vm peak input voltage
I m peak input current
w angular frequency
Pin input power
Po optput power
VC voltage of CB storage capacitor
VC max maximum voltage values of CB
VC min minimum voltage values of CB
I*3 the normalized amplitude of the third
harmonics
I∗5 the normalized amplitude of the fifth
harmonics
1 3 5
( )y
D t
duty cycle with third & fifth harmonics
injection
( )y fit
D t
fitting function of the dutycycle
(harmonics injection)
( )
p pki t
primary peak current
( )
p avi t
primary average current
( )
s pki t secondary peak current
( )s av
i t
secondary average current
IO output current
Lp primary inductance
REFERENCES
[1] Shelf-Life Evaluation of Aluminuin Electrodytic
Capacitcirs(IEEE Trans. Components, Hybrids, and
Manufacturing Technology)
[2] Current Source Ballast for High Power Lighting
Emitting Diodes without Electrolytic Capacitor (Y. X.
An Electrolytic Capacitor-Less LED Driver using Harmonics Injection Technique
(IJSRD/Vol. 4/Issue 03/2016/270)
All rights reserved by www.ijsrd.com 1016
Qin, 2Henry S. H. Chung, Senior Member, IEEE, 3D.
Y. Lin, and 4S. Y. R. Hui, Fellow, IEEE)
[3] A Flicker-free Electrolytic Capacitor-less AC-DC LED
Driver(Shu Wang, Xinbo Ruan, Kai Yao, Zhihong Ye)
[4] Means of Eliminating Electrolytic Capacitor in AC/DC
Power Supplies for LED Lightings(Linlin Gu, Xinbo
Ruan, Senior Member, IEEE, Ming Xu, Senior
Member, IEEE, and Kai Yao)
[5] A Method of Reducing the Peak-to-Average Ratio of
LED Current for Electrolytic Capacitor-Less AC–DC
Drivers(Beibei Wang, Xinbo Ruan, Senior Member,
IEEE, Kai Yao, and Ming Xu, Senior Member, IEEE)