Download O A RIGINAL RTICLES

4215
Journal of Applied Sciences Research, 8(8): 4215-4221, 2012
ISSN 1819-544X
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLES
Investigation of Harmonic Generation from Low Wattage LED Lamps
Sohel Uddin, Hussain Shareef, Azah Mohamed and M A Hannan
Department of Electrical, Electronics and System Engineering, Universiti Kebangsaan Malaysia, 43600, Bangi,
Selangor, Malaysia
ABSTRACT
Light Emitting Diodes (LEDs) are versatile and energy efficient when compared to the conventional light
sources. LEDs represent a transformational change in how light is produced. However, there are significant
differences between conventional lighting sources and LEDs in terms of voltage and current operating
requirements which may affect the power quality (PQ) of AC mains. Therefore, this paper investigates one of
the main PQ related harmonic generations from LED bulbs available in the market. It is done by conducting
laboratory tests on various LED lamps and tapping the load current behaviour under different conditions. Then
frequency domain analysis is performed to investigate the generated harmonics. Harmonic levels of different
wattage, combinations of various LED bulbs and Compact Fluorescent Lamps (CFLs) are experimentally
evaluated and compared. The results show that most of the LED lamps produce high level of harmonics and it is
comparable with respect to harmonics generated from CFLs.
Key words: LED lamps, CFLs, total harmonic distortion, power quality.
Introduction
Lighting accounts for roughly 20% of the electricity consumption all over the world. To promote energy
saving, many governments in the world have introduced directives to ban energy inefficient incandescent light
bulbs and replace it with other technologies like LEDs (Dilouie, 2005; Huang et al., 2007). LEDs work on a
completely different principle than the Compact Fluorescent Lamps (CFLs). In the LED lighting technology,
when each electron recombines with an atom, it emits a particle of light known as a photon. Because all of the
light is being produced at the junction, it requires many LEDs to light a large area.
In general lighting applications, a compact AC/DC converter should be used in one lighting fixture to
supply DC current to LED chips which introduce nonlinearity to the system. As a nonlinear load, LED bulbs
produce highly distorted currents (Cuk et al., 2010). Although the input power of a single LED bulb is quite
low, a large number of customers using LED bulbs and CFLs per premises could create significant power
quality problems (Dwyer et al., 1995). Therefore a good understanding of the LED bulb’s harmonic producing
characteristics becomes necessary.
A large number of studies were conducted on LEDs as an energy efficient lamp but most of researchers pay
their attention on the internal ballast circuit design and enhancing their performance (Gu et al., 2009; Chen and
Chung, 2011; Qu et al., 2011). A few contributions focus on harmonic emissions of LEDs lamps (Blanco and
Parra, 2010; Cuk et al., 2010, Uddin et al., 2012). According to Cuk et al, the widespread use of LEDs and
CFLs could increase voltage distortion in the distribution networks depending upon the characteristics of the
network. However, the work mainly uses CFLs in the analysis. Also power rating and power factor of conducted
LED was very small and only single LED was used. Therefore, this cannot give exact characteristic. On the
related research field of the harmonic content of CFLs, a large number of papers have been published. Reference
(Watson et al., 2009) discovers that the increase in the use of CFLs by the customers may exceed the
permissible IEEE harmonic limits of non-linear loads. Therefore, CFLs with “Star Rating” (with embedded
harmonics filter) is recommended to use. There are also many published works that concludes the impact of
CFLs in distorting voltage and current waveforms, which is largely below the set standards (Munasinghe and
Abeyratne, 2006; Matvoz and Maksic, 2008; Watson et al., 2009). The study goals are generally to educate
consumers about pros and cons of CFLs.
This paper presents a detail harmonics analysis of LED lamps. This is characterized by measurement tests,
using various available LED bulbs. The tests are carried out to observe their current and voltage waveforms and
analyzed them in terms of power rating, number of lamps and effect of combination of various LED lamps. The
test results are also compared for their performance with equivalent CLFs harmonics and with IEC 61000-3-2
harmonic standard (Std. IEC).
Corresponding Author: Sohel Uddin, Department of Electrical, Electronics and System Engineering, Universiti
Kebangsaan Malaysia, 43600, Bangi, Selangor, Malaysia
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J. Appl. Sci. Res., 8(8): 4215-4221, 2012
Operating Principal of LED Lamps:
LEDs require a constant current source from a low DC voltage source, obtained from the AC mains.
Therefore, it is necessary to use a converter to regulate the voltage and control the current applied to the LEDs.
The buck, boost, flyback and resonant converters are well known in literature as a power source to the LEDs,
(Oliveira et al., 2007).
Fig. 1 depicts a block diagram of typical low-wattage LED ballast. It includes the AC line input voltage,
typically 220-240 VAC 50/60 Hz, an EMI filter to block circuit-generated switching noise, a rectifier with
smoothing capacitor, a PWM controlled constant current source converter for DC to DC conversion, and an
array of LEDs. Since the rated load powers are low, the directives governing the injection of harmonics are not
particularly strict (Shareef et al., 2009), and therefore power factor control circuits may or may not be found in
low-wattage LED lamp ballasts. However, to reduce the generated harmonics and to improve the power factor it
is possible to introduce either an input passive filter, valley filled circuits, IC controlled active filtering
configurations.
Fig. 1: Typical block diagram of LED ballast circuit
Experimental Procedure:
To analyze the characteristics of the LED lamps, 12 samples of with different power ratings from various
manufacture, as shown in Table 1, were tested. All the tested lamps are designed to operate at 220-240 V and
have power consumptions rating of 3 W to 10 W.
Table 1: Technical data for tested lamps.
Trade
name
Philips Cool Daylight
Philips Cool Daylight
Philips Warm Daylight
Osram Daylight
Osram Daylight
Osram Cool White
Osram Warm White
Osram Warm White
Toshiba Cool White
Bright cool White
Cash Warm White
Evenzo Cool White
Philips Genic
Osram Duluxstar
Type
of
lamp
LED
LED
LED
LED
LED
LED
LED
LED
LED
LED
LED
LED
CFL
CFL
Nominal
power
P (W)
4
5
7
4
6
8
3
10
5.5
5
7
3
5
5
Equivalent to
incandescent
P (W)
25
40
40
25
30
40
25
50
30
40
40
15
25
25
Luminous
flux
(lm)
250
350
350
250
365
450
250
950
290
230
580
150
235
240
Life
span
(Years)
25
25
25
25
25
25
25
25
40
6
20
18
4
3
To obtain accurate data concerning the exact current harmonic content of LED bulbs, an experimental setup
as shown in Fig. 2 is assembled. It consists of four components namely, Fluke 434 power quality analyzer,
Fluke i30s current clamp, LED bulb(s) under test, and a personal computer to analyze the signals. Each lamp is
kept switched on for 10 minutes before the measurements are taken for stabilization. Each lamp is tested for four
times to eliminate any error during different period of the day. The captured current waveforms were analyzed
by using Fluke 434 and MATLAB software. Furthermore, for comparisons purposes, 2 samples of CFLs
indicated in Table 2 are also tested using the same procedure.
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J. Appl. Sci. Res., 8(8): 4215-4221, 2012
Fig. 2: Experimental setup
Experimental Results and Discussion:
In this section, measurements of various test conducted on LED lamps and CFLs are analyzed and
discussed. The lamp current waveforms were analyzed using the Fourier Theorem. It provide frequency
spectrum of the lamp currents represented by the fundamental sinusoidal component and a series of higher order
harmonic components at frequencies that are integer multiples of the fundamental frequency. The square roots
of the sum of the amplitudes of the harmonic present the total harmonic distortion (THD).
Findings from single pieces of lamps:
The purposes of these tests are to explore the type of harmonic filters used in the LED ballast circuit and
harmonic emissions from all the tested lamps. The tests also provide an insight about the harmonic generation
levels of same branded lamps with different power rating, different branded lamps with same active power
rating.
The typical current waveforms illustrated in Fig. 3 are obtained from different lamps tested. From the figure
it can be noted that the current waveforms is not sinusoidal. It means that they inject harmonic into the power
system. Furthermore the figure also indicates that the ballast in dissimilar LED bulbs use different filtering
methods to reduce harmonic generation. For example, most of the Phillips brand LED bulbs tested utilize the
Valley-filled circuit, the Toshiba 5.5 W lamp contains a passive filter, Osram 8 W sample embed an active filter,
and some other tested lamps does not implement any filtering technique.
To demonstrate further, relative harmonic currents of all tested lamps are presented in Table 2. Note that
some of the tested LED bulbs generate quite a high level of harmonic which produce unacceptable limits of
harmonics when referred to IEC 61000-3-2 standard described earlier. From Table 2, it can be noted that lamps
having the trademark of Philips, have THDI values between 63 and 65, while Osram brand LED bulbs with
power rating less than 6 W produce high levels of harmonics which is in the range of 173 to 175 %. This is
because these LED bulbs do not use any filter in their ballast circuit. However, in case of 8 W and 10 W Osram
LED lamps, they produce the lowest THDI which is in the rage of 30 to 35 %. All other tested lamps have THDI
value greater than 100 % as seen in Table 2.
Table 2: Harmonic contents of single LED lamps
Tested
lamp
Fund
3rd
Philips 4 W
100
34.61
Philips 5 W
100
36.92
Philips 7 W
100
32.34
Osram 4 W
100
89.24
Osram 6 W
100
91.96
Osram 8 W
100
22.25
Osram 10 W
100
32.12
Evenzo 3 W
100
90.7
Bright 5 W
100
86.65
Cash 7 W
100
91.23
Toshiba 5.5 W
100
73.4
Harmonic (%)
5th
6.28
7.16
11.6
70.65
77.05
15.04
4.68
77.34
75.92
74.81
45.4
7th
22.27
19.81
23.4
51.19
58.51
2.34
2.67
58.89
61.75
56.41
35.62
9th
18.94
19.39
19.03
38.57
41.01
9.73
6.45
45.32
48.87
41.06
31.38
THDI
63.05
63.83
64.23
173.9
174.3
30.94
34.78
164.4
167.2
168.2
106.3
4218
0.3
0.2
0.1
0
-0.1
-0.2
No Filter
0
5
10
Time (ms)
Current (A)
0.2
15
Passive Filter
0.1
0
-0.1
-0.2
0
5
10
Time (ms)
15
Current (A)
0.2
20
Valley Fill
0.1
0
-0.1
-0.2
0
5
10
Time (ms)
15
0.1
Current (A)
20
20
Active Filter
0
-0.1
0
5
10
Time (ms)
15
20
Current Harmonic (%) Current Harmonic (%) Current Harmonic (%) Current Harmonic (%)
Current (A)
J. Appl. Sci. Res., 8(8): 4215-4221, 2012
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
THD=170-175 %
1
3
5
7
9
11
13
Harmonic Order (n)
15
17
19
THD=105-110 %
1
3
5
7
9
11
13
Harmonic Order (n)
15
17
19
THD=63-70 %
1
3
5
7
9
11
13
Harmonic Order (n)
15
17
19
THD=30-35 %
1
3
5
7
9
11
13
Harmonic Order (n)
15
17
19
Fig. 3: Various types of current waveforms obtained from different tested LED bulbs.
Findings from group of lamps:
The purpose of these tests is to investigate the effect of harmonic characteristic, when the quantity of LED
lamps is changed. Tables 3 and 4 show the result when the number of same wattage lamps with same trade make
is increased. From Tables 3 and 4 it can be observed that, there is no effect of adding more LED lamps in the
circuit on harmonic generation. This is because the wave shapes generated by adding similar lamps is unaffected
except the magnitude of current drawn from the system. Similar observation is obtained when the lamps with
different power is combined from the same manufacturer considering the type of ballast used. Table 5 shows the
results of combining various wattage bulbs from Philips.
To understand the harmonic accumulation due to various branded LED bulbs, first two combinations
namely, Philips 4 W-Osram 4 W and Evenzo 3 W-Osram 3 W are chosen for this study to illustrate the effect of
combining same wattage lams from different manufacturers. Fig. 4 (a) shows current and voltage waveform of
these two combinations. From Fig. 4 (a) it can be noted that combining different branded LED lamps produce
different kind of current wave shape from their individual current waveform characteristics. This is due to the
superposition of individual current wave shapes. Fig. 4 (b) illustrated harmonic spectrum of those two
combinations where the harmonic generation of these combinations are much lower than the highest harmonic
producing lamp alone.
In the second tests to observe the effect of combinations of various LED lamps with different
manufacturers, a mixture of lamps from the test samples in Table 1 are connected in parallel. Table 6 shows the
result of few combinations of LED lamps irrespective of wattage and brand. From Table 6 it is noted that
different LED lamps combination generates different level of THDI. For example combination-A produce less
harmonics and combination-D produce high THDI value. This occur because in combination-A, all lamps have
better ballast circuit but in combination-D, majority of lamps have no-filtering circuit.
Table 3: Harmonic contents of group of 7 W LED lamps from Philips.
No. of
Power
lamps
P (W)
Fund
3rd
1
7
100
32.34
2
14
100
31.94
3
21
100
31.58
Harmonic (%)
5th
7th
11.62
23.48
12.43
22.52
12.22
23.17
9th
19.03
18.46
18.32
THDI
64.23
64.56
63.59
Table 4: Harmonic contents of group of 6 W LED lamps from Osram.
No. of
Power
lamps
P (W)
Fund
3rd
1
6
100
91.96
2
12
100
92.14
3
18
100
91.21
Harmonic (%)
5th
7th
77.05
58.51
77.76
59.92
78.48
59.12
9th
41.01
42.76
44.34
THDI
174.38
174.63
172.85
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J. Appl. Sci. Res., 8(8): 4215-4221, 2012
Table 5: Harmonic contents from group of various wattage LED lamps of Philips.
Combination
Total
of lamps
power (W)
4+5
9
4+5+7
16
4+5+5+5
19
4+4+5+7
20
4+5+7+7
23
4+7+7+7
25
THDI
(%)
64.3
64.2
63.6
62.8
63.9
63.7
0.3
Philips 4 W-Osram 4 W
Evenzo 3 W-Osram 3 W
Current (A)
0.2
0.1
0
-0.1
-0.2
-0.3
0
5
10
Time (ms)
(a)
15
20
Current Harmonic (%)
100
Philips 4 W & Osram 4 W
(THD=103.9 %)
80
60
40
20
0
1
3
5
7
9
11
13
15
17
19
21
23
Harmonic Order (n)
(b)
25
27
29
31
Current Harmonic (%)
100
33
35
37
39
Evenzo 3 W & Osram 3 W
(THD=129.2 %)
80
60
40
20
0
1
3
5
7
9
11
13
15
17
19
21
23
Harmonic Order (n)
(c)
25
27
29
31
33
35
37
39
Fig. 4: Test results of the group of lamps (a) Current waveform (b) Harmonic spectrum: Philips 4 W-Osram 4
W combination (c) Evenzo 3 W-Osram 3 W combination
As a result combined effect of combination-D is more problematic than combination-A. Therefore,
harmonic penetration of different type of LED lamps depends on the combined current waveform. Furthermore,
from Table 6, it can be noted that harmonics from the combination of LED lamps in a circuit can be decreased
to an acceptable level recommended by IEC 61000-3-2 standard although some individual lamps exceed this
standards.
Table 6: Harmonic generated by combination of LED lamp irrespective of wattage and brand.
Combination
Lamps in parallel
A
Philips 5 W, Philips 7 W and Osram 8 W
B
Philips 5 W, Philips 7 W, Osram 8 W, Bright 5 W and Cash 7 W
C
Philips 7 W, Osram 6 W, Evenzo 3 W, Bright 5 W and Cash 7 W
D
Philips 7 W, Osram 4 W, Osram 6 W, Evenzo 3 W and Bright 5 W
E
Philips 7 W, Osram 4 W, Osram 6 W, Cash 7 W, Toshiba 5.5 W, Evenzo 3 W, and Bright 5 W
THDI (%)
40.9
70.2
111.2
114.3
103.8
Comparison of harmonics from LED lamps and CFLs:
Since CFLs are the most commonly used energy efficient lamps today, it is important to compare the
performance of new LED lamps with CFLs in terms of harmonic generation. For this purpose, Philips and
Osram brand LED lamps are compared with CFLs from same manufacturer. Fig. 5 ill-starred the current
waveform and the harmonic spectrum obtained for Philips 5 W LED and CFL lamps. From Fig. 5 (a) it is clear
that the ballast technology used in both types of lamps are different although the peak currents are nearly same.
When the harmonic spectrum is analysed as in Fig. 5 (b) it is understood that LED lamps of same wattage from
this manufacture is better compared to that of their CFLs in terms of harmonics.
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J. Appl. Sci. Res., 8(8): 4215-4221, 2012
400
Philips (LED) 5 W
Philips (CFL) 5 W
200
Voltage
Current (A)
0.2
0
0
-0.2
-200
-0.4
0
5
10
Time (ms)
(a)
-400
20
15
100
Current Harmonic (%)
Voltage (V)
0.4
Philips (LED) 5 W
Philips (CFL) 5 W
80
60
40
20
0
1
3
5
7
9
11
13
15
17
19
21
23
Harmonic Order (n)
(b)
25
27
29
31
33
35
37
39
Fig. 5: Test results of Philips 5 W LED bulbs and 5 W CFL: (a) Lamp current and voltage waveforms (b)
Individual harmonic spectrum.
Current (A)
0.4
400
Osram (LED) 4 W
Osram (LED) 6 W
Osram (CFL) 5 W 200
Voltage
0.2
0
0
-0.2
-200
-0.4
0
5
10
Time (ms)
(a)
-400
20
15
100
Current Harmonic (%)
Voltage (V)
To further investigate, harmonic levels of LED lamps compared to CFLs from other manufacturers, Osram,
4 W and 6 W LED lamps are compared to Osram’s 5 W CFLs as depicted in Fig. 6. It is seen from Fig. 6 (a),
the 4 W and 6 W LED lamps draw higher peak current than that required by 5 W CFLs of Osram. These high
peaks introduce more harmonics into the systems. Therefore it can be concluded that not all LED lamps produce
high harmonics compared to CFLs although they are manufactured by same company.
As a final test, the combined effect of CFLs and LED lamps are investigated by using Philips 5 W, Osram 5
W of CFLs and all LED lamps used in this study. Table 7 illustrates the harmonics generated from combination
of CFLs and LED lamps and their respective THDI value. From Table 7, it is clear that combination –A generate
the lowest THDI value equal to 79.12 %. This value is lower than the THDI value of 106.4 % and 103.6 %
obtained when only CFLs or LED combination is used respectively. Similar observations are obtained for
Combination-B and Combination-C as well.
Osram (LED) 4 W
Osram (LED) 6 W
Osram (CFL) 5 W
80
60
40
20
0
1
3
5
7
9
11
13
15
17
19
21
23
Harmonic Order (n)
25
27
29
31
33
35
37
39
(b)
Fig. 6: Test results of Osram 4 W, 6 W LED bulbs and 5 W CFL: (a) Lamp current and voltage waveforms (b)
Individual harmonic spectrum
Table 7: Harmonic contents from a group of various wattage LED lamps and CFLs
Combination
LED lamps
CFLs
A
Philips 4 W + Osram 4 W
Philips 5 W + Osram 5 W
B
Philips 7 W + Osram 4 W + Osram 6 W +
Philips 5 W + Osram 5 W
Bright 5 W + Evenzo 3 W
C
Philips7 W + Osram 6 W + Bright 5 W +
Philips 5 W + Osram 5 W
Cash 7W + Evenzo 3 W
THDI (%)
79.12
87.03
87.57
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J. Appl. Sci. Res., 8(8): 4215-4221, 2012
Conclusion:
This paper has presented several experimental results on harmonic generation from LED lamps that are
currently being used for domestic, commercial and industrial lighting. In the experiments various types of LED
lamps from different manufactures were tested to evaluate their harmonic performance in terms of power rating,
type of ballast used and combination of various LED lamps. Furthermore a comparison of harmonic contents of
LED lamps and CFLs were also made. From the experiments it is fund that all LED bulbs generate harmonics
due to the use of power electronic converter as a ballast to drive LED arrays in the bulbs. The tested lamps
THDI values range between 30.94 % and 174.38 %. It is also noted that different manufactures of LED lamps
use diverse ballast technologies to reduce harmonic generation which includes ballast with passive filters, active
filters, and valley-filled circuit. When LED lamps with same ballast type are used together, the harmonic
generation remains almost constant dictated by the individual lamps. However, when LED lamps with different
ballast types are used together, the harmonic generation changes and found to be lower than the harmonic levels
generated by highest producer of harmonic in combined group. It is also noted that harmonic characteristics of
LED lamps and CFLs of equivalent wattage from same vendor depend on the type of ballast used. Finally, use
of LED lamps and CFLs together could provide lower harmonics than using only LED lamps and CFLs for
lighting applications.
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