Investigation of Harmonic Generation from Low Wattage LED Lamps

Transcription

1 Journal of Applied Sciences Research, 8(8): , 212 ISSN X This is a refereed journal and all articles are professionally screened and reviewed 4215 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, 436, 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 2% 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, 25; Huang et al., 27). 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., 21). 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., 29; Chen and Chung, 211; Qu et al., 211). A few contributions focus on harmonic emissions of LEDs lamps (Blanco and Parra, 21; Cuk et al., 21, Uddin et al., 212). 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., 29) 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, 26; Matvoz and Maksic, 28; Watson et al., 29). 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 harmonic standard (Std. IEC). Corresponding Author: Sohel Uddin, Department of Electrical, Electronics and System Engineering, Universiti Kebangsaan Malaysia, 436, Bangi, Selangor, Malaysia

2 J. Appl. Sci. Res., 8(8): , 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., 27). Fig. 1 depicts a block diagram of typical low-wattage LED ballast. It includes the AC line input voltage, typically VAC 5/6 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., 29), 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 V and have power consumptions rating of 3 W to 1 W. Table 1: Technical data for tested lamps. Trade Type Nominal Equivalent to Luminous Life name of power incandescent flux span lamp P (W) P (W) (lm) (Years) Philips Cool Daylight LED Philips Cool Daylight LED Philips Warm Daylight LED Osram Daylight LED Osram Daylight LED Osram Cool White LED Osram Warm White LED Osram Warm White LED Toshiba Cool White LED Bright cool White LED Cash Warm White LED Evenzo Cool White LED Philips Genic CFL Osram Duluxstar CFL 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 i3s current clamp, LED bulb(s) under test, and a personal computer to analyze the signals. Each lamp is kept switched on for 1 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.

3 J. Appl. Sci. Res., 8(8): , 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 standard described earlier. From Table 2, it can be noted that lamps having the trademark of Philips, have THD I 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 1 W Osram LED lamps, they produce the lowest THD I which is in the rage of 3 to 35 %. All other tested lamps have THD I value greater than 1 % as seen in Table 2. Table 2: Harmonic contents of single LED lamps Tested Harmonic (%) lamp Fund 3 rd 5 th 7 th 9 th THD I Philips 4 W Philips 5 W Philips 7 W Osram 4 W Osram 6 W Osram 8 W Osram 1 W Evenzo 3 W Bright 5 W Cash 7 W Toshiba 5.5 W

4 J. Appl. Sci. Res., 8(8): , No Filter Passive Filter Valley Fill Active Filter THD= % THD=15-11 % THD=63-7 % THD=3-35 % 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 THD I. For example combination-a produce less harmonics and combination-d produce high THD I 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 Harmonic (%) lamps P (W) Fund 3 rd 5 th 7 th 9 th THD I Table 4: Harmonic contents of group of 6 W LED lamps from Osram. No. of Power Harmonic (%) lamps P (W) Fund 3 rd 5 th 7 th 9 th THD I

5 J. Appl. Sci. Res., 8(8): , Table 5: Harmonic contents from group of various wattage LED lamps of Philips. Combination Total THD I of lamps power (W) (%) Philips 4 W-Osram 4 W Evenzo 3 W-Osram 3 W (a) Philips 4 W & Osram 4 W (THD=13.9 %) (b) Evenzo 3 W & Osram 3 W (THD=129.2 %) (c) 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 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 THD I (%) A Philips 5 W, Philips 7 W and Osram 8 W 4.9 B Philips 5 W, Philips 7 W, Osram 8 W, Bright 5 W and Cash 7 W 7.2 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 13.8 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.

6 J. Appl. Sci. Res., 8(8): , Philips (LED) 5 W Philips (CFL) 5 W Voltage Voltage (V) (a) 1 Philips (LED) 5 W 8 Philips (CFL) 5 W (b) Fig. 5: Test results of Philips 5 W LED bulbs and 5 W CFL: (a) Lamp current and voltage waveforms (b) Individual harmonic spectrum. 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 THD I value. From Table 7, it is clear that combination A generate the lowest THD I value equal to %. This value is lower than the THD I value of 16.4 % and 13.6 % 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 2 Voltage -2 Voltage (V) (a) 1 Osram (LED) 4 W 8 Osram (LED) 6 W Osram (CFL) 5 W (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 THD I (%) 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 87.3 Bright 5 W + Evenzo 3 W C Philips7 W + Osram 6 W + Bright 5 W + Cash 7W + Evenzo 3 W Philips 5 W + Osram 5 W 87.57

7 J. Appl. Sci. Res., 8(8): , 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 THD I values range between 3.94 % and %. 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. References Blanco, A.M. and E.E. Parra, 21. Effects of High Penetration of CFLs And LEDs on the Distribution Networks. In the Proceeding of the 14 th International Conference on Harmonics and Quality of Power, pp: 1-5. Chen, N. and H.S.H. Chung, 211. A Driving Technology for Retrofit LED Lamp for Fluorescent Lighting Fixtures with Electronic Ballasts. IEEE Transactions on Power Electronics, 26(2): Cuk, V., J.F.G. Cobben, W.L. Kling and R.B. Timens, 21. An Analysis of Diversity Factors Applied to Harmonic Emission Limits for Energy Saving Lamps. In the Proceeding of the 14 th International Conference on Harmonics and Quality of Power, pp: 1-6. DiLouie, C., 25. Advanced Lighting Controls: Energy Savings, Productivity, Technology and Applications. 1st Edn., Fairmont press. Dwyer, R., A.K. Khan, M. McGranaghan, L. Tang, R.K. McCluskey, R. Sung and T. Houy, Evaluation of Harmonic Impacts from Compact Fluorescent Lights on Distribution Systems. IEEE Transactions on Power System, 1(4): Gu, L., X. Ruan, M. Xu and K. Yao, 29. Means of Eliminating Electrolytic Capacitor in AC/DC Power Supplies for LED Lightings. IEEE Transactions on Power Electronics, 24(5): Huang, B.J., P.C. Hsu, M.S. Wu and C.W. Tang, 27. Study of System Dynamics Model and Control of a High-Power LED Lighting Luminaire. Energy, 32(11): accessed 29. Matvoz, D. and M. Maksic, 28. Impact of Compact Fluorescent Lamps on the Electric Power Network. In the Proceeding of the 13 th International Conference on Harmonics and Quality of Power, pp: 1-6. Munasinghe, K.D.A. and S.G. Abeyratne, 26. Power Quality and Harmonic Loads. In the Proceeding of the 1 st International Conference on Industrial and Information Systems, pp: Oliveira, A.A.M.D., T.B. Marchesan, A. Campos and R.N.D. Prado, 27. Distributed Emergency Lighting System LEDs Driven By Two Integrated Flyback Converters. In the Proceeding of the 42 nd Annual Meeting on Industry Applications Conference, pp: Qu, X., S.C. Wong and C.K. Tse, 211. Resonance Assisted Buck Converter for Offline Driving of Power LED Replacement Lamps. IEEE Transactions on Power Electronics, 26(2): Shareef, H., A. Mohamed and N. Marzuki, 29. Analysis of Ride Through Capability of Low-Wattage Fluorescent Lamps During Voltage Sags. International Review of Electrical Engineering, 4(5): Std. IEC , 29. Limits for Harmonic Current Emissions (Equipment Input Current 16A Per Phase). International Electrotechnical Commission (IEC). Uddin, S., H. Shareef, A. Mohamed and M.A. Hannan, 212. An Analysis of Harmonics from LED Lamps. In the Proceeding of the Asia-Pacific Symposium of Electromagnetic Compatibility, pp: Watson, N.R., T.L. Scott and S.J.J. Hirsch, 29. Implications for Distribution Networks of High Penetration of Compact Fluorescent Lamps. IEEE Transactions on Power Delivery, 24(3):