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A SINGLE STAGE ELECTRONIC BALLAST FAMILY FOR HIGH PRESSURE SODIUM LAMPS Dos Reis, F. S., IEEE Member; Clima, J. C. M.; Tonkoski Jr., R., IEEE Student Member; Maizonave, G. B., Ceccon, G. B., Bombardieri, A., Dos Reis, R. W. Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, Brazil. FENG – DEE – LEPUC f.dosreis@ieee.org Abstract – In the recent years many authors [1-4] are to be about thirty percent of total consumption of electrical working to obtain single stage HPF electronic ballast energy in the country. Because of these, innumerable for fluorescent and HID lamps to achieve cost research groups around the world, like [1-8], have reduction and to comply with international standard dedicated their efforts to the development of new requirements. Usually to obtain HPF in electronic topologies and new control techniques for different kinds ballast for high pressure sodium lamps a Power Factor of discharge lamps. Corrector (PFC) is used between the mains and the Most of magnetic ballast manufacturers had to develop electronic ballast [5]. In this paper will be reported the electronic ballasts for discharge lamps to guarantee their study and implementation of two single stage high survival in business because the consumers started to power factor (HPF) electronic ballasts for high demand more and more this type of product. It also pressure sodium (HPS) lamps using a LCC filter, one simplifies the production line, which has expressive using a half-bridge inverter and the second one using a physical reduction and productivity increase in relation the full-bridge inverter. The main idea in this work is to line that produces the conventional ballasts. Now, the present two simple electronic ballasts topologies with challenges for industries are the reduction of production HPF for HPS lamps working with a 220 V RMS mains costs, the reduction of converter size, unitary power factor voltage. Design criteria, simulation and experimental and null harmonic distortion which implies in a substantial results will be also presented. These topologies present improvement of energy quality consumed by ballasts. In some drawbacks like moderate THD, lamp power Brazil, the development of electronic ballasts for HID limitation once the converter works as a Buck inverter lamps is being made by a few groups of researchers. and it is not an ideal PFC. PF around .95 are easily However in a close future, these ballasts will be in the obtained. This paper intends to warn other researchers production lines of main national manufacturers. about these structures limitation, but may be an In the power electronics group of PUCRS (LEPUC) an interesting option for some applications. smart public illumination system was developed, where an electronic ballast with dimming capability is controlled by I. INTRODUCTION a central using SMS technology, this ballast, called Master, controls a whole neighborhood of slave ballasts Nowadays, an important topic of awareness is the thru a power line communication system. This system is importance of environment preservation. In this direction, presented on figure 1. important efforts have been made in the diverse areas of knowledge. In electrical engineering field, this phenomenon has reflected in searching for alternatives energy systems, higher efficiency on available resources utilization, losses reduction in equipments and to increase power quality. In the last few years the market was flooded by a great number of electronic ballasts for fluorescent lamps operating in high frequency, especially by compact fluorescent lamps. Its utilization was widely stimulated by Brazilian media for energy economy, due the fact that luminous efficiency increases with the frequency for this kind of lamp. Brazil faced a serious energy crisis in 2001. Many corrective actions were taken to mitigate this serious problem. One of them was the energy rationing which consisted in overtaxing or even cutting energy supply from consumers which exceeds the prefixed energy quotes. Also Figure 1. Smart Ilumination System proposed by LEPUC. many electric energy concessionaires had distributed gratuitously compact fluorescent lamps for residential The purpose of this paper is to report the development consumers, showing the importance of illumination’s of two low cost single stage HPF electronic ballasts for segment inside the global energy consumption, estimated HPS lamps for a 220 VRMS mains voltage developed for full bridge-inverter was also explored by the same authors utilization with this system. Each ballast was implemented in [10], in order to increase the available RMS lamp using a different converter topology. The design criteria voltage. The utilization of these topologies will be debated will be presented in this work for the proposed circuits. in this paper. There are many kind of high intensity discharge lamps; however, this work will focus only the high-pressure II. STUDIED ELECTRONIC BALLASTS sodium lamps (HPS), widely used in public illumination. The HPS lamps radiate energy on a great part of the visible Both studied single stage high power factor electronic spectrum. Those lamps provide a reasonable color ballast for high pressure sodium lamps structure reproduction (it has IRC 23 color reproduction index). incorporates a bridge rectifier and an input LC filter to They are available up to 130 lm/W of luminous efficiency minimize the EMI generated by the electronic ballast. Two and color temperature of 2100 K, approximately. inverters topologies were proposed to supply the HPS The HPS lamps, as any other HID lamps, need ballast to lamp, using this simple concept to avoid the utilization of operate correctly. The ballast is an additional equipment an external PFC. connected between the power line and the discharge lamp. Figure 3 shows the electrical diagram of the first The ballast has two main functions: to guarantee lamps proposed circuit. In this circuit it was proposed the ignition through the application of a high voltage pulse utilization of a half bridge inverter connected to the LCC between the lamp electrodes and to limit the current that filter. The capacitor CF in this figure has the main function will circulate through it. The lamp would be quickly of receive the reactive current from the electronic ballast. destroyed without current limitation, due the negative This arrangement provides high power factor to the resistance characteristic of the lamp, as can be observed in electronic ballast because in this case the capacitor CF is figure 2. not a bulk capacitor. Actually this is a small capacitor in The HPS lamps have many particularities when they the range of nano Faradays. operate in high frequency, such as: Can be modeled by a resistance in steady state; Can have luminous intensity controlled; The spectrum color reproduction can be modified; Presents the acoustic resonance phenomenon, which can result in the arc extinguishing until Fig. 3. Half Bridge HPF Electronic Ballast. the lamp destruction; The second electronic ballast studied used a full bridge inverter topology as showed in figure 4. The input stage of this topology has the same characteristic as the topology presented on figure 3. The main difference between HB and FB inverters topologies is the available RMS voltage applied to the LCC filter; this crucial difference will affect the application of the topology. Figure 2. - Typical voltage versus current curve for HID lamps. In order to achieve low cost electronic ballast for HPS lamps with HPF a single stage converter was conceived. Fig. 4. Full Bridge HPF Electronic Ballast. The idea is very simple: Once, in high frequency, the HPS lamps have a resistive behavior, why the electronic ballast III. BALLAST DESIGN EXAMPLE (inverter and LCC filter) can not be connected directly to the full bridge rectifier? This idea will be discussed in this To verify the performance of the proposed systems LCC paper. two electronic ballasts, one for a 250 W HPS lamp and In [9], it was studied the possibility of using this concept another for a 70 W HPS Lamp were designed. The applied to a half bridge (HB) inverter. Unfortunately, in nominal lamp voltage (Vlamp) was obtained from the this arrangement the half bridge inverter reduces the lamp’s manufacturer datasheet and its value is 100 VRMS available RMS lamp voltage and therefore, restricts the for the 250 W HPS Lamp and 70 VRMS for the 70W HPS maximum output power about 70 W for HPS lamps. The Lamp. The electronic ballast input power voltage comes from the output of an input bridge rectifier; consequently, this input voltage is mains dependent. In the present design 2 2 Vmains example the mains voltage adopted was considered to be V1stRMS _( FB ) 198,07 V (3) equal to Vmains= 220 VRMS. The switching frequency chosen was 68 kHz. Assuming the resistive comportment of the lamp, we can estimate the value of its resistance If we compare the available RMS voltage for each (Rx), where x represents the nominal power of the lamp, topology, for systems with same mains voltages, the full after ignition using equation 1. bridge topology will generate a higher RMS voltage value than the half bridge inverter as it was expected. As it can be observed in equation 2, the half bridge topology will Vlamp 2 1002 R250W 40 never generate the necessary voltage to achieve the lamp P 250W (1) full rated power, witch impossibilities the design of the HB ballast for most of 250 W HPS lamps with a 220 VRMS Vlamp 2 702 R70W 70 mains, so the half bridge topology is indicated for low P 70W power HPS lamps, where the necessary lamp RMS voltage is lower than 100 VRMS. Hence the topology chosen for where P is the lamps power. the 70 W HPS lamp was the half bridge (HB) one and for the 250 W HPS lamp was the Full Bridge (FB) one. As it was indicated in [5], the best relationship between In this study an expression was obtained to determine the switching frequency and the tank resonance frequency the peak voltage across the capacitor CP. This expression, before the lamp turn on is 0/s = 3, guaranteeing the high shown in equation (4), is valid before the lamp start up for voltage generation for the lamp ignition and limiting the the HB topology. For the FB topology the VCp would be peak current at the MOSFET to acceptable levels. If it was twice the value obtained for the HB converter. In this adopted to work at resonance 0 = s in theory we would design criteria sample the parameters would be only have the possibility of an infinite voltage generation over obtained for the HB topology, considering that for the full the lamp which could be good for a quickly lamp turn on. bridge topology there are no difference on this procedure, On the other hand current would also rise to infinite only some equations must be adequated for this case. because the impedance of the circuit formed by L, C S and 2 Vmains CP is null just before the lamp is turned on. This operation Vcp RESR (4) mode will result in the MOSFET’s and driver’s 1 e 4 L F destruction. Where, RESR is the circuit equivalent series resistance and F is the switching frequency. Preliminary tests demonstrated that necessary peak voltage (Vopk) to guarantee the lamp ignition is about 3.8 kV. A typical RESR value is 6.5 Ω. Manipulating equation (4) may be obtained the value of inductor L in equation (5) for the HB topology. Figure 5. Simplified circuit for the LCC Ballast. RESR L 4 F 219.5 H For the circuit showed in figure 5, in the case of a half 2E ln 1 bridge inverter, the voltage Ve is an asymmetrical wave Vopk (from 0 to Vpk sin (t)V). In the case of a full bridge (5) inverter, the voltage Ve is a symmetrical wave (from Vpk The resonance frequency may be calculated using sin (t) to - Vpk sin (t)V). A good simplification to equation (6). study the system behavior comes from the frequency 1 Fo domain approach. To use this approach the first harmonic 1 2 L component for this wave must be knew. Bum & Hee [5] 1 1 presented the first harmonic peak amplitude for a half C p Cs bridge inverter considering an ideal fixed DC bus voltage (6) (E). In the present case, the first harmonic peak amplitude Considering the fact that the switching frequency is was obtained using the same method but the DC bus estimated to be three times lesser then the resonance voltage (E) was replaced by the mains voltage resulting in frequency and, usually, capacitor CP is, at least, 10 times expression (2) for a half bridge inverter and in expression smaller then capacitor CS, equation 6 may be simplified (3) for a full bridge inverter. The experimental results into equation 7, because the effect of the capacitance C S is validate this procedure: almost null. 1 F 2 Vmains 6 L Cp V1stRMS _( HB ) 99, 035V (2) (7) Manipulating equation (7), it can be obtained the value GLCC (GLCC=70/99 =0.707), for different values of Kc as for the capacitor CP as it is shown in equation (8). design parameter. Using the graphic of figure 5, a Kc 1 =1/32 was adopted. This relationship will allow achieving Cp 2, 767nF 6 F the desired GLCC relationship in the frequency where the 2 L (8) lamp is turned on, hence after the start up the HID lamp is To determinate the real value of the RESR, an driven at rated power. experimental circuit using a 220 µH inductor L and a 2,7 nF capacitor CP was stimulated with a 60 V peak-to-peak square wave signal, which generated a 660 V signal over the lamp terminals, allowing the determination of RESR using equation 4. This RESR was obtained experimentally and its value was 6.5 Ω. Before the lamp startup a leakage current flows into the lamp. To determine the equivalent lamp resistance before the startup, the following measurement was made: a 10 Ω resistor was placed in series with the lamp. The obtained equivalent lamp resistance was 100kΩ. If this resistance is taken to account a new RESR = 5.7 Ω could be easily obtained. The reference [2] and our experimental results allow us to consider that after lamps ignition, the lamp resistance is too low considering the CP reactance. Therefore, it can be deduced the equation 9: Figure 7. LCC transfer function for different values of Kc. 1 // R R CP (9) With the Kc relationship, the value of CS may be obtained using equation 11 for a GLCC=0.707. Consequently, after lamp ignition, the equivalent circuit Cp 1 is showed in figure 6. Kc Cs Kc C p 89,17nF (12) L Cs Cs 32 Ve R IV. EXPERIMENTAL RESULTS Two prototypes, one using the HB topology and another Figure 6. – Ballast equivalent circuit after ignition. using the FB topology for 70 W and 250 W HPS lamps After lamp ignition the ballast must guaranty that RMS respectively were built. The main components and voltage over the lamp do not overcome the nominal value. parameters used in these implementations are shown in The RMS lamp voltage Vlamp can be obtained using the table 1. well known voltage divider, equation 10 presents this Table 1. Main components value and design parameters. result: FulL Bridge Half Bridge R Vlamp Vm Vmains 220 V 220 V Z (10) The modulus of the impedance of the circuit can be Fs 68 kHz 68 kHz calculated with equation 10, and is presented in equation 11. To simplify the design of the LCC filter the L 220 uH 220 uH parameterized LCSR circuit transfer function was obtained and the result is shown in figure 7. Cp 2,7 nF 2,7 nF 1 (11) G ( j , K c ) K c Cs 55 nF 90 nF 1 K c 2 2 Where Kc is the capacitor relationship factor defined as Fmains 60 Hz 60 Hz Kc = CS/CP, the relationship of switching frequency and resonance frequency of the circuit of figure 4, R is the lamp resistance after startup and τ is the parameterized A conventional SMPS power line filter with differential L 2 and common mode mitigation paths was used. The EMI time constant R Cp . Filter topology used is presented on Figure 8 and very Figure 7 presents the relationship between the RMS good results were obtained. Usually a capacitor between lamp voltage and the RMS first harmonic voltage, the line and the filter is used, in this project the input Vlamp/V1stRMS, called as parameterized lamp voltage gain capacitor was suppressed once it will block the PLC communications between the other units as schematized in Fig. 1. The experimental results are presented for the FB topology, since for the half bridge topology the results obtained are similar. Figure 8. Topology of the EMI Filter used. In figure 9, voltage and current in the mains are shown for the FB ballast. It may be observed that the voltage and current in these waveforms have almost null displacement Figure. 10. Voltage and current in the lamp in a low factor. The current waveform presented would be similar frequency period. to a usual converter operating in the discontinuous conduction mode if no EMI filter was used. With the waveforms presented in figure 7, the power factor was calculated and the value found is PF=0.98, which would be in conformity with all known ballast standards. Figure 11. Voltage in the DC bus and current in the output of the rectifiert. Figure 12 presents the harmonic components for the voltage waveform presented in figure 7. The presence of the third, fitth and seventh harmonic components in the Figure. 9. Voltage (200 V/Div.) and Current (2 A/Div.) in the mains. mains is observed. The THD obtained was 2,49 %. According to IEEE Std. 519-1992, the THD expected in In figure 10 is showed the lamp’s voltage and current. It the mains is below 5%. The current waveform may be observed that nearby each zero crossing, the lamp decomposition in harmonic components from the ballast is turned off and on, as well as it happens with regular proposed is shown in figure 13. It was found a moderated electromagnetic ballasts. This phenomenon is attributed to harmonic content, the THD obtained was 19,83%, the non-linear lamps characteristic. During this period the considering the IEC 61000-3-2, the fifth and seventieth lamp is reigniting because the voltage available was too harmonic component exceeds the indicated limits for class low to keep the arc in the lamp, so the lamp is turned off. C equipments. For the fifth harmonic, the limit indicated is This phenomenon reflects into the input current waveform, 10 % and for the seventieth is 3 %. where in each beginning of semi cycle the current goes nearby zero causing a flattening in the waveform. The crest factor obtained was around 2. In Figure 11 is shown the voltage in the DC bus, where it may be observed that voltage goes close to zero what causes the extinction of the lamp’s arc. In the same figure it is observed the current in the output of the rectifier. Figure 12. Harmonics present in the mains voltage. VIII. REFERENCES [1] Tsai-Fu Wu; Te-Hung Yu; Meng-Chian Chiang; “Single- stage electronic ballast with dimming feature and unity power factor”; Power Electronics, IEEE Transactions on , Volume: 13 , Issue: 3 , May 1998; Pages:586 – 597. [2] Ribas, J.; Alonso, J.M.; Calleja, A.J.; Lopez, E.; Cardesin, J.; Garcia, J.; Rico, M.; “Single-stage high-power-factor self- oscillating electronic ballast for fluorescent lamps with rapid start”; Power Electronics Congress, 2002. Technical Proceedings. CIEP 2002. VIII IEEE International , 20-24 Oct. 2002 Pages:15 – 20. [3] Martin, F.J.F.; Viejo, C.B.; Anton, J.C.A.; Garcia, M.A.P.; Figure 13. Harmonics present in the input current. Rico-Secades, M.; Alonso, J.M.; “Analysis and design of a high power factor, single-stage electronic ballast for high-intensity VI. CONCLUSION discharge lamps”; Power Electronics, IEEE Transactions on , Volume: 18, Issue: 2, March 2003; Pages:558 – 569. [4] Co, M.A.; Brumatti, M.; Simonetti, D.S.L.; Vieira, J.L.F.; The half bridge topology will never generate the “Single stage electronic ballast for HID lamps”; Industry necessary voltage to achieve the lamp full rated power 250 Applications Conference, 2003. 38th IAS Annual Meeting. W with a 220 VRMS mains, witch impossibilities the design Conference Record of the , Volume: 1 , 12-16 Oct. 2003; of these ballast in this case, in this case the full bridge Pages:339 - 344 vol.1 topology will generate the necessary voltage for to a high [5] Bum Suk Kang; Hee Jun Kim; High Power Factor power HPS lamp. The half bridge topology is suitable for Electronic Ballast for High Pressure Sodium Lamp, TENCON lamps less than 250 W once the main restriction is the 99. Proceedings of the IEEE Region 10 Conference, Volume: 2, available RMS voltage. This paper described a single stage Dec 1999, Page(s): 887 -890 vol.2. high power factor electronic ballast for high pressure [6] Ben Yaakov, S.; Gulko, M.; “Design and performance of an electronic ballast for high-pressure sodium (HPS) lamps, sodium lamps using half and full bridge inverter. This Industrial Electronics”, IEEE Transactions on Volume: 44 Issue: ballast presents a very low cost because it avoids an 4, Aug 1997, Page(s): 486 -491. external PFP. [7] Alves, J.A.; Perin, A.J.; Barbi, I.; “An electronic ballast The behavior of the full bridge topology and the half with high power factor for compact fluorescent lamps”; Industry bridge topology achieved was similar. The phenomenon of Applications Conference, 1996. Thirty-First IAS Annual the acoustic resonance was not observed, maybe because Meeting, IAS '96., Conference Record of the 1996 IEEE the lamp was excited by a modulated power signal, ,Volume: 4 , 6-10 Oct. 1996; Pages:2129 - 2135 vol.4. however an investigation on this subject is encouraged . A [8] Prado, R.N.D.; Bonafldo, S.A.; “A high-power-factor very high power factor was obtained. The crest factor electronic ballast using a flyback push-pull integrated converter”; Industrial Electronics, IEEE Transactions on ,Volume: 46 , found was not good enough considering fluorescent lamps, Issue: 4 , Aug. 1999; Pages:796 – 802. however for HPS lamps this crest factor is not considered [9] Dos Reis, F.S., Canalli, V.M, Lima, J. C., Tonkoski, R. Jr., critical. Sarmanho, U, Edar, F., Santos, Toss, M, Ramos, F.M., Garcia, L.L., Callai, P., Da Silva, N. B.R, Godinho, L.A., Líbano, F.B., VII. ACKNOWLEDGEMENT Low Cost High Power Factor Electronic Ballast For High Pressure Sodium Lamps, VI Induscon, Joinville, 2004. The authors gratefully acknowledge the support to this [10] Dos Reis, F.; Tonkoski, R.; Maizonave, G.B.; Lorenzoni, work provided by INTRAL S.A. (Ballast and Fixture L.C.; Sarmanho, U.; Ceccon, G.B..; Lima, J.C.M.. ” Full Bridge Manufacturer), LEPUC (Power Electronic Laboratory Single Stage Electronic Ballast for a 250 W High Pressure Sodium Lamp”, IEEE 36th Conference of Power Electronics PUC), CEEE (Companhia Estadual de Energia Elétrica) Specialists, Recife, 2005, Page(s):1094 – 1099. and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior).