ACOUSTICAL RESONANCE AVOIDANCE FOR METAL HALIDE LAMPS

Transcription

1 ACOUSTICAL RESONANCE AVOIDANCE FOR METAL HALIDE LAMPS Fernando Soares dos Reis* Reinaldo Tonkoski Jr. Gert Bolten Maizonave Anderson S. dos Santos Marcelo Toss Pontifícia Universidade Católica do Rio Grande do Sul PUCRS Department of Electrical Engineering Av. Ipiranga, Porto Alegre, RS BRASIL Phone: (+55 51) / 224 Fax: (+55 51) Topic Area: Power Electronics Subject Area: Power Electronic Devices and Systems Keywords: Acoustical Resonance, Electronic Ballasts, MH lamps and Resonant Filters.

2 ACOUSTICAL RESONANCE AVOIDANCE FOR METAL HALIDE LAMPS Pontifícia Universidade Católica do Rio Grande do Sul PUCRS Department of Electrical Engineering Av. Ipiranga, Porto Alegre, RS BRASIL Phone: (+55 51) / 224 Fax: (+55 51) Abstract This paper presents analysis, design and implementation of a high frequency electronic ballast for metal halide lamps. Extensive experiments using resonant electronic ballast have been performed on 70W metal halide lamps to investigate different control methods for avoiding the phenomenon known as acoustic resonance. A high frequency ballast, capable of operating lamps from different manufacturers, was developed for test the methods.

3 ACOUSTICAL RESONANCE AVOIDANCE FOR METAL HALIDE LAMPS F. S. Dos Reis, M. Toss, A. S. dos Santos, G. B. Maizonave and R. Tonkoski Jr. Pontifícia Universidade Católica do Rio Grande do Sul - PUCRS Department of Electrical Engineering Porto Alegre, RS - BRASIL f.dosreis@ieee.org Abstract-This paper presents analysis, design and implementation of a high frequency electronic ballast for metal halide lamps. Extensive experiments using resonant electronic ballast have been performed on 70W metal halide lamps to investigate different control methods for avoiding the phenomenon known as acoustic resonance. A high frequency ballast, capable of operating lamps from different manufacturers, was developed for test the methods. solutions are the following: Keywords: Acoustical Resonance, Electronic Ballasts, MH lamps and Resonant Filters. I. INTRODUCTION Metal halide lamps have attracted much attention in recent years, because they offer excellent color rendition, long life and compact volume, in contrast to fluorescent lamps and incandescent lamps. Similarly to fluorescent lamps, the HID lamps present negative impedance effect and the need for using some currentlimiting device. The electromagnetic ballast can be used; however, it has high weight and size, poor regulation and great sensibility to line voltage fluctuation [3, 4]. In principle, the use of high frequency electronic ballast can reduce the size and the weight of the ballast and improve the system efficacy. This feature is especially attractive for low-wattage HID lamps because the overall lighting package is expected to be small-sized. However, the operation of high-pressure HID lamps with high-frequency current waveforms is hampered by the occurrence of stationary pressure waves called acoustical resonance. The phenomenon of acoustical resonance is characteristic of the HID lamps operating at frequencies higher than 1 khz and they appear when the modulation of the power in the lamp exceeds a threshold value. Figure 1 illustrates this phenomenon. The arc distortion causes fluctuation on the emitted light, variation of the color temperature, variation of lamp voltage and, in worst cases, rupture of the discharge tube [1]. Many ballast circuit topologies or control methods [3-5] have been proposed to avoid instability caused by acoustic resonance. There are basically two proposed Figure 1: Acoustic resonance phenomenon. 1) Operation at frequencies free of acoustic resonance. Typical ballasts used in this approach can be: Low frequency ballast: it is based on the fact that there isn t acoustic resonance in frequency below 1 khz [6]. The disadvantages of this method are the circuit complexity of and low efficiency. Tuned high-frequency ballast: requires fore determination of the zone which is free acoustic resonance. It is however very difficult to select the same window for all lamps marked because the acoustical resonance is a function of tube geometry, gas density and temperature [3]. It also varies with manufacturing tolerance and with lamp age [4]. Extra high-frequency ballast: referring to the operation above the maximum resonance frequency range. The disadvantages of this method are the high losses in the switching components and EMI problems because the high frequency discharge arc is a powerful noise-radiating antenna [5]. Real-time auto tracking system: it is the same idea of tuned high-frequency, the difference is that the realtime auto tracking system detects the acoustic resonance and changes the frequency. The main problem of this method is detecting low intensity acoustic resonance, because the changes on the electrical parameters are very little, and therefore hard to detect [6].

4 2) Distribute the lamp power spectrum so that the lamp power at the acoustic resonance frequency may not exceed the threshold value. Typical ballast used in this approach can be: Modulation of the switching frequency ballast: this concept consists of changing the frequency in order to keep the lamp input energy distributed over a frequency range. Ideally this should be done in a frequency range where acoustical resonance is not usually observed. Modulation of phase angle ballast: It bases on the idea that constant phase variation disrupts the excitation of acoustic resonance. The disadvantage of this method is the higher current in each phase jump [6]. Non-sinusoidal voltage in the lamp ballast: the concept is used a high frequency square-wave operation for distributing power spectrum in a theoretically infinite number of harmonics. The problem is the limitation of lower order harmonics and electromagnetic interference (EMI) problems. Comparing the advantages and disadvantages of the mentioned techniques for eliminating the acoustic resonance, it can be said that the concepts of tuned high-frequency together with modulation of the switching frequency represents the best choice, because the ballast and control circuitry is simple and inexpensive. This paper is organized as follows. Section II presents a description of the proposed ballast. Section III shows a study about the zones free of acoustic resonance for 70W halide lamps from different manufacturers. Section IV demonstrates the modulation technique for the ballast s switching frequency, used for avoiding the acoustic resonance phenomenon. The conclusions of this work are presented in section V. II. THE HALF BRIDGE LCC BALLAST advantage that the output voltage can be regulated for applied high voltage in start up the HID lamps. The resonant filter circuit design was made based on a method described in [7]. This calculation assumes that the lamp is a pure resistance, as stated previously [2]. Using the drive makes possible to manually change the frequency on the lamp to check the zone free acoustical resonance and testing the concept of modulation of the ballast s switching frequency. III. EXPERIMENTAL RESULTS A 75W High Pressure Metal Halide Lamp ballast prototype was built in order to verify the influence of the proposed frequency modulation system in reducing the acoustical resonance phenomenon, Figure 3 shows this prototype. This work was accomplished as a joint effort between one of the largest ballast companies in this country and the university. The final commercial package is shown in Figure 4. A great degree of integration was achieved, as one can observe, thanks to the use of SMD (Surface Mounting Design) in the control and drive circuitry, which is not shown in figure 4. Figure 3: Assembled prototype. The obtained experimental results from this prototype will be now presented. The ballast was implemented using a LCC filter, as shown in figure 2. The chosen topology is the half bridge inverter using a resonant LC series C parallel, as can be seen on Figure 2. D1 S1 + Ls E DRIVE - Cs D2 Cs Lamp S2 Figure 2. High frequency inverter with resonant circuit. The LC series C parallel resonant converter has the Figure 4: Commercial package. For the measurement of the lamp ignition voltage, a high-voltage probe is essential, because the lamp peak voltage can be higher than 5 kv. The obtained results, depicted in figure 5, where obtained, for three different lamp manufacturers, using a Tektronics P6015A voltage probe, and an Tektronics THS720P oscilloscope, as it shown in Figure 6.

5 1 > C H 2 Pk-Pk 2.64kV The voltage, the current and the power waveforms in the lamp, after lamp ignition are shown in figure X3, in blue, red and green, respectively. The voltage waveform is almost sinusoidal, and the current is in phase with it, and the instantaneous power (green) waveform also demonstrates the resistive characteristic of the HID MHL in high frequencies. 1) Ch 2: 500 Volt 100 ms C H 2 Pk-Pk 2.98kV 1 > 12 3 > 1) Ch 2: 500 Volt 100 ms 1) Ch 1: 50 Volt 20 us 2) Ch 2: 1 A 20 us 3) Math: 500 W 20 us Figure 7: Voltage, current and power waveforms. 1 > 1) Ch 2: 500 Volt 100 ms C H 2 Pk-Pk 800kV Figure 5: Lamp ignition waveform for 3 different lamp manufacturers. Figure 6: Measurement apparatus. IV. THE ACOUSTICAL RESONANCE-FREE ZONE Richard Redl and Jon D. P. state in reference [3], that there exist frequency ranges free of acoustical resonance inside these frequencies for HID MHL: khz, khz and >1 MHz. A wide experimental evaluation study has been accomplished in this work in order to determinate these resonancefree zones. Figure 8 shows the results for lamps from five different lamp manufacturers. The proposed inverter in Section II was used to determine the frequency ranges free of acoustical resonance. This was accomplished by inspection of the light in the bulb, while slightly changing ballast frequency. As one can see, the resonance-free zones are very narrow and their positions very model-dependant. From Figure 8 one may remark that, there really are those zones; however, there are no single regions which are totally free of acoustical resonance, in the studied frequency range. The chosen range was from 18 to 28 khz, because lower frequencies imply audible noise, and in higher ones there are problems with increasing commutation losses in the switching components and electromagnetic interference (EMI). The absence of such a resonance-free zone in the adopted frequency range made necessary finding an effective way of avoiding the phenomenon for the various lamp models available in market.

6 V. MODULATION OF THE SWITCHING FREQUENCY VI. CONCLUSION In order to avoid acoustical resonance, a frequency modulation technique was applied to the ballast drive. This technique consists on applying a two-level discrete frequency changing modulation surrounding the central frequency of 22.5 khz. Different modulation tones were used, from 1 to 11 khz. In the performed tests, the ballast was turned on and the frequency was adjusted first for light and then for heavy acoustical resonance. When the lamp is under light acoustical resonance the modulation of the switching frequency completely avoids the resonance. However, when the lamp is under heavy acoustical resonance the modulation is not enough for completely eliminate the resonance. For all tested lamps, the windows with and without acoustical resonance is large (18 khz to 25 khz). Figure 9 shows that modulation tones above 9 khz result in complete absence of visual acoustical resonance. For this reason the modulation of the switching frequency represents a reasonable approach in solving the problem of acoustic resonance. This paper presented a ballast circuit for HID lamps with acoustic resonance avoidance. More recently, HID sources, especially metal halide (MH), have been used in small retail and residential environments. HID lamps produce a large quantity of light in a small package in comparison with incandescent and fluorescent sources. HID lighting is typically used when high levels of light are required over large areas and when energy efficiency and/or long life are desired. The methods for avoiding the resonance are studied and the low cost and efficient method was select. A prototype was implemented to validate the proposed methods. Comparisons between the different types of light bulbs had been carried through and made possible to justify the choice of the HID MH lamp as focus of the present study, because of its excellent features. Simultaneously to the study of the acoustic resonance, a design method for the LCC filter was elaborated this design criteria will be presented in the final paper as well as more experimental results. Figure 8. Obtained ranges for safe operation with some 70W MH lamps.

7 Frequency [khz] Figure 9. Tone s frequency influence in the acoustical resonance mitigation, for the same respective studied above manufacturers. Green areas are free of acoustical resonance for all lamp manufacturers, white areas are free of this effect for some lamp builders, and red areas showed low intensity resonance for some lamp manufacturers. Prototype ballast was implemented and made possible to carry through frequency scan, in order to verify the existence of acoustic resonance-free zones, in the main marks of HID MH lamps commercialized in the Brazilian market. Since it was not possible to find a single frequency or interval of frequencies free of acoustic resonance, which is common to all the lamps, a method of resonance elimination was implemented, using a twotone frequency operation mode. For the validation of such method, experimental verifications were made using the HID MH lamps commercialized in the Brazilian market. This study made possible to establish an effective modulation index, with which it was possible to obtain the total elimination of the visual acoustic-resonance, for all lamps analyzed. VII. REFERENCES [1] J. J. de Groot, J. M. van Vliet. The high pressure sodium lamp, Philips Technical Library, Macmillan Education, [2] T. J. Liang, K. H. Su and W. H. Fu. High Frequency Electrical Circuit Model of Metal Halide Lamp. IEEE, pp [3] Richard Redl and Jon D. P. A New High Frequency and High Efficiency Ballast for HID Lamps: Topology, Analysis, Design, and Experimental Results. APEC [4] J.Zhou, L. Ma, Z. Qian and K. Hong, Acoustical Resonance in High Intensity Discharge Lamps and its Possible Solutions, 97 International Symposium on Green Lights in China, pp , [5] J. Zhou, F. Tao, F. C. Lee, N. Onishi and M. Okawa, High Power Density Electronic Ballast for HID Lamps IEEE, pp , [6] A. S. André, A. J. Perin, C. C. Tavares and J. Moia, Electronic Ballast for High-Pressure Sodium Lamps with Acoustic Resonance Avoidance. COPEB [1] [7]F. E. Bisogno, A. R. Seidel, R. Holsbach and R. N. do Prado, Resonant Filter Applications in Electronic Ballast. IEEE, pp , 2002.