White-Noise Modulation of High-Frequency High-Intensity ...

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS. VOL 34. NO. 3. MAY/JUNE 1998 597

White-Noise Modulation of High-Frequency High-Intensity Discharge Lamp Ballasts

Laszlo Laskai, Senior Member, IEEE, Prasad N. Enjeti, Senior Member, IEEE, and Ira J. Pitel, Senior Member, IEEE

Abstract-In this paper, a new method is proposed to avoid acoustic-resonance-related instabilities in metal halide lamps when operated with a high-frequency electronic ballast. Angle modulation of the inverter switching pattern has been used as a vehicle to randomize lamp driving frequency and to limit lamp power spectrum below the instability threshold. The optimal modulating pattern is obtained by studying the angle-modulated spectra by periodic and random signals. Analysis is supported by simulations and verified experimentally with the ballasting of 250-W lamps.

Index Terms-Acoustic resonance, ballast, high-intensity dis- charge lamp, metal halide lamp, white-noise modulation.

I. INTK~DUCTI~N N 0 FLICKER, improved lumen maintenance, control over lamp power and light color, longer lifetime, and smaller

and lighter ballasts are some of the advantages for driving metal halide and other high-intensity discharge (HID) lamps from a high-frequency source [l], [2], [13]. Nevertheless, due to the occurrence of acoustic resonances, high-frequency ballasting of HID lamps has been a major challenge.

The acoustic-resonance-related instabilities are rather well described theoretically [2]-[8]. The periodic input power and the subsequent energy exchange by elastic collisions be- tween charged particles and neutral gas are the source of pressure perturbations. As the input frequency is increased. and an eigenfrequency is approached, a pressure-wave mode becomes propagational, which, in turn, perturbs the discharge path. Lamp properties that determine the eigenfrequencies are known to vary with manufacturing tolerances (different geometry or filling) and by lamp age.

Apart from lamp-related factors, which can be optimized to reduce resonances [2], [ 141, innovative ballasting methods are needed to make high-frequency operation possible with existing lamps. Tuned high-frequency operation requires the knowledge of resonance-free zones and, to operate in these

Paper MSDAD 97-I, presented at the 1994 Industry Applications Society Annual Meeting, Denver CO, October 2-7, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Production and Application of Light Committee of the IEEE Industry Applications Society. Manuscript released for publication May 19, 1997.

L. Laskai was with the Department of Electrical Engineering, Texas A&M University, College Station, TX 77843-3148 USA. He is now with Corporate Research and Development, General Electric Company, Schenectady, NY 12301 USA (e-mail: [email protected]).

P. N. Enjeti is with the Department of Electrical Engineering, Texas A&M University, College Station. TX 77843-3148 USA (e-mail: en- [email protected]).

I. J Pitel is wth Magna-Power Electronics, Inc., Boonton. NJ 07005 USA (e-mail: [email protected]).

Pubhsher Item Identifier S 0093-9994(98)03878-X.

zones, resonant frequencies must be known and repeatable between different lamps and manufacturers. Considering all factors involved, it is not practical to operate HID lamps without some form of ameliorative measure.

Lamp power spectrum spreading is one way to prevent acoustic resonances, since generation of acoustic waves occurs only if the sound-wave source is sufficiently high in the sensi- tive frequency region. A nonsinusoidal lamp voltage [9]-[ 111, for instance, a square-wave voltage or an angle-modulated lamp voltage [lo], [12]-[15], has such a distributed power spectrum. Square-wave operation distributes lamp spectra in a theoretically infinite number of harmonics. Still, disadvantages to this approach are limited power specwal term reduction in lower order harmonics and aggravated electromagnetic interference problems.

Angle modulation, an alternative, is well contained [IS], [ 191. Wide-band frequency modulation [ 13]-[ 151 and phase- shift keying [ 121, with predetermined modulating patterns, have been utilized to prevent lamp instabilities of a given type. However, these modulations are not adequate to prevent instabilities for all lamps of a given power rating made by various manufacturers.

In response to these concerns, this paper proposes a new method of stabilizing high-frequency operation of metal halide lamps. The proposed method limits lamp power spectrum below an instability threshold by randomizing the inverter frequency. Randomization of the switching pattern, by way of angle modulation or by randomization of the pulse position or the pulsewidth, has been used to reduce acoustic noise in motors and EM1 in switching power supplies [21]-[24].

Angle-modulation process with random noise produces a power density spectrum that is proportional to the first-order probability density of the modulating noise. When lamp volt- age (or current) frequency is modulated by random noise, lamp power spectral density is continuous with low amplitude and narrow bandwidth. This allows the use of high (2 resonant inverters, preferred in electronic ballasting.

The proposed method retains all the advantages of conven- tional pulsewidth modulation (PWM), that is, real-time control, linear operation, good transient response, and it contributes to reduced EM1 in the ballast.

In Section II of this paper, spectral behavior of angle- modulated waves with periodical modulation is investigated. In Section Ill, the proposed random modulations are discussed and compared to periodical modulations. Experimental results of the prototype ballast [ 151 and practical implemenration issues in Section IV conclude the paper.

0093-9994/98$10.00 0 1998 IEEE

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 34. NO. 3. MAY/JUNE 1998

YHI 4 1caPa lXl* rn". Frequency

(a) (b)

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Cc) Fig. 1. Nornuked amplitude spectra of (a) an unmodulated wave (/I = 0) and two angle-modulated waves (b) I, > 10 and (c) 1, = 50

II. ANGLE MODULATION WITH PERIODIC SIGNALS

We shall first consider the spectral characteristics of angle- modulated waves by periodic signals. Several periodic mod- ulating patterns shall be examined, with the objective of finding the optimal periodic modulating pattern. The desired pattern is determined by the spectra1 behavior of the modulated wave, that is, spectral density distribution, maximum spectral components, and required bandwidth.

(-x’ < t < x)), and its integrable as (v(t)/ in (--30, xj) [16], [ 171. Hence, the amplitude spectral density V(f) is defined as a Fourier transform of the modulated wave v(t):

s

32 V(f) = v(t)e-+tdt (2)

-z-a

The spectra1 behavior of the modulated wave by standard modulating patterns, such as sine wave, square wave, trian- gular, and saw tooth, have been investigated in prior research [12]-[15].

where w(= 2~,f) is the modulated wave angular frequency. Further, in the interval (O,T), the average power spectral density S,(f), across unit resistance load, is

The commonly used description of a sinusoidal angle- where IV(f)1 denotes the modulus of the amplitude spectrum modulated wave is vu 1.

v(t) = A0 cos Q(t) where Q(t) = w,t - @(t) (1)

where the instantaneous phase Q(t) or Q(t) contains the modulating signal A0 is a constant, t represents time, and LJ, is the angular frequency of the carrier, in this case, lamp voltage (or lamp current) [16]-[19].

A. Angle Modulation by Sine Wave

The power spectrum density S,,(f) of an angle-modulated wave modulated by a sinusoidal modulating signal v,,,(t) = Z30 cos w,t, for sufficiently small frequency deviations and slow sweeps about the carrier frequency, is

Phase and frequency modulations are two closely related angle-modulation methods. In the case of phase modulation, the modulating signal is directly proportional to the instanta- neous phase Q(t) or Q(t), and for frequency modulation, the modulating signal is directly proportional to the first derivative of Q(t) or CD(t). where

To study spectra1 behavior of the modulated wave v(t) in steady state, we shall define its amplitude spectra1 density V(f) and its average power spectral density S,(f), assuming that, in mathematical terms, v(t) is a real function, defined over

& nl = 1 for m = 1 E - 2 77L - for m # I

CL = PsAl or CL = CLF~I.

LASKAI rr ul.: WHITE-NOISE MODULATION OF HIGH-FREQUENCY HID LAMP BALLASTS 599

modulation index, p

Fig. 2. Normalized maximum term versus modulating index

For phase and frequency modulations LL~A~ and PFhI, the modulation index p is defined as

where D+ and DF represent constants. Typical spectra for several modulation indices are shown in Fig. I. Observe the relationship between amplitude of the power spectrum to the modulation index.

The average power of the modulated wave

is independent with angle modulation; however, carrier and sidebands, spaced at fc i mf,, can vary. According to (4), the magnitude of the spectral terms is determined by &(p), denoting Bessel functions of the first kind. Fig. 2 illustrates the impact of the modulation index increase on the maximum spectral term 1 S, (f ) 1 ,l,aX.

The maximum spectral term, which can excite an acoustic resonance, can be minimized by making p > 10. For the theoretical limit case [17], or CL + co, the power spectra is

(8)

as illustrated in Fig. 3(a). In summary, wideband sine-wave modulations lead to uneven spectral distributions.

According to (4), angle-modulated spectra require an infinite bandwidth. In practice, according to Carson’s estimate, 98% of the total power is contained in a bandwidth determined by the maximum frequency deviation and maximum frequency of the modulating signal [ 161. For wide-band modulations, the required bandwidth is

for phase and frequency modulations, respectively. If the maximum frequency deviation is held constant, a

decrease in modulating frequency fa carries a proportional

/ 1 /

(a) (b) Cc) Fig. 1. Limiting spectra for (a) sine wave, (b) square wave, and (c) sym metrical sweep or saw tooth.

decrease in bandwidth. This is an obvious conclusion from (9) for phase modulations. In a similar manner, the same principle applies to a frequency-modulated spectrum, since the modulating index, (6), is inversely proportional to the modulating frequency.

Fig. 4 shows the experimental current waveforms for pe- riodic modulations. Sine-wave modulated lamp current and its amplitude spectrum are shown in Fig. 4(a) and (b). It has been experimentally determined that a tenfold reduction in the maximum current spectral term is necessary to stabilize all trial lamps. To obtain this reduction, the required bandwidth for sine-wave modulating signal was BWFI\,~ = 35 kHz @FhI z 170 and fa = 100 Hz).

The choice of center frequency had no bearing on the results; it was varied in the range of 2040 kHz, a range limited by our setup. For the depicted spectrum, the center frequency was tuned to keep the power spectrum just above the audio range. Note that the pressure driving frequency is twice the supply frequency, since the average rate of energy absorbed by electrons is proportional to the square of the input voltage [4]. For sine-wave modulations, this means that, by distributing energy in the 1742-kHz frequency range, we are preventing pressure perturbances in the 34-84-kHz range.

One disadvantage of such a wide bandwidth, noticeable in Fig. 4(b), is undesirable amplitude modulation. Resonant networks, which are frequently used in high-frequency ballast for impedance matching, attenuate spectral components un- evenly. This can cause high-current crest factors in the lamp and shorten lamp life.

B. Angle Modulation by a Square Wuve

As previously discussed, we wish to estimate the spectral behavior for high-modulation indices. Due to similarities in phase- and frequency-modulated spectra, as highlighted in the previous section, we shall consider only the frequency- modulated spectrum. Fig. 5 shows a typical amplitude spec- trum obtained by simulations for CLFhI = 20. As ,+fil i w, the FM wave spectral density becomes

So(f)FlvI = ${6[f - (fc - bFhIfa)]

+ s[f - (fc + ~Fhlfa)j) (11)

where To( = 27r/wa) is the square-wave signal period. The lim- iting form spectrum is illustrated in Fig. 3(b). Theoretically, all energy is in two delta pulses at the boundaries of the required

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 34. NO. 3. MAY/JUNE 1998

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Fig. 4 Experimental lamp current waveforms: (a) and (b) for sine-wave modulating signal; (c) and (d) for square-wave modulating signal; and (e) and (f) for symmetrical sweep. (For all time-domain waveforms horizontal scale: 2 ms/div and vertical scale: I A/div; for all frequency-domain waveforms horizontal scale: 5 kHz/div and vertical scale: 0.1 Aldiv.)

LASKAI ~‘1 u/ WHITE-NOISE MODULATION OF HIGH-FREQUENCY HID LAMP BALLASTS 601

V(f) IV(f)

04

5K 6K IOK

Frequency 12K 14K 15K

Fig. 5. Typical square-wave-modulated amplitude spectrum (/tt.~~ = 20)

5& 6K 8K 1OK 12K 14K 15K

Frequency

Fig. 6. Amplitude spectrum for symmetrical sweep (/(I.RI = 20)

bandwidth. Somewhat better distribution can be achieved with a more complex or random sequence [ 121, [ 161, [20].

Experimental waveforms are shown in Fig. 4(c) and (d). For a tenfold maximum current spectral term reduction, the required bandwidth is BWF~~ = 30 kHz (fa = 100 Hz). This shows little benefit over sine-wave angle modulations.

C. Modulation by Saw Tooth or Symmetrical Sweep

Frequency modulations by a saw tooth or a symmetrical sweep produce a similar spectrum. A typical amplitude spec- trum for symmetrical sweep, shown in Fig. 6, suggests an even power distribution and a well-utilized bandwidth. As PFhr + w, the spectral density for both modulating signals, shown in Fig. 3(c), becomes

where pyhrfa represents the maximum frequency deviation, and w~(= 27r/To) is the modulating signal frequency. Accord- ing to (12), the modulation index increase is proportional to the maximum amplitude decrease; unlike for sine-wave-modulated spectra, this relationship is linear.

Experimental results, illustrated in Fig. 4(e) and (f), show a 50% reduction in bandwidth over that of sine-wave mod- ulation.

Fig. 7. Spectrum of band-limited white noise and correlated FM wave spectrum.

III. PROPOSED BAND-LIMITED WHITE-NOISE MODULATIONS

Angle-modulated spectrum, produced through intermodula- tion by carrier and periodic modulating signal, as described in (4) for sine-wave modulations (Fig. l), has a discrete spectral density. When random noise is the modulating signal, which has a continuous spectrum, in addition to carrier- related discrete term, the principal part of the angle-modulated spectrum is continuous.

Strictly speaking, amplitude and power spectral densities V(f) and S,(f), as defined in (2) and (3) do not exist for random processes, since integral in (2) does not converge as t + LIZ,. However, this can be circumvented in mathematical terms by utilizing the Wiener-Khintchine relationship between autocorrelation function R\.(t) of a random process V(t), defined as

R\-(T) = E{V(t)V(t + 7)) (13)

where E(e) denotes the expected value operator and power spectral density function S,(f). According to this relationship,

S,(f) = F{&,(T)} = 11 RL+),-jdT dr. (14)

Power spectral density function S,(f) is defined as the Fourier transform of the autocorrelation function RL, (t).

While the mathematical tools for analysis of the angle modulations by random processes change from before, as noise is described in terms of statistical properties, essential properties, such as one estimated by Carson’s rule, remain the same.

According to the principle of adiabatic frequency sweeps [ 171, for large modulation indices, the power density of the angle-modulated wave is proportional to the first-order proba- bility density of the frequency-modulating process. Hence, for phase modulation by a random noise VA,(t), the modulated wave spectral density is

where

and IJ~(LG) represents the density distributions of the derivate of the modulating noise.

602 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS. VOL. 34. NO. 3. MAY/JUNE 199X

: : . . . . . . . . ..I .._... .-

-. .: ,: ..:., ,: I

103.0 HZ 102.0 hz

Fig. 8. (a) Experimental modulating noise time-domain waveform (hori- zontal scale: 20 ms/div, vertical scale: 100 mV/div), and (b) its spectrum (horizontal scale: 25 Hz/div, vertical scale: 50 mV/div).

. i,.(r) ..i . . . . :... i. :,. .:... j . 1 .

. . .._ ..:...:.........:. ,.:...,... 1 f : . ; ‘.“’ : : . : i l...., .-.,,. . . . ..I. ,.i m 2O.UmV-b

Fig. 9. (a) Experimental band-limited white-noise-modulated lamp current (horizontal scale: 2 ms/div, vertical scale: 1 Aldiv) and (b) its fast Fourier transform (FIT) (horizontal scale: 5 kHz/div, vertical scale: 0.1 A/div).

Frequency-modulated wave spectral density by noise process yv(r?), with a bandwidth Ow,v, is similar to the phase-modulated one, ( 15), since phase modulation by a noise process Vnr(t) is equivalent to frequency modulation by noise process I&(t). Hence,

where

In this instance, spectral density is proportional to the first- order density distribution WI(Y) of the modulating noise h(t).

When noise is the modulating signal, the presence or absence of a discrete carrier term emerges as a difference between angle-modulated wave spectra. The exact calculation of the carrier contribution is relatively complicated and is beyond the scope of this paper. For phase modulations, the

Relevant experimental waveforms are shown in Figs. 8 and 9. Fig. S(b) shows the FFT of the band-limited white noise, where bandwidth ilwnr = fa = 100 Hz has been selected to equal the modulating frequency used in periodical modulations. For illustration. the corresoondina time-domain noise contribution around f = 0 vanishes rapidly, and there I

is always a residual carrier term. The existence of a carrier term in a frequency-modulated spectrum is a function of noise spectral characteristics at and around f = 0. When the modulating noise spectrum contains terms in this range, all energy is in the continuum and no carrier appears [ 171.

White noise, as do most tractable noise signals, has a normal or Gaussian distribution. Hence, according to the principle of adiabatic sweep, the main contribution of the frequency- modulated spectrum, (16), is a term proportional to Gaussian distribution. Spectral densities of the band-limited white noise and the correlated frequency-modulated wave are illustrated in Fig. 7.

According to (16), spectral reduction is achieved by increas- ing the modulating index PF. Like before, this will increase modulated-wave spectral bandwidth. As for periodic signals, this can be counterbalanced by reducing the modulating noise bandwidth awnr.

LASKAI er ol WHITE-NOISE MODULATION OF HIGH-FREQUENCY HID LAMP BALLASTS 603

b

Fig. 10. A unity power factor electronic ballast.

b

(4 (b)

(cl Fig. 11. Arc appearance with (a) 60.Hz magnetic ballast, (b) high-frequency electronic ballast with acoustic resonances, and (c) high-frequency electronic ballast without acoustic resonances.

waveform is also shown in Fig. 8(a). The time-domain lamp rectifier section and a half-bridge series resonant inverter, current waveform, Fig. 9(a), shows virtually no sign of am- interfacing the lamp with the dc bus, as discussed in [15]. plitude modulations, and according to its FFT, Fig. 9(b), A digital pseudorandom sequence generator has been used the modulated wave bandwidth is BWN = 2.5 kHz. This to generate white noise [2.5]. Uneven attenuation, shown represents a bandwidth reduction of around 14 times over in Fig. 8(b), results from the second-order low-pass filter, comparable sinusoidal modulations. however, it carries no significance as lamp power spectrum

is determined by probability density of the modulating noise and its bandwidth.

IV. EXPERIMENTAL SETUP Two different lamps, MVR250AJ and M250/U, made by GE Experimental waveforms, discussed during the analysis, and Osram, were used in the experiments. Arc appearances

were obtained with an electronic ballast, shown in Fig. 10. with a conventional 60-Hz ballast, with a high-frequency bal- The ballast, developed at the Power Electronics Laboratory, last with acoustic resonances and with a high-frequency ballast Texas A&M University, consists of a unity power factor input without acoustic resonances, are shown in Fig. 11. There were

604 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS. VOL. 34. NO. 3. MAY/JUNE 1998

no observable differences between important lamp properties for 60.Hz or stable high-frequency operation. Observe that arc bowing in horizontally operated 60-Hz arc is not present at high frequencies. However, this change had no effect on luminous flux or light quality.

V. CONCLUSION

In this paper, a new modulation method has been pro- posed to avoid acoustic-resonance-related problems in metal halide lamps when operated with high-frequency electronic ballasts. Angle modulation has been utilized to randomize the inverter switching frequency and to limit lamp power spectrum below the instability threshold. Along with the proposed band-limited white-noise modulations, three different angle- modulation strategies were described, sine wave, square wave, and symmetrical sweep.

To obtain stable operation with 250-W metal halide lamps, which were used for experimental verification, the dominant spectral terms were reduced by tenfold. To achieve this reduc- tion, required modulated-wave bandwidth for the periodical modulating signals was 15-35 kHz and the proposed random signal approach required only 2.5 kHz. The center or carrier frequency was selected to be just above the audio frequency range, hence, reducing EMI-related concerns.

The proposed stabilizing method allowed the use of high Q resonant inverters for HID lamp ballasting. Experiments with 250-W lamps, made by different manufacturers, showed good results.

111

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1. J. Pitel, “Emerging lighting control technologies: The alternatives and trade-offs,” .I. Illurn. Eng. Sot., vol. 12, no. 4, pp. 624-632, Apr. 1985. J. de Groat and J. van Vhet, The High-Pressure Lamp. Deventer, The Netherlands: Kluwer Technische Boeken, 1986. M. Schulz and K. U. Ingard, “Acoustic kink instability in an argon discharge,” Phys. Fluids, vol. 10, no. 5, pp. 1031-1036, May 1967. P. M. Morse and K. U. lngard, Theoretical Acoustics. New York: McGraw-Hill, 1968. H. L. Wetting, “Acoustic resonances in cylindrical high-pressure arc dischar-ges,” J. Appl. Phys., vol. 49, no. 5, pp. 2680-2683, May 1978. J. W. Denneman, “Acoustic resonances in high-frequency operated low wattage metal halide lamps,” Philips J. Res.. vol. 38, nos. 4/5, pp. 263-272, 1983. J. M. Davenport and R. J. Petti, “Acoustic resonance phenomena in low wattage metal halide lamps,” J. Illurn. Eng. Sot., vol. 12, no. 4, pp. 6333642, Apr. 1985.

181 R. Schafer and H.-P. Stormberg, “Investigations of the fundamental

191

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longitudinal acoustic resonance of high pressure discharge lamps,” J. Appl. Phw., vol. 53, no. 5, pp. 3476-3481, May 1982. H. P. Stormberg and R. Schafer, “Excitation of acoustic instabilities in discharge lamps with pulsed supply voltage,” Lighfing Res. Techrrol., vol. 15, no. 3, pp. 127-132, 1983. Y. Koshimura er al., “Stable high-frequency operation of high intensity discharee lamos and their ballast desian.” in Proc. CIE 20th Session. 1983, pp. E3&E36/2. J. Park ef al., ‘Solid state chopper ballast for gaseous discharge lamps,” U.S. Patent 3 890537, 1975..- Gamer et al., “Method of operating a high-pressure metal vapor dis- charge lamp and circuit arrangement for carrying out this method,” U.S. Patent 4705991, 1987. H. I. Faehnrich and E. Rausch, “Electronic ballasts for metal-halide lamps,” J. Illurn. Eng. Sot., pp. 131-141, Summer 1988. S. Wada et al., “Study of HID lamps with reduced acoustic resonances,” .I. Illurn. Eng. Sot., pp. 1622175, Winter 1987. L. Laskai, P. Enjeti, and 1. J. Pitel, “A unity power factor electronic ballast for metal halide lamps, ” in Proc. IEEE Applied Power Elrctmnics

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J. D. Gibson, Principles qf Digitcrl and Analog Communications. New York: Macmdlan, 1993. D. Middleton, Introduction fo Statistical Communication Theory. New York: McGraw-Hill, 1960. J. R. Carson and T. C. Fry, “Variable frequency electric circuit theory with aoolication to the theorv of freouencv modulation.” Bell Svst. Tech. J., voi.‘l6, pp. 513-540, 1937. I . El. Van der Pal, “Frequency modulation,” Proc. IRE, vol. 18, no. 7, pp. 1194-1205, July 1930. R. R. Anderson and J. Salz, “Spectra of digital FM,” Llrll Syst. Tech. J.. vol. 44, pp. 1165-I 189, JulyyAug. 1965. T. G. Habetler and D. M. Divan, “Acoustic noise reduction in sinusoidal PWM drives using randomly modulated carrier,” IEEE Trans. Power Electron., vol. 6, pp. 356-363, July 1991. T. Tanaka er a/., “Random switching control in dc-dc converters,” in Proc. IEEE Power Electronics Specialist Co@, 1989, pp. 500-507. A. M. Stankovic et al.. “Monte-Carlo verification of power spectrum formulas for random modulation schemes,” presented at the 3rd IEEE Workshop Computers in Power Electronics, Berkley, CA, 1992. A. M. Trzynadlowski et al., “Random pulse modulation technique for voltage controlled drive systems,” ht. J. Electron., vol. 68, no. 6, pp. 1027-1037, 1990. P. Horowitz and W. Hill, Art of Elrctronics. Cambridge, U.K.: Cam- bridge Univ. Press, 1980.

Laszlo Laskai (M’87-SM’96) received the Dip].- lug. degree from the University of Novi Sad, Novi Sad, Yugoslavia, in 1982 and the Ph.D. degree from Texas A&M University, College Station, in 1994, both in electrical engineering.

From 1983 to 1986, he was with Investpro- ject, Novi Sad, Yugoslavia, working on standby power generation and power distribution for large industrial consumers. From 1986 to 1990, he was with Chronar Corporation, Princeton, NJ where he was involved in the development of power conver-

sion equipment for photovoltaic applications and high-frequency ballasts for gaseous discharge lamps. Since 1994, he has been with Corporate Research and Development, General Electric Company, Schenectady, NY. His curreut research interests are in lighting and medical electromcs.

Dr. Laskar currently serves as Chairman and Transactions Editor for the Production and Application of Light Committee of the IEEE lndustr-y Applications Society (IAS). He is also an active member of the IAS Industrial Power Conversion Committee.

Prasad N. Enjeti (S’86-M’EE-SM’95) received the B.E. degree from Osmania University, Hyderabad, India, in 1980, the M.Tech. degree from the Indian Institute of Technology, Kanpur, India, in 1982, and the Ph.D. degree from Concordia University, Montreal, Que., Canada, in 1987, all in electrrcal engineering.

Following receipt of the Ph.D. degree, he joined the Department of Electrical Engineering, Texas A&M University, College Station, where he is cur- rently an Associate Professor. His primary research

interests are advance converters for power supplies and motor drives, power quality issues and active power filter development, utility interface issues and “clean” power converter designs. and electronic ballasts for Huorescent HID lamps. He is the Lead Developer of the Power Quality Laboratory, Texas A&M University, and is actively involved in many projects with industries and is engaged in teaching, research, and consulting in the area of power electronics, power quality, and clean power utility interface issues.

Prof. Enjeti is a Registered Professional Engineer in the State of Texas. He is Transactions Editor for the Industrial Power Converter Committee (IPCC) of the IEEE Industry Applications Society (IAS) and an Associate Editor of the IEEE TRANSACTIONS ONPOWER ELECTRONICS. He was the recipient of the IAS Second and Third Best Paper Awards in 1993 and 1996, respectively, the award for the second best transactions paper published in midyear 1994 to midyear 1995 in the IEEE TRANSACTIONS ONINDUSTRYAPPLICATIONS, and

corlj:, 1994, pp. 31-37. the IAS Magazine Prize Article Award m 1996.

LASKAI ~‘f ol.. WHITE-NOISE MODULATION OF HIGH-FREQUENCY HID LAMP BALLASTS

Ira J. Pitel (M’73-SM’82) received the B.S. degree from Rutgers-The State University of New Jersey, New Brunswick, the M.S. degree from Bucknell

, University, Lewisburg, PA, and the Ph.D. degree from Carnegie-Mellon University, Pittsburgh, PA, in 1972, 1975, and 1978, respectively.

From 1973 to 1976, he was with GTE Sylvania, researching high-frequency ballasting techniques for gaseous discharge lighting. He joined Bell Labora- tories in 1978 and Exxon Enterprises in 1979. At Exxon, he was involved in high-power converter

structures for ac motor drives, power processing for advanced battery systems, and controlled lighting. He was eventually transferred to one of Exxon’s subsidiaries, Cornell-Dubilier Electronics, where he was Manager of Research and Development. In 1981, he founded Magna-Power Electronics, Boonton, NJ, a company specializing in custom and standard power conditioning products. As President, he is responsible for contract research and development and manufacturing of its line of IO-500.kW dc power supplies. In 1986. he joined Texas A&M University as an Adjunct Associate Professor. HIS research interests are high-power ac-to-dc converters, static inverters, spacecraft power supplies. and specialty lightmg controls. He holds 21 patents in the field of power electronics.

Dr. Pitel is the co-recipient of the 1995 Society Prize Paper Award of the IEEE Industry Applications Society (IAS). He served as Committee Chairman of the IAS Industrial Power Converter Committee in 1988-1989, Department Chairman of the IAS Industrial Power Conversion Systems Department in 1994-l 995, and IAS Society Secretary and Vice President in 1997 and 1998, respectively. He is a member of Eta Kappa Nu and Tau Beta Pi.

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