T- filters based dual-control dimmable electronic ballast

Transcription

1 3rd International Conference on Mechatronics, obotics and Automation (ICMA 5 T- filters based dual-control dimmable electronic ballast Huadong Wang, a,xu Cai, b,lili Liu Electronic Information and Electrical Engineering, Electrical Engineering, Shanghai Jiao Tong University, Shanghai, China Electronic Information and Electrical Engineering, Electrical Engineering, Shanghai Jiao Tong University, Shanghai, China 3 Jiangsu Key Laboratory of Large Engineering Equiment Detection and Control, Xuzhou Institute of Technology, Xuzhou, Jiangsu, China 3, c* a huadong.wang@shsdec.com, b xucai@sjtu.edu.cn, c dxwlll@sina.com Keyword: HID; Acoustic resonator;t-tye filter; Dimmer; Dual control Abstract: This aer describes a method for the analysis and design of dual control dimming UHF electronic ballasts. It includes a PFC converter circuit and a T-tye inverter circuit, the ballast oerating at the highest oint above the acoustic resonance frequency can effectively avoid the high-intensity discharge (HID lams acoustic resonance roblems. T-tye filter can achieve a very narrow deth range of dimming frequency, while achieving low lam current crest factor, keeing the lam current a erfect sine wave. Dimming with dual control, adjusting the duty cycle of the two frequencies to change the lam ower can reduce the EMI of FM dimming. Its effectiveness has been verified by exeriments. Introduction HID lights acoustic resonant frequency have a relationshi with the lam geometry, the lam gas arameters, is generally considered the acoustic resonance occurs at a secific frequency range (several tens of KHz. Acoustic esonance can cause the light arc instability and the fluctuation of outut ower or even burst the lam.therefore, how to avoid the occurrence of HID lights Acoustic esonance, is a major toic of the research on electronic ballast. There are the commonly used methods: DC, low frequency square-wave, swee and UHF work. The smaller values of high frequency magnetic comonents, smaller in size, but the higher costs of the drive chi, but also high-frequency magnetic material and higher costs, general elections at 3K~4K frequencies, can effectively overcome the acoustic resonance, cost and size are minimal. The higher the frequency of the magnetic comonent, the value is smaller, the size is smaller, but the higher the cost driver chi, but also need a high-frequency magnetic material costs, the general election in the frequency of 3K ~ 4K, can effectively overcome the acoustic resonance, and the cost is the smallest. Loss is greater with the higher frequency switch, a reasonable choice of toology and arameters designed to make the switch work in the soft switch, to ensure high efficiency. Ballast dimming is also a direction of research. Commonly used methods as follows:. Adjustable light []: PFC usually used BOOST circuit, voltage is limited and the dimming range is limited.. Modulation the duty cycle dimming []: full-bridge inverter circuit, the control method is comlicated and costly. Half-bridge inverter circuit, lam crest factor is higher, shorten the life of the lam. 3. FM dimming [3]: series and arallel inverter circuit commonly used to achieve dee dimming 5. The authors - Published by Atlantis Press 49

2 frequency changes, the switch over a wide frequency range are difficult to achieve soft switching, the article [4] resented dee dimming by T-filter narrower frequency range. However, the continuous frequency changes make the difficult to the EMI filter design. This aer based on the dual control dimming method based on t-tye UHF electronic ballast dimming: Lams oerating on two frequency, achieve dimming by changing the duty ratio of the two frequencies. If the two frequencies are fast enough there will be no Flash. For there are only two oerating frequencies, the EMI filter design is easy. T-tye filter make little difference between the two frequencies, to ensure that the switch is easy to achieve soft switching at two frequencies oint, ensuring high efficiency. Working rincile Igniter UI S Cd L I L I S C Lam Figure schematic diagram of ballast Ballast rincile is shown in Figure, consists of half-bridge Inverter circuit and t-tye filter, Cd is blocking caacitor, L rovide the ignition transformer with high ignition voltage (3KV-4KV, steady-state oeration when the secondary side is T tye filter inductor L.This aer Using arasitic caacitance and arasitic MOSFET body diode to achieve switch ZVS, no additional soft-switching circuit, with low cost efficiency. HID lam is aroximately equivalent to a resistance when oerations at a steady-state, T-tye filter voltage transmission characteristics: H T ( jw 3 - jw L L C - w L C + jw + ( L + L Figure H -f curve ( H is the voltage transfer ratio for values. Figure (, Figure shows t-filters can be accomlished dimming within a very narrow frequency range. Select of the T-tye filter arameters determine whether the circuit can work roerly and the switch can achieve soft switching, a reasonable choice of L, L, and C values, can make T-tye filter lam ignition, the lam lights u and working roerly have shown sensibility working condition, to ensure the realization of soft-switching. State aroximation is oen when the ignition, can be obtained: Z o ( jw - L C w jc w Z ( jw o ( ( (3 Figure voltage transfer ratio The start can be aroximately the short-circuited state, can be obtained: Z s ( jw jw L L L L C ( + - w L C w - (4 4

3 Z ( jw s (5 f LL L L C + (6 I I - L C w U I ( L L LL w w + - (7 U + - (8 I ( L L LL w w At the steady state, the lam is equivalent to the resistor ( U / P, can be obtained: Vom H( jw H w (- w LC + ( L + L - LL w VI (9 Z ( jw H ( L Cw ( Cw - + ( w ( L + L - LLCw Cw Z( jw arctan -arctan ( LC w LC w - - ( Switching frequency f> f to meet dimming characteristic. Metal halide lam ignition current should be more than twice the rated current, we can learned by (8 that the L should be larger; In order to reduce the loss of the switch,current should be as small as ossible, we can learned by (7 that the L should be larger, therefore,the L should consider a comromise, a reasonable choice of L can make the circuit can work roerly. Soft switch realization: from (3 (5 we can see, we can achieve soft switching at ignition and start. Steady oeration without considering the imact of arasitic caacitance: U i sin( ( Z( jw I Z( jw H U È I w( L+ L -LL w (-LC w - (-LC w Cw Î T C S U I i To sum u: T-resonant circuit arameters should satisfy (4, in order to meet the dee dimming, ignition, start-u and during the entire dimming soft switching characteristics. Ï f > LL C L + L Vom H w (- w LC + ( L + L - LL w VI Ì wt Z( jw < (- D - w T < Z( jw I U I > I ( L + L - LL w w - LCw I U < I I ( L + L - LL w w rating MAXswitch ( (3 Ó (4 Dual control FM dimming ballasts, fundamental and harmonic frequencies are adjusted with the change in light outut varies; create difficulties to the EMI filter design [5]. This aer use the dual control to 4

4 solve this roblem, two fundamental switching frequencies is control by a modulation frequency. With only two harmonic frequencies exist, EMI filter design easy. Since the control of modulation frequency so that the switching frequency of the two harmonic ower density is very small, which in turn makes EMI filtering criteria easily met. V gs (S f S f S a T T Figure 3 dual control switch drive waveform Dual control rincile: changing switching frequency fs and fs duration in one cycle of t and t, varying the ratio of the rated ower and minimum ower, to achieve the urose of adjusting the ower outut. In the dimming stage the lam oerates in two alternating frequencies, and t and t are continuous times, ower control is achieved by changing the length of t and t. Driving waveform shown in Figure 3, t and t and the relationshi between the modulation duty ratio α of: t α T, t (-α T, where T is the modulation eriod. Modulation duty cycle α, ballast comletely work at the highest frequency oint, minimum outut ower; α, ballasts fully oerational oint of the lowest frequency, maximum outut ower. When α is between and, the outut ower ranging between minimum and maximum, the outut ower increases with increasing α. So the changes in α can achieve dimming. In dual control, two basic switching frequency fs, fs and the choice of modulation frequency is very imortant for EMI characteristics of the circuit. FS and fs should be as close as ossible, fs and f ratio should be between to [6] t Design Considerations Parametric design method based on the second art of this article, there is 5W metal halide lam design arameters: fs4khz,fs5khz,fkhz,boost outut voltage is 38V, lam s rated ower P 5W, rated voltage U V, the equivalent resistance 67Ω, the duty cycle D 3/8, the inductor L 8uH, L 45uH, caacitance C 3.4nF, Cd uf. The test results Figure 4 is a saber simulation waveform, modulation ratio α.5, the modulation frequency f KHz. (A 4KHz lam voltage waveform; (b 5KHz lam voltage waveform; (c Voltage waveform during the oeration of the lam; (d The switch current flourier analysis grahics, fundamental frequency KHz, from the figure, the highest oint at 5KHz, no need to consider the working frequencies, the switching current at MHz EMI, needs to be removed, Other frequency amlitude is very small, the design of EMI filter only to remove the interference of MHz frequency. Thus, the dual-dimming makes EMI filter easy to design. (a 4KHz lam voltage waveform (b 5KHz the lam voltage waveform 4

5 (cthe lam voltage waveform during oeration (d Switch current Fourier synthesis grahical Figure4 double-frequency control simulation waveforms x:5ns/div y:5v/div5adiv CH lam voltage CH lam current (a 4.7KHz lam voltage current waveform x:5ns/div y:v/diva/div CH lam voltage CH lam current (b 55.KHz lam voltage current waveform x:5ns/div y:v/diva/div (c 4.7KHz Switch tube voltage current waveform 43

6 x:5ns/div y:v/diva/ (d 55.KHz Switch tube voltage current waveform x:5us/div y:5v/div, 5A/div (e lam voltage current waveformα.5 Figure5 Exerimental waveforms of lam voltage and lam current Figure5 shows the exerimental waveforms (The high frequency comonent in the lam current waveform is due to cascade Ω samling resistance in the measurement (a 4.7KHz lam voltage current waveform; (b 55.KHz lam voltage current waveform;(c 4.7KHz Switch tube voltage current waveform;(d 55.KHz Switch tube voltage current waveform;(e When modulation ratio α.5, the lam voltage current waveform. From the exerimental waveforms: lam voltage current Waveform is a erfect sine wave, crest factor is low; Switch tube at two frequencies both to achieve soft switching, switch tube advantages of low loss and efficient. There were no acoustic resonance and stroboscoic throughout the exeriment. So double-frequency control is a good method of dimming control Figure6 is the exerimental data of dual frequency dimming s dimming range: dimming range is wide, a linear relationshi between modulation and inut ower. Figure6 the curve of modulation ratio relative to the inut ower Conclusion This article resents a novel UHF electronic ballast with dimming feature based on t-tye filter, it also describes the oerating concet and design method. When the oerating frequency exceeds 4KHz, Silent resonance occurred and the lam voltage current waveform is a erfect sine wave. Dee dimming within a very narrow frequency range can be achieved by t-tye filter. There are only two oerating frequencies in the dual frequency control, frequency modulation reduces the two frequencies harmonic ower density. Switch at two frequencies both to achieve soft switching, switch tube advantages of low loss and efficient. 44

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