Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 94 === This dissertation presents two frequency modulation schemes for high-frequency high-power-factor (HPF) electronic ballast for metal halide (MH) lamps. Nowadays, the commercial three-stage HPF low-frequency square-wave-driven ballast is complicated and has large circuit components. To reduce components, high-frequency-driven ballast is favorable. However, one important problem of high-frequency-operated MH lamps is the acoustic resonances. A typical two-stage HPF constant-frequency (CF) controlled ballast consists of a PFC converter and a half-bridge series-resonance parallel-loaded (HB-SRPL) inverter. The switching frequency of the inverter should be chosen at some frequency bands that are free of acoustic resonances. However, the acoustic-resonance frequencies are different from every single lamp or the same wattage lamp of various brands. Therefore, this dissertation presents a two-stage frequency-modulated (FM) and a single-stage complex FM (CFM) controlled ballast for MH lamps with free of acoustic resonances. By using MATLAB software, the amplitude spectrum of lamp current for CF, FM, and CFM control method are analyzed and compared.
The lamp current under CF control can be treated as an AM wave. It can be seen that the power on the carrier frequency is much larger than that on the upper and lower sidebands. Thus, if the carrier frequency is located within the frequency window at which acoustic resonance may occur, an unstable discharging arc happens in the MH lamp. This dissertation presents an FM-controlled ballast and the modulating signal is the PFC output voltage ripples. The lamp current under FM control can be treated as an FM wave. In contrast with CF control, it can be seen that the amplitude spectrum of the carrier frequency is successfully spread, and the energy of certain eigen-frequency supplies to the MH lamp is largely decreased. Owing to its FM operation that allows for an adequately modulated index, no acoustic resonance occurs. However, if the frequency deviation range is not wide enough or inappropriate frequency of the modulating signal, acoustic resonances probably occur.
In response to these concerns, a single-stage high-frequency CFM-controlled electronic ballast, which integrates a PFC converter with a HB-SRPL inverter, for MH lamps is also developed in this dissertation. The modulating signal is a combination of the PFC output voltage ripples and the high-frequency sine-wave signal from the Wein-bridge oscillator. The lamp current under CFM control can be treated as a CFM-like wave, which mixes AM with FM. Compared with FM control, the proposed CFM-control scheme allows the power spectrum of the MH lamp to effectively expand and become a continuous spectrum with reduced amplitudes. Thus the lamp effectively achieves acoustic-resonance-free operation.
In this dissertation, a prototype ballasts utilizing FM control scheme, which has features of high power factor (>0.99), low crest factor (<1.45) of lamp current, and an internal modulating signal, has been built and test. Furthermore, a CFM-controlled prototype ballast, which has features of high power factor (>0.99), high efficiency (90%), and an easy-to-implement controller, has been developed and tested. Experimental results were carried out on three different brands of 70W metal-halide-type HID lamps to verify the functionalities of the proposed FM control schemes.
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