In a conventional electronic ballast for a fluorescent lamp, inductor-capacitor-transformer tank circuit is used. A Piezoelectric Transformer (PT) can potentially be used to replace such a tank circuit to save space and cost. In the past, ballast design using a PT requires selecting a PT from available samples which are normally not matched to specific application and therefore resulting in poor performance. In this thesis, a design procedure was proposed for designing a PT tailored for a 120-V 32-W electronic ballast with high power factor, high efficiency and Zero-Voltage-Switching (ZVS) of the inverter transistors that drive the lamp. This involves selection of PT materials, determination of geometries and the number of physical layers of the PT. A radial mode piezoelectric transformer prototype based on this design process was fabricated by Face Electronics Inc. and was tested experimentally, the results showed that the ballast using this custom-made PT achieved high power factor, Zero-Voltage-Switching and a 83% overall efficiency. / Master of Science

This study investigates the starting characteristics of metal halide lamps. A laboratory electronic ballast was built to drive metal halide lamps with a programmable low-frequency square-wave current. The lamp current at each stage of the starting transient can be independently adjusted. Experiments were conducted on 150-W metal halide lamps. By examining the waveforms of transient voltage, current and power, the starting period can be classified into four stages, breakdown, glow discharging, glow-to-arc transition, and thermal equilibrium. In addition, the stable operation is defined by observing the variations of the lamp arc, lighting spectrum and luminous output. Based on the investigation results, four starting scenarios are presented and examined to learn the different acceleration schemes. Experimental evidence shows that the starting time of a metal halide lamp can be effectively shortened by increasing the lamp current during the start-up transition. More importantly, a specifically-regulated operating power enables the lamp to further enhance the luminance producing, and hence to greatly reduce the starting transient period.

The research searches for an identification strategy which is able to recognize three small-wattage metal halide lamps rated at powers of 20-W, 35-W and 70-W from three world-wide prominent brands of GE, OSRAM and PHILIPS. A two-stage constant-power starting scenario is adopted to successfully start all three kinds of lamps without causing a tremendous power during the identification process. At the first stage, the tested lamps are started by a constant power of 25 W. The 20-W lamps can be distinguished from the others by their relatively high lamp voltages at the 30th seconds after being ignited. Then, the other lamps are driven up to 35 W to manifest the voltage difference of between the 35-W and 70-W lamps, and thus can be recognized at the 40th seconds. After being made out, the lamps are operated at their rated powers. Eventually, a verification checking with protection is introduced to prevent the tested lamps from over power operation. Experiments have been done on numerous new and aged lamps. The experimental results evidence that the electronic ballast with the proposed identification strategy can recognize three lamps¡¦ rated powers correctly during the starting transition, and drive the lamp to its rated power before entering the steady-state.

Five new single-stage power factor correction (PFC) techniques are developed for single-phase applications. These converters are: Integrated single-stage PFC converters, voltage source charge pump power factor correction (VS-CPPFC) converters, current source CPPFC converters, combined voltage source current source (VSCS) CPPFC converters, and continuous input current (CIC) CPPFC converters. Integrated single-stage PFC converters are first developed, which combine the PFC converter with a DC/DC converter into a single-stage converter. DC bus voltage stress at light load for the single-stage PFC converters are analyzed. DC bus voltage feedback concept is proposed to reduce the DC bus voltage stress at light load. The principle of operations of proposed converters are presented, implemented and evaluated. The experimental results verify the theoretical analysis. VS-CPPFC technique use a capacitor in series with a high frequency voltage source to achieve the PFC function. In this way, the input inductor is eliminated. VS-CPPFC AC/DC converters are developed, and their performance is evaluated. VS-CPPFC electronic ballasts with and without dimming function are also presented. The average lamp current control with duty ratio modulation is developed so that the lamp operates in constant power with a low crest factor over the line variation. The experimental results verify the CPPFC concept. CS-CPPFC technique employs a capacitor in parallel with a high frequency current source to obtain the PFC function. The unity power factor condition and principle of operation are analyzed. By doing so, the switch has less switching current stress, and deals only with the resonant inductor current. Design considerations and experimental results of the CS-CPPFC electronic ballast are presented. VSCS-CPPFC technique integrates the VS-CPPFC with the CS-CPPFC converters. The circuit derivation, unity power factor condition and design considerations are presented. The developed VSCS-CPPFC converters has constant lamp operation, low crest factor with a high power factor even without any feedback control. CIC-CPPFC technique is developed by inserting a small inductor in series with the line rectifier for the conceptual VS-CPPFC, CS-CPPFC and VSCS-CPPFC circuits. The circuit derivation and its unity power factor condition are discussed. The input current can be designed to be continuous, and a small line input filter can be used. The circulating current in the resonant tank and the switching current stress are minimized. The average lamp current control with switching frequency modulation is developed, so the developed electronic ballast operates in constant power, low crest factor. The developed CIC-CPPFC electronic ballast has features of low line input current harmonics, constant lamp power, low crest factor, continuous input current, low DC bus voltage stress, small circulating current and switching current stress over a wide range of line input voltage. / Ph. D.

This research attempts to ignite metal halide lamps once with a single-pulse to avoid the problems of uncomfortable light strobes and irregularly high voltage and current stresses on circuit components caused by multiple strikes in conventional electronic ballasts. Metal halide lamps with single-pulse ignition, however, have difficulty in sustaining the lamp arc when operated with a low-frequency square-wave current. Experimental results indicate that the lamp exhibits an extremely small equivalent resistance as the electrode gap has being broken down. In this stage, the ballast has to keep the lamp current not declining to zero in the first half cycle. On the other hand, the lamp acts like open-circuited during commutation when driven by an alternating current. A sufficient energy from the ballast is needed to continue the arc in the next half-cycle. The transition waveform of the lamp arc current after being broken down is analyzed and the required energy for sustaining the lamp arc is calculated accordingly. Based on the investigation results, a starting scenario with appropriately designed circuit parameters for single-pulse ignition can be figured out. The starting scenario has been experimentally implemented on a 70 W metal halide lamp to demonstrate that the metal halide lamp can be successfully started up with single-pulse ignition.

Three programmed rapid-start control schemes for the electronic ballasts with a half-bridge series-resonant inverter are proposed to improve the starting performance of the rapid-start fluorescent lamps. Included are: (1) programmed rapid-start control scheme with an ac switch, (2) programmed rapid-start control scheme with inductively coupled filament-heating circuit, and (3) programmed frequency control scheme with a series-resonant energy-tank. The first control scheme is simply to add a solid-state ac switch onto the series-resonant electronic ballast to provide programmed rapid-start for the rapid-start fluorescent lamp. The ac switch is turned on to have a zero voltage across the lamp to eliminate the glow current during the preheating interval. By adjusting the operation frequency and the duty-ratio, the electronic ballast produces first an adequate resonant current for preheating the cathode filaments, then a sufficiently high lamp voltage for ignition, and finally a stable lamp arc of the required lamp power. The second control scheme is accomplished by adding two auxiliary windings on the inductor of the power-factor-correction (PFC) circuit for the filament-heating circuits. During the preheating period, the PFC circuit is activated to provide the filament heating while the inverter remains idle to keep the lamp voltage at zero and hence to eliminate the glow current. After the filaments have been heated to the appropriate temperature, the inverter is initiated to ignite the lamp and then operate it at the required power. The third control scheme is realized by programming the operation frequency of the electronic ballast with an additional series-resonant energy-tank on the load resonant network. During the preheating interval, the electronic ballast is programmed to operate at the resonance frequency of the series-resonant energy-tank to reduce the lamp voltage and hence to eliminate the glow discharge. With carefully designed circuit parameters, the electronic ballast is able to provide an adequate current for preheating. After the emission temperature has been reached, the operation frequency is adjusted to generate a high lamp voltage for ignition, and then is located at the steady-state frequency driving the lamp with the desired power and filament current. In this dissertation, the mode operations of the proposed ballast circuits are analyzed in accordance with the conducting conditions of the power switches. The equivalent resistance model of fluorescent lamp is implemented to calculate the performances of the ballast-lamp circuit at steady-state. The design equations are derived and the computer analyses are performed with the fundamental approximation on the equivalent circuit models of fluorescent lamps. In addition, in order to accurately predict the operating characteristic of the preheating circuit, a mathematical model is developed to interpret the variations of the filament resistance during preheating. Finally, the laboratory electronic ballasts with the proposed control schemes are built and tested. Satisfactory performances are obtained from the experimental results.

The fault phenomena of fluorescent lamps are investigated by observing the operations in the last period of the life cycle. Accordingly, fault detecting and protection circuits are designed. Before coming to the life-end, the lamps can be started up, but are operated abnormally. A ruddy glow may occur at one end of the cathode filaments and an unstable arc may happen to the lamp. Obviously, the light efficiency becomes relatively low. The arc instability eventually results in a totally damaged fluorescent lamp. It is found that both waveforms of the lamp voltage and the lamp current are asymmetrical and have unequal positive and negative peak values. The asymmetry is more significant for the lamp voltage. In addition, a dc component is present in the lamp voltage. Based on these investigated results, the detection and protection circuits are designed for high-frequency electronic ballasts under dimming operations as well at the rated power. The experiments show that the detection and protection circuits can work effectively.

A single-stage high-power-factor electronic ballast with auto frequency searching capability provides a compact and efficient solution for ballasting metal halide lamps. The circuit configuration is originated from the integration of a buck-boost converter and a half-bridge resonant inverter. The buck-boost converter is designed to operate in discontinuous current mode (DCM) to improve the input power factor and at the same time to regulate the output lamp power. The resonant inverter operating at a high frequency is adopted to obtain a high efficiency on the power conversion circuit. The control strategy of auto frequency searching is realized by a microprocessor along with the acoustic resonance detection circuit. To avoid the acoustic resonance, an auto-frequency-searching method is used to search ¡§quite windows¡¨ on operating metal halide lamps with the high-frequency electronic ballast. Provided the acoustic resonance should happen to the lamp on operation, the electronic ballast will automatically change the operating frequency until a stable frequency is located. When the operating frequency has been changed, the duty-ratio of the buck-boost converter is adjusted to regulate the lamp power at the rated value. Experimental tests are carried out on a laboratory with 70-W metal halide lamps to verify the effectiveness of the auto-frequency- searching control.

Fluorescent lamps with ac current generate alternating lamp power and thus the light fluctuates at twice the operating frequency. To observe the light fluctuation from a fluorescent lamp, a light detector is built by using high sensitivity phototransistors in this thesis. The test results show that the light output waveform is very similar to that of the lamp power. It is also found that the light output from the whole lamp tube is not identical because the light output fluctuation becomes significant when close to the end of the lamp. When the lamp comes to the life-end, its light output is different from those produced by lamps of good conditions. In attempts to further discuss the features of light fluctuation, an electronic ballast with balanced multi-phase outputs is designed and built to reduce the variation in the light output. With a balanced multi-phase operation, the resultant light output from lamps¡¦ multi-phase currents should be a constant. An experimental 3-phase electronic ballast circuit is built to test this theoretical prediction. Experimental tests confirm that the light fluctuation can be effectively reduced by operating lamps with balanced multi-phase currents.

In this thesis, a novel electronic ballast that includes a repeatedly resonating ignition circuit is proposed for metal halide lamps. The proposed electronic ballast features a two-stage structure that comprises a power factor corrector and a full-bridge inverter used for current control, filtering and ignition. The full-bridge inverter consists of a leg operating at low-frequency with unidirectional switches and a leg operating at high frequency with bidirectional switches. The low-frequency side performs repetitive resonating on the load circuit with inductors and capacitors to accumulate a high voltage for ignition. Adjusting the duty-ratio of the high-frequency side allows for the regulation of the lamp current. The inductors and capacitors in the load circuit function not only producing the high ignition voltage but also filtering out high-frequency components, so that to drive the lamp with a low-frequency square-wave current. The proposed electronic ballast employing the full-bridge inverter with the specially designed control scheme and circuit parameters allows the metal halide lamp to tackle the demanding starting transient and steady state operation. With a simpler circuit structure and a reduced component count, the product cost will be much lower.