Research On Ballast Technologies For High Intensity Discharge Lamps

Energy conservation is gaining more and more worldwide attention because of the shortage of non-renewable energy resources. With the fast social and economic development, the electricity for lighting accounts for more and more of the total electricity demand. Green lighting projects have been developed for which many policies and technical measures have been taken in more and more developed and developing countries around the world. The electrical ballast with high efficiency has been widely regarded as one of the effective solutions to save electricity; therefore, the research in depth on the electrical ballast is necessary and valuable.Power factor correction strategy (PFC) for electronic ballast with high efficiency is an effective technique helping to meet the green power requirements and avoid interfering with other sensitive electrical equipments on the same power line by mitigating the current waveform distortion. PFC strategy has become one of the critical techniques for electric ballast. Based on the analysis of power factor correction circuit in the critical conduction mode, the design have been carried out for the voltage and current loops of boost power factor correction circuit in conduction mode when average current control strategy is applied. Interleave boost PFC circuit can effectively reduce the current ripple and minimize the current rating of power switch. The cost of the converter can be significantly reduced with very good performance of power factor correction. In order to effectively reduce the ripple in the output current and mitigate EMI noise, the interleave strategy is applied for electric ballast of 1000W metal halide lamp.There are several special requirements for the start-up circuit of HID lamps since the impedance of one lamp in the start-up process is much different from that of the same lamp in steady state. At the beginning, the lamp has very high impendence, consequently high voltage is required for glow-discharge and arc-discharge by exciting the atoms in the lamp; at steady state, the lamps show low impedance and only low voltage is needed. Up to now, there are usually two start-up methods, resonance start-up method and high voltage-pulse startup method. For high voltage-pulse startup method, voltage overshoot induced in the startup process may damage the circuit or shorten the lamp life span. In the thesis, a novel boost type startup circuit with magnitude-adjustable voltage pulse is proposed which can provide very reliable startup of the lamp and effectively reduce the voltage and current surge. Furthermore, a novel boost type startup circuit which combines the two methods is proposed. The circuit proposed circuit may generate voltage harmonic with different frequency and different duty cycle to excite the resonance on the primary side of the boost inductor. Therefore, on the secondary side of the inductor high voltage is induced to reliably ignite the lamp.During the transition from start-up to the steady state of HID lamp, the lamp voltage, current and then the power change a lot. The study in thesis focuses on the change in the characteristic parameters of the lamp during the transition, especially high current caused in start-up process. A strategy combining the constant frequency control and stage-wise constant power control is proposed. The proposed strategy can effectively reduce the start-up high current resulting in improving reliability of the ballast and increasing the lifespan of the lamp.With the employment of renewable energy sources, such as solar energy, electric ballast with low dc voltage input has found its wide applications. Since its input voltage is low dc voltage, this type of electric ballast usually employs the topology with two power stages which is combination of dc boost circuit and push-pull inverter. However, the circuit usually suffers magnetic biasing, for that one solution featuring open loop control and constant duty cycle is proposed. The method to design the circuit parameters is also provided, as an example, LCC parameters and half-bridge circuit is designed and one 1000W electric ballast with 24V dc input voltage was built and the test results show it fulfilled the design requirements.Rectifying effect is the typical characteristic of most HID lamps of late stage which leads the unidirectional current of the lamp. The dc component of the current causes the inductor to saturate and show low impedance, therefore, the temperature of main inductor rises rapidly and be damaged if no overheat protection measures. By analyzing the changes in electrical parameters of several critical components of the electric ballast with bridge type inverter, one method to accurately measure rectifying effect is proposed in the thesis. This method has been applied for electric ballast of 250W metal halide lamp and can help to protect the ballast.