Research On The Key Technologies Of Electronic Ballasts For Electrodeless Lamp

Electrodeless lamp is widely used in the lighting areas such as mines, tunnels etc. due to high efficiency, no flicker and long life. Since electrodeless lamp has negative resistance characteristic, it must be driven by ballast, so it is significant to analysis and design the ballast. With consideration of electrodeless lamp load characteristics, this paper makes deep research on key issues of electronic ballasts for electrodeless lamp, such as circuit structure, load matching, resonant characteristic, parameter design, frequency tracking and dimming etc.. The main research contents are as follows:Firstly, the paper introduces the load characteristics of electrodeless lamp and circuit structure and operating principle of electronic ballast, and raises the key issues of load matching between the two circuit structures of electronic ballast and electrodeless lamp. According to the load characteristics in different operating processes of electrodeless lamp, the output characteristics of electronic ballast from ignition to steady state are analyzed, and the matching schemes that are suitable for different electrodeless lamp characteristics are obtained.An expression of the resonant frequency, considering the influence of load change, is deduced by analyzing the circuit characteristics of third-order and forth-order resonant converter. Based on the special load characteristics of electrodeless lamp, optimized designs of resonant parameters are proposed. With consideration of different lamp power, ignition, load-mutation, a maximum power output and operating states of the inverter in steady state, resonant parameter design methods balancing the ignition high voltage, maximum power and ZVS qualification are proposed for third-order and forth-order resonant converter. Different power laboratory prototypes have been built to confirm the validity of the proposed method.As to the drifting problem of natural resonant frequency for electrodeless lamp system, a digital frequency tracking control strategy is proposed. By analyzing the phase relations between resonant tank variables, a frequency tracking control strategy is proposed by phase difference feedback. As to dimming control, two dimming strategies are presented:a combination of pulse density modulation (PDM) and pulse frequency modulation (PFM), and a combination of improved pulse density modulation and pulse frequency modulation. The proposed dimming strategies can solve the problem of the narrow dimming range for PFM and the discontinuous dimming for PDM, and make the lamp work stably and reliably. A 100W laboratory prototype has been built and experimental results confirm the validity of the proposed scheme.A multi-phase parallel load resonant converter suitable for high-power electrodeless lamp is proposed, and its operating principle and circuit characteristics are analyzed. Based on this, a combination of phase-shifted and phase-locked control strategy is presented to realize the dimming control of electrodeless lamp. The converter can always operate in the vicinity of the resonant frequency when the driver signals are in-phase or phase-shifted operating, and the resonant frequency drifting problems are solved. The impact of phase-shifted angle on soft-switching of switches is analyzed in detail. The relationships between the current of each phase, circulating current, output power and phase-shifted angle are deduced. Finally, a 460W electronic ballast laboratory prototype has been built and experimental results confirm the feasibility of the proposed scheme.