Research And Design On Digital Electronic Ballast For High Wattage Metal Halide Lamps

Metal halide lamps have wide application in the field of lighting, because of their high efficacy, good colour rendition, long life and other advantages. High wattage metal halide lamps are widely used in gyms, plant workshops and other large-scale lighting places. Because of its negative V-I characteristics, metal halide lamp has to work with ballast, and the electromagnetic ballast is still widely used. Electromagnetic ballast has many disadvantages such as its large size, heavy weight, low power factor and high THD. The electric power quality and environment are deteriorated by the extensive use of electromagnetic ballast.The use of electronic ballast will change the status. Analysis and research of digital electronic ballast for high wattage MH lamp are presented in this paper. The characters of high wattage MH lamp, the operating principles of digital electronic ballast built with MCU and the advantages as well as disadvantages compared with the electromagnetic ballast are presented firstly. An active power factor correction (APFC) circuit and a full-bridge inverter with LCC resonant circuit are adopted as the electronic ballast main topology. Also, a 8-bit Freescale MCU is used as the core of electronic ballast in order to make the ignition, power control and failure protection more convenient.The control strategies during the ignition stage, startup stage and steady stage of high wattage MH lamp are also a key component of this study. Based on the analysis of voltage gain of LCC network, a digital controlled soft-start-up method is proposed. During the run-up stage, constant frequency and power-set increased method are used in order to avoid over power. During the steady stage, a simple method based on the average input power of the inverter is used to achieve the constant lamp power. Based on the analysis of MH lamp's acoustic resonance phenomenon, a digital variable frequency modulation method is proposed to eliminate acoustic resonance of MH lamp operating at high frequency.In this paper, 1000W MH lamp is set as the control object. The circuit topology is designed and its parameters are calculated. Then simulation, MCU program and control flow chart are given. A digital electronic ballast prototype...