Research On MH Lamp Electronic Ballast With Digital Control Technique

Metal halide(MH) lamps have become attractive lighting sources for their outstanding features, such as high lighting efficiency, good color rending, and long life time. Electronic ballasts have to be used due to the negative impedance characteristic of the MH lamps. MH lamps require an adequate high ignition voltage to start, and their impedance varies largely from starting to stability during operation, and MH lamp electronic ballasts need to work at different modes at different stages. First,the paper proposed a novel digital control strategy after analyzing existing drawbacks with analog control, and it not only can realize the control requirement of the starting and stability during operation, but also can achieve advanced control techniques. To avoid acoustic resonance efficiently , the three-stage low-frequency square-wave electronic ballast is proposed, and the ZVRT BUCK circuit is detailed and simulated,and an additional high voltage pulse generator is constructed to make the MH lamp be safely turned on. Second , according to the characteristic of the MH lamp, a discrete linearization control scheme is proposed, including constant voltage, constant current in starting and constant power in stability during operation. Optimized PID control strategy is adopted to output accurate control strategy according to different stages, to realize the dynamic matching between the electronic and the MH lamp. A digital controller is designed and implemented to demonstrate advantages over analog counterpart in the application. Third, a MH lamp electronic ballast with digital control technique and high power factor low-frequency square-wave is designed,and experimental results are shown to verify the validity of the proposed ballast.